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In our study, we estimated earthquake source parameters and spectral decay characteristics of 378 seismograms corresponding to 80 small earthquake events with magnitudes ranging from 1.5 to 3.5. These earthquakes occurred between July 2011 and May 2012 in the Siang region of the Arunachal Himalaya which is not well-studied. To estimate source parameters, the classical Brune model is employed and through the analysis, a scaling relationship is established between the estimated corner frequency ( f c ) and seismic moment ( M 0 ), which can be expressed as M 0 = 1 × 1 0 22 f c - 3.18 . This relationship is in close agreement with previous studies conducted in the Arunachal and Himachal Himalaya regions. It provides support for deviations from self-similarity in the study area, offering valuable insights into the tectonics and structural heterogeneity beneath the Arunachal Himalaya. Our analysis revealed variations in source radius, ranging from 154.4 m to 312.6 m, and seismic moment, spanning from 2.37 × 1011 N-m to 9.32 × 1013 N-m. Interestingly, we observed an increasing trend in stress drop, ranging from 0.013 MPa to 3.26 MPa, within the same range of seismic moment. This significant variation in stress drop primarily occurs in the upper 10–15 km of the Earth's crust, indicating shear brittle failure in this upper crustal region. Furthermore, we conducted an in-depth examination of spectral parameters, including f c high-cut frequency (fmax), and high-frequency spectral decay parameter kappa (κ). Our study highlighted the dependence of κ and fmax estimates on both source characteristics and propagation path, with the source having the most substantial influence. This observation was substantiated through statistical analyses. Additionally, we explored the effect of recording site characteristics on κ and observed a significant contribution of shallow geology at the recording site. This was evident through a negative correlation between the site component of κ (κ0) and VS30, indicating that the local geology of the recording site plays a significant role in spectral parameter estimation. Based on our comprehensive data analysis and statistical observations, we conclude that the variations in source and decay parameters for earthquakes of different magnitudes are attributed to the diverse structural heterogeneities and complex seismotectonic processes underlying the Arunachal Himalaya region. [ABSTRACT FROM AUTHOR]

Seismic events produced by block rotations about vertical axis occur in many geodynamic contexts. In this study, we show that these rotations can be accounted for using the proper theory, namely micropolar theory, and a new asymmetric moment tensor can be derived. We then apply this new theory to the Kaikōura earthquake (2016/11/14), Mw 7.8, one of the most complex earthquakes ever recorded with modern instrumental techniques. Using advanced numerical techniques, we compute synthetic seismograms including a full asymmetric moment tensor and we show that it induces measurable differences in the waveforms proving that seismic data can record the effects of the block rotations observed in the field. Therefore, the theory developed in this work provides a full framework for future dynamic source inversions of asymmetric moment tensors. [ABSTRACT FROM AUTHOR]

Three seismic gaps lie along the Pacific Coast of Mexico, the Tehuantepec, Guerrero, and Colima–Jalisco gaps. In the Tehuantepec seismic gap, there has not been a M > 7 earthquake since 1902 until the M w = 8.2 in 2017 which was an intraplate event. Furthermore, there has not been significant seismic activity in the Guerrero gap for over fifty years; therefore, it is considered as potentially likely to produce a major event. Based on historical seismicity and the National Seismological Service of Mexico's earthquakes catalog, the last major earthquake in the Colima–Jalisco gap struck in 1995 with M w = 8.0 . To better understand the tsunami hazards due to the generation of near-field tsunamis in Mexico, in this work we characterize hypothetical events of magnitudes M w = 8.0 , M w = 8.2 , and M w = 8.2 in the Tehuantepec, Guerrero, and Colima–Jalisco gaps, respectively. We generated 99 earthquakes with stochastic k - 2 finite fault slip distributions and one earthquake with uniform slip distribution at each seismic gap. The non-planar geometry of the megathrust for each rupture area was taken into account. For each seismic gap, we compute the vertical co-seismic displacement by adding up the contribution from all point sources distributed over a grid mesh on each of the faults. Under the passive tsunami generation assumption, we simulated the tsunami wave-field propagation to obtain the coastal amplitude along the Pacific coast of Mexico. The numerical results show likely maximum peak amplitudes of ∼ 8 m, ∼ 14 m, and ∼ 15 m, in Tehuantepec, Guerrero, and Colima–Jalisco gaps, respectively. The uniform slip distribution assumption over stochastic scenarios shows an average underestimation factor of 1.3 for the three seismic gaps. While our computations were carried out carefully and accurately, our models have limitations. Thus, our results cannot be used as an authoritative tsunami hazard assessment. [ABSTRACT FROM AUTHOR]

Earthquake diffusion and the migration behaviour of seismic clusters are commonly studied to provide insight on the spatiotemporal evolution of seismicity and the interplaying driving mechanisms. Using a high-resolution relocated catalogue, we study the variations of the earthquake diffusion rates in the Western Gulf of Corinth during 2013–2014, a period with abundant local seismicity, including intense microseismic background, seismic swarms and mainshock-aftershock sequences. We treat earthquake occurrence as a point process in time and space and estimate the diffusion rates of the main seismic sequences and the background seismicity in terms of normalized spatial histograms and the evolutions of the mean squared distance of seismicity with time. The statistical analysis of the studied seismic sequences reveals that the mean squared distance of the hypocentres increases slowly with time, at a much lower rate than for a normal diffusion process. Such findings confirm previous results on weak earthquake diffusion, analogous to subdiffusion, in regional and clustered seismicity. In addition, seismic swarms associated with pore fluid pressure diffusion present considerably higher diffusion exponents compared to mainshock-aftershock-type sequences that are consistent with primary or secondary stress triggering effects and stress corrosion. The observed variations of the earthquake diffusion rates indicate the stochastic nature of the phenomenon and may provide novel constraints on the triggering mechanisms of clustered seismic activity in the Western Gulf of Corinth and in other seismically active regions. [ABSTRACT FROM AUTHOR]

In this article, we describe a method for predicting of the epicenter location region of Kamchatka and Commander earthquakes (EQs). It is based on the properties of the precursory atmospheric ULF/ELF (1–30 Hz) radiation and the spatial statistics of local EQs in relation to the Kuril-Kamchatka and Aleutian trenches. From this statistics, it follows that more than 90% of events with magnitude (ML) of more than 5 occur in the gap ~ 150 km west of the Kuril-Kamchatka trench and north-east of the Aleutian trench. Additionally, we obtain the approximate location of the epicenter by determining the position of the radiation source. We suppose that it is caused by gas eruption from the hearth of the EQ to the trench and has the nearest location to the EQ epicenter. Further, we obtain other parameters of supposed position of the epicenter from spatial statistics of EQs relative to the projection of radiation source, which approximately coincides with gas emanation area in the ocean surface. The main drawbacks of the method are the dependence of its accuracy on the industrial interferences and the ambiguity of determining the epicenter location in the case of single-point registration of radiation when the main lobe of the azimuthal distribution of radiation crosses both trenches. [ABSTRACT FROM AUTHOR]

Pakistan and its surroundings are among the most seismically active regions in the world. Occurrence of major earthquakes in Pakistan is a real hazard for life. In this study, an attempt has been made to estimate the seismic hazard in terms of earthquake occurrence conditional probabilities in different zones of Pakistan. We assumed that the temporal data of earthquakes, that occurred in different regions of Pakistan follow a certain probability distribution. In present study, the 10 probability models that include the exponential, gamma, generalized Pareto, inverse Pareto, kappa, log-logistic, lognormal, Pareto, transformed gamma and Weibull are used to analyze the interevent times of the earthquakes with M w ≥ 5.5 in different regions of Pakistan. In current study, Pakistan territory has been divided into five different seismic zones based on their tectonic settings. Parameters of the considered distributions are estimated by using the maximum likelihood method using the reviewed earthquake catalogue compiled by Centre for Earthquake Studies (CES), Pakistan. The best suitable model in each seismic zone is selected through various model selection criteria. The results show that the log-logistic distribution provides the best representation of earthquake temporal data of plate convergence zones; while the gamma distribution best explains the temporal seismicity of other tectonic regimes including the transform plate boundary, fold and thrust belts and stable plains. The most suitable gamma and log-logistic models are used for the earthquake occurrence probabilities in different regions of Pakistan. The highest (> 96 %) and the least (> 30 %) earthquake occurrence conditional probabilities are respectively observed for Zones I and V among five seismic zones for different combinations of elapsed time (τ) and time interval (υ) . The estimated probability of M w ≥ 5.5 event reaches (60–98)% in next (3–9) years time interval without any elapsed time (τ = 0) in Zones II to IV (the time periods corresponding to 3–9 years time interval are 2016–2022, 2020–2026 and 2019–2025 in Zones I, II and III respectively) since the last event occurrence time in each of these seismic zone. The mean values of the interevent time for an earthquake occurrence of M w ≥ 5.5 in Zone-I to Zone-V are respectively calculated as 0.90, 1.78, 4.52, 3.35 and 11.76 years, respectively. The results of the present study indicate that Zone-I has potential capability of producing an earthquake of magnitude 5.5 or higher in next 3 years (2019–2021) time interval since the last event occurrence in May 2018. The earthquake hazard curves associated with earthquake occurrence probabilities are also developed in order to understand the current and future earthquake mechanism in the study region. [ABSTRACT FROM AUTHOR]

An improved pattern informatics (PI) method, inspired by the soup-of-groups model, is developed in this study. This improved method reveals its potential in reducing the noise that, when the classical PI is applied, can yield misleading conclusions about the existence of "hotspots" in the vicinity of the epicenter of a strong earthquake. The application of this new method to Italian seismicity from 1985 to 2018 properly reveals "hotspots" around the two strongest earthquakes that occurred in 2009 (L'Aquila earthquake) and 2016 (Norcia earthquake), suggesting its utility in studies devoted to earthquake prediction. [ABSTRACT FROM AUTHOR]

In the present paper, a new method referred to as the Poisson probability map (PMAP) method is presented for identifying and visualizing seismic quiescence. With the PMAP, the P-value is defined as the probability that consecutive earthquakes occur according to a homogeneous Poisson process: the smaller the P-value, the less frequently the longer time interval is observed, i.e. the more significant the seismic quiescence. The PMAP method was applied to the sequence which preceded the Kurile Islands earthquake that occurred on 15 November 2006 [Mw = 8.3 and the centroid = (154.33 °E, 46.71 °N)]. The seismic quiescence is identified by a small P-value of 9.0 × 10–5 that was found to start in 1990.1, which lasted for 15.4 years and ended in 2005.5 within a circular area centered at (153.8 °E, 47.1 °N) and with a radius of 26 km. This seismic quiescence has not previously been recognized using any other method. [ABSTRACT FROM AUTHOR]

The Gutenberg–Richter (G–R) relationship can be derived as the Gibbs distribution. For a given earthquake set (all earthquakes in a given region, time period, magnitude range, tectonic settings) the Gibbs probability density function for magnitudes, with a given b value in its exponent, is the most uniform distribution under the constraints of the magnitude range and mean value. Therefore, it represents our limited knowledge about the system output: the only pieces of information are the mean value and the magnitude range. Honest earthquake forecasts can be based on such a distribution, since it represents all and only available information about the seismic system. The b value can change among different earthquake sets (in time, space, magnitude ranges, or tectonic settings), since it is related to earthquake rupture dynamics, or seismic source characteristics. The relationship between the b value and the exponent β in the rupture area vs. maximum slip scaling, A ∝ D β , results from viewing earthquake recurrence time in connection with the slip budget. This makes a link between earthquake statistics (the G–R law) and physics (fault characteristics). Specifically, the relationship enables us to explain different ranges of b values at megathrust faults, in dependence on interplate asperity and coupling distributions, as well as on amounts of sediments and fluids in subduction channels. The approach differs from common interpretations of the G–R law in that the b value becomes a field variable, not a constant. It is always the Gibbs distribution for a given magnitude range that we use due to our ignorance about the system outcome, and it is the b value that variates, depending on our knowledge about the system physics. This is important for seismic forecasts, which are mostly based on the G–R relationship. First, because the physical processes leading to the largest earthquakes can be revealed by observing the b value variations. Second, because earthquake generation process can be thought of as sampling with constraints, where the b value and the magnitude range are the constraints. [ABSTRACT FROM AUTHOR]

The 2016 Kumamoto earthquake occurred on April 16, 2016, and induced the complex distribution of surface ruptures and fault displacements, which revealed the difficulty of evaluating off-fault displacement hazards. The evaluation of off-fault displacements is necessary for the site investigation of an important facility, such as nuclear installations, but is difficult because off-fault displacements are thought to occur on unmapped or small-scale structures. A probabilistic fault displacement hazard analysis (PFDHA) assesses an off-fault displacement hazard as well as an on-fault one. Several PFDHA models have been developed from fault displacement datasets parsed by global-specific and Japanese-various faulting types. We developed a procedure to assess off-fault displacement hazards based on probabilistic and numerical simulation approaches. In the probabilistic approach, we constructed strike-slip and reverse-slip PFDHA models from a dataset of Japanese fault displacements. The off-fault components in PFDHA had a probability of non-zero off-fault displacement and an attenuation relationship. In the case of evaluating the site of an important facility, detailed field surveys were performed to collect numerous site-specific information. There is little site-specific data of off-fault displacements in Japan. The trench surveys were performed at off-fault displacement sites from the 2016 Kumamoto earthquake. The two trench sites were selected based on a linear low-coherence zone derived from the InSAR analysis, which emphasizes small-scale displacements. The excavation survey result at one site suggests a shorter recurrence interval than that of the active fault long-term evaluation. We also performed a probabilistic fault hazard analysis (PFDHA) of the trench sites by using the global strike-slip model and Japanese PFDHA models with and without the site-specific data. For the PFDHA results without site-specific data, the difference in the annual rates of exceedance between the global strike-slip and Japanese models increased with increasing fault displacements. This is because of the reduced decrease in the attenuation relationship of Japanese models. The differences in the annual rates of exceedance constrained with the site-specific data are independent of fault displacements due to variation in the probability of non-zero off-fault displacement between the global strike-slip and Japanese PFDHA models. These results suggest that the off-fault PFDHA models have high variability. In the case of PFDHA evaluation with several models, the individual PFDHA components are carefully selected by considering the individual effects. The site-specific short recurrence interval revealed by the trench survey leads to higher annual rates of exceedance. [ABSTRACT FROM AUTHOR]

Asperity models for ground motion prediction is widely used in Japan. Here we expand the application of these asperity models to predict fault displacement caused by surface rupture. The proposed approach is rather simple and practical for the use in fault displacement hazard analysis in nuclear installations and other critical infrastructures, as it is the emphasis of the current topical issue. The proposed method mainly consists of two steps. The first step consists in the characterization of asperities at the seismogenic zone based on the kinematic asperity source model following Irikura's recipe (Irikura and Miyake in Pure Applied Geophysics, 168:85–104, 2011) for strong ground motion prediction. Since the kinematic model does not take into account surface rupture mechanism, this first step assumes that the fault is buried, and then by trial and error procedure the stress drop on the asperities are estimated, so that the average slip at each asperity be consistent with the ones from the kinematic model. At this stage, the dynamic model predicts strong ground motion consistent with those from the kinematic model. In the second step, the surface rupture is included by calibrating the shallow layer (SL) with stress drop, strength excess and critical slip distance, so that the final fault displacement along the fault be consistent with observations. The 2010 Mw 7.0 Darfield (New Zealand) earthquake is used to test the proposed method. Surface-rupturing was observed in several sites along the main fault reaching values of fault displacement larger than 5 m. The main fault of this earthquake is strike-slip, almost vertical. Therefore, a simplified planar fault asperity model to capture the main features of the fault displacement is assumed. The fault dimensions are assumed to have a length of 60 km and a width of 24 km with three asperities. The preferred model of the first step predicts average slip for each asperity of 2.7, 2.7, and 2 m corresponding, respectively, to stress drops of 6.0 MPa, 8.5 MPa, and 7.0 MPa. In the second step, the surface rupture is calibrated assuming a SL zone of 3 km depth. We found that negative stress drop is not necessary in the SL, because this strongly inhibits surface rupturing. Our preferred model produces fault displacement distribution closer to the observed ones, but average slip at each asperity increases to 3.4 m, 3.2 and 2.8 m. This increase in average slip is due to the contribution of surface rupturing. Ground motion differences between fault-surface rupturing and buried models are negligible, except at the very near-source. These differences are attributed to the SL rupture that mainly affect the ground motion at the very near-source. Overall, our simple asperity model captures the main features of the observed fault displacement and near-source ground motion, proving that the proposed simple and practical two step-procedure provides meaningful estimate of fault displacement and near-source ground motion consistent with observations, as such, this method has the potential to be used in practical fault displacement hazard analysis. [ABSTRACT FROM AUTHOR]

We analyzed a kinematic earthquake rupture generator that combines the randomized spatial field approach of Graves and Pitarka (Bull Seismol Soc Am 106:2136–2153, 2016) (GP2016) with the multiple asperity characterization approach of Irikura and Miyake (Pure Appl Geophys 168:85–104, 2011) (IM2011, also known as Irikura recipe). The rupture generator uses a multi-scale hybrid approach that incorporates distinct features of both original approaches, such as small-scale stochastic rupture variability and depth-dependent scaling of rupture speed and slip rate, inherited from GP2016, and specification of discrete high slip rupture patches, inherited from IM2011. The performance of the proposed method is examined in simulations of broadband ground motion from the 2016 Kumamoto, Japan earthquake, as well as comparisons with ground motion prediction equations (GMPEs). We generated rupture models with multi-scale heterogeneity, including a hybrid one in which the slip is a combination of high- slip patches and stochastic small scale variations. We find that the ground motions simulated with these rupture models match the general characteristics of the recorded near-fault motion equally well, over a broad frequency range (0–10 Hz). Additionally, the simulated ground motion is in good agreement with the predictions from Ground Motion Prediction Equations (GMPEs). Nonetheless, due to sensitivity of the ground motion to the local fault rupture characteristics, the performance among the models at near-fault sites is slightly different, with the hybrid model producing a somewhat better fit to the recorded ground velocity waveforms. Sensitivity tests of simulated near-fault ground motion to variations in the prescribed kinematic rupture parameters show that average rupture speeds higher than the default value in GP2016 (average rupture speed = 80% of local shear wave speed), as well as slip rate durations shorter than the default value in GP2016 (rise time coefficient = 1.6), generate ground motions that are higher than the recorded ones at periods longer than 1 s. We found that these two parameters also affect the along strike and updip rupture directivity effects, as illustrated in comparisons with the Kumamoto observations. [ABSTRACT FROM AUTHOR]

The Spanish Geophysical Data National Archive (Toledo Geophysical Observatory) is a centre created by Instituto Geográfico Nacional to collect all the geophysical documentation produced in all of the observatories IGN has had in operation throughout its history. All this information is transferred to the Geophysical Data National Archive where it is reviewed, classified and catalogued in a database, to be eventually filed in the records repository of the Archive, with the appropriate conditions for their future preservation. Its contents are digitized as backup and to meet the data requests received in this Archive. For the study of earthquakes throughout the twentieth century, this Archive has a large volume of information. The documents most consulted by researchers are the seismic records from the IGN Geophysical Observatories, but also the Archive houses an important collection of complementary information. [ABSTRACT FROM AUTHOR]

In this study, we developed a new search algorithm to find a multi-fault model of a complex earthquake using tsunami data, and applied it to the January 23, 2018 M7.9 Kodiak earthquake. Our method includes a Green's function based time reverse imaging (GFTRI) approach to invert for sea surface displacement using tsunami waveforms, followed by inversion of the sea surface displacement for the earthquake slip distribution. The global CMT focal mechanism for this event indicates that faulting occurred on a steeply dipping fault striking either N–S (right lateral) or E–W (left lateral), while subsequent work reveals a more complex pattern of strike-slip faulting. We carried out a number of source inversions using different combinations of faults to find the model based on an extremum for residual errors. Our results suggest that the rupture occurred on at least three faults oriented in approximately N–S and E–W directions. We further explored the fault-geometry parameters by perturbing them within a range suggested by previous work. We found that the sea surface displacement model is best fit by our preferred three fault-model with the set of parameters (strike, dip, rake): ( 165 ∘ , 60 ∘ , 154 ∘ ) and ( 265 ∘ , 60 ∘ , 10 ∘ ) for N–S and E–W directions, respectively. [ABSTRACT FROM AUTHOR]

On the basis of the continuous and dense GPS observations covering the northern segment of the Xiaojiang fault zone (n-XJFZ) from March 2012 to March 2016, we present the velocity field, spatiotemporal deformation, slip rate and locking depth of the n-XJFZ. The results provide strong support for achieving a better understanding of the deformation behavior of this fault. The heterogeneity of the GPS velocity field and relatively nonuniform distribution of seismicity suggest that the observational area is fragmented. Shear strain has been accumulating with an almost constant azimuth, which is consistent with the trends of the mapped major faults. The 2014 Ms 6.5 Ludian earthquake produced a sudden change in the dilatational strain, which was almost constant prior to the event, and an increase in the shear strain rate. The near-field deformation of the n-XJFZ estimated with the near-field data was larger than expected, revealing that the n-XJFZ is becoming more locked. These results imply that the seismic risk in the study area is currently rising and that, similar to the 2014 Ms 6.5 Ludian earthquake, future earthquakes will possibly occur away from mapped faults. [ABSTRACT FROM AUTHOR]

Some researchers have suggested that significant electromagnetic changes that can be detected prior to strong earthquakes are associated with the tectonics and subsurface structures beneath monitoring stations. Numerical simulation seems to support this phenomenon. However, to date, few field measurement data are available to address this issue. In this work, we used the shifting correlation method to analyze 2-month recordings of 20 geoelectric stations in Taiwan and found at least two stations had recorded geoelectric signals significantly correlated with known seismic events. These two stations are installed on large reverse faults, which are probably characterized by high stress concentrations before earthquakes. In addition, they share the same resistivity variation pattern, namely, a conductor layer sandwiched between two high-resistivity layers. Moreover, both stations are above the electrical resistivity boundaries, which means they have an increased probability of recording the abnormal disturbance once EM signals have been emitted from EQs. Our analysis results support the viewpoint that lateral and vertical electrical resistivity variation and conductors in the subsurface may be able to amplify seismic electric signals. [ABSTRACT FROM AUTHOR]

Interest in and pertinent studies related to the seismic hazard in the Himalayan region have increased significantly since the instrumental era, and each damaging earthquake encourages its reestimation. In the work presented herein, the non-Poissonian probabilities of exceedance of magnitudes in a specified time in the future were investigated for different elapsed times based on the recurrence time intervals of past earthquakes in the Himalaya, using the Weibull, log-normal, gamma, and inverse Gaussian stochastic models. The whole Himalayan arc is divided into four seismogenic source zones, viz. the Northwestern Himalayas (zone 1), the Central Seismic Gap Region (zone 2), the Eastern Nepal and Sikkim (zone 3), and the Eastern Himalayas (zone 4), by considering approximately 380 years of seismological data. The suitability of each stochastic model for each zone was estimated using the Kolmogorov–Smirnov (K–S) test, to describe the different physical processes responsible for earthquake occurrence. The results show that the gamma, inverse Gaussian, log-normal, and inverse Gaussian models were most suitable for zones 1–4, respectively, for M ≥ 6.0. The cumulative probability of recurrence intervals reaches up to 90% in 30 years for zones 1 and 2, 49 years for zone 3, and 41 years for zone 4. The estimated conditional probability reaches 90% in 30 years in zone 1, 35 years in zone 2, and 50 years in zones 3 and 4. The most suitable models for M ≥ 7.0 were found to be the log-normal for zones 1, 2, and 3 and gamma for zone 4. The cumulative probability for M ≥ 7.0 reaches 90% in 85 years in zone 1, 86 years in zone 2, 93 years in zone 3, and 148 years in zone 4. The estimated conditional probabilities reach 90% in 80 years in zone 1, 90 years in both zone 2 and 3, and 150 years in zone 4. It is strongly recommended that model suitability be evaluated in complex regions such as the Himalaya before proceeding with seismic hazard assessments. The heterogeneous and complex tectonics of the Himalayas, differentiated plate motions, different stress release patterns (spatially and temporally), and locking/unlocking of faults/thrusts are some of the reasons responsible for the different probabilistic models describing the earthquake occurrence phenomena in these four zones. [ABSTRACT FROM AUTHOR]

The historical and the present seismicity catalogues of the Garhwal Himalaya have been studied for their spatio-temporal variations and their implications on the seismotectonics of the region. The Micro-Seismicity, Fractal dimensions (Dc) and Frequency Magnitude Distribution (b-value) coupled with the available literature on geology, geomorphology and geophysics have been used to derive the seismotectonics and stress level changes in the region. The seismic cross sections for the relocated micro-seismicity, focal mechanisms and the swath profiles (for the presence of Physiographic Transition 2 (PT2) at the foothill of the Higher Himalaya) indicate the constant presence of the Mid-Crustal Ramp (MCR) in the detachment plane and its active seismogenic nature. The comparison of this scenario suggests the constant presence of seismogenically active MCR structure throughout the Central Seismic Gap. The seismic cross sections further reveal that the sensu stricto Main Central Thrust (Munsiari Thrust) is also a site of generation of the micro-seismicity in few segments due to its reactivation by thrusting along the MCR. The high fractal dimension value (Dc = 1.47) suggests the heterogeneous nature of the region, owing to the presence of local faults and transverse tectonics. The high stress accumulation in the Garhwal Himalaya with low b value (b = 0.70) suggests the high probability of occurrence of a larger or greater earthquake in the near-future. Further, the study also reveals that the 2011 Chamoli earthquake of M 5.0, preceded by a quiescence period of nearly a year shows different stress levels before and after its occurrence, which is well constrained with the increased moderate earthquake activity around the Chamoli region. This increased seismic activity and stress conditions in the Chamoli region suggest the high possibility of the occurrence of major earthquakes, hence the study recommend for a detailed seismic hazard evaluation of the region. [ABSTRACT FROM AUTHOR]

We study source characteristics of the September 28, 2017 Mw 7.5 Palu (Sulawesi, Indonesia) earthquake that occurred in central Sulawesi and triggered devastating tsunami waves along the coastal plains of the island. We apply point-source teleseismic P- and SH-body waveform inversion and kinematic slip inversion techniques to obtain double-couple source mechanism and comprehensive finite-fault slip model of the source. The overall results show a strike-slip faulting mechanism (strike: 353° ± 5°, dip: 65° ± 5° and rake angles: − 4° ± 5°) with a small amount of dip-slip component at a shallow focal depth of 16 ± 2 km associated with the NW–SE trending left-lateral Palu-Koro strike-slip fault in the central Sulawesi region. The P- wave first motion polarity readings recorded at near-field and regional seismic stations are found to be reasonably consistent with the source mechanism solution of the earthquake and estimated error limits. We have extensively studied and considered the rupture velocity to be about 4.1 km/s during the slip inversion as previously proposed by seismological and geodetic studies for this event. The obtained finite-fault slip distribution model displays a rupture starting from the hypocentre located at 16 km, and then it propagated south accompanied by high amount of displacement, and reached the surface. The model has two slip-patches of 2.0–4.0 m at north of the fault plane, and 5.0–6.3 m at south near Palu city, which is very well matched with the observed damage and destruction related to the earthquake. The fault length and width, average slip and stress drop values are estimated to be 150 km, 45 km, 1.5 m and 13 bars, respectively. We have also obtained total source duration to be about 40 s with the most of seismic energy released at 10 s and 25 s. Furthermore, a small dip-slip component is evidently observed from both source models, and we suggest that this oblique shear which reflects the bending of slip vector along the strike direction could be comparatively responsible for tsunami generation along the left-lateral Palu-Koro Fault. The validation of this hypothesis could be done by evaluating the results of the mathematical tsunami simulations based on the comprehensive non-uniform slip models along with a high-resolution bathymetry data, which provides the details of the continental shelf in Palu bay. [ABSTRACT FROM AUTHOR]

The Ventura Thrust system in California is capable of producing large magnitude earthquakes. Geological studies suggest that the fault geometry is complex, composed of multiple segments at different dips: thrust ramps dipping 30°–50° linked with bed-parallel décollements dipping < 10°. These latter types of gently dipping faults form due to preexisting weaknesses in the crust, and therefore have different frictional parameters from thrust ramps; the faults also experience different stresses because of how stresses are resolved onto the fault planes. Here, we use a two-dimensional fault model to assess how geometry and frictional properties of the ramp/décollement system should affect the seismic cycle. We test velocity-strengthening, velocity-weakening, and conditionally stable décollements, and in addition explore how the dip angle of the décollement changes the earthquake behavior. A velocity-strengthening décollement cannot replicate the through-going earthquake ruptures that have been inferred for the Ventura fault system. We therefore suggest that this and other décollements may be better represented using a velocity-weakening or conditionally stable response. Our results show that minor variations in fault geometry produce slip amounts and recurrence intervals that differ only by 10–20%, but do not fundamentally alter the types of earthquakes and interseismic slip. We conclude that geological constraints on fault geometry are typically sufficient to produce modeled earthquake sequences that are statistically consistent with paleoseismic records. However, both frictional parameters along the fault and effective normal stress influence earthquake rupture patterns significantly. More research is needed to adequately constrain these quantities in order for earthquake rupture models to work as effective predictors of fault behavior. [ABSTRACT FROM AUTHOR]

The surface deformation associated with the 2010 Mw 8.8 Maule earthquake in Chile was recorded in great detail before, during and after the event. The high data quality of the continuous GPS (cGPS) observations has facilitated a number of studies that model the postseismic deformation signal with a combination of relocking, afterslip and viscoelastic relaxation using linear rheology for the upper mantle. Here, we investigate the impact of using linear Maxwell or power-law rheology with a 2D geomechanical-numerical model to better understand the relative importance of the different processes that control the postseismic deformation signal. Our model results reveal that, in particular, the modeled cumulative vertical postseismic deformation pattern in the near field (< 300 km from the trench) is very sensitive to the location of maximum afterslip and choice of rheology. In the model with power-law rheology, the afterslip maximum is located at 20–35 km rather than > 50 km depth as suggested in previous studies. The explanation for this difference is that in the model with power-law rheology the relaxation of coseismically imposed differential stresses occurs mainly in the lower crust. However, even though the model with power-law rheology probably has more potential to explain the vertical postseismic signal in the near field, the uncertainty of the applied temperature field is substantial, and this needs further investigations and improvements. [ABSTRACT FROM AUTHOR]

The generation of the 2011 Tohoku-oki earthquake has been modeled by many authors by considering a dynamic weakening mechanism such as thermal pressurization (TP). Because the effects of TP on afterslip have not been investigated, this study develops a 3D quasi-dynamic model of the earthquake cycle to investigate afterslip of the Tohoku-oki earthquake, considering TP and the geometry of the plate boundary. We employ several velocity-weakening (VW) patches for Mw 7 class events, and two large shallow VW patches. The frictional properties are set as velocity-strengthening (VS) outside the VW patches. The results show that, during megathrust earthquakes, fast slip propagates to the surrounding VS regions near the VW patches owing to weakening by TP. Following Mw 9 events, large afterslips occur in regions below the northern shallow rupture area in the off-Fukushima region close to the Japan Trench, which is consistent with observations. In the VS region near the VW patches, during the early afterslip period, frictional behavior exhibits less VS with increasing slip velocity due to pore pressure reduction. We also consider the frictional properties of the shallow plate boundary fault off Tohoku, which exhibits a transition from VW to VS from low to high slip velocities. The results show the occurrence of slow slip events (SSEs) at intervals of a few decades at the shallow plate boundary. During megathrust events, the VW property at low slip velocity promotes slip along the shallow SSE region more than the case with VS property throughout the entire velocity range. [ABSTRACT FROM AUTHOR]

In earthquake seismology, an independent earthquake can produce a set of clusters having fore- and/or aftershocks. The main purpose of seismicity declustering is to refine a given earthquake catalog in order to retain independent events. The goal of retention of independent events by only declustering is a crucial benchmark for most of the mainshock-based analysis in seismology. In the present article, we used a re-updated unified earthquake catalog of Turkey and obtained several declustered catalogs applying different declustering methods. To compare the performance of applied declustering methods, each declustered catalog was then examined by simulation envelopes and Monte Carlo tests using some summary statistics for temporal and spatial point patterns. We found that the declustering method of Zhuang et al. (2002) based on the Epidemic Type Aftershock Sequence (ETAS) model, original version, and particularly Grünthal's variant of the Gardner and Knopoff (1974) method seemed to be most successful in finding and removing clusters in space and time for the earthquake catalog of Turkey examined. [ABSTRACT FROM AUTHOR]

Seismologists are increasingly adopting data mining and machine learning techniques to detect weak earthquake signals in large seismic data sets. The detection performance of these new methods, especially their sensitivity and false detection rate, depends on the choice of feature representation for waveform data. We have previously introduced Fingerprint and Similarity Thresholding (FAST), a new method for waveform-similarity-based earthquake detection that uses a pattern mining approach to detect earthquake signals without template waveforms. FAST has two key steps: fingerprint extraction and efficient indexing for similarity search. In this work, we focus on FAST fingerprint extraction: the method used to map short-duration waveforms to a set of features, called waveform fingerprints, used for detection. We describe the FAST fingerprint extraction method, a data-adaptive variation on the Waveprint audio fingerprinting method tailored for use in continuous seismic data. We compare the performance of the FAST fingerprint extraction method with existing fingerprinting techniques designed for audio identification. To overcome the challenges associated with using limited or incomplete event catalogs to evaluate detection algorithms, we propose a framework for quantifying the performance of different fingerprint extraction methods in the context of blind similarity-based detection. Our framework uses computational experiments on benchmark data sets, constructed with known event waveforms, to compute a measure of fingerprint effectiveness. We use this framework to show that, among the audio fingerprinting schemes considered in this work, our proposed FAST fingerprint extraction method achieves the most consistent performance in distinguishing similar, low signal-to-noise earthquake waveforms from noise in waveform data sets from eight stations in the Northern California Seismic Network. [ABSTRACT FROM AUTHOR]

In 2016, the Mw 5.9 Menyuan earthquake occurred at the western end of the Tianzhu seismic gap in the middle segment of the left-lateral strike-slip Haiyuan fault system. Studying the focal mechanism of the Menyuan earthquake and its correlation with historical seismicity is of great significance in understanding the tectonic style of the Haiyuan fault system and assessing the Tianzhu gap seismic risk. Using Sentinel-1A radar imagery, we obtain the coseismic deformation field of the Menyuan earthquake in the LOS direction and invert the deformation field slip distribution model. Based on the interseismic deformation field reflected by GPS data and the relocated results of aftershocks provided by previous studies, we then analyze the seismogenic nodal plane of the Menyuan earthquake and consider the west-dipping model to be the most likely seismogenic solution. The west-dipping model indicates that the average slip of the Menyuan earthquake is 0.41 m, and the average rake angle is 68°, with a magnitude of Mw 5.905. Considering the historical strong earthquakes and viscoelastic layered crust, the results from Coulomb failure stress modeling indicate that the Coulomb stress loading caused by the historical strong events promoted the occurrence of the 2016 Menyuan earthquake. Both the low seismicity within the Tianzhu gap and the cluster phenomenon of medium earthquakes on the Lao Hu Shan (LHS) and Leng Long Ling (LLL) faults have strong correlations with the stress change distribution resulting from the historical strong earthquakes. A series of medium events occurring on the north side of the LLL fault, represented by the 2016 Menyuan earthquake, would raise the seismic risk on the western end of the Tianzhu gap. [ABSTRACT FROM AUTHOR]

The casualties and financial losses caused by large earthquakes have led to an awareness of prediction importance of such earthquakes. The earthquake prediction is divided into four categories: long term, intermediate term, short term, and immediate. The M8 algorithm is one of the intermediate-term middle-range prediction algorithms primarily used to predict earthquake of magnitude 8 or more and is applied later for smaller magnitudes. The Iranian Plateau is less exposed to earthquake with magnitude 8 or more and it is observed that the seismicity rate in this region is generally low. Thus; the original M8 is not suitable for applying in this region. The objective of this study is to modify the M8 algorithm for Prediction of Major M7.0+ Earthquakes in the Iranian Plateau. The major earthquake of magnitude 7 or more in the Iranian plateau from 1975 to 2018 is considered as the target earthquakes. The hit rate times 1 minus alarm rate is defined as objective function and the particles swarm optimization meta-heuristic algorithm is used to maximize it. The optimum M8 could predict 14 out of 17 large earthquakes in the Iranian plateau while occupying 31.7% of the spatio-temporal space as the alarm. The results show that by employing an optimization algorithm, we can modify the M8 algorithm for efficient prediction of the target magnitudes less than 8 in the regions with low seismicity rate. [ABSTRACT FROM AUTHOR]

The present study estimates source parameters and proposes scaling relationships for moderate size earthquakes (mb 3.7-5.8) in seismically active North-East India region. The study is based upon the spectral analysis of high-quality waveforms comprising of P- and S-waves obtained from strong ground motion (SMA) records of 50 earthquakes that has occurred in the region. A two-step procedure is adopted to estimate the earthquake source parameters. It has been observed that the average seismic moment and source radii vary from 1.05 × 1015 to 1.99 × 1017 N-m and 500 to 2000 m, respectively. The average corner frequency ratio [fC(P)/fC(S)] of P-wave and S-wave is found to be 1.2, which shows the shift in the corner frequency. The total estimated energy varies between 9.22 × 1010 and 1.42 × 1014 J, while the average stress drop varies from 1.8 to 29.4 MPa. One of the major outcome of this study is that the stress drop does not vary significantly with the magnitude and self-similarity exist among the earthquakes in North-East India region. The scaling relation between the seismic moment and the corner frequency is Mofc3=1.35×1017N- ms-3. The median stress drop value for NE India region is found to be about 9.2 MPa. The earthquake source parameters and the scaling relations developed in this study will be useful for carrying scenario based seismic hazard analysis studies in the NE India region. [ABSTRACT FROM AUTHOR]

Site response analysis is conducted at 37 seismic stations located in the Gauteng, North West and Free State provinces in South Africa, using the Nakamura H/V spectral ratio technique on records of the Orkney 5 August 2014 earthquake. The earthquake, of magnitude ML = 5.5, led to the unfortunate death of one person and damage of more than 600 houses. Intensity data collected soon after the event showed that the effects of the earthquake appeared to vary significantly across the region. This motivated the authors to conduct a more detailed investigation of the effects of site conditions on seismic station records in the region. Resonance frequency values obtained from the H/V ratios were observed to vary strongly across the region and also within seismic station clusters. Similar behaviour was observed with the peak amplitude of the ratios at the resonance frequency, except for the Johannesburg area whose results showed a relatively simple shape of the ratios implying less complex velocity structure. All the H/V ratios exhibit dominant peaks at resonant frequencies that varied between 0.5 and 35 Hz. The average observed resonant frequency was f = 7.9 Hz. The amplitude of the dominant peaks also varied strongly from 1.66 to 11.69, with only two sites exhibiting maximum peaks with amplitude smaller than 2. These results serve as a strong motivation or justification for the on-going microzonation studies in South Africa, where a detailed study of the velocity structure will be used to obtain reliable information on site amplification and resonance. [ABSTRACT FROM AUTHOR]

In this paper, we report the co-seismic temperature response of the Ms6.3 Kangding earthquake in Sichuan, China, which occurred within a bedrock temperature monitoring station network constructed in the east of the Qinghai-Tibet Plateau. Results indicate that two kinds of co-seismic responses of bedrock temperature, exponential and step-rise ones, were recorded at different stations. As for the former, the amplitude of co-seismic response is about 5.6-11.5 mK (the average value is 7.33 mK), while the latter is about 0.31-0.98 mK (the average value is 0.52 mK). These two kinds of responses would be indicative of the two different mechanisms for change in temperature. On the one hand, the exponential responses represent the effects of fluid advection along the borehole wall, which are associated with a finite quantity of heat produced by earthquake-driven transient fluid flow. The step-rise responses, on the other hand, represent the direct response of temperature to change in the crustal stress accompanying with earthquake. We still tested relationship between stress variation and temperature response on the rock samples taken from the boreholes, and the average value is 0.77 mK/MPa. Upon thus, these step-rise temperature responses imply that co-seismic change in mean stress is about 0.40 MPa. We simplify effects of fluid by presuming a one-dimensional model where the flow is either up or down based on a pressure change due to compression or tension. The stress state, compression or tension, deduced by the direction of the fluid flow is qualitatively accordant with the direct response of bedrock temperature to stress change. In summary, characteristic changes in bedrock temperature occurred coincidentally with the earthquake at different stations, agreeing generally with regional stress adjustments accompanying the earthquake. Changes in bedrock temperature do seem to offer a useful means of monitoring dynamic changes in shallow crustal stress. [ABSTRACT FROM AUTHOR]

The Galati-Izvoarele region, located in eastern Romania, came into the public attention relatively recent, when hosted an unusual intense earthquake sequence. During September-November 2013, several hundred shallow crust earthquakes were recorded in the area. There were several attempts to explain the phenomenon, and hypotheses more or less documented have been formed. Some speculations occurred on the potential connection between the seismic swarm and oil industry activities. The paper summarizes the results of local geophysical surveys conducted in the area, jointly analysed with the observed seismicity. The main results of the study reveal the Galati-Izvoarele region as a seismic-active area belonging to the northwest prolongation of North Dobrogea mobile zone. The earthquakes were generated mainly in a highly fragmented local graben-like structure, transversally superposed on the descending slope of the North Dobrogea Promontory. The graben fault system was and might be (re)activated each time when tectonic forces acting in the Carpathians foreland intensify. Changes in the intensity of tectonic forces may reflect in the slip acceleration along Peceneaga-Camena Fault, as observed at the Baspunar Geodynamic Observatory. For example, the paroxysmal phase of the Galati-Izvoarele swarm was shortly preceded by a significant increase of the Peceneaga-Camena Fault slip rate recorded at Baspunar Geodynamic Observatory. To conclude, the Galati-Izvoarele region must be seen as a seismic-prone area and any significant increase of the tectonic stress in the Carpathians foreland may generate another seismic sequence in an unpredictable future. [ABSTRACT FROM AUTHOR]

Statistical methods are useful tools to aid the recognition of patterns and extract information from a large amount of data available through resources such as earthquake catalogs. Visibility graph analysis is one of these relatively new statistical techniques that can be applied on data in the form of time series, and map them into a graph of nodes and connections, which makes it possible to use network theory for characterizing the original data. We present a study applying visibility graph analysis to a seismicity catalog for the Alaska crust and the Aleutian subduction zone. The catalog is gathered from the United States Geological Survey database, for the years between 1900 and mid 2017. A history of several earthquakes and a variety in seismic features, both near surface and at depth, make this region one of the richest areas to investigate possible seismic patterns and correlations. The focus here is on examining the previously suggested correlation between b value of the Gutenberg-Richter relation and the k-M slope from a visibility graph analysis. The visibility graph method defines a k degree or connectivity degree for each event according to its magnitude and position in time series. The k-M slope represents the slope of the regression line of these pairs of magnitude and connectivity degree, as a single number for each zone. We calculate the k-M slope for selected zones for Alaska and the Aleutians and add it to the data from previous worldwide studies and the results verify and improve the linear universal relationship between b value and k-M slope suggested by past studies, which indicates that the visibility graph analysis can work as an alternative approach for studying earthquake sequence. [ABSTRACT FROM AUTHOR]

The time variation of several statistical parameters describing the complex time dynamics of the seismicity of Azerbaijan from 2010 to 2016 is investigated. Besides the well-known Gutenberg-Richter b value and the coefficients of variation, two quantities, derived by the recent method of horizontal visibility graph are analysed, namely the mean connectivity degree, which depicts an innovative way to link seismic events, and the Kullback-Leibler divergence (KLD) that informs about the irreversibility of the seismic process. Our findings indicate the emergence of pre- and co-seismic patterns in the time variation of all the analysed parameters in relationship with the strongest events of the Azerbaijan seismic catalog. In particular, the typical increase-decrease behavior has been found in b before the occurrence of large shocks. Similarly, the coefficients of variation signals are statistically significant high value in the period when the largest events occur and in most cases even before they struck the area. The mean connectivity degree and the KLD show several anomalous values in association with the occurrence of large events, in agreement with the view of earthquakes as irreversible ruptures of the crust. [ABSTRACT FROM AUTHOR]

We present refined finite fault models (FFM) for the 2014 Cephalonia (Keffalinia, Kefalonia) seismic sequence (Mw ~ 6.0), at the NW edge of the Aegean Arc (Ionian Sea). The area represents the seismically most active part of Europe and a continental promontory in which fault modeling is a challenge because of structural complexity and poor coverage by seismological, GPS and InSAR data. Inversion was based on GPS data and a new algorithm permitting fusion of slip vectors of individual earthquakes and of their cumulative dislocation and accepting constraints and collocation-type analysis of uncertainties. Computed FFM, which correspond to an essentially strike-slip fault and a blind, shallow oblique slip thrust, were assessed by sensitivity analysis and InSAR data and are consistent with the tectonic fabric of the area. They can also explain the observed extreme peak ground accelerations. The 2014 faults, in combination with FFMs of the 2003 and 2015 Leucas (Lefkada, Lefkas) earthquakes farther NE and of the 1983 M7.0 earthquake farther SW, constrain a > 100 km long immature, strike-slip fault zone along/close to the Cephalonia-Leucas coasts. This fault pattern, previously regarded as a poorly documented Cephalonia Transform Fault, consists of occasionally overlapping oblique slip segments with variable geometric and kinematic characteristics in a shear zone landwards of the plate interface, as evidence from seismic profiles reveals. This pattern may explain the enigmatic superimposition of shear and compression in the NW edge of the Aegean Arc. [ABSTRACT FROM AUTHOR]

In this paper, we report on an analysis of rupture processes of mining-induced events using the Empirical Green Function approach. The basic goal of this analysis is to estimate the dynamic stress drop—the quantity describing frictional forces at a slipping fault plane during the unstable part of an earthquake. The presented results cover 40 selected events with magnitude Mw ranging between 2.1 and 3.6 occurring in the Rudna copper mine (Poland) between 1996 and 2006. The spatial extent of the seismic network operated by the mine enabled us to estimate not only the dynamic stress drop but also the rupture velocities for most of the events studied. The results are analyzed in terms of correlations of the ratio of static to dynamic stress drop with other parameters characterizing the rupture processes. We also pose a question about the conditions of occurrence of over- and undershooting stress drop mechanisms. For all but two events, the estimated dynamic stress drop ranges between 0.1 and 4 MPa and is dominated by lower values. There are only two exceptions when it reaches the level of the order of 10 MPa. The reliability of these two exceptional cases is low, however. The rupture velocity, needed for dynamic stress drop calculation, was estimated from observed directivity effects. The obtained values ranged between 0.2 and almost 0.9 shear wave velocity, with dominating low velocities. The ratio of static to dynamic stress drop does not clearly correlate with the seismic scalar moment, source radius estimated according to Madariaga's model, or static stress drop. It only positively correlates with the rupture velocity and ranges from values lower than 1 (undershooting mechanisms), mostly for slow events, up to values larger than 1 (overshooting mechanisms) for the majority of fast events. For all events with overshooting-type mechanisms, the estimated rupture velocity Vr was larger than half of the S-wave velocity Vs. On the other hand, for the undershooting-type events the associated rupture velocity was in most cases smaller than 0.6 Vs and large rupture speed was observed only in a few cases for this type of events. [ABSTRACT FROM AUTHOR]

The characteristics of radiation and propagation of seismic waves required in various seismological applications, especially in seismic hazard assessment, are estimated in northern Finland based on records of local earthquakes (~ 80 records from four stations, Mw ~ 1.5 to 4.1, h ~ 3 to 25 km). Northern Finland possesses relatively low seismic activity; however, rather strong earthquakes occurred there in the past. We applied coda-normalization method to estimate the quality factor Q(f)~ Q0fn and then verified and corrected the Q(f) estimates at low frequencies by stochastic simulations. We obtained Q0~ 80 to 100, n ~ 1.1 to 1.2 for hypocentral distances of ~ 20 to 150 km, and Q0~ 180 to 350, n ~ 0.7 to 0.9 for hypocentral distances of ~ 150 to 320 km. Other parameters were estimated by the empirical methods and stochastic simulation of local earthquakes (ML > 2.0). We estimated the stress drop (∆σ ~ 200 bars), geometrical spreading (as a two-segment function: 1/R for R ~ 0 to 80 km and 1/80 for R ~ 80 to 300 km), the duration of seismic motion depending on the hypocentral distance, kappa value (κ ~ 0.001 to 0.03 s), and some other parameters. The obtained high estimates of the stress drop, along with rather high Q values, may result in noticeably increased (compared to those that could be expected on average) PGA estimates in seismic hazard assessment in northern Finland. [ABSTRACT FROM AUTHOR]

We have investigated several relationships between ML, M(NEIC) and Mw for the earthquakes locally recorded in the Saint Peter and Saint Paul Archipelago (SPSPA), Equatorial Atlantic. Because we only have one station in the area, we could not derive attenuation relations for events recorded at different distances at different stations. Our approach was then to compare our ML estimates with magnitudes reported by NEIC. This approach produced acceptable results particularly for epicentral distance smaller than 100 km. For distances greater that 100 km, there is a systematic increase in the residuals probable due to the lack of station correction and our inability to accurately estimate Q. We also investigate the Mw—M(NEIC) relationship. We find that Mw estimates using S-wave produce smaller residuals when compared with both M(NEIC). Finally, we also investigate the ML—Mw relationship and observe that given the data set we have, the 1:1 holds. We believe that the use of the present methodologies provide consistent magnitude estimates between all the magnitudes investigated that could be used to better assess seismic hazard in the region. [ABSTRACT FROM AUTHOR]

'What is the maximum possible ground motion near an earthquake fault?' is an outstanding question of practical significance in earthquake seismology. In establishing a possible theoretical cap on extreme ground motions, the representation integral of elasticity, providing an exact, within limits of applicability, solution for fault radiation at any frequency, is an under-utilized tool. The application of a numerical procedure leading to synthetic ground displacement, velocity, and acceleration time histories to modeling of the record at the Lucerne Valley hard-rock station, uniquely located at 1.1 km from the rupture of the M 7.2 Landers, California event, using a seismologically constrained temporal form of slip on the fault, reveals that the shape of the displacement waveform can be modeled closely, given the simplicity of the theoretical model. High precision in the double integration, as well as carefully designed smoothing and filtering, are necessary to suppress the numerical noise in the high-frequency (velocity and acceleration) synthetic motions. The precision of the integration of at least eight decimal digits ensures the numerical error in the displacement waveforms generally much lower than 0.005% and reduces the error in the peak velocities and accelerations to the levels acceptable to make the representation theorem a reliable tool in the practical evaluation of the magnitude of maximum possible ground motions in a wide-frequency range of engineering interest. [ABSTRACT FROM AUTHOR]

We study the complex rupture history of the 2016 Mw6.4 Meinong earthquake and the 2010 Mw6.2 Jiaxian earthquake in southern Taiwan by simultaneously inverting near-field strong-motion records, local and teleseismic broadband waveforms along with long-period surface waves. The focal mechanism results reveal that both earthquakes may rupture two different blind faults. The rupture of the 2016 event is dominated by the strike-slip motion with minor thrust faulting, while the 2010 event is a relatively high-angle thrust earthquake. Our preferred finite-fault source models suggest that the coseismic rupture history of the 2016 event should be relatively more complex than the 2010 event. During the 2016 event, two main patches of slip characterize the coseismic slip history. The cumulative seismic moment within 12 s of rupture is about 5.36 × 10 N m, which is 1.9 times of the moment of the 2010 event. The slip of the 2016 event is associated with relatively larger perk slip of 0.7 m at shallower depth (~18-19 km), higher average slip of 0.3 m and faster slip rate with the maximum value of 3.4 m/s. Our kinematic models can shed some light on the cause of the difference in seismic hazard between these two earthquakes, and will be further applied to analyze the deep blind fault structure in southern Taiwan. [ABSTRACT FROM AUTHOR]

Pattern informatics (PI), load/unload response ratio (LURR), state vector (SV), and accelerating moment release (AMR) are four previously unrelated subjects, which are sensitive, in varying ways, to the earthquake's source. Previous studies have indicated that the spatial extent of the stress perturbation caused by an earthquake scales with the moment of the event, allowing us to combine these methods for seismic hazard evaluation. The long-range earthquake forecasting method PI is applied to search for the seismic hotspots and identify the areas where large earthquake could be expected. And the LURR and SV methods are adopted to assess short-to-intermediate-term seismic potential in each of the critical regions derived from the PI hotspots, while the AMR method is used to provide us with asymptotic estimates of time and magnitude of the potential earthquakes. This new approach, by combining the LURR, SV and AMR methods with the choice of identified area of PI hotspots, is devised to augment current techniques for seismic hazard estimation. Using the approach, we tested the strong earthquakes occurred in Yunnan-Sichuan region, China between January 1, 2013 and December 31, 2014. We found that most of the large earthquakes, especially the earthquakes with magnitude greater than 6.0 occurred in the seismic hazard regions predicted. Similar results have been obtained in the prediction of annual earthquake tendency in Chinese mainland in 2014 and 2015. The studies evidenced that the ensemble approach could be a useful tool to detect short-to-intermediate-term precursory information of future large earthquakes. [ABSTRACT FROM AUTHOR]

This study considers the statistics of fluid-induced and remotely triggered seismicity at The Geysers geothermal field, California. Little seismicity was reported before steam extraction began in 1960. Beginning in 1980 the residual water associated with power generation was re-injected, producing induced seismicity. Beginning in 1997 large-scale injections of cold water began to enhance the generation of steam. This led to an increase in M < 1.2 earthquakes from approximately 5 per month to 20. Two excellent seismic networks generate two earthquake catalogs for the fluid-induced seismicity at The Geysers. Although this seismicity satisfies Gutenberg-Richter (GR) scaling to a good approximation, the scaling parameters differ. We propose a correction that eliminates this problem. We show that the seismicity at The Geysers is nearly independent of time for the period 2009-2014 and suggest that this supports our hypothesis that the seismic moment release is in near balance with the geodetic moment accumulation in the region. Our study demonstrates that aftershocks of the larger fluid-induced earthquakes also satisfy GR scaling as well as Omori's law for their time dependence. Our results support the hypothesis that the earthquakes are caused by the reduction in friction on faults due to the injected fluids. Statistics of remotely triggered earthquakes and their associated aftershocks at The Geysers are also presented. The 8/24/14 M = 6.02 South Napa earthquake triggered an M ≈ 4.38 event as well as some 80 other M > 1.25 events. The GR and decay statistics are given. However, to separate aftershocks from remotely triggered earthquakes, an additional triggered sequence is studied. The M = 7.2 4/4/10 Baja earthquake triggered some 34 M > 1.25 earthquakes at The Geysers in the first hour including an M = 3.37 event. We conclude that the remotely triggered seismicity is dominated by local aftershocks of the larger remotely triggered earthquakes. [ABSTRACT FROM AUTHOR]

In this study, we analyze the space-time evolution of the seismic strain release in the area shocked by the still ongoing Italian Central Apennines seismic crisis started on August 24, 2016 and culminated with the October 30 main shock of M 6.5. Specifically, we examine the variation in time and space of the seismic strain release rate with the aim of identifying the presence of peculiar seismicity patterns, such as seismic gaps, according to the seismic cycle theory. To this end, seismic strain rates are checked for consistency with strain rates from GPS measurements to possibly adjust them for missing events due to limited seismic catalog extension or incompleteness at large magnitudes. Our results has revealed that the seismic crisis followed a long-term quiescence of about 310 years, characterized by the absence of M6.5+ earthquakes, and marked by an almost steady release of seismic deformation. Such temporal gap started after the occurrence of two nearby strong events in 1703 (Valnerina and L'Aquila earthquakes with magnitudes of 6.9 and 6.7, respectively) and terminated with the beginning of the current Central Apennines seismic crisis. [ABSTRACT FROM AUTHOR]

Crustal gravitational potential energy (GPE) change induced by earthquakes is an important subject in geophysics and seismology. For the past forty years the research on this subject stayed in the stage of qualitative estimate. In recent few years the 3D dynamic faulting theory provided a quantitative solution of this subject. The theory deduced a quantitative calculating formula for the crustal GPE change using the mathematic method of tensor analysis under the principal stresses system. This formula contains only the vertical principal stress, rupture area, slip, dip, and rake; it does not include the horizontal principal stresses. It is just involved in simple mathematical operations and does not hold complicated surface or volume integrals. Moreover, the hanging wall vertical moving (up or down) height has a very simple expression containing only slip, dip, and rake. The above results are significant to investigate crustal GPE change. Commonly, the vertical principal stress is related to the gravitational field, substituting the relationship between the vertical principal stress and gravitational force into the above formula yields an alternative formula of crustal GPE change. The alternative formula indicates that even with lack of in situ borehole measured stress data, scientists can still quantitatively calculate crustal GPE change. The 3D dynamic faulting theory can be used for research on continental fault earthquakes; it also can be applied to investigate subduction earthquakes between oceanic and continental plates. Subduction earthquakes hold three types: (a) crust only on the vertical up side of the rupture area; (b) crust and seawater both on the vertical up side of the rupture area; (c) crust only on the vertical up side of the partial rupture area, and crust and seawater both on the vertical up side of the remaining rupture area. For each type we provide its quantitative formula of the crustal GPE change. We also establish a simplified model (called CRW Model) as follows: for Type B and Type C subduction earthquakes, if the seawater average depth on the vertical up side of the rupture area is less than a tenth of the hypocenter depth, then take the approximation that the seawater above the continental plate is replaced by the upper crustal material of the continental plate. The formula of quantitative calculating the crustal GPE change is also provided for this model. Finally, for 16 September 2015 Mw 8.3 Illapel Chile earthquake, we apply CRW Model and obtain the following results: the crustal GPE change is equal to 1.8 × 10 J, and the hanging wall vertical moving-up height is 1.9 m with respect to the footwall. We believe this paper might be the first report on the quantitative solution of the crustal GPE change for this subduction earthquake; our results and related method will be helpful in research into the earthquakes in Peru-Chile subduction zone and the Andean orogeny. In short, this study expounds a new method for quantitative determining the crustal GPE change caused by subduction earthquakes, which is different from other existing methods. [ABSTRACT FROM AUTHOR]

The magnitude-frequency relationship is a fundamental statistic in seismology. Customarily, the temporal variations of b values in the magnitude-frequency distribution are demonstrated via 'sliding-window' approach. However, the window size is often only tuned empirically, which may cause difficulties in interpretation of b value variability. In this study, a continuous-time hidden Markov model (HMM) is applied to characterize b value variations of New Zealand shallow earthquakes over decades. HMM-based approach to the b value estimation has some appealing properties over the popular sliding-window approach. The estimation of b value is stable over a range of magnitude thresholds, which is ideal for the interpretation of b value variability. The overall b values of medium and large earthquakes across North Island and northern South Island in New Zealand vary roughly at a decade scale. It is noteworthy that periods of low b values are typically associated with the occurrences of major large earthquakes. The overall temporal variations of b values seem prevailing over many grids in space as evidenced by a comparison of spatial b values in many grids made between two periods with low or high b values, respectively. We also carry out a pre-seismic b value analysis for recent Darfield earthquake and Cook Strait swarm. it is suggested that the mainshock rupture is nucleated at the margin of or right at low b value asperities. In addition, short period of pre-seismic b value decrease is observed in both cases. The overall time-varying behavior of b values over decades is an indication of broad scale of time-varying behavior associated with subduction process, probably related to the convergence rate of the plates. The advance in the method of b value estimation will enhance our understanding of earthquake occurrence and may lead to improved risk forecasting. [ABSTRACT FROM AUTHOR]

The problem of estimating the maximum possible earthquake magnitude $$m_\mathrm{max}$$ has attracted growing attention in recent years. Due to sparse data, the role of uncertainties becomes crucial. In this work, we determine the uncertainties related to the maximum magnitude in terms of confidence intervals. Using an earthquake catalog of Iran, $$m_\mathrm{max}$$ is estimated for different predefined levels of confidence in six seismotectonic zones. Assuming the doubly truncated Gutenberg-Richter distribution as a statistical model for earthquake magnitudes, confidence intervals for the maximum possible magnitude of earthquakes are calculated in each zone. While the lower limit of the confidence interval is the magnitude of the maximum observed event,the upper limit is calculated from the catalog and the statistical model. For this aim, we use the original catalog which no declustering methods applied on as well as a declustered version of the catalog. Based on the study by Holschneider et al. (Bull Seismol Soc Am 101(4):1649-1659, 2011), the confidence interval for $$m_\mathrm{max}$$ is frequently unbounded, especially if high levels of confidence are required. In this case, no information is gained from the data. Therefore, we elaborate for which settings finite confidence levels are obtained. In this work, Iran is divided into six seismotectonic zones, namely Alborz, Azerbaijan, Zagros, Makran, Kopet Dagh, Central Iran. Although calculations of the confidence interval in Central Iran and Zagros seismotectonic zones are relatively acceptable for meaningful levels of confidence, results in Kopet Dagh, Alborz, Azerbaijan and Makran are not that much promising. The results indicate that estimating $$m_\mathrm{max}$$ from an earthquake catalog for reasonable levels of confidence alone is almost impossible. [ABSTRACT FROM AUTHOR]

The paper considers Poisson temporal occurrence of earthquakes and presents a way to integrate uncertainties of the estimates of mean activity rate and magnitude cumulative distribution function in the interval estimation of the most widely used seismic hazard functions, such as the exceedance probability and the mean return period. The proposed algorithm can be used either when the Gutenberg-Richter model of magnitude distribution is accepted or when the nonparametric estimation is in use. When the Gutenberg-Richter model of magnitude distribution is used the interval estimation of its parameters is based on the asymptotic normality of the maximum likelihood estimator. When the nonparametric kernel estimation of magnitude distribution is used, we propose the iterated bias corrected and accelerated method for interval estimation based on the smoothed bootstrap and second-order bootstrap samples. The changes resulted from the integrated approach in the interval estimation of the seismic hazard functions with respect to the approach, which neglects the uncertainty of the mean activity rate estimates have been studied using Monte Carlo simulations and two real dataset examples. The results indicate that the uncertainty of mean activity rate affects significantly the interval estimates of hazard functions only when the product of activity rate and the time period, for which the hazard is estimated, is no more than 5.0. When this product becomes greater than 5.0, the impact of the uncertainty of cumulative distribution function of magnitude dominates the impact of the uncertainty of mean activity rate in the aggregated uncertainty of the hazard functions. Following, the interval estimates with and without inclusion of the uncertainty of mean activity rate converge. The presented algorithm is generic and can be applied also to capture the propagation of uncertainty of estimates, which are parameters of a multiparameter function, onto this function. [ABSTRACT FROM AUTHOR]

Strong mining-induced earthquakes exhibit various aftershock patterns. The aftershock productivity is governed by the geomechanical properties of rock in the seismogenic zone, mining-induced stress and coseismic stress changes related to the main shock's magnitude, source geometry and focal mechanism. In order to assess the quantitative aftershock productivity potential in the mining environment we apply a forecast model based on natural seismicity properties, namely constant tectonic loading and the Gutenberg-Richter frequency-magnitude distribution. Although previous studies proved that mining-induced seismicity does not obey the simple power law, here we apply it as an approximation of seismicity distribution to resolve the number of aftershocks, not considering their magnitudes. The model used forecasts the aftershock productivity based on the background seismicity level estimated from an average seismic moment released per earthquake and static stress changes caused by a main shock. Thus it accounts only for aftershocks directly triggered by coseismic process. In this study we use data from three different mines, Mponeng (South Africa), Rudna and Bobrek (Poland), representing different geology, exploitation methods and aftershock patterns. Each studied case is treated with individual parameterization adjusted to the data specifics. We propose the modification of the original model, i.e. including the non-uniformity of M , resulting from spatial correlation of mining-induced seismicity with exploitation. The results show that, even when simplified seismicity distribution parameters are applied, the modified model predicts the number of aftershocks for each analyzed case well and accounts for variations between these values. Such results are thus another example showing that coseismic processes of mining-induced seismicity reflect features of natural seismicity and that similar models can be applied to study the aftershock rate in both the natural and the mining environment. [ABSTRACT FROM AUTHOR]

Anomalies in polarization angles of teleseismic waves have been used to understand effect of scattered arrivals from subsurface heterogeneities. Seismological data recorded in southern India show polarization anomalies up to 5° for several stations. These anomalies are most pronounced for earthquakes from western and southern azimuths. Furthermore, stations located near the boundary of Dharwar craton and southern Granulites are more affected by scattered waves. Considering that many of the nearby stations show similar patterns of polarization anomalies, it is likely that the source of scattered energy is located at shallower depths. The non-stationary nature of seismic arrivals warrants determination of frequency-dependent polarization. Result obtained using multi-taper spectral analysis method indicates that data are contaminated at frequencies greater than ~2 Hz for most of the stations. Furthermore, surface-wave records also indicate off-azimuth arrivals, and quasi-Love waves indicating heterogeneities or anisotropy in the subsurface. These small-scale heterogeneities that may be located in crust may be important for studies using converted phases and ground motion prediction studies. [ABSTRACT FROM AUTHOR]

According to the historical earthquake catalog of Italy, the country experienced a pulse of seismicity between the 17th century, when the rate of destructive events increased by more than 100%, and the 20th century, characterized by a symmetric decrease. In the present work, I performed a statistical analysis to verify the reliability of such transient, considering different sources of bias and uncertainty, such as completeness and declustering of the catalog, as well as errors on magnitude estimation. I also searched for a confirmation externally to the catalog, analyzing the correlation with the volcanic activity. The similarity is high for the eruptive history of Vesuvius, which agrees on both the main rate changes of the 17th and 20th centuries and on minor variations in the intermediate period. Of general interest, beyond the specific case of Italy, the observed rate changes suggest the existence of large-scale crustal processes taking place within decades and lasting for centuries, responsible for the synchronous activation/deactivation of remote, loosely connected faults in different tectonic domains. Although their origin is still unexplained (I discuss a possible link with the climate changes and the consequent variations of the sea level), their existence and long lasting is critical for seismic hazard computation. In fact, they introduce a hardly predictable time variability that undermines any hypothesis of regularity of the earthquake cycle on individual faults and systems of interconnected faults. [ABSTRACT FROM AUTHOR]

We applied the Hilbert-Huang transform (HHT) method to extract the infrasound generated by the 2013 Lushan earthquake and its following aftershocks in China from a nearly continuous infrasound recode made 130 km from the earthquake epicenter. An improved STA/LTA algorithm was adopted for detecting the ambient infrasonic events from the data record. A powerful processing technique for non-stationary signal, the HHT, was applied to extract the significant intrinsic mode functions (IMFs) of the infrasonic signal associated with the earthquakes. The features of the extracted IMFs, such as the dominant frequency, the maximum amplitude and the spectral entropy, were investigated using Hilbert spectral analysis. Regression analysis between the maximum amplitude in the infrasound spectra and the magnitudes of the earthquakes was carried out to verify the source of the infrasound events detected. The results demonstrated that the HHT method could successfully identify the infrasound related to the earthquakes. [ABSTRACT FROM AUTHOR]

The seismic spectrum can be constructed by assuming a Brune spectral model and estimating the parameters of seismic moment ( M ), corner frequency ( f ), and high-frequency site attenuation ( κ). Using seismic data collected during the 2010-2011 Canterbury, New Zealand, earthquake sequence, we apply the non-linear least-squares Gauss-Newton method, a deterministic downhill optimization technique, to simultaneously determine the M , f , and κ for each event-station pair. We fit the Brune spectral acceleration model to Fourier-transformed S-wave records following application of path and site corrections to the data. For each event, we solve for a single M and f , while any remaining residual kappa, $$\kappa_{\text{r}}$$ , is allowed to differ per station record to reflect varying high-frequency falloff due to path and site attenuation. We use a parametric forward modeling method, calculating initial M and f values from the local GNS New Zealand catalog M magnitudes and measuring an initial $$\kappa_{\text{r}}$$ using an automated high-frequency linear regression method. Final solutions for M , f , and $$\kappa_{\text{r}}$$ are iteratively computed through minimization of the residual function, and the Brune model stress drop is then calculated from the final, best-fit f . We perform the spectral fitting routine on nested array seismic data that include the permanent GeoNet accelerometer network as well as a dense network of nearly 200 Quake Catcher Network (QCN) MEMs accelerometers, analyzing over 180 aftershocks M ≥ 3.5 that occurred from 9 September 2010 to 31 July 2011. QCN stations were hosted by public volunteers and served to fill spatial gaps between existing GeoNet stations. Moment magnitudes determined using the spectral fitting procedure ( M ) range from 3.5 to 5.7 and agree well with M , with a median difference of 0.09 and 0.17 for GeoNet and QCN records, respectively, and 0.11 when data from both networks are combined. The majority of events are calculated to have stress drops between 1.7 and 13 MPa (20th and 80th percentile, correspondingly) for the combined networks. The overall median stress drop for the combined networks is 3.2 MPa, which is similar to median stress drops previously reported for the Canterbury sequence. We do not observe a correlation between stress drop and depth for this region, nor a relationship between stress drop and magnitude over the catalog considered. Lateral spatial patterns in stress drop, such as a cluster of aftershocks near the eastern extent of the Greendale fault with higher stress drops and lower stress drops for aftershocks of the 2011 M 6.2 Christchurch mainshock, are found to be in agreement with previous reports. As stress drop is arguably a method-dependent calculation and subject to high spatial variability, our results using the parametric Gauss-Newton algorithm strengthen conclusions that the Canterbury sequence has stress drops that are more similar to those found in intraplate regions, with overall higher stress drops that are typically observed in tectonically active areas. [ABSTRACT FROM AUTHOR]