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The geological activity in Sichuan and Yunnan of China is intense, and large earthquakes such as the Tonghai earthquake in 1970 have caused huge casualties and economic losses. Therefore, it is significant to reduce the long-period earthquake damage of dams and high-rise buildings to reproduce the near-fault long-period ground motion characteristics of the Tonghai earthquake. In this paper, the finite difference method is used to predict the long-period characteristics of the Tonghai Ms 7.8 earthquake. Considering the uncertainty of the initial fracture point, number of asperities, and slip angle, 18 seismic scenarios are established. The predicted results are verified by comparing intensity, attenuation relation and pulse probability distribution. At the same time, based on the velocity pulse recognition method, the pulse probability distribution of the near-field is obtained. We selected six seismic scenarios with high probability from 18 seismic scenarios. Our results show that the spatial distribution and pulse probability distribution of near-field simulated ground motion is significantly affected by the initial rupture positions. After the characteristics of the largest asperity on the fault are determined, the remaining asperities have limited influence on the spatial distribution of simulated ground motion. This study expands the application scope of the finite difference method, which can simulate the seismic intensity characteristics of destructive earthquakes in areas with few seismic records. [ABSTRACT FROM AUTHOR]

According to theory, earthquakes may produce disturbances in surrounding areas and affect the major earthquake occurrence rate of surrounding faults. The MS 6.6 Jinghe Earthquake on 9th August, 2017 occurred in the Tienshan Seismic Belt where there is much tectonic activity and many strong earthquakes occur. The impact of this earthquake on major earthquake activity of surrounding areas is worth studying. This paper attempts to combine two models: the Brownian passage-time (BPT) model, which describes the quasi-periodic recurrence of major earthquakes, and the Coulomb Failure Stress model, which describes rock failure on faults. The amount of change in the rate of major earthquake occurrence caused by a nearby earthquake was calculated, and changes in major earthquake activity in the surrounding areas after the Jinghe Earthquake were re-estimated. There are few differences in major earthquake occurrence rate change by stress disturbances calculated with the BPT model or the Coulomb Failure Stress model. Calculation results are consistent with actual earthquake cases. The 2017 Jinghe Earthquake increased major earthquake activity on the Boluokenu Fault and Yili Basin North Fault, and the expected major earthquake recurrence times of the two faults were advanced by 11 years and 59 years, respectively. Conclusions of this paper provide a reference for time-dependent seismic hazard assessments in related areas. [ABSTRACT FROM AUTHOR]

The goal of this paper is to describe cluster analyses of the focal mechanism solutions estimated from local and teleseismic measurements and stress inversions to support the recent and previously published studies in the investigated region, that is the Vrancea seismic zone. We have applied different established clustering methods—e.g. hierarchical density-based clustering for applications with noise (HDBSCAN) and agglomerative hierarchical analysis—to the geographical coordinates, focal depths and parameters of the focal mechanism solutions of the gathered seismic events. We have attempted to develop a fully automated algorithm for the classification of earthquakes and to support the further investigation of stress inversions. This algorithm does not call for the setting of hyper-parameters by the users, thus the contribution from any bias of the user can be reduced significantly and the time required to carry out the clustering can also be decreased. In most cases, the resulting stress tensors are in close agreement with those we found in the literature. [ABSTRACT FROM AUTHOR]

Nowcasting refers to the use of proxy data to estimate the current dynamic state of driven complex systems such as earthquakes, neural networks, or the financial markets. In previous papers, methods to nowcast earthquakes have been presented based on the natural time count of small earthquakes after the last large earthquake in a defined, seismically active geographic region. In this method, a large geographic region is identified in which a local region of interest is embedded. The primary assumption in the method is that the frequency-magnitude statistics of the local region are the same as the frequency-magnitude relation of the large region. The nowcasting technique relies on seismic catalogs that are complete in the sense that all events whose magnitude is larger than a completeness threshold have been detected. For this reason, the previous papers have been limited to nowcasting large earthquakes with magnitudes of approximately M7.5. In this article, we extend the nowcasting method to great global earthquakes of magnitudes as large as M9 by defining the surrounding large region as the entire earth. We then analyze the current hazard of a number of selected "local" regions and rank the regions in terms of current risk of great earthquakes. These great events also present significant hazards for generating mega-tsunamis as well as local damage due to intense shaking. We also perform a sensitivity analysis to establish the reliability of the nowcasts. One of our main results is that the eastern Aleutian Islands, site of the M8.6 earthquake of 1 April 1946, is currently the region most at current risk of a great earthquake larger than M8.0. We finish by presenting comments on the applicability of our methods for anticipating the occurrence of great destructive earthquakes and tsunamis. [ABSTRACT FROM AUTHOR]

This paper begins with a critical assessment of the concept of macroseismic intensity, on which traditional scales, such as MSK and EMS, are based. The main shortcoming identified is the model's failure to consider the spectral features of ground motion. This omission may lead to erroneous seismic zonation, as shown in the paper. As a result, the model is of little interest to engineers who must design and build safe structures while adopting economical solutions. The paper presents a way to radically improve this situation. The starting point for this approach was the experience of the destructive Vrancea earthquake of 1977.03.04, which made it clear that intensity appears to be different for structures having natural periods pertaining to different spectral domains. The solution proposed to the shortcomings of the traditional intensity concept is postulated on a system of analytical expressions, covering definitions of global intensities, of intensities related to oscillation frequency and of intensities related to a definite spectral band. The latter definition lies at the basis of a definition of discrete intensity spectra. Illustrative applications are presented, in relation to global intensities and to discrete intensity spectra. We then analyze an illustrative case in which the use of traditional macroseismic survey techniques led to erroneous seismic zonation. Finally, some conclusions and recommendations are presented. Based on the authors' long-term experience, we strongly recommend close interaction between seismologists and engineers in working groups and joint projects targeted on radical improvement of the basic concepts of seismic intensity and of specific analysis procedures. [ABSTRACT FROM AUTHOR]

The Gulf of Aqaba is one of the most active places around Egypt, with several earthquake sequences having occurred there through ancient and modern times. In the last century, four earthquake sequences took place in the gulf (1983, 1990, 1993, and 1995). Recently, on 27 June 2015, a sequence of 96 earthquakes with local magnitudes ranging from 0.7 to 5.2 was recorded by the Egyptian National Seismological Network (ENSN). On 16 May 2016, another earthquake sequence started and continued for several consecutive days, with 95 events with local magnitudes ranging from 1.6 to 5.5 being centered south of the 27 June 2015 sequence. In this paper, we analyse the complete waveform and polarity data set of both earthquake sequences to determine their focal mechanisms and to update our knowledge of the stress field in the Gulf of Aqaba. Through the results obtained, we conclude that, the Gulf of Aqaba is affected by a primary structure of a left-lateral strike-slip fault with a minor normal component in most segments. Our study also infers the presence of a secondary structure, which is indicated to be a right-lateral strike-slip with a minor reverse component. [ABSTRACT FROM AUTHOR]

— The paper discusses the very recent seismotectonic and geological investigations for the Sofia valley. It also reviews available historical and recent seismological data. One possible variant of seismic zoning (interpretation of available geological and seismological data) is used to evaluate uniform probability Fourier spectra of strong ground motion at Sofia City. The distribution of the maximum expected displacements, using 1-D models and SHAKE’91 techniques for 50 years of exposure time is mapped. The maps of eigensolution results for 30 m, 50 m depths to the rock are illustrated. These issues are important for definition of design parameters for evaluation of seismic safety of underground infrastructure, as well as for tall structures. [ABSTRACT FROM AUTHOR]

Among the schemes for earthquake forecasting, the search for semi-periodicity during large earthquakes in a given seismogenic region plays an important role. When considering earthquake forecasts based on semi-periodic sequence identification, the Bayesian formalism is a useful tool for: (1) assessing how well a given earthquake satisfies a previously made forecast; (2) re-evaluating the semi-periodic sequence probability; and (3) testing other prior estimations of the sequence probability. A comparison of Bayesian estimates with updated estimates of semi-periodic sequences that incorporate new data not used in the original estimates shows extremely good agreement, indicating that: (1) the probability that a semi-periodic sequence is not due to chance is an appropriate estimate for the prior sequence probability estimate; and (2) the Bayesian formalism does a very good job of estimating corrected semi-periodicity probabilities, using slightly less data than that used for updated estimates. The Bayesian approach is exemplified explicitly by its application to the Parkfield semi-periodic forecast, and results are given for its application to other forecasts in Japan and Venezuela. [ABSTRACT FROM AUTHOR]

This paper aimed at assessing gravity variations as precursors for earthquake prediction in the Tibet (Xizang)-Qinghai-Xinjiang-Sichuan Region, western China. We here take a statistical approach to evaluate efficiency and possibility of earthquake prediction. We used the most recent spatiotemporal gravity field variation datasets of 2002-2008 for the region that were provided by the Crustal Movement Observation Network of China (CMONC). The datasets were space sparse and time discrete. In 2007-2010, 13 earthquakes (> M 6.0) occurred in the region. The observed gravity variations have a statistical correlation with the occurrence of these earthquakes through the Molchan error diagram tests that lead to alarms over a good fraction of space-time. The results show that the prediction efficiency of amplitude of analytic signal of gravity variations is better than seismicity rate model and THD and absolute value of gravity variation, implying that gravity variations before earthquake may include precursory information of future large earthquakes. [ABSTRACT FROM AUTHOR]

Site effect is usually associated with local geological conditions, which increase or decrease the level of shaking compared with standard attenuation relations. We made an attempt to see in the macroseismic data of Italy some other effects, namely, hot/cold spots in the terminology of O lsen (in Bull. Seismol. Soc. Am. 90, 6B, 577-594, ), which are related to local fault geometry rather than to soil conditions. We give a list of towns and villages liable to amplify (+) or to reduce (-) the level of shaking in comparison with the nearby settlements. Relief and soil conditions cannot always account for the anomalous sites. Further, there are sites where both (+) and (-) effects are observed depending on the earthquake. The opposite effects can be generated by events from the same seismotectonic zone and along the same direction to the site. Anomalous sites may group themselves into clusters of different scales. All isolated anomalous patterns presented in this paper can be used in hazard analysis, in particular, for the modeling and testing of seismic effects. [ABSTRACT FROM AUTHOR]

We present the basis for a method for estimating the return period of large and medium earthquakes that is independent of current deterministic and probabilistic approaches. The two standard techniques of seismic hazard assessment-probabilistic seismic hazard assessment (PSHA) and deterministic seismic hazard assessment (DSHA)-suffer from limited knowledge of seismic prehistory. A further weakness of PSHA is its requirement of homogeneous seismic activity within a seismic zone. Moreover, PSHA and DSHA were developed for seismically active areas and, thus, cannot reliably be used in areas of medium and low activity. In this paper we propose the combined use of geodetic strain rate data and the seismic moment data set determined for past seismic events. This combination represents a new and independent approach to estimation of future seismic activity. Using a modified version of Kostrov's (Phys Solid Earth 1:23-40, ) equation and the catalogue of seismic moments, the minimum return period of the strongest earthquakes of a source area is estimated. [ABSTRACT FROM AUTHOR]

Izmir, the third largest city and one of the major economic centers in Turkey, has more than three million residents and one-half million buildings. The city, located in a seismically active region in western Anatolia, was a subject of the 1997 RADIUS (Risk Assessment Tools for Diagnosis of Urban Areas against Seismic Disaster) project. In this paper, the seismic hazard of Izmir is investigated through probabilistic seismic hazard assessment. First, the seismic setting of Izmir is presented. Considering the statistics of earthquakes that took place in the region during the period 1900-2005, a simple seismic hazard model is used to facilitate the assessment. To account for modeling uncertainties associated with the values of seismicity parameters, a logic tree procedure is employed in carrying out the seismic hazard computations. The resulting weighted average seismic hazard, presented in terms of peak ground acceleration and associated probability of exceedence, could be considered the 'best estimate' of seismic hazard for Izmir. Accordingly, for a return period of 475 years, for rock sites, a PGA value of 0.34 g is calculated. This PGA hazard estimate is close to the current code-recommended design acceleration level for Izmir. [ABSTRACT FROM AUTHOR]

We develop stochastic approaches to determine the potential for tsunami generation from earthquakes by combining two interrelated time series, one for the earthquake events, and another for the tsunami events. Conditional probabilities for the occurrence of tsunamis as a function of time are calculated by assuming that the inter-arrival times of the past events are lognormally distributed and by taking into account the time of occurrence of the last event in the time series. An alternative approach is based on the total probabilitiy theorem. Then, the probability for the tsunami occurrence equals the product of the ratio, r (= tsunami generating earthquakes/total number of earthquakes) by the conditional probability for the occurrence of the next earthquake in the zone. The probabilities obtained by the total probability theorem are bounded upwards by the ratio r and, therefore, they are not comparable with the conditional probabilities. The two methods were successfully tested in three characteristic seismic zones of the Pacific Ocean: South America, Kuril-Kamchatka and Japan. For time intervals of about 20 years and over the probabilities exceed 0.50 in the three zones. It has been found that the results depend on the approach applied. In fact, the conditional probabilities of tsunami occurrence in Japan are slightly higher than in the South America region and in Kuril-Kamchatka they are clearly lower than in South America. Probabilities calculated by the total probability theorem are systematically higher in South America than in Japan while in Kuril-Kamchatka they are significantly lower than in Japan. The stochastic techniques tested in this paper are promising for the tsunami potential assessment in other tsunamigenic regions of the world. [ABSTRACT FROM AUTHOR]

Seismic hazard in terms of spectral acceleration ( SA) has been estimated for the first time in northern Algeria. For this purpose, we have used the spatially-smoothed seismicity approach. The present paper is intended to be a continuation of previous work in which we have evaluated the seismic hazard in terms of peak ground acceleration ( PGA) using the same methodology. To perform these evaluations, four complete and Poissonian seismic models have been used. One of them considers earthquakes with magnitudes above M S 6.5 in the last 300 years, that is, the most energetic seismicity in the region. Firstly, seismic hazard maps in terms of SA, at periods of 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5 and 2.0 sec, with 39.3% and 10% probability of exceedance in 50 years, have been obtained. Therefore, uniform hazard spectra ( UHS) are computed and examined in detail for twelve of the most industrial and populated cities in northern Algeria. All the reported results in this study are for rock soil and 5% of damping. It is noteworthy that, in the seismic hazard maps as well as in the UHS plots, we observe maximum SA values in the central area of the Tell. The higher values are reached in the Chleff region (previously El Asnam), specifically around the location of the destructive earthquakes of September 9, 1954 ( M S 6.8), and October 10, 1980 ( M S 7.3). These maximum values, 0.4 g and 1.0 g, are associated with periods of about 0.2 and 0.3 sec for return periods of 100 and 475 years, respectively. [ABSTRACT FROM AUTHOR]

This paper presents an analysis of the distribution of the time t between two consecutive events in a stationary point process. The study is motivated by the discovery of unified scaling laws for t for the case of seismic events. We demonstrate that these laws cannot exist simultaneously in a seismogenic area. Under very natural assumptions we show that if, after rescaling to ensureEt =1, the interevent time has a universal distributionF, thenFmust be exponential. In other words, Corral’s unified scaling law cannot exist in the whole range of time. In the framework of a general cluster model we discuss the parameterization of an empirical unified law and the physical meaning of the parameters involved. [ABSTRACT FROM AUTHOR]

— The 1940 (Mw=7.7) and 1977 (Mw=7.4) Vrancea earthquakes (Romania) inflicted heavy damage and casualties in Bucharest and the statistics indicate a recurrence interval of 25 years for Mw ≥ 7.0 events. Under these circumstances, the seismic microzonation represents important information for detailed urban planning that establishes an appropriate level of preparedness to the earthquake threat. This paper reviews the main studies concerning the seismicity of the Vrancea region, the site conditions of the city, the characterization of the building stock, and the codes of practice that regulate the antiseismic design. The first-order microzonation of Bucharest was performed starting from the existing database of structural and geotechnical parameters. New insights originating from direct instrumental observation and interpretation of the local effects as well as realistic numerical modeling that update and improve the input data necessary for a detailed microzoning map of the city are also discussed. [ABSTRACT FROM AUTHOR]

We analyse the seismic catalogue of the local earthquakes which occurred at Somma-Vesuvius volcano in the past three decades (1972–2000). The seismicity in this period can be described as composed of a background level, characterised by a low and rather uniform rate of energy release and by sporadic periods of increased seismic activity. Such relatively intense seismicity periods are characterised by energy rates and magnitudes progressively increasing in the critical periods. The analysis of the b value in the whole period evidences a well-defined pattern, with values of b progressively decreasing, from about 1.8 at the beginning of the considered period, to about 1.0 at present. This steady variation indicates an increasing dynamics in the volcanic system. Within this general trend it is possible to identify a substructure in the time sequence of the seismic events, formed by the alternating episodes of quiescence and activity. The analysis of the source moment tensor of the largest earthquakes shows that the processes at the seismic source are generally not consistent with simple double-couples, but that they are compatible with isotropic components, mostly indicating volumetric expansion. These components are shown to be statistically significant for most of the analysed events. Such focal mechanisms can be interpreted as the effect of explosion phenomena, possibly related to volatile exsolution from the crystallising magma. The availability of a reduced amount of high quality data necessary for the inversion of the source moment tensor, the still limited period of systematic observation of Vesuvius micro-earthquakes and, above all, the absence of eruptive events during such interval of time, cannot obviously permit the outlining of any formal premonitory signal. Nevertheless, the analysis reported in this paper indicates a progressively evolving dynamics, characterised by a generally increasing trend in the seismic activity in the volcanic system and by a significant volumetric component of recent major events, thus posing serious concern for a future evolution towards eruptive activity. [ABSTRACT FROM AUTHOR]

We analyze high-resolution borehole strainmeter signals to constrain the fault plane solutions and locations of the 2009 Fengpin-Hualien earthquakes, in eastern Taiwan. The December M w 6.6 earthquake has ruptured a narrow section of the Collision Seismic Zone (within depth of 34 to 44 km), an active structure located offshore northeast Taiwan. The October M w 6.3 event has ruptured the deep section of the Longitudinal Valley fault (25–32 km depth) located between Fengpin and Fanglin. Coulomb stress changes induced by the October event in the hypocenter region of the December event are low (< +30 kPa), which suggests that the latter event was not induced by static stress transfer. The December event is characterized by an abundant seismicity for about 2.5 days following the mainshock. The temporal evolution between the aftershock rate and geodetic strain suggests that seismicity could have been controlled by a short-lived frictional afterslip. Besides, we infer that significant positive static Coulomb stress changes (> +100 kPa) induced by this sequence at shallow to moderate depths in the Longitudinal Valley (0–12 km) may have influenced the occurrence of large mainshocks in eastern Taiwan during the past decade. Conversely, limited stress (< +30 kPa) is transferred to the shallow, locked section of the southernmost Ryukyu trench. This study emphasizes the importance of borehole strain measurements in active regions to enhance detection of seismic and aseismic events unresolved by surface geodesy. [ABSTRACT FROM AUTHOR]

We review properties and processes of earthquake rupture zones based on field studies, laboratory observations, theoretical models and simulations, with the goal of assessing the possible dominance of different processes in different parts of the rupture and validity of commonly used models. Rupture zones may be divided into front, intermediate, and tail regions that interact to different extents. The rupture front is dominated by fracturing and granulation processes and strong dilatation, producing faulting products that are reworked by subsequent sliding behind. The intermediate region sustains primarily frictional sliding with relatively high slip rates that produce appreciable stress transfer to the propagating front. The tail region further behind is characterized by low slip rates that effectively do not influence the propagating front, although it (and the intermediate region) can spawn small offspring rupture fronts. Wave-mediated stress transfer can also trigger failures ahead of the rupture front. Earthquake ruptures are often spatially discontinuous and intermittent with a hierarchy of asperity and segment sizes that radiate waves with different tensorial compositions and frequency bands. While different deformation processes dominating parts of the rupture zones can be treated effectively with existing constitutive relations, a more appropriate analysis of earthquake processes would require a model that combines aspects of fracture, damage-breakage, and frictional frameworks. [ABSTRACT FROM AUTHOR]

Induced seismicity is an increase in seismic activity caused by human engineering. Examples of such activity include mineral exploration, large water reservoir construction, and exploitation of underground oil and gas storage. The authors studied the seismicity in the Uglegorsky district of the Sakhalin region, where the Solntsevskoye brown coal field is located, which is the most promising on the island. Its area is over 100 km2, and productive strata of the Verkhneduiskaya formation with a thickness of up to 600 m contain 12 coal seams, eight of which are working. Active mining of brown coal is carried out at the Solntsevsky coal mine, and blasting operations are performed on a large scale, which therefore does not exclude the relation between seismic processes and anthropogenic seismicity. Earthquake recurrence curves for two decades beginning from 2000 to the present were constructed in this work to compare the characteristics of the seismic regime in the study area. The difference in the slope angle of the recurrence graph during the period of 2011–2020 (the period of the most active development of the Solntsevsky coal mine) relative to the previous decade is quite significant. Maps of the spatiotemporal distribution of seismic event epicenters in the vicinity of Solntsevsky coal mine were constructed, and contraction of zones of seismic event concentration to the mining areas, first of all to the Solntsevsky coal mine, was found. Such a combination allows us to note an increase in seismicity in the region during the past few years and a change in its character from natural to mixed natural and technogenic. The focal mechanisms of the largest earthquakes occurring in the Uglegorsky district were constructed in order to confirm the change in the nature of the seismicity and reasons for earthquake occurrence in the study area. The mechanisms of seismic events of 2020 were classified as strike-slip faults, which is not characteristic of most earthquakes in the territory of Sakhalin Island. The authors made an attempt to determine the regularities of the parameters of the produced blasts and earthquakes through dynamic parameters of the seismic event foci by studying the frequency content of earthquakes and blasts in order to determine a corner frequency from the focal velocity spectrum. [ABSTRACT FROM AUTHOR]

A strong earthquake with a magnitude Mw = 7.0 occurred on February 13, 2020, at a depth of 142 km in the vicinity of the Southern Kuril Islands. Over recent decades, there has been an anomaly near the focal zone in the earthquake distribution over the layers of the double seismic focal zone in accordance with the seismic dislocation kinematic type compared to the other areas of the intermediate depths of the southern part of the Kuril arc. Inversion of the earthquake focal mechanisms of intermediate depth was performed for the southern part of the Kuril Islands along the upper and lower layers of the seismic focal zone. In the upper layer, compression prevails along the slab; the axis of maximum compression σ3 is mainly parallel to the slab and is oriented at an angle of 140–160° (320–340°) to the direction of its dip, i.e., subparallel to the Pacific Plate motion vector in the mantle in this area. The stress state of extension along the slab prevails in the lower layer; the axis of minimum compression σ1 is parallel to the slab and is mainly rotated by 20° (200°) clockwise from the direction of its dip. This orientation of the principal stress axes could indicate that, in addition to the slab unbending, their formation is affected by the mantle resistance to its movement. In the upper and lower layers, we marked the areas where the shear stress prevails that correspond to the kinematic type of transform faults, which are presumably seismically active on the descending plate. The most complex pattern of the stress state of the medium was obtained near the focus of the earthquake that occurred on February 13, 2020. Here, in the upper layer, an area with the stress state of extension and orientation of the principal axes corresponds more to the lower layer. Seismic quiescence is observed in the lower layer, near the focus of this earthquake within the area 60 km wide along the island arc and at the entire interval of intermediate depths. [ABSTRACT FROM AUTHOR]

A ground motion model (GMM) for interface subduction zone earthquakes of Northeast India (NEI) and its adjacent countries is developed for the first time. Countries adjacent to NEI are Bangladesh, Bhutan, China, Myanmar and Nepal. High-magnitude earthquakes occur frequently in these regions due to buildup of high-stress parameters in the subduction zone of the Indian tectonic plate. Strong motion data are too few and sparse to develop a robust GMM for this region. We used both finite-fault simulations and a stochastic point-source model in developing our GMM. In our GMM, we used 50,000 ground motion samples which were stochastically simulated for different moment magnitudes (Mw) of 5.0–9.0 and hypocentral distances of 30–300 km using a point-source seismological stochastic model and finite fault model. In this study, we calculated stress drop (∆σ), quality factor Q(f) and all other region-specific seismic input parameters from the past strong motion records of interface subduction zone earthquakes of NEI and its adjacent countries. We used these seismic input parameters in ground motion simulation. Sensitivity analyses of the input parameters were also performed to check the bias of the present model. Our GMM was validated by comparing it with the existing NEI interface strong motion records. We compared our GMM with other GMMs developed for interface subduction zone earthquakes for different regions in the world. We also compared our GMM with point-source and finite-fault simulation models. Ground motion parameters estimated using the point-source model are comparatively higher than the finite-fault simulation model. Horizontal components of peak ground acceleration (PGA) and spectral acceleration (Sa) can be estimated for NEI using our GMM. [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]

It is necessary to have reliable data on the distributions of earthquake hypocenters in the study area to solve many geological and geophysical problems, in particular, the forecast of strong earthquakes, seismic zoning and earthquake-proof construction. In turn, the completeness of the data on the distribution of earthquake hypocenters and the accuracy of their determination largely depends on the effectiveness of the observing system. The efficiency of the modern Ukrainian network of seismological observations that consists of 28 stations is estimated in this article. By the effectiveness of the seismological observation network we mean the ability of the network to record events with minimal magnitudes at certain epicentral distances and allowing us to determine its main parameters (time in the focus and coordinates of hypocenters) with minimal errors depending on the position of the earthquake hypocenter. Calculation of the minimum magnitude of earthquakes for the Ukrainian seismological network shows if each seismic station increase of susceptibility to 50,000 units then the seismological the network confidently registers earthquakes with a magnitude of 3 or more throughout the Ukraine. The errors in the determination of the coordinates of epicenters of earthquakes in latitude (δφ) (km) and in longitude (δλ) (km) do not exceed 1.0 km in the center of the network and 5.0 km on the periphery of the network. The values of errors in determining the depths of the earthquake (H) (km) centers in the center of the network does not exceed 5.0 km but on the whole territory of Ukraine does not exceed 20 km. The optimal configuration of the network of Ukrainian seismic stations based on the C-criterion of optimality, introduced earlier to the theory design of optimal experiments by one of the authors of the article, is proposed. [ABSTRACT FROM AUTHOR]

A broadband seismological station (PRIMA) installed offshore Nice airport (southeastern France) reveals a strong amplification effect of seismic waves. PRIMA station was in operation for 2 years (9/2016 to 10/2018) on the outer shelf at a water depth of 18 m. Situated at the mouth of the Var River, this zone is unstable and prone to landslides. A catastrophic landslide and tsunami already occurred in 1979, causing 10 casualties. Given the level of seismicity of the area, it is important to infer the impact of an earthquake on this zone. We analyze the recordings of earthquakes and seismic noise at the PRIMA station by comparing them to nearby inland stations. We find that the seismic waves are strongly amplified at PRIMA at some specific frequencies (with an amplification factor greater than 10 at 0.9 Hz). Using geological and geophysical data, we show that the main amplification frequency peak (at 0.9 Hz) is due to the velocity contrast between the Pliocene sedimentary layer and fine-grained sediments dated from the Holocene, at about 100 m depth. This velocity contrast is also present along the Var valley, but the level of amplification detected on PRIMA station is larger. Using numerical simulations of seismic waves in a 2D model that accounts for the pinch-out geometry related to the termination of the Holocene sedimentary layer, we can partially explain this amplification. This offshore site effect could have a crucial impact on the triggering of a submarine landslide by an earthquake in this region. More generally, this effect should be taken into account for the modeling of landslides and induced tsunamis triggered by seismic waves. [ABSTRACT FROM AUTHOR]

We examined the scaling relationships of inland crustal earthquakes occurring in tectonically active regions such as the Japanese Islands. Two important points related to reliable scaling relationships are discussed empirically: the objective estimation of source parameters such as the seismic moment and rupture area, and the regionality of the scaling. Rupture areas are objectively estimated by trimming heterogeneous slip distributions obtained from waveform inversion. Two trimming procedures have been proposed to determine effective rupture areas, by Somerville et al. (Seismol Res Lett 70:59–80, 1999) and Thingbaijam and Mai (Bull Seismol Soc Am 106:1802–1816, 2016). We confirmed that both trimmed rupture areas agree well with each other when applied to the same dataset. The source scaling characteristics are known to depend on the seismotectonic regime. We investigate the source scaling relationships of inland crustal earthquakes in Japan using source parameters obtained from 36 slip models for 22 recent events (Mw 5.4–7.1) by waveform inversion analysis. We confirmed that the source scaling relationships consisting of two stages were almost the same as those obtained for crustal earthquakes on the US West Coast by Hanks and Bakun (Bull Seismol Soc Am 92:1841–1846, 2002). For larger earthquakes (Mw > 7.4) in seismically active regions, Tajima et al. (ZISIN2; J Seismol Soc Jpn 66:31–45, 2013) found saturation of fault displacements showing the third stage. Combining the earthquake data of Mw 5.4–7.1 in this study with those of Mw 7.0–8.0 compiled by Murotani et al. (Pure Appl Geophys 172:1371–1381, 2015), we conclude that the scaling relationship for rupture area versus seismic moment coincides with the three-stage source scaling relationship using source parameters extracted from waveform inversions. [ABSTRACT FROM AUTHOR]

The East Kunlun Fault (EKF) is one of the largest and most active sinistral strike-slip faults in the Qinghai–Tibet Plateau. Since 1900, many earthquakes of magnitude > 7 have occurred in this region. The Maqin–Maqu Segment (MMS), a seismic gap underlying a densely populated zone, is particularly important. While the area has been extensively researched to assess seismic risk, refined asperity geodetic imaging is deficient. We combined multiple sets of GPS and leveling observations to obtain spatial–temporal distributions of locking along the EKF. We delineated the probable asperity ranges according to the fault plane locking and the distribution of small earthquakes. Long-term observations on GPS velocity (1999–2013) and leveling (1970–2013) indicate that the Dulan–Maduo segment (DMS) of the EKF has a 140-km-long strong coupling section, and both the MMS and the eastern Ruoergai segments have a 40-km-long locking range. The 2013–2015 GPS velocity observations show that from Maqu to Maqin, the locked DMS and MMS lengths increased to 200 km and 240 km, respectively, while the locked eastern Ruoergai segment decreased and migrated 60 km to the west. This change in locking over time implies that the post-seismic effects of surrounding earthquakes have had significant impacts on the EKF. The locking area derived from 2015 to 2017 GPS velocity shows a growing trend and indicates the connectedness between the two speculative asperities. Combining the distribution of historical earthquakes and the precision positioning of small earthquakes, we conclude that the geodetic imaging of the EKF indicates that the MMS and DMS are high-risk zones for destructive earthquakes. [ABSTRACT FROM AUTHOR]

The 1960 M9.5 Valdivia and 1964 M9.2 Alaska earthquakes caused a decimeters high secondary zone of uplift a few hundred kilometers landward of the trench. We analyze GPS data from the 2010 M8.8 Maule and 2011 M9.0 Tohoku-Oki earthquakes to reveal the persistent existence of a secondary zone of uplift due to great earthquakes at the megathrust interface. This uplift varies in magnitude and location, but consistently occurs at a few hundred kilometers landward from the trench and is likely mainly coseismic in nature. This secondary zone of uplift is systematically predicted by our 2D visco-elasto-plastic seismo-thermo-mechanical numerical simulations, which model both geodynamic and seismic cycle timescales. Through testing hypotheses in both simple and realistic setups, we propose that a superposition of two physical mechanisms could be responsible for this phenomenon. First, a wavelength is introduced through elastic buckling of a visco-elastically layered fore-arc that is horizontally compressed in the interseismic period. The consequent secondary zone of interseismic subsidence is elastically rebound during the earthquake into a secondary zone of relative uplift. Second, absolute and broader uplift is ensured through a mass conservation-driven return flow following accelerated slab penetration due to the megathrust earthquake. The dip and width of the seismogenic zone and resulting (deep) coseismic slip seem to have the largest affect on location and amplitude of the secondary zone of uplift. These results imply that subduction and mantle flow do not occur at constant rates, but are rather modulated by earthquakes. This suggests a link between deep mantle and shallow surface displacements even at time scales of minutes. [ABSTRACT FROM AUTHOR]

Various studies have investigated the link between seismic activity and ionospheric precursory phenomena. Many of these retrospective case studies have supported the existence of pre-earthquake ionospheric anomalies by examining past earthquake events using a variety of analytical methods. Based on existing methodologies, however, the conversion of a retrospective analysis to a prospective forewarning scenario is not a straightforward process. The obstacles to its potential adoption stem mainly from assumptions made during data analysis and interpretation. In this study, several parameters pertaining to existing approaches for the detection of these ionospheric anomalies are highlighted and discussed, in particular ionosphere total electron content (TEC). A detailed examination is conducted to understand the roles that each of these parameters play in the detection process and the consequent difficulties when adopting them in a prospective analysis. These issues include accounting for variations in ionosphere characteristics owing to different measurement platforms (e.g. ground- and space-based observations) and statistical methods (e.g. standard deviation envelopes) used in detecting anomalies. Furthermore, the necessity of excluding space weather contributions in the underlying TEC fluctuations poses a challenge in determining the validity of observed ionospheric anomalies. The notion of an "earthquake preparation zone" is also evaluated in the context of the ionosphere, along with its implications in a forewarning scenario. These issues need to be addressed in current research in order to enable its possible application in earthquake forewarning. [ABSTRACT FROM AUTHOR]

Seismogenic nodes capable of generating shallow earthquakes with M ≥ 5.0 have been identified in the northeast part of Egypt using the pattern recognition approach. The study region includes the Sinai Peninsula and the northern part of the Eastern Desert between the Nile River and the Red Sea, which comprises the new capital of Egypt and Suez Canal projects and represents a place for much future development. We apply a phenomenological approach based on pattern recognition for identifying seismogenic nodes. The methodology is based on the idea that earthquakes nucleate at nodes: specific structures forming around fault intersections. Morphostructural zoning (MZ) is applied to map nodes over the entire study region without using a priori knowledge of regional seismicity. The pattern recognition is employed to pinpoint seismogenic nodes where earthquakes with M ≥ 5.0 may occur in the future. As a result, seismogenic nodes capable of generating earthquakes with M ≥ 5.0 have been defined in the Sinai Peninsula and the northern part of the Eastern Desert. We also found characteristic geological-geophysical features that discriminate seismogenic nodes (D) from non-seismogenic ones (N). Information on the potential seismic sources represents the main issue in seismic hazard evaluation. Seismogenic nodes prone to earthquakes with M ≥ 5.0, as described in this work, may contribute to the definition of earthquake source zones in the northeast of Egypt because some of the D nodes are potential sources of seismic risk for critical facilities (e.g., Ismailia Tunnels) and large metropolitan areas (e.g., Nile Valley). This information can contribute to the revision of seismic zoning or microzoning and improve the performance of seismic hazard studies of Egypt by adding a new source of information about seismogenic nodes to the seismogenic zones. [ABSTRACT FROM AUTHOR]

We observed abnormal changes of the water temperature in Yushu (YSWT) well, China, most of which were followed by earthquakes. This study statistically analyzes the correlation between the magnitude and duration of the anomalies in YSWT and earthquakes in the Tibetan block and its margins. The effectiveness of using observed YSWT data to predict earthquakes was quantitatively examined by the Molchan error diagram method. The results show that (1) the YSWT underwent several abnormal changes marked by “V”-shaped patterns, which might be related to several earthquakes that occurred in the Tibetan block and its margins. The extent and duration of the abnormal changes in the YSWT were linearly related to the magnitude of the earthquake; i.e., the higher the magnitude, the greater the change in the YSWT, and the shorter the duration. (2) Abnormal changes in the YSWT are somewhat predictive of earthquakes with magnitudes ≥5.5 (≥M5.5) within 800 km of the Yushu well and ≥M6.5 earthquakes in the Tibetan block and its margins. The prediction has a probability gain of approximately 2, and the most likely time period for an earthquake to occur is within approximately 3 months after the occurrence of an YSWT anomaly. Most of the anomalies in YSWT appeared before earthquakes in the thrust of block margins. Notably the larger strains from the earthquake did not produce any response. We speculate that the preseismic responses reflect the regional tectonics, such as the motion of the Indian plate, straining sub-blocks of the Tibetan block. [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 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]

Satellite gravimetry has proven to be a useful tool to identify mass anomalies along a subduction interface, interpreted as heterogeneities related to the rupture process during megathrust earthquakes. In the last years, different works, reinforced with data derived from satellite gravity missions as GRACE and now GOCE, have analyzed not only the static component of the Earth gravity field, but also its temporal variations and relation to the seismic cycle. In particular, during the last decade, the Chilean margin has been affected by three megathrust earthquakes (with Mw >8): Maule 2010 Mw = 8.8, Pisagua 2014 Mw = 8.2 and recently the Mw = 8.3 Illapel event. Then, the recently completed GOCE mission (November 2009 to November 2013) offered a unique opportunity to study the Maule February 2010 and Pisagua April 2014 events by means of gravity gradients, directly measured at satellite height altitudes, which allowed mapping density heterogeneities with greater detail than the gravity anomaly which has been used in most studies up to now. In the present work, we use the last GOCE model (GO_CONS_GCF_2_DIR_R5), the one of higher spatial resolution ( N = 300, λ/2 ≈ 66 km) derived from satellite-only data. The methodology used is the same as that to study the previous events, with the addition that now we derived a relation between the associated depths of a causative mass with a determined degree of the spherical harmonic expansion. This allowed to 'decompose' the gravimetric signal, by cutting off the degree/order of the harmonic expansion, as depth increases. From this analysis, we found that prominent oceanic features such as the Challenger fracture zone and the Juan Fernandez ridge played a key role in latitudinal seismic segmentation for the Illapel earthquake rupture zone, acting as barriers/attenuators to the seismic energy release. We compared the slip model from Tilmann et al. (Geophysical Research Letters 43: 574-583. doi:10.1002/2015GL066963, 2016) for the Illapel earthquake with vertical gravity gradient with and without sediment correction, and at different degree/order of the harmonic expansion. From this analysis, we inferred that prominent oceanic features over the subducting Nazca plate play a key role in seismic segmentation not only at heavily sedimented trenches, but also at sediment-starved segments. [ABSTRACT FROM AUTHOR]

In 1991, a new seismic monitoring network named SIL was started in Iceland with a digital seismic system and automatic operation. The system is equipped with software that reports the automatic location and magnitude of earthquakes, usually within 1-2 min of their occurrence. Normally, automatic locations are manually checked and re-estimated with corrected phase picks, but locations are subject to random errors and systematic biases. In this article, we consider the quality of the catalogue and produce a revised catalogue for South Iceland, the area with the highest seismic risk in Iceland. We explore the effects of filtering events using some common recommendations based on network geometry and station spacing and, as an alternative, filtering based on a multivariate analysis that identifies outliers in the hypocentre error distribution. We identify and remove quarry blasts, and we re-estimate the magnitude of many events. This revised catalogue which we consider to be filtered, cleaned, and corrected should be valuable for building future seismicity models and for assessing seismic hazard and risk. We present a comparative seismicity analysis using the original and revised catalogues: we report characteristics of South Iceland seismicity in terms of b value and magnitude of completeness. Our work demonstrates the importance of carefully checking an earthquake catalogue before proceeding with seismicity analysis. [ABSTRACT FROM AUTHOR]

Instrumentally recorded seismicity from 1970/01/01 to 2014/01/01 of the central China north-south seismic belt (21.0°-41.5°N, 97.5°-107.5°E) was analyzed, emphasizing the applicability of the predictive algorithms based on the assumptions of meta-stable equilibrium. The seismicity in this region was shown to exhibit ergodicity from 1980 to the present, with sub-region dependence, and interrupted by the 2008 Wenchuan earthquake. pattern informatics algorithm, a statistical physics-based predictive model for five-year time scale, is put to forward forecast test for the period 2014/01/01 to 2019/01/01. [ABSTRACT FROM AUTHOR]

Based on the load/unload response ratio (LURR) theory, spatial and temporal variation of Y/ Y (value of LURR/critical value of LURR under 90 % confidence) in the western United States and its adjacent area (31°-44°N, −128° to −112°E) during the period from 1980 to 2011 was studied. The selected study area was zoned into 20 sub-regions, in each of which the fault geometry and the focal mechanisms were very similar such that the stress fields were almost uniform. The loading and unloading periods were determined by calculating perturbations in the Coulomb failure stress in each sub-regions induced by earth tides. Earthquakes occurring in these sub-regions were identified as a loading or unloading type, and the response rate was chosen as the Benioff strain that can be calculated from earthquake magnitude M. With a time window of 1 year, a time moving step of 1 month, a space window of a circle region with a radius of 100 km, and a space moving step of 0.5° latitudinally and longitudinally, snapshots of the evolution of Y/ Y were generated. Scanning results show that obvious Y/ Y anomalies can be detected near the epicenter of all big earthquakes larger than M6.5 in regions with reasonable seismic monitoring abilities. They also show Y/ Y anomalies occurred several years prior to the big earthquakes and the lasting time of the anomaly is from one year to several years. For some LURR anomalous regions, however, no earthquakes occurred. According to the characteristics of LURR anomalies, two regions with a high risk of big earthquakes were detected. One is between the northern region of the Bay Area and the Mendocino triple junction (38°-40°N, −124° to −122°E) and the other is between Lake Tahoe and Mono Lake (37.5°-39.5°N, −120° to −118°E) along the border of California and Nevada. [ABSTRACT FROM AUTHOR]

A straightforward Bayesian statistic is applied in five broad seismogenic source zones of the northwest frontier of the Himalayas to estimate the earthquake hazard parameters (maximum regional magnitude M, β value of G-R relationship and seismic activity rate or intensity λ). For this purpose, a reliable earthquake catalogue which is homogeneous for M ≥ 5.0 and complete during the period 1900 to 2010 is compiled. The Hindukush-Pamir Himalaya zone has been further divided into two seismic zones of shallow ( h ≤ 70 km) and intermediate depth ( h > 70 km) according to the variation of seismicity with depth in the subduction zone. The estimated earthquake hazard parameters by Bayesian approach are more stable and reliable with low standard deviations than other approaches, but the technique is more time consuming. In this study, quantiles of functions of distributions of true and apparent magnitudes for future time intervals of 5, 10, 20, 50 and 100 years are calculated with confidence limits for probability levels of 50, 70 and 90 % in all seismogenic source zones. The zones of estimated M greater than 8.0 are related to the Sulaiman-Kirthar ranges, Hindukush-Pamir Himalaya and Himalayan Frontal Thrusts belt; suggesting more seismically hazardous regions in the examined area. The lowest value of M (6.44) has been calculated in Northern-Pakistan and Hazara syntaxis zone which have estimated lowest activity rate 0.0023 events/day as compared to other zones. The Himalayan Frontal Thrusts belt exhibits higher earthquake magnitude (8.01) in next 100-years with 90 % probability level as compared to other zones, which reveals that this zone is more vulnerable to occurrence of a great earthquake. The obtained results in this study are directly useful for the probabilistic seismic hazard assessment in the examined region of Himalaya. [ABSTRACT FROM AUTHOR]

In seismically active regions, faults nucleate, propagate, and form networks that evolve over time. To simulate crustal faulting processes, including the evolution of fault-zone properties, a rheological model must incorporate concepts such as damage rheology that describe the various stages of the seismic cycle (strain localization, subcritical crack growth and macroscopic failure) while accounting for material degradation and healing and off-fault deformation. Here we study the fundamental patterns of strain-localisation within the framework of a continuum damage rheology by performing a shear band analysis (linear instability analysis) and comparing predictions of shear band orientations with numerical results of the nonlinear problem. We find (analytically and numerically) that the angle between the shear band and the less compressive (transverse) direction is between 47° in compression tests with a strain ratio of 0.25 (highly confined compression test), and 60° for a strain ratio higher than 1.4 (axial compression and transverse extension). In addition we find that shear bands exhibit local dilation ( I > 0) in a wide range of strain ratios excluding only simulations with highly confined compression (which yield compacting shear bands or non-localized deformation). Finally, we discuss the applicability of the damage model for simulating deformation in the seismogenic, brittle crust. [ABSTRACT FROM AUTHOR]

We explore fractal properties of two observed seismicity distributions prior to the 2003 M 7.4 Colima, Mexico and 1992 M 7.3 Landers, USA earthquakes, together with several mathematical fractal distributions and two non-fractal ones, in order to estimate minimum reliable sample sizes, determine whether fractality for observed seismicity is essentially different from random uniform distributions, and explore the possibility of extracting premonitory information from fractal characteristics of seismicity before large earthquakes. Sample sizes above 800 events for whole catalogs appear to be sufficient to maintain ordered multifractality and to yield dimension estimates that vary smoothly and reliably. Fractal estimates appear to be best for whole catalogs that include aftershocks. The fractal characteristics of spatial distributions of seismicity are essentially different from those of the uniform random distribution, which is the null hypothesis of a non-fractal distribution with minimum information. The fractal dimensions and afractality measures of seismicity distributions change with time and show distinctive behaviors associated with foreshocks and main events, although these behaviors are different for each example. Results suggest the possibility of a priori identification of foreshocks to large earthquakes. A combination of fractal dimension and afractality measures over time may be helpful in large earthquake premonitory studies. [ABSTRACT FROM AUTHOR]

Using global positioning system (GPS) technology, significant postseismic surface displacements were observed within the first 4 months after the 2001 Mw 7.8 Kunlun earthquake which occurred in China. In this study, we investigated the mechanisms that may have possibly contributed to the postseismic deformations that have been observed. Based on the modeling results, we find that an afterslip model can interpret postseismic displacements in the near field even when the fault plane is extended to the bottom of the crust (~70 km). Models based on the viscoelastic relaxation theory showed a large discrepancy in the spatial pattern of the deformation compared with what has been observed. Thus, we infer that both mechanisms cannot interpret the observed postseismic deformation independently. A combination of afterslip and viscoelastic relaxation can further improve the data fit, especially at sites far from the fault. With maximum afterslip of ~0.4 m occurring at a depth of 10 km in the central section, the combined model shows that the estimated afterslip occurred mostly on and below the coseismic rupture plane, as well as on its eastern extension. The estimated moment released by the afterslip in the first 4 months is almost 40% of that released by the coseismic slip. The best-fitting viscoelastic relaxation model shows a 'weak' upper mantle with a viscosity of ~1.0 × 10 Pa s. The combined model also suggests the existence of a lower crust with viscosity larger than 1.0 × 10 Pa s, although it cannot be constrained accurately. [ABSTRACT FROM AUTHOR]

Seismic hazard and risk are two very important concepts in engineering design and other policy considerations. Although seismic hazard and risk have often been used interchangeably, they are fundamentally different. Furthermore, seismic risk is more important in engineering design and other policy considerations. Seismic hazard assessment is an effort by earth scientists to quantify seismic hazard and its associated uncertainty in time and space and to provide seismic hazard estimates for seismic risk assessment and other applications. Although seismic hazard assessment is more a scientific issue, it deserves special attention because of its significant implication to society. Two approaches, probabilistic seismic hazard analysis (PSHA) and deterministic seismic hazard analysis (DSHA), are commonly used for seismic hazard assessment. Although PSHA has been proclaimed as the best approach for seismic hazard assessment, it is scientifically flawed (i.e., the physics and mathematics that PSHA is based on are not valid). Use of PSHA could lead to either unsafe or overly conservative engineering design or public policy, each of which has dire consequences to society. On the other hand, DSHA is a viable approach for seismic hazard assessment even though it has been labeled as unreliable. The biggest drawback of DSHA is that the temporal characteristics (i.e., earthquake frequency of occurrence and the associated uncertainty) are often neglected. An alternative, seismic hazard analysis (SHA), utilizes earthquake science and statistics directly and provides a seismic hazard estimate that can be readily used for seismic risk assessment and other applications. [ABSTRACT FROM AUTHOR]

If aseismic slip occurs on a fault or its deeper extension, both seismicity and crustal deformation around the source would be affected. Anomalous phenomena of this kind are revealed from earthquake occurrence data and geodetic records during a period of 10 years leading up to the March 2005 M 7.0 earthquake west of Fukuoka that occurred off the northern coast of Kyushu, Japan. Seismicity rate anomalies (quiescence and activation) took place relative to the rates expected by the ETAS model in a number of seismic zones in and around the Kyushu District. The seismic zone of the relative quiescence and activation consistently corresponds to the zone of the negative and positive ΔCFS (Coulomb failure stress change), respectively, assuming the precursory aseismic slips on the M 7.0 source fault. In addition, we consider the time series of geodetic baseline distances between permanent GPS stations in the Kyushu District for the same period, which also supports the possible precursory slips rather than the known slow slips beneath the Bungo Straight, off the eastern coast of Kyushu. [ABSTRACT FROM AUTHOR]

Poisson Hidden Markov models (PHMMs) are introduced to model temporal seismicity changes. In a PHMM the unobserved sequence of states is a finite-state Markov chain and the distribution of the observation at any time is Poisson with rate depending only on the current state of the chain. Thus, PHMMs allow a region to have varying seismicity rate. We applied the PHMM to model earthquake frequencies in the seismogenic area of Killini, Ionian Sea, Greece, between period 1990 and 2006. Simulations of data from the assumed model showed that it describes quite well the true data. The earthquake catalogue is dominated by main shocks occurring in 1993, 1997 and 2002. The time plot of PHMM seismicity states not only reproduces the three seismicity clusters but also quantifies the seismicity level and underlies the degree of strength of the serial dependence of the events at any point of time. Foreshock activity becomes quite evident before the three sequences with the gradual transition to states of cascade seismicity. Traditional analysis, based on the determination of highly significant changes of seismicity rates, failed to recognize foreshocks before the 1997 main shock due to the low number of events preceding that main shock. Then, PHMM has better performance than traditional analysis since the transition from one state to another does not only depend on the total number of events involved but also on the current state of the system. Therefore, PHMM recognizes significant changes of seismicity soon after they start, which is of particular importance for real-time recognition of foreshock activities and other seismicity changes. [ABSTRACT FROM AUTHOR]

Recently the equilibrium property of ergodicity was identified in an earthquake fault system (T iampo et al., Phys. Rev. Lett. 91, 238501, ; Phys. Rev. E 75, 066107, ). Ergodicity in this context not only requires that the system is stationary for these networks at the applicable spatial and temporal scales, but also implies that they are in a state of metastable equilibrium, one in which the ensemble averages can be substituted for temporal averages when studying their behavior in space and time. In this work we show that this property can be used to identify those regions of parameter space which are stationary when applied to the seismicity of two naturally-occurring earthquake fault networks. We apply this measure to one particular seismicity-based forecasting tool, the Pattern Informatics index (T iampo et al., Europhys. Lett. 60, 481–487, ; R undle et al., Proc. National Acad. Sci., U.S.A., Suppl. 1, 99, 2463, ), in order to test the hypothesis that the identification of ergodic regions can be used to improve and optimize forecasts that rely on historic seismicity catalogs. We also apply the same measure to synthetic catalogs in order to better understand the physical process that affects this accuracy. We show that, in particular, ergodic regions defined by magnitude and time period provide more reliable forecasts of future events in both natural and synthetic catalogs, and that these improvements can be directly related to specific features or properties of the catalogs that impact the behavior of their spatial and temporal statistics. [ABSTRACT FROM AUTHOR]

An earthquake sequence at the transform plate boundary in South Iceland, that included two magnitude 6.5 earthquakes in June 2000, was anticipated on the basis of a centuries-long seismicity pattern in the area. A program of radon monitoring in geothermal water from drill holes, initiated in 1999, rendered distinct and consistent variations in radon in association with these events. All seven sampling stations in a 50 × 30 km zone covering the epicentral area showed a consistent pattern. Four types of change could be identified: 1) Preseismic decrease of radon. Anomalously low values were measured 101–167 days before the earthquakes. 2) Preseismic increase. Spikes appear in the time series at six stations 40–144 days prior to the earthquakes. These anomalies were large and unusual if compared to a 17-years history of radon monitoring in this area. 3) Coseismic step, most likely related to the coseismic change in groundwater pressure observed over the entire area. 4) Postseismic return of the radon values to the preseismic level about three months later, also concurrent with groundwater pressure changes. [ABSTRACT FROM AUTHOR]

A probabilistic seismic hazard assessment was performed for the Japanese islands and surrounding areas. Seismic hazard parameters characteristic of the seismic history of the regions were obtained. The probability of occurrence of a large M ≥ 7 earthquake within a 10- and 50-year period was also calculated. Regions of very high levels of hazard occur where the Pacific, Phillipine and Eurasian Plates meet. High probabilities of occurrence of a large M ≥ 7 earthquake within a 10- and 50-year period occur within the region where the Pacific Plate subducts with the Eurasian Plate. [ABSTRACT FROM AUTHOR]

- Analysis of the Koyna-Warna earthquake catalog (1968-1996) shows that on an average there is a positive correlation between thebvalue (decrease) and fractal dimensions (decrease in bothD2s and D2t) of earthquake epicenters 0.5 and 2.5 years prior to 1973 (M5.2) and 1980 (M5.5) events, respectively, except a negative correlation for about five years (1988-1993) prior to the 1993/1994 sequence (M5.4). This positive correlation indicates a weaker clustering, or that the epicenters tend to fill the two-dimensional plane. While the origin of the negative correlation seems to be that during periods of large events (lowbvalue), there is strong clustering around the main shock epicenter (high fractal dimension). Interestingly, during the last year (1995-1996) of the studied period both thebvalue and correlation dimensions rose significantly, suggesting that stress release occurs through increased levels of low magnitude and increasingly scattered seismicity, suggesting an increased risk of larger magnitude events. Incidentally, during 2000 three earthquakes of magnitudeM= 5.0, one earthquake ofM4.0, 45 earthquakes of magnitudeM3.0-3.9, and several thousand earthquakes ofM<3 have occurred in the region. Thus it can be inferred that at local scales the relationship yields both positive and negative correlation that appears to be controlled by different modes of failure within the active fault complex. [ABSTRACT FROM AUTHOR]

- It has long been realized that the linear Gutenberg-Richter model arduously describes the frequency-magnitude relationship for the magnitude span ranging from small to large earthquakes because of the breakdown of the self-similarity rule due to the cha [ABSTRACT FROM AUTHOR]

The South Iceland seismic zone is, roughly speaking, situated between two sections of the mid-Atlantic ridge, i.e., the Reykjanes Ridge southwest of Iceland and the Eastern Volcanic Zone on the island. It is a transform zone, where earthquakes are expected to occur on E-W-trending left-lateral shear faults, equivalent to conjugate, N-S-oriented right-lateral, rupture planes. In fact, earthquakes take place on en-échelon N-S-oriented faults, which is indicated by the distribution of main shock intensities, aftershocks as well as by surface fault traces. The stress field continuously generated in the fault zone by opening of the adjacent ridges is computed and superimposed on the stress field changes induced by a series of 13 earthquakes (M ≥ 6) between 1706 and 2000. The level of the pre-seismic stress field is analysed as well as the size of the area under high stress. Finally, the post-seismic stress field of June 2000 is analysed, to see where high stresses might have accumulated. The modelling indicates that the rupture planes located on separated parallel N-S-striking zones are dense enough to lead to an area-wide stress release by the series of events. The obtained pre-seismic stress level for most events is high and stable with the exception of situations when several strong shocks occur over a time span of several days, i.e., display typical main shock-aftershock patterns. The size of areas under high stress aside from of the rupture plane, i.e., where no event occurs at the specific time, is of medium to small size. [ABSTRACT FROM AUTHOR]