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The establishment of a unified earthquake catalog is a basic requirement for attaining a detailed seismological analysis and an improved seismic hazard assessment. Accordingly, the current research paper aims to present a reliable instrumental unified earthquake catalog for the northern part of Algeria. This unified catalog is compiled using regional empirical relationships derived from converting different magnitude scales to an advanced physical-based moment magnitude scale suggested in the recent literature and denoted by Mwg. The regression methodology used in this study is called the New General Orthogonal Regression approach (N.GOR), which was selected since it is the most trustworthy procedure for scaling the magnitudes to Mwg. To highlight the significance of using the N.GOR, the obtained outcomes of the scaling relations were compared with those issued from the conventional general orthogonal regression (GOR) method, which is deemed to be the most dependable methodology used worldwide for magnitude conversion problems. The unified earthquake catalog was assembled from 1954 to 2022. Reliably converting the original magnitudes into homogenized moment magnitude leads to a complete and consistent unified earthquake catalog. Indeed, the unified moment magnitude catalog presented in this paper could provide reliable data for studying earthquakes distribution and the assessment of seismic hazards in the north of Algeria. [ABSTRACT FROM AUTHOR]

The tectonic setting of Lebanon in the eastern Mediterranean region is a restraining bend along the Dead Sea Transform Fault, which is the plate boundary between Arabia and Africa. Within the Lebanese Restraining Bend, the plate boundary splays into several fault branches that are mapped onshore Lebanon and known to have contributed to the evolution of the Lebanese structural framework. Different models have been proposed about the geological structures offshore Lebanon, and how those structures could relate to the onshore tectonics. Based on 2D seismic reflection data, a previously interpreted thrust fault system offshore Lebanon referred to as "Mount Lebanon thrust" was suggested to be responsible for the 9 July 551 M 7.2 earthquake, which was one of the most destructive in the history of the Levant. This thrust system has been accepted as the main structure behind the offshore seismic activity. The objective of this paper is to use current 3D seismic reflection data in order to interpret the main tectonic structures offshore Lebanon, and to differentiate features formed by tectonic activity from others caused by different mechanisms such as subsurface salt movement. Such information is very useful in understanding the tectonic framework of the region from the earthquake geology perspective. A bathymetric map of the Lebanese offshore area was generated and used to delineate the seafloor features. Major and minor faults were interpreted and used to identify and understand the behavior of potential tsunami-generating structures. After careful investigation of the offshore area using the available 3D seismic data, the authors were not able to confirm the existence of Mount Lebanon thrust. Instead, they propose that the Latakia ridge that lies between Lebanon and Cyprus is a major and prominent structure that can trigger high-magnitude tsunamigenic earthquakes. [ABSTRACT FROM AUTHOR]

Large-magnitude earthquakes in northern Chile and southern Peru occur every 108 years on average. It should be noted that over 143 years since the catastrophic earthquake of May 9, 1877, any similar events were completely absent. In 2007, a 7.7 Mw earthquake occurred near Tocopilla, and in 2014 a catastrophic M = 8.1 earthquake hit Pisagua. It is believed that only part of the energy accumulated over 143 years has been released during those events, while most of it is yet to be released. Thus, we can conclude that a serious tsunami hazard exists for all coastal cities of southern Peru and northern Chile. In this paper, on the basis of the available historical data and geodynamic studies, numerical simulation of the historical catastrophic earthquake and tsunami of May 9, 1877 is carried out assuming the blockwise earthquake source configurations. We implemented 23 simulation scenarios for different kinematic behavior patterns of such a source, sequentially updating the source fragmentation to reduce the misfit between the simulated and observed wave height data. Using the proposed methodology, for each scenario, the generation of a tsunami source is simulated and the computation of wave fields up to the 5-m isobath is carried out. The results obtained are compared with historical data. Analysis of the entire set of simulated earthquake scenarios makes it possible to choose a tsunamigenic earthquake scenario with the most adequate characteristics of tsunami waves in the coastal zone. [ABSTRACT FROM AUTHOR]

Quickly determining earthquake size by extracting information after P-wave arrival is a critical issue for earthquake early warning systems. However, early warning parameters are often calculated using a fixed-length (3–5 s) P-wave time window for rapid magnitude estimation. In this paper, we directly investigate magnitude-scaling relationships within the available P-wave time window (APTW, defined as the window period starting from the trigger time of the P wave and ending at the arrival of the S wave) and explore a new real-time magnitude estimation approach (the APTW method). The results of an offline application demonstrate the good performance of the APTW method in terms of the stability of magnitude estimation for small to moderate earthquakes and improved estimation for large earthquakes. The APTW method can provide estimates earlier, and the estimated magnitudes are more stable. The proposed method of establishing magnitude relationships could provide an alternative choice for magnitude estimation in earthquake early warning systems. [ABSTRACT FROM AUTHOR]

In this paper, we explore the Western Pacific subduction impact on the geodynamics of the Asian continent. The data on migration of slow strain and earthquakes from the Nankai, Japan and Kuril-Kamchatka segments of the Western Pacific subduction zone deep into mainland Asia are analyzed. The calculations performed on five profiles, crossing the Kuril Islands, the Japanese Archipelago and Sakhalin Island toward the Asian continent, have revealed the transverse migration of earthquakes from the Japan–Kuril-Kamchatka subduction zone. The velocities of hypocenter migration of M ≥ 4.5 earthquakes from the Kuril-Kamchatka Trench via northern and central Sakhalin vary from 6 to 17 km/year, on average, at different depths. The profiles crossing the islands of Hokkaido and Sakhalin show the M ≥ 4.earthquake migration from the Kuril and Japan trenches at velocities of 8–27 km/year. [ABSTRACT FROM AUTHOR]

A modified k-nearest-neighbors method is introduced that provides an efficient nonlinear estimate of the intensity of a point process (field) based on locations of events. The method is applied to perform a detailed statistical analysis of the spatial structure of the seismic intensity field (in the context of this paper, the term "intensity" refers to the intensity of the seismic field, and should not be mistaken for the intensity of ground motion caused by an earthquake). The proposed method requires neither a preliminarily delineated area nor a normalization procedure for the estimates. In contrast to many interpolation methods, estimates based on the proposed method are statistically justified. The "uncertainty relation" between the spatial smoothing effect and random errors is established for the method in an explicit form. A procedure for choosing the number of nearest neighbors k* that controls the effective radius of smoothing is suggested. The proposed method is applied to analyze the seismic intensity field in two seismogenic regions surrounding the Kuril Islands and Japan during the period from 1904 to 2011. Spots of increased seismic activity in these regions are localized by the new method, and some quantitative statistical characteristics of these spots are determined and discussed. [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]

This paper presents the quantification of the role of structural parameters and impedance contrast in the insulation and meta-capacity of a city for Rayleigh waves at an earthquake engineering scale. The feasibility of developing heterogeneous and homogeneous meta-cities in a soft sediment deposit is investigated using the meta-behavior of structures and meta-blocks in the epicentral zone of shallow crustal earthquakes. The Rayleigh wave and horizontally propagating plane SH-wave responses of the city with different structural parameters and impedance contrast are simulated at the top of the structure as well as at the free field after crossing the city. It is concluded that the structures act as a meta-structure for the Rayleigh waves but not for the Love waves, and the meta-capacity of the city increases with the increase in the number and stiffness of structures and decrease in damping and impedance contrast. An increase in the width of bandgaps at different longitudinal modes of vibration of structures is obtained with a decrease in impedance contrast, particularly when it is less than 15. It is concluded that meta-blocks can be developed using appropriate ceramic material considering the half-space impedance to develop a desired bandgap for Rayleigh waves. Based on the obtained increase in the city's insulation capacity for Rayleigh waves with the increase in the number and width of structures and decrease in impedance contrast, it is recommended that engineers consider the urban layer as lying in the path of Rayleigh waves for the estimation of seismic hazard in the epicentral zone of shallow crustal earthquakes. [ABSTRACT FROM AUTHOR]

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]

In December 2007, an Mw2.2 earthquake occurred in a gabbroic dike at 3.3 km depth in a deep gold mine in South Africa. The fore- and aftershock activity was analyzed in an effort to understand the preparation and generation processes of earthquakes; these findings have already been published. The present paper focuses on the stress state in the source region of the mainshock. A 90-m-long borehole across the mainshock fault was drilled ~ 1.5 years after the mainshock and logged by an optical televiewer. The fault can be identified by severe damage to the borehole wall at the point where the borehole intersected the aftershock cluster. Except for a 10-m section in the hanging wall of the fault, borehole cores were fully recovered. Borehole breakout (BO) and core disking (CD) were found to occur. Two stress measurement techniques [Deformation Rate Analysis (DRA) and Diametrical Core Deformation Analysis (DCDA)] were applied to the borehole cores. By combining their results with occurrence criteria for BO and CD, the principal stress state in the source region of the mainshock was determined. The principal directions in the hanging wall of the fault were nearly identical to the virgin stress state, while it was significantly disturbed in the footwall. The vertical stresses were 106 MPa and 40 MPa in the hanging wall and footwall, respectively. The significant difference in the vertical stress between the two sides of the fault can be explained by the stress redistribution associated with a nonuniform slip on a nonplanar fault. [ABSTRACT FROM AUTHOR]

Earthquake depth frequency distribution is often used as a constraining factor in assessing lithospheric strength. The accuracy of hypocenter locations is therefore a key factor in these types of analyses. This paper presents a summary of earthquake depth distributions in the Baikal rift system reported in various previous studies. Datasets on both background seismicity and aftershock sequences were analyzed by taking into account hypocenter depth uncertainties. The results show that the most seismically active part of the Earth's crust is in a depth range of 10–25 km. The lower cutoff depth varies for different datasets from 20 to 40 km. The latter value corresponds to the Kichera sequence and coincides with the Moho depth, but other datasets show that the lower 8–18 km of the crust is aseismic. The South Baikal basin is distinguished by the shallower cutoff depth (20–24 km) compared to the datasets outside of it. The peak depths of the earthquake depth frequency distributions vary from 8 to 23 km. Given the depth uncertainties, only the Kumora sequence appears to have double peaks at 9–10 km and 16–17 km. Variations in the lower limit of earthquake distribution and depth of the main peak may imply a spatial change in the depth of the brittle–ductile transition and consequently in the thermomechanical properties of the crust. [ABSTRACT FROM AUTHOR]

Monitoring precursory decline in groundwater radon at the Antung hot spring is a useful means of forecasting the magnitude and precursor time of local disastrous earthquakes. With the help of a case study in southeastern Taiwan, this paper demonstrates the effect of tectonic setting in the subduction zone on the correlation between radon decline, precursory time and earthquake magnitude. Given a radon-monitoring site located near the plate boundary in the tectonic setting of advanced arc-continental collision, the observed radon decline and precursory time prior to the earthquakes in the tectonic setting of initial arc-continental collision are smaller than those observed prior to the earthquakes occurring on the plate boundary in the tectonic setting of advanced arc-continental collision. In the advanced arc-continental collision state, the coupling between the plates is strong and the stress transfer is efficient, whereas in the incipient collision state, the coupling and stress transfer are not as good. It also takes additional time lag and attenuation for the stress transfer from one tectonic setting to the other. This paper presents the difference in the precursory behavior of groundwater radon between earthquakes which occurred in two different tectonic settings: advanced and initial arc-continental collision. [ABSTRACT FROM AUTHOR]

China suffers severe continental earthquakes. The 2008 Wenchuan earthquake (Ms 8.0) and the 2014 Ludian earthquake (Ms 6.5) are two representative examples from the modern era. The Wenchuan earthquake caused considerable economic losses, and the Ludian earthquake caused unexpected losses with only moderate magnitude. Based on disability-adjusted life years (DALYs), this paper first calculates aggregated disaster losses and the contributions of three factors: number of deaths or missing persons, number of people affected, and direct economic losses. Then, the losses per unit energy released or area affected are calculated for each earthquake to investigate which of the two earthquakes caused more damage. The paper finishes by investigating the implications and revealing three results. (1) The Wenchuan earthquake induced more damage than the Ludian earthquake, but the latter had relatively higher losses per unit energy than the former. (2) Injuries and affected people contributed most to the total losses for each earthquake, more than fatalities or direct damage. This outcome means that unnoticed aspects have the most severe disaster impacts. In addition, long-term impacts of earthquakes are more serious than usually acknowledged, and more attention needs to be paid to these. (3) The damage from moderate earthquakes can exceed expectations, meaning that disaster mitigation policies in all regions are necessary, regardless of the degree of anticipated hazard. [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]

Site and path effects are always required to isolate the source term from a recorded seismograph for the estimation of source characteristics. In this paper, the site and path effects are assessed in terms of site amplification and anelastic attenuation (quality factor), respectively, to obtain an isolated source term for the estimation of earthquake source parameters in the Kinnaur Himalaya. These terms are then applied to calculate the source parameters of 75 local earthquakes in the range 1.5 ≤ moment magnitude (Mw) ≤ 3.6 recorded in the Kinnaur region. The scaling relations of earthquake source parameters are also established for this region. The site amplification curves and S-wave quality factor Qs(f) are determined and further utilized to correct the Fourier spectrum of earthquake records. The obtained source spectrum corrected for these two terms is compared with the theoretical source spectrum based on the Brune (J Geophys Res 75:4997–5009, 1970) source model. The root-mean-square error (RMSE) between the observed and theoretical spectrum is formulated by implementing iterative forward modeling. The obtained range of source parameters of 75 events reveals ranges of 2.73 × 1011–3.44 × 1014 N-m for seismic moment, 0.03–13 bar for stress drop, 0.3–0.9 km for source radius, and 5.64 × 1002–1.19 × 1008 J for radiated energy. [ABSTRACT FROM AUTHOR]

The present study reports measurements of radon in groundwater conducted in China between January and December 2013. During the measurement period, a great Ms = 6.6 earthquake occurred in Gansu Province, China. The paper analyses data derived from three nearby stations via monofractal and multifractal detrended fluctuations analysis and explores whether pre-earthquake fractal and long-memory trends exist in the time series. Several critical epochs with characteristic pre-seismic long-lasting fractal patterns are identified in segmented parts of the series. In the whole data series, the fluctuation function, scaling exponent and generalised Hurst exponent depend on the fractal scales, which indicates multifractality. The multifractal spectrum of the raw, shuffled and truncated series showed a significant increase in the degree of fluctuation that can be explained as a pre-earthquake indicator attributable to the Gansu earthquake due to its very large magnitude. [ABSTRACT FROM AUTHOR]

Because of the scarcity of recorded seismic ground motions from Vrancea intermediate-depth source that can be used in designing a structure, engineers are bound to use scaled, artificial, or simulated accelerograms. Out of these options, the first two might incompletely account for the phenomena that may appear. Although complicated, simulated accelerograms provide one of the best options for defining the seismic demand in engineering design, but further research is needed to adapt the simulation methods to the source, path, and site-specific characteristics. As some parameters used in simulations were not addressed yet specifically for the Vrancea-intermediate seismic source, the specific path duration is investigated in this paper. Using a database with the recorded ground motions from March 4, 1977, August 30, 1986, May 30 and May 31, 1990, October 27, 2004 Vrancea earthquakes (the only five recorded earthquakes with moment magnitudes at least equal to 6), the path and magnitude dependent duration specific to Vrancea intermediate-depth seismic source to be used in the stochastic simulation is developed. [ABSTRACT FROM AUTHOR]

Research on earthquake occurrences using a statistical methodology based on point processes has mainly focused on the data featuring earthquake catalogs which ignores the effect of environmental variables. In this paper, we introduce inhomogeneous versions of the Cox process models which are able to quantify the effect of geological factors such as subduction zone, fault, and volcano on the major earthquake distribution in Sulawesi and Maluku, Indonesia. Specifically, we compare Thomas, Cauchy, variance-gamma, and log-Gaussian Cox models and consider parametric intensity and pair correlation functions to enhance model interpretability. We perform model selection using the Akaike information criterion (AIC) and envelopes test. We conclude that the nearest distances to the subduction zone and volcano have a significant impact on the risk of earthquake occurrence in Sulawesi and Maluku. Furthermore, the Cauchy and variance-gamma cluster models fit well the major earthquake distribution in Sulawesi and Maluku. [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]

Grouping of earthquakes into distinct clusters is applied to improve mechanism identification and pattern recognition for active seismicity in a region. One of the important issues concerning earthquake data clustering is determining the optimum number of clusters (ONC) at the early stages of algorithms. In this paper a robust method based on K-nearest neighbor search (KNNS) is presented to achieve three goals: improving output accuracy, improving output stability, and adding the ability to weight the features used in ONC determination. By introducing a new formula, the proposed method utilizes the error calculated for clustered data based on the similarity between the members in each cluster. An outlier attenuation algorithm is also used to improve the performance of the method. Both the Krzanowski–Lai Index (KLI) and the silhouette coefficient (SC), as two conventional methods, were used to compare the results and evaluate the performance. Experiments on synthetic data sets verified the effectiveness of the method, with considerable differences found. The clustering of a real earthquake catalogue related to the seismogenic province of Zagros in Persia using our proposed methodology suggests using 13-cluster analysis for clustering based on the spatiotemporal features with the same weights, and seven-cluster analysis for a case where priority is given only to the spatial parameters of the epicenters. Under the same circumstances, the KLI and SC methods suggest three and 18 clusters, respectively. The results of the experiments on synthetic data sets indicate that the proposed method is quantitatively more stable and more accurate than the other two methods. [ABSTRACT FROM AUTHOR]

This paper presents the first uniformly processed comprehensive database on strong motion acceleration records for the extensive regions of western Himalaya, northeast India, and the alluvial plains juxtaposing the Himalaya. This includes 146 three components of old analog records corrected for the instrument response and baseline distortions and 471 three components of recent digital records corrected for baseline errors. The paper first provides a background of the evolution of strong motion data in India and the seismotectonics of the areas of recording, then describes the details of the recording stations and the contributing earthquakes, which is finally followed by the methodology used to obtain baseline corrected data in a uniform and consistent manner. Two different schemes in common use for baseline correction are based on the application of the Ormsby filter without zero pads (Trifunac 1971) and that on the Butterworth filter with zero pads at the start as well as at the end (Converse and Brady 1992). To integrate the advantages of both the schemes, Ormsby filter with zero pads at the start only is used in the present study. A large number of typical example results are presented to illustrate that the methodology adopted is able to provide realistic velocity and displacement records with much smaller number of zero pads. The present strong motion database of corrected acceleration records will be useful for analyzing the ground motion characteristics of engineering importance, developing prediction equations for various strong motion parameters, and calibrating the seismological source model approach for ground motion simulation for seismically active and risk prone areas of India. [ABSTRACT FROM AUTHOR]

Seismic risk analyses aim at establishing a relation that links the earthquake activity rate to the magnitude, using earthquake catalogs. The most widely used relation is the log-linear relation proposed by Gutenberg and Richter (Science 83:183–185, 1936) and Gutenberg and Richter (Bull Seismol Soc Am 46(3):105–145, 1945): log E N m = a - b m , where E N m is the mean number of earthquakes which magnitude is greater than m, with modification at larger magnitudes by Cosentino et al. (Bull Seismol Soc Am 67:1615–1623, 1977), Kijko and Sellevoll (Bull Seismol Soc Am 79(3):644–654, 1989), Page (Bull Seismol Soc Am 58:1131–1168, 1968), Pisarenko and Sornette (Pure Appl Geophys 160:2343–2364, 2003) and Weichert (Bull Seismol Soc Am 70(4):1337–1346, 1980). That relation leads to an Exponential distribution for the magnitudes, that we assume to be truncated to a maximum magnitude m max , a priori fixed under geophysical considerations. The objective of this paper is to simultaneously estimate the parameters (a, b) from data which main features are: (a) data are observed on unequal observation periods; (b) magnitudes are imprecisely known. Within the assumption that earthquakes are modeled by a continuous Poisson point process, we propose an estimator of (a, b) that maximizes the likelihood of that Poisson point process which has been discretized on classes of magnitudes. The asymptotic distribution of the estimator is a Normal distribution of dimension 2. That distribution is used to propagate the estimation uncertainties on (a, b) until the recurrence model. Uncertainty analyses enable to draw the 5 % and 95 % quantile curves around the estimated recurrence model. [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]

Earthquakes with submarine foci are generally located with high uncertainties, and their focal mechanisms are poorly resolved, due to the confinement of the monitoring network onshore and the consequent poor azimuthal coverage. The use of amphibious networks, combining ocean-bottom seismometers (OBSs) and land stations, helps to reduce the epicentral distance and the azimuth gap, thus better constraining the hypocentral locations and decreasing the focal mechanism uncertainties. A second important factor in improving the location accuracy for offshore seismicity is the use of a suitable velocity model. The objective of this paper is to study how the combination of an amphibious network with 3D crustal models can improve offshore earthquake hypocenter locations and focal mechanisms. The study area is SW Iberia near Cape St. Vincent, which generated some of the most striking earthquakes and tsunamis in Europe in past centuries, such as the 1755 Lisbon earthquake (Imax = X). We deployed an array of six broadband OBSs 200 km offshore Cape St. Vincent to study the seismicity of the region for a period of 8 months. During this period, we detected 52 earthquakes, the largest with magnitude M (mbLg) ≈ 5. Thirty-eight earthquakes are relocated using land stations in Iberia and North Africa and the OBS array with different velocity models. Focal mechanisms and moment tensors are computed for a data set of seven earthquakes based on first-motion polarities, body-wave amplitude spectra and waveform cross-correlation. We show that if we include offshore OBS data and consider accurate 3D velocity models to locate earthquakes, the focal parameter uncertainties decrease substantially, thus improving the depth constraint. We also show that the locations and focal mechanisms obtained using the amphibious network agree with the regional stress pattern in the SW Iberia region. [ABSTRACT FROM AUTHOR]

During May 12–14, 2018, the International Conference for the Decade Memory of the Wenchuan Earthquake, in connection to the 4th International Conference on Continental Earthquakes (4th ICCE) and the 12th General Assembly of the Asian Seismological Commission (ASC), was held in Chengdu, China. There have been several outcomes of the Conference (for example, the book published jointly by Higher Education Press and Springer) as well as the present special issue. Among the 58 submissions, 34 have been accepted after peer review. Some of the papers came from the presentations during the Conference, but with additional submissions, the scope of this special issue is far beyond that of the proceedings of the meeting. [ABSTRACT FROM AUTHOR]

The MS8.0 earthquake that occurred in Wenchuan, Sichuan in 2008 provides an important case for the study of operational earthquake forecasting and short-term aftershock forecasting of major disaster-inducing earthquakes in China. This paper focuses on the comparative study of the applicability of the epidemic-type aftershock sequence (ETAS) model, the Reasenberg–Jones (R–J) model and the Omi–R–J model, which are widely adopted internationally for short-term aftershock forecasting and seismic hazard mitigation strategy research. We compare the stability of model parameters and aftershock occurrence rate forecasting, and evaluate the effectiveness of forecasting using the N-test and T-test with multiple time windows. The results show that the sequence parameters of the ETAS model, the R–J model and the Omi–R–J model tend to stabilize after 15.50, 15.50 and 6.00 days following the earthquake respectively, and the attenuation of the Wenchuan MS8.0 earthquake is rather normal. Compared to the ETAS model and the R–J model, the Omi–R–J model obtain steadier model parameters in a shorter time with significantly smaller parameters pORJ, cORJ, bORJ and standard deviations. Among the three models, the overall aftershock occurrence rate forecasted by the R–J model is the highest, followed by the Omi–R–J model, while that of the ETAS model is the lowest. N-test results show overall forecasting effectiveness of 93.8, 80.7 and 97.7% for the ETAS, R–J and Omi–R–J models, respectively, with the ETAS and Omi–R–J models superior to the R–J model, and the Omi–R–J model slightly better than the ETAS model. The overall "information gain per earthquake" calculation results show that the ETAS model is superior to the Omi–R–J and R–J models, while the Omi–R–J model is better than the R–J model; thus the combined use of the ETAS and Omi–R–J models by focusing on their respective strengths might ensure optimal performance. These "maneuverable" forecasting approaches to short-term aftershock model forecasting will play a vital role in efficient post-disaster relief, emergency management decision-making and post-disaster reconstruction. [ABSTRACT FROM AUTHOR]

A systematic inspection of the magnetic field and electron density, recorded by Swarm three-satellite constellation over the seismic region hit by the 2016–2017 Amatrice-Norcia (Central Italy) seismic sequence, has allowed us to identify some possible precursory anomalies, when disturbed periods of the geomagnetic conditions are properly taken into account and/or avoided. This paper aims at studying and interpreting the electromagnetic phenomena occurred before and during the 2016–2017 Amatrice-Norcia (Central Italy) seismic sequence, in order to look for any possible evidence of precursory anomalies. Results show magnetic field and electron density anomalies of four tracks that precede the major earthquakes of the seismic sequence. After an inspection of the geomagnetic conditions, a Swarm Charlie track, acquired on 20/08/2016 that precedes by 3.2 days the beginning of the whole seismic sequence, remains unexplainable with the normal geomagnetic disturbance phenomena of the Earth's magnetic field. Furthermore, we carry out a blind study of possible relationship between abnormal magnetic field signals detected by Swarm satellites during geomagnetic quiet conditions and major seismic events from about 4 months before the start of the seismic sequence until about the first 8 months from the seismic sequence (i.e. a total of one year of analysed data). We find a very interesting increase of such anomalies starting about 40 days before the beginning of the seismic sequence. It coincides and follows surface and atmospheric alterations, resulting in a temporal sequence of anomalies from Earth's surface up to ionosphere, supporting the possibility of lithosphere–atmosphere–ionosphere coupling models. [ABSTRACT FROM AUTHOR]

In this paper we investigated the feasibility of using the higher-frequency waveforms to characterize the seismicity in the Koyna–Warna region, globally well-known for its reservoir-triggered earthquakes. The local seismicity and source parameters have been extensively explored by many researchers using various types of data, e.g. analog data, broadband seismological data, and deep seismic sounding data. However, here we have utilized the seismological data recorded by 97 temporary 4.5-Hz geophones to locate the local seismicity in the region. We first investigated an appropriate 1-D P-wave velocity model through the inversion of P- and S-times. In order to compensate for the thick and laterally heterogeneous basalt, we incorporated the station corrections in the 1-D velocity inversion process. The station correction varies from + 0.09 to − 0.20 s for the P-waves, with clear demarcations of positive and negative station corrections corresponding to the northern and southern regions, respectively. The patterns of positive and negative station corrections suggested that the northern part is characterized by lower velocity, while slighter higher velocities present in the southern part of the study area are relative to the estimated 1-D velocity model. The earthquake locations are further improved by using the double-difference (hypoDD) approach, which enabled us to accurately map shallow subsurface seismogenic faults in the region. The data comprises 10,062 P-wave and 9049 S-wave catalog differential times from 348 earthquakes (1.0 ≤ ML ≤ 4.5). The precisely relocated earthquakes (ERH < 0.05 km ERZ < 0.5 km and rms < 0.02 s) form the three clusters of earthquakes in the NW–SE direction along the lineaments close to Warna Reservoir. The observed seismicity trends on the surface could be due to the vertical manifestations of faults or fractures. Their alignments are confirmed by the analysis of focal mechanism which exhibits a predominant normal type of faults with one nodal plane consistent with the main alignment of the seismic events. [ABSTRACT FROM AUTHOR]

China suffers severe earthquake disasters along the Pacific Rim. Rapid urbanization, population growth and economic production have dramatically changed China both spatially and temporally. Exposure has increased rapidly compared with hazards and vulnerability, and exposure has increased earthquake risks more than hazards and vulnerability. Based on county-level data, this paper emphasizes the rising exposure of high earthquake risk regions (HERRs) by analyzing the concentration of population and GDP in HERRs. The results reveal three findings. (1) Population and GDP transferred to HERRs from 2000 to 2010. The vast majority of the population growth (88%) and GDP growth (63.8%) occurred in HERRs, and 16.4% of the population growth and 16.4% of the GDP growth occurred in counties where an earthquake of M 7.5 + may take place. (2) The shift of population and GDP growth in East China was more dramatic than that in West, Central and Northeast China. Overall, 56.8% of the population growth and 38.0% of the GDP growth occurred in HERRs in East China. (3) The Theil index showed that the internal population distribution for each region was also distinct. East China had the largest population growth in HERRs but had the most separation among the regions in China. In both 2010 and 2000, East China had the largest internal Theil index. The population and GDP were concentrated in the places with high earthquake risks, especially in the developed areas of East China. And East China had the most internal inequality. Increasing earthquake risks are a challenges for the country's social and economic development. [ABSTRACT FROM AUTHOR]

This article characterizes the regions of earthquake slip that are responsible for strong motion generation (SMG), using extreme value theory (EVT). A three-step iterative procedure involving Zipf plot, mean excess function plot and moment ratio plot is used to define the threshold value for a slip model. This threshold slip demarcates the region of SMG in the slip model. The iterative procedure ensures that slip values above the threshold slip follow generalized Pareto distribution (GPD). The regions where slip is greater than the corresponding threshold slip are defined as regions of SMG. A total of 159 slip samples filtered from the SRCMOD catalogue are analyzed in this paper. In order to identify the region of SMG, the first step is to obtain effective slip dimensions. A novel method based on strong motion duration (SMD) is proposed to obtain the effective dimensions of slip model. In the next step, the iterative procedure is employed to obtain threshold slip and the regions of SMG for all the slip samples. The corresponding area of SMG is estimated from the number of sub-faults in the region of SMG and the sub-fault dimensions. Regression analysis is carried out to establish source scaling relationships for the rupture parameters with respect to seismic moment. The considered rupture parameters are effective length, effective width, effective area, effective mean slip, threshold slip and area of SMG of the slip model. On a logarithmic scale, these rupture parameters are observed to follow a linearly increasing trend with the seismic moment. The proposed equations can be used to estimate the rupture parameters for future earthquake events. [ABSTRACT FROM AUTHOR]

Recently, coda-wave interferometry has been used to monitor temporal changes in subsurface structures. Seismic velocity changes have been detected by coda-wave interferometry in association with large earthquakes and volcanic eruptions. To constrain the spatial extent of the velocity changes, spatial homogeneity is often assumed. However, it is important to locate the region of the velocity changes correctly to understand physical mechanisms causing them. In this paper, we are concerned with the sensitivity kernels relating travel times of coda waves to velocity changes. In previous studies, sensitivity kernels have been formulated for two-dimensional single scattering and multiple scattering, three-dimensional multiple scattering, and diffusion. In this paper, we formulate and derive analytical expressions of the sensitivity kernels for three-dimensional single-scattering case. These sensitivity kernels show two peaks at both source and receiver locations, which is similar to the previous studies using different scattering models. The two peaks are more pronounced for later lapse time. We validate our formulation by comparing it with finite-difference simulations of acoustic wave propagation. Our formulation enables us to evaluate the sensitivity kernels analytically, which is particularly useful for the analysis of body waves from deeper earthquakes. [ABSTRACT FROM AUTHOR]

Large earthquakes have semi-periodic behavior as a result of critically self-organized processes of stress accumulation and release in seismogenic regions. Hence, large earthquakes in a given region constitute semi-periodic sequences with recurrence times varying slightly from periodicity. In previous papers, it has been shown that it is possible to identify these sequences through Fourier analysis of the occurrence time series of large earthquakes from a given region, by realizing that not all earthquakes in the region need belong to the same sequence, since there can be more than one process of stress accumulation and release in the region. Sequence identification can be used to forecast earthquake occurrence with well determined confidence bounds. This paper presents improvements on the above mentioned sequence identification and forecasting method: the influence of earthquake size on the spectral analysis, and its importance in semi-periodic events identification are considered, which means that earthquake occurrence times are treated as a labeled point process; a revised estimation of non-randomness probability is used; a better estimation of appropriate upper limit uncertainties to use in forecasts is introduced; and the use of Bayesian analysis to evaluate the posterior forecast performance is applied. This improved method was successfully tested on synthetic data and subsequently applied to real data from some specific regions. As an example of application, we show the analysis of data from the northeastern Japan Arc region, in which one semi-periodic sequence of four earthquakes with M ≥ 8.0, having high non-randomness probability was identified. We compare the results of this analysis with those of the unlabeled point process analysis. [ABSTRACT FROM AUTHOR]

This paper presents new models of the seismic velocity structure of Eastern Anatolia, Turkey. We applied a local earthquake tomography method to arrival time data produced by local and regional events in Eastern Anatolia to understand the three-dimensional seismic velocity and Vp/Vs models and their correlation with the geological evolution and tectonic processes in the study area. The data are obtained from 78 broadband seismic stations, owned by the Earthquake Department of the Disaster and Emergency Management Presidency, for the period between 2008 and 2017. Seven depth cross sections are taken along various segments of the East Anatolian Fault Zone. Travel times of 53,099 phase readings (29,122 P-phase and 23,977 S-phase picks) from 4249 high-quality earthquake recordings are analysed to develop 3-D Vp (lithological) and Vp/Vs (petrological) models of the study area. The resulting P-wave velocities describe intrusive magmatic bodies, sediment thickness and the structure of the basin. The Vp/Vs structures aid to limit the position of the faults, areas of weakness, and gas- or liquid-saturated units with regions of high pore pressure. Four main seismic crustal layers down to 40 km are determined. The upper crust (0–8 km) has Vp ≤ 4.6 km/s, whereas in the middle crust (~ 9–20 km) a Vp perturbation between 4.6 and 5.8 km/s is observed. In the lower crust (~ 20–35 km), Vp changes from 5.9 to 7.3 km/s and in the upper mantle layer (below 36 km), Vp exceeds 7.4 km/s. In all cases, seismic velocities are well-resolved in the first 40 km. Tomograms are compatible with the geological characteristics of the region. Dominant high P-velocity values are observed beneath the collision zone. Conrad discontinuity is detectable at 20 km depth, while Moho depth is observed to vary between 30 and 40 km in the study area. [ABSTRACT FROM AUTHOR]

Statistical quantification of observed seismicity is important for understanding earthquake dynamics and future risk in any seismic-prone region. In this paper, we implement the idea of nowcasting (Rundle et al. in Earth and Space Science 3:480–486, 2016) to examine the current uncertain state of earthquake hazard assessment in the seismically active Bay of Bengal (BoB) and adjacent regions. First, we utilize the concept of "natural time" (Varostos et al. in Physical Review E 71:032102, 2005), rather than clock time, to develop a statistical distribution of inter-event counts of "small" earthquakes occurring between "large" earthquakes. Using relevant statistics of natural time, we then calculate the earthquake potential score (EPS) as the cumulative number of small earthquakes since the last large event in the selected region. The EPS, which provides the nowcast value for a region, reveals the current state of earthquake hazard in that region. Therefore, by indirect means, the EPS provides us with a simple yet transparent estimation of the current level of seismic progress through the regional earthquake cycle of recurring events in a geographical area. To illustrate the nowcasting approach in the study region, we computed EPS values for the two most seismically exposed megacities, Dhaka and Kolkata, considering events of M ≥ 4 within a radius of 250 km around their respective city centers. We found that the current EPS values corresponding to M ≥ 6 events in Dhaka and Kolkata were approximately 0.72 and 0.40, respectively. The practical applicability of these values is discussed in conjunction with sensitivity analysis of the threshold magnitudes. [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]

Tectonic movement is closely related to earthquake preparation. Across-fault sites and InSAR data are applied to reveal crust deformation from different precision, different temporal scale, and different spatial scale. In this paper, Xianshuihe fault zone is taken as an example; dislocation model in near-fault field is derived from screw dislocation model proposed by Savage and Burford (1973), which can reveal the locking information of the across-fault site using baseline data. Locking depth of each across-fault site on Xianshuihe fault zone is calculated using baseline data, which indicates that the locking depth of Laoqianning across-fault site is about 18 km and the locking depth of other sites is shallow. Time series analysis of SBAS-InSAR is used to study interseismic tectonic deformation. Deformation field from InSAR reveals the left-lateral slip property of Xianshuihe fault zone. The average locking depth is about 2-4 km calculated by the pixels' slip rate around in near-fault field, which indicates that locking depth is shallow and consistent using InSAR data as well as across-fault data. Screw model is used to obtain the best-fitting result of fault locking depth and slip rate. Layered dislocation model is put forward to explain shallow locking depth of fault zone. According to the theory of fault-slip deficit and seismic moment equilibrium, accumulative seismic moments caused by fault slip and the release amount of MS ≥ 5.0 earthquakes are calculated to estimate seismic risk of study area. All results indicate that Qianning segment of Xianshuihe fault zone is the future danger area with strong earthquakes. [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]

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]

There are many studies on the anomalous variations of the ionospheric TEC prior to large earthquakes. However, whether or not the morphological characteristics of the TEC anomalies in the daytime and at night are different is rarely studied. In the present paper, based on the total electron content (TEC) data from the global ionosphere map (GIM), we carry out a statistical survey on the spatial-temporal distribution of TEC anomalies before 1339 global M6.0+ earthquakes during 2003-2014. After excluding the interference of geomagnetic disturbance, the temporal and spatial distributions of ionospheric TEC anomalies prior to the earthquakes in the daytime and at night are investigated and compared. Except that the nighttime occurrence rates of the pre-earthquake ionospheric anomalies (PEIAs) are higher than those in the daytime, our analysis has not found any statistically significant difference in the spatial-temporal distribution of PEIAs in the daytime and at night. Moreover, the occurrence rates of pre-earthquake ionospheric TEC both positive anomalies and negative anomalies at night tend to increase slightly with the earthquake magnitude. Thus, we suggest that monitoring the ionospheric TEC changes at night might be a clue to reveal the relation between ionospheric disturbances and seismic activities. [ABSTRACT FROM AUTHOR]

The objective of this paper is to evaluate seismic-led point source and non-point source water pollution, under the seismic hazard of 10 % probability of exceedance in 50 years, and with the minimum value of the water quality standard in Sichuan, China. The soil conservation service curve number method of calculating the runoff depth in the single rainfall event combined with the seismic damage index were applied to estimate the potential degree of non-point source water pollution. To estimate the potential impact of point source water pollution, a comprehensive water pollution evaluation framework is constructed using a combination of Water Quality Index and Seismic Damage Index methods. The four key findings of this paper are: (1) The water catchment that has the highest factory concentration does not have the highest risk of non-point source water contamination induced by the outbreak of potential earthquake. (2) The water catchment that has the highest numbers of cumulative water pollutants types are typically located in the south western parts of Sichuan where the main river basins in the regions flow through. (3) The most common pollutants in sample factories studied is COD and NH-N which are found in all catchments. The least common pollutant is pathogen-found present in W1 catchment which has the best rating in the water quality index. (4) Using water quality index as a standardization parameter, parallel comparisons is made among the 16 water catchments. Only catchment W1 reaches level II water quality status which has the rating of moderately polluted in events of earthquake induced water contamination. All other areas suffer from severe water contamination with multiple pollution sources. The results from the data model are significant to urban planning commissions and businesses to strategically choose their factory locations in order to minimize potential hazardous impact during the outbreak of earthquake. [ABSTRACT FROM AUTHOR]

Twenty papers on the study of tsunamis and respective tsunamigenic earthquakes are included in Volume II of the PAGEOPH topical issue 'Tsunami Science: Ten Years after the 2004 Indian Ocean Tsunami'. The papers presented in this second of two special volumes of Pure and Applied Geophysics reflect the state of tsunami science during this time, including five papers devoted to new findings specifically in the Indian Ocean. Two papers compile results from global observations and eight papers cover Pacific Ocean studies, focusing mainly on the 2011 Tohoku earthquake and tsunami. Remaining papers in this volume describe studies in the Atlantic Ocean and Mediterranean Sea and tsunami source studies. Overall, the volume not only addresses the pivotal 2004 Indian Ocean and 2011 Tohoku tsunamis, but also examines the tsunami hazard posed to other critical coasts in the world. [ABSTRACT FROM AUTHOR]

On February 28th, 1969, a large earthquake (M SB w sb = 7.8) strokes the Iberian Peninsula and northern Morocco, producing some casualties and important damage and economic losses. This earthquake is the last large earthquake that has occurred in this region, very near where the catastrophic 1755 Lisbon earthquake took place. The paper by Udías ([11]) is a review of large tsunamigenic earthquakes that occurred at SW of Iberia before the 1755 Lisbon earthquake. [Extracted from the article]

Hydrological and geochemical changes have been studied extensively in China for the purpose of earthquake prediction since 1966. This paper gives a brief overview of the findings, which have been reported mainly in Chinese so far. Parameters studied include water level; water temperature; and radon, hydrogen and mercury concentrations. Significant changes have been observed before some large or even intermediate-sized earthquakes, among many cases that did not show any such changes. Background noise caused by other environmental variables and possible mechanisms for the pre-earthquake anomalies are discussed. Due to the complexity of earthquake prediction, much more monitoring efforts as well as sophisticated analytic and synthetic efforts are needed in the future. [ABSTRACT FROM AUTHOR]

An Mw 8.2 earthquake and tsunami occurred offshore the Pacific coast of México on 2017-09-08, at 04:49 UTC. Costa Rican tide gauges have registered a total of 21 local, regional and far-field tsunamis. The Quepos gauge registered 12 tsunamis between 1960 and 2014 before it was relocated inside a harbor by late 2014, where it registered two more tsunamis. This paper analyzes the 2017 México tsunami as recorded by the Quepos gauge. It took 2 h for the tsunami to arrive to Quepos, with a first peak height of 9.35 cm and a maximum amplitude of 18.8 cm occurring about 6 h later. As a decision support tool, this tsunami was modeled for Quepos in real time using ComMIT (Community Model Interface for Tsunami) with the finer grid having a resolution of 1 arcsec (~ 30 m). However, the model did not replicate the tsunami record well, probably due to the lack of a finer and more accurate bathymetry. In 2014, the National Tsunami Monitoring System of Costa Rica (SINAMOT) was created, acting as a national tsunami warning center. The occurrence of the 2017 México tsunami raised concerns about warning dissemination mechanisms for most coastal communities in Costa Rica, due to its short travel time. [ABSTRACT FROM AUTHOR]

Tidal stresses are generated in any three-dimensional body influenced by an external inhomogeneous gravity field of rotating planets or moons. In this paper, as a special case, stresses caused within the solid Earth by the body tides are discussed from viewpoint of their influence on seismic activity. The earthquake triggering effects of the Moon and Sun are usually investigated by statistical comparison of tidal variations and temporal distribution of earthquake activity, or with the use of mathematical or experimental modelling of physical processes in earthquake prone structures. In this study, the magnitude of the lunisolar stress tensor in terms of its components along the latitude of the spherical surface of the Earth as well as inside the Earth (up to the core-mantle boundary) were calculated for the PREM (Dziewonski and Anderson in Phys Earth Planet Inter 25(4):297-356, 1981). Results of calculations prove that stress increases as a function of depth reaching a value around some kPa at the depth of 900-1500 km, well below the zone of deep earthquakes. At the depth of the overwhelming part of seismic energy accumulation (around 50 km) the stresses of lunisolar origin are only (0.0-1.0)·103 Pa. Despite the fact that these values are much smaller than the earthquake stress drops (1-30 MPa) (Kanamori in Annu Rev Earth Planet Sci 22:207-237, 1994) this does not exclude the possibility of an impact of tidal forces on outbreak of seismic events. Since the tidal potential and its derivatives are coordinate dependent and the zonal, tesseral and sectorial tides have different distributions from the surface down to the CMB, the lunisolar stress cannot influence the break-out of every seismological event in the same degree. The influencing lunisolar effect of the solid earth tides on earthquake occurrences is connected first of all with stress components acting parallel to the surface of the Earth. The influence of load tides is limited to the loaded area and its immediate vicinity. [ABSTRACT FROM AUTHOR]

The objective of this paper is to analyze the temporal clustering of large global earthquakes with respect to natural time, or interevent count, as opposed to regular clock time. To do this, we use two techniques: (1) nowcasting, a new method of statistically classifying seismicity and seismic risk, and (2) time series analysis of interevent counts. We chose the sequences of Mλ≥7.0 and Mλ≥8.0 earthquakes from the global centroid moment tensor (CMT) catalog from 2004 to 2016 for analysis. A significant number of these earthquakes will be aftershocks of the largest events, but no satisfactory method of declustering the aftershocks in clock time is available. A major advantage of using natural time is that it eliminates the need for declustering aftershocks. The event count we utilize is the number of small earthquakes that occur between large earthquakes. The small earthquake magnitude is chosen to be as small as possible, such that the catalog is still complete based on the Gutenberg-Richter statistics. For the CMT catalog, starting in 2004, we found the completeness magnitude to be Mσ≥5.1. For the nowcasting method, the cumulative probability distribution of these interevent counts is obtained. We quantify the distribution using the exponent, β, of the best fitting Weibull distribution; β=1 for a random (exponential) distribution. We considered 197 earthquakes with Mλ≥7.0 and found β=0.83±0.08. We considered 15 earthquakes with Mλ≥8.0, but this number was considered too small to generate a meaningful distribution. For comparison, we generated synthetic catalogs of earthquakes that occur randomly with the Gutenberg–Richter frequency–magnitude statistics. We considered a synthetic catalog of 1.97×105Mλ≥7.0 earthquakes and found β=0.99±0.01. The random catalog converted to natural time was also random. We then generated 1.5×104 synthetic catalogs with 197 Mλ≥7.0 in each catalog and found the statistical range of β values. The observed value of β=0.83 for the CMT catalog corresponds to a p value of p=0.004 leading us to conclude that the interevent natural times in the CMT catalog are not random. For the time series analysis, we calculated the autocorrelation function for the sequence of natural time intervals between large global earthquakes and again compared with data from 1.5×104 synthetic catalogs of random data. In this case, the spread of autocorrelation values was much larger, so we concluded that this approach is insensitive to deviations from random behavior. [ABSTRACT FROM AUTHOR]

Natural Time (“NT”) refers to the concept of using small earthquake counts, for example of M > 3 events, to mark the intervals between large earthquakes, for example M > 6 events. The term was first used by Varotsos et al. (2005) and later by Holliday et al. (2006) in their studies of earthquakes. In this paper, we discuss ideas and applications arising from the use of NT to understand earthquake dynamics, in particular by use of the idea of nowcasting. Nowcasting differs from forecasting, in that the goal of nowcasting is to estimate the current state of the system, rather than the probability of a future event. Rather than focus on an individual earthquake faults, we focus on a defined local geographic region surrounding a particular location. This local region is considered to be embedded in a larger regional setting from which we accumulate the relevant statistics. We apply the nowcasting idea to the practical development of methods to estimate the current state of risk for dozens of the world’s seismically exposed megacities, defined as cities having populations of over 1 million persons. We compute a ranking of these cities based on their current nowcast value, and discuss the advantages and limitations of this approach. We note explicitly that the nowcast method is not a model, in that there are no free parameters to be fit to data. Rather, the method is simply a presentation of statistical data, which the user can interpret. Among other results, we find, for example, that the current nowcast ranking of the Los Angeles region is comparable to its ranking just prior to the January 17, 1994 Northridge earthquake. [ABSTRACT FROM AUTHOR]

The load–unload response ratio (LURR) method is proposed to measure the damage extent of source media and the criticality of earthquake. Before the occurrence of a large earthquake, anomalous increase in the time series of LURR within the certain temporal and spatial windows has often been observed. In this paper, a dimensional analysis technique is devised to evaluate quantitatively the magnitude and time of the ensuing large earthquake within the anomalous areas derived from the LURR method. Based on the π-theorem, two dimensionless quantities associated with the earthquake time and magnitude are derived from five parameters (i.e. the seismic energy (ES), the average seismic energy (EW), the maximum value of LURR’s seismogenic integral (IPP), the thickness of seismogenic zone (h), the time interval from IPP to earthquake (T2), and the shear strain rate (γ˙)). The statistical relationships between the earthquakes and the two dimensionless quantities are derived by testing the seismic data of the 50 events of M4.5 ~ 8.1 occurred in China since 1976. In earthquake prediction, the LURR method is used to detect the areas with anomalous high LURR values, and then our dimensional analysis technique is applied to assess the optimal critical region, magnitude, and time of the ensuing event, when its seismogenic integral is peaked (IPP). As study examples, we applied this approach to study four large events, namely the 2012 MS5.3 Hami, 2015 MS5.8 Alashan, 2015 MS8.1 Nepal earthquakes, and the 2013 Songyuan earthquake swam. Results show that the predicted location, time, and magnitude correlate well with the actual events. This provides evidence that the dimensional analysis technique may be a useful tool to augment current predictive power of the traditional LURR approach. [ABSTRACT FROM AUTHOR]

Nowcasting is a new method of statistically classifying seismicity and seismic risk (Rundle et al. 2016). In this paper, the method is applied to the induced seismicity at the Geysers geothermal region in California and the induced seismicity due to fluid injection in Oklahoma. Nowcasting utilizes the catalogs of seismicity in these regions. Two earthquake magnitudes are selected, one large say $$M_{\lambda } \ge 4$$ , and one small say $$M_{\sigma } \ge 2$$ . The method utilizes the number of small earthquakes that occurs between pairs of large earthquakes. The cumulative probability distribution of these values is obtained. The earthquake potential score (EPS) is defined by the number of small earthquakes that has occurred since the last large earthquake, the point where this number falls on the cumulative probability distribution of interevent counts defines the EPS. A major advantage of nowcasting is that it utilizes 'natural time', earthquake counts, between events rather than clock time. Thus, it is not necessary to decluster aftershocks and the results are applicable if the level of induced seismicity varies in time. The application of natural time to the accumulation of the seismic hazard depends on the applicability of Gutenberg-Richter (GR) scaling. The increasing number of small earthquakes that occur after a large earthquake can be scaled to give the risk of a large earthquake occurring. To illustrate our approach, we utilize the number of $$M_{\sigma } \ge 2.75$$ earthquakes in Oklahoma to nowcast the number of $$M_{\lambda } \ge 4.0$$ earthquakes in Oklahoma. The applicability of the scaling is illustrated during the rapid build-up of injection-induced seismicity between 2012 and 2016, and the subsequent reduction in seismicity associated with a reduction in fluid injections. The same method is applied to the geothermal-induced seismicity at the Geysers, California, for comparison. [ABSTRACT FROM AUTHOR]