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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]

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]

Two large earthquakes occurred in the western part of China in 2008, one of them being the Yutian (35.6°N, 81.6°E) M7.3 earthquake that occurred on March 21 (BJT) and the other the Wenchuan (31.0°N, 103.4°E) M8.0 earthquake that occurred on May 12 (BJT). In this paper, the West Continental China (included in 20.0°-50.0°N, 70.0°-110.0°E region) was the study region for verifyong the predictability of the pattern informatics (PI) method using the receiver-operating characteristic curve (ROC) test and R score test. Different forecasting maps with different calculating parameters were obtained. The calculating parameters were the grid size Δ x, base time t, reference interval t to t, change interval t to t, and forecasting interval t to t. In this paper, the base time t fixed to June 1, 1971, the ending forecast time t fixed to June 1, 2008, and the forecasting interval t to t changed from 1 to 10 years, and the grid sizes were chosen as 1° × 1° and 2° × 2°, respectively. The results show that the PI method could forecast the Yutian M7.3 and Wenchuan M8.0 earthquakes only using suitable parameters. Comparing the forecast results of grid sizes 1° × 1° and 2° × 2°, the models with 2° × 2° grids were better. Comparing the forecast results with different forecasting windows from 1 to 10 years, the models with forecasting windows of 4-8 years were better using the ROC test, and the models with forecasting windows of 7-10 years were better using the R score test. The forecast efficiency of the model with a grid size of 2° × 2° and forecast window of 8 years was the best one using either the ROC test or the R score test. [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]

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]

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]

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]

The North-South earthquake belt (NSEB) is one of the major earthquake regions in China. The studies of crustal structure play a great role in understanding tectonic evolution and in evaluating earthquake hazards in this region. However, some fundamental crustal parameters, especially crustal interface structure, are not clear in this region. In this paper, we reconstructed the crustal interface structure around the NSEB based on both the deep seismic sounding (DSS) data and the gravity data. We firstly reconstructed the crustal structure of crystalline basement (interface G), interface between upper and lower crusts (interface C) and Moho in the study area by compiling the results of 38 DSS profiles published previously. Then, we forwardly calculated the gravity anomalies caused by the interfaces G and C, and then subtracted them from the complete Bouguer gravity anomalies, yielding the regional gravity anomalies mainly due to the Moho interface. We then utilized a lateral-variable density interface inversion technique with constraints of the DSS data to invert the regional anomalies for the Moho depth model in the study area. The reliability of our Moho depth model was evaluated by comparing with other Moho depth models derived from other gravity inversion technique and receiver function analysis. Based on our Moho depth model, we mapped the crustal apparent density distribution in the study area for better understanding the geodynamics around the NSEB. [ABSTRACT FROM AUTHOR]

There are limitations in conventional earthquake loss procedures if attempts are made to apply these to assess the social and economic impacts of recent disastrous earthquakes. This paper addresses the need to develop an applicable model for estimating the significant increases of earthquake loss in mainland China. The casualties of earthquakes were studied first. The casualties of earthquakes are strongly related to earthquake strength, occurrence time (day or night) and the distribution of population in the affected area. Using data on earthquake casualties in mainland China from 1980 to 2000, we suggest a relationship between average losses of life and the magnitude of earthquakes. Combined with information on population density and earthquake occurrence times, we use these data to give a further relationship between the loss of life and factors like population density, intensity and occurrence time of the earthquake. Earthquakes that occurred from 2001 to 2003 were tested for the given relationships. This paper also explores the possibility of using a macroeconomic indicator, here GDP (Gross Domestic Product), to roughly estimate earthquake exposure in situations where no detailed insurance or similar inventories exist, thus bypassing some problems of the conventional method. [ABSTRACT FROM AUTHOR]

The shifting correlation method (SCM) is proposed for statistical analysis of the correlation between earthquake sequences and electromagnetic signal sequences. In this method, the two different sequences were treated in units of 1 day. With the earthquake sequences fixed, the electromagnetic sequences were continuously shifted on the time axis, and the linear correlation coefficients between the two were calculated. In this way, the frequency and temporal distribution characteristics of potential seismic electromagnetic signals in the pre, co, and post-seismic stages were analyzed. In the work discussed in this paper, we first verified the effectiveness of the SCM and found it could accurately identify indistinct related signals by use of sufficient samples of synthetic data. Then, as a case study, the method was used for analysis of electromagnetic monitoring data from the Minxian-Zhangxian M 6.5 ( M 6.1) earthquake. The results showed: (1) there seems to be a strong correlation between earthquakes and electromagnetic signals at different frequency in the pre, co, and post-seismic stages, with correlation coefficients in the range 0.4-0.7. The correlation was positive and negative before and after the earthquakes, respectively. (2) The electromagnetic signals related to the earthquakes might appear 23 days before and last for 10 days after the shocks. (3) To some extent, the occurrence time and frequency band of seismic electromagnetic signals are different at different stations. We inferred that the differences were related to resistivity, active tectonics, and seismogenic structure. [ABSTRACT FROM AUTHOR]

The concept of state vector stems from statistical physics, where it is usually used to describe activity patterns of a physical field in its manner of coarsegrain. In this paper, we propose an approach by which the state vector was applied to describe quantitatively the damage evolution of the brittle heterogeneous systems, and some interesting results are presented, i.e., prior to the macro-fracture of rock specimens and occurrence of a strong earthquake, evolutions of the four relevant scalars time series derived from the state vectors changed anomalously. As retrospective studies, some prominent large earthquakes occurred in the Chinese Mainland (e.g., the M 7.4 Haicheng earthquake on February 4, 1975, and the M 7.8 Tangshan earthquake on July 28, 1976, etc) were investigated. Results show considerable promise that the time-dependent state vectors could serve as a kind of precursor to predict earthquakes. [ABSTRACT FROM AUTHOR]

Five large earthquakes of M ≥ 7.0 (based on the magnitude scale of the China Earthquake Networks Center) occurred in and near the Tibetan Plateau during 2008-2014, including the Wenchuan M8.0 earthquake on May 12, 2008 (BJT). In this paper, the Tibetan Plateau was chosen to be the study region, and calculating parameters of pattern informatics (PI) method with grid of 1° × 1° and forecasting time interval of 8 years were employed for the retrospective study according to the previous studies for M7 earthquake forecasting. The sliding step of forecasting interval was 1 year, and the hotspot diagrams of each forecasting interval since 2008 were obtained year by year. The relationships among the hotspots and the M ≥ 7.0 earthquakes that occurred during the forecast intervals were studied. The predictability of PI method was tested by verification of receiver-operating characteristic curve (ROC) and R score. The results show that the successive obvious hotspots occurred during the sliding forecasting intervals before four of the five earthquakes, while hotspots only occurred in one forecasted interval without successive evolution process before one of the five earthquakes, which indicates that four of the five large earthquakes could be forecasted well by PI method. Test results of the predictability of PI method by ROC and R score show that positive prospect of PI method could be expected for long-term earthquake forecast. [ABSTRACT FROM AUTHOR]

On January 8, 2022, the MS 6.9 Menyuan earthquake occurred in Menyuan, Qinghai province, China; the epicenter was on the fault terrace of the Lenglongling and Tuolaishan faults. To investigate the coseismic and pre-seismic deformation associated with the event, we constructed physical models using interferometric synthetic aperture radar (InSAR) and global navigation satellite system (GNSS) data and inverted the fault slip distribution, fault coupling fraction, fault slip deficit and strain rate. The primary inversion results were as follows: (1) The InSAR coseismic deformation pattern indicates that the left-lateral strike-slip deformation occurred in the NW–SE direction, with the maximum relative displacement in the line-of-sight direction being 1.3 m. (2) The coseismic slip mainly occurred in a 30 × 25 km region at a depth of 0–8 km. The maximum fault slip was 3.81 m with a moment magnitude (MW) of 6.6. (3) Based on the fault coupling inversion, the seismogenic fault was strongly locked (> 0.96) up to a depth of ~ 10 km before the Menyuan earthquake. The coseismic rupture zone in the fault strike direction was significantly smaller than the pre-seismic locked region. (4) The pre-seismic strain rates revealed NE–SW compressive and NW–SE tensile deformations, reflecting a considerable left-lateral strain accumulation in the seismogenic region, with a maximum shear strain rate of 2.6 × 10–8/year. Therefore, attention must be paid to the seismic hazards posed by the Tuolaishan and Lenglongling faults adjacent to the seismogenic region. [ABSTRACT FROM AUTHOR]

The general characteristics of the recent horizontal crustal movement in the Chinese Mainland and the horizontal crustal movements before the Kunlun Mountain earthquake of M8.1 on Nov. 14, 2001 and two earthquakes of M 8.0 and M 7.9 occurred in Sept. 2003 around the Chinese Mainland are analyzed with GPS data obtained in the Crustal Movement Observation Network of China (CMONOC). Relative vertical displacements observed in the last five years at fiducial stations show that there was a significant correlation between the length of day and the vertical displacements at most stations in western China. [ABSTRACT FROM AUTHOR]

Earthquakes threaten people's lives and property, especially when cities are affected. Thus, detecting the crustal structure and seismogenic background beneath cities is important if we are to lessen losses. Because the city of Zhumadian in Henan Province, China, is a well-developed area with a large population, more attention should be paid to earthquake detection. We therefore collected data from 15 magnetotelluric (MT) stations along a 55-km survey line across Zhumadian. Then, subsequent to acquisition, processing, and data inversion, we developed a preferred electrical resistivity model. We accurately relocated original earthquakes during the period between 1981 and 2019 within the study area using the double-difference earthquake location algorithm. The relocated earthquakes were projected onto our preferred MT model. The new resistivity model presented here reveals that saturated rocks, including rocks with porosities of 4.31–19.69% and moderate salinities of 10 g/L pore fluid and/or graphite, form conductive features in the upper crust. We also show that aqueous fluids derived from metamorphic dehydration within the lower crust and mantle, not melts, constitute mid-crustal conductors and facilitate detachment structures. The data show that the relocated earthquakes are located adjacent to the boundaries between conductive and resistive areas as well as at the bottom of fault fracture zones. These outcomes imply that the combination of rock failure and fault slipping triggers earthquakes. [ABSTRACT FROM AUTHOR]

Mixture density networks (MDNs) are a class of neural network algorithms in the Bayesian framework that can invert for parameters and estimate the parameter uncertainties at the same time. We test MDNs by inverting the fault geometric parameters in a synthetic test with Okada's model and demonstrate the efficiency and robustness of the model. To further describe the MDNs algorithm, we invert regional static GPS displacement data for the 2013 Ms7.0 Lushan Earthquake in China to obtain the fault geometric parameters. The inverted geometric parameters, which are in the form of distributions, agree well with the published solutions for this event once the 99.7% confidence interval are taken into account. The 99.7% confidence intervals of the strike and dip angles are [ 187. 5 ∘ , 220. 4 ∘ ] and [ 20. 76 ∘ , 49. 76 ∘ ], respectively. To demonstrate the applicability of the inverted geometric parameters, we invert the slip distribution of the Lushan earthquake with the inverted parameters and GPS displacements. From the slip distributions considering the distributions of the parameters, we obtain the 99.7% confidence intervals of the magnitude Mw, maximum slip and depth of maximum slip, which are [6.51, 6.65], [0.30, 0.74] m and [9.43, 13.61] km, respectively. [ABSTRACT FROM AUTHOR]

Using a seismicity simulation program based on the Coulomb-Navier failure criterion and the stress transfer mechanism, we added extensions to make the model compatible with different input files and to increase computational efficiency. After testing with a two-vertical-parallel-fault model, we applied this model to the Taiyuan region. The frequency–magnitude data of the simulation results fit well with the observation catalogue, which at the same time tends to follow the characteristic earthquake theory instead of the Gutenberg-Richter law. In addition, a single fault region with a higher slip rate seems to have lower b-values, suggesting a higher risk of strong earthquakes. We have also performed data fitting between the simulation results and the Poisson process of corresponding parameters, along with testing for energy conservation. [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]

To adaptively forecast forthcoming large aftershocks of the 2008 Mw7.9 Wenchuan, China, earthquake, we construct a new hazard model to describe the occurrence rate of aftershocks in a study region along the Longmenshan fault. The model is denoted by SRJ since it is a combination of the Reasenberg–Jones (RJ) model and a spatial hazard model that is obtained by taking a reference of previous earthquakes in the study region. We employ the maximum likelihood (ML) method to estimate the SRJ model based on aftershocks that occurred within 1 or 2 days after the Wenchuan earthquake. The probabilities of M ≥ 5.0 aftershocks at each of the grids in the study region during next few days are then computed according to the estimated SRJ model, and hence the corresponding relative aftershock hazard (RAH) map is constructed. Finally, according to a variety of criteria for evaluating the hazard maps on depicting possible rupture area of forthcoming large aftershocks, the SRJ-based RAH map is demonstrated to be more efficient than the RAH maps constructed based on the RJ model incorporated with the gridding method using a fixed radius or varying radii. [ABSTRACT FROM AUTHOR]

Various physical, geophysical, geochemical, electrical and hydrological parameters are measured on the surface and in shallow/deep boreholes throughout mainland China to obtain early warning signals of impending earthquakes. Numerous wells are equipped with water level and temperature sensors for continuous observations of the water level and groundwater temperature. An analysis of water temperature data from boreholes equipped with water temperature sensors reveals that nearly half of the boreholes show coseismic response associated with the Wenchuan earthquake (Mw 7.9, 12 May, 2008). The coseismic response of the groundwater temperature cannot be differentiated from the groundwater flow or movement when the earthquake occurred, but there is no fixed relationship between the temperature variation and the water flow. At the same time, we observed that the rock temperature in dry wells can record the seismic events and even the pre-seismic abnormal information. The spatial distribution of the coseismic groundwater temperature response is random and irregular, which does not support the dislocation model of seismic faults at the regional or larger scale. Changes in the groundwater temperature are closely related to the borehole temperature gradient, lithology profile and geological environment of the borehole and depths of the aquifers. The mechanism of the coseismic groundwater temperature response can be explained by an enhanced permeability induced by an earthquake. The groundwater temperature increases if the temperature sensor in the borehole is located near the deep-circulating aquifer and decreases if the sensor is near the shallow-circulating aquifer when seismic waves arrive. The groundwater temperature may be slightly affected or even unchanged if the temperature sensor is far from the aquifer during the propagation of seismic waves. However, it was hard to conclude the changes of rock temperature observed in six dry wells. [ABSTRACT FROM AUTHOR]

We relocate earthquakes occurring 1 week before and 1 month after the 2016 Yunlong Ms5.0 earthquake by simultaneously using P (and S) travel times and waveform cross-correlation data in the double-difference relocation algorithm. We then use the well-relocated earthquakes as template events and scan through the continuous waveforms to search for and locate weak events by using the match and locate method. A total of 4602 events are detected by using 660 templates, which is ~ 3 times the number of events listed in the Yunnan Seismic Networks catalogue. Our refined catalogue reveals three stages of seismic activity and energy release processes during the 2016 Yunlong Ms5.0 earthquake sequence. We also refine the focal depths and mechanisms of 12M ≥ 3.0 earthquakes using the broadband waveform modeling method. Both the relocated hypocenters and focal mechanisms of the 12M ≥ 3.0 earthquakes delineate fault strike and dip angles of ~ 200° and ~ 75°, respectively, indicating that the seismogenic fault could be a NNE-striking blind or subfault located between the Weixi-Qiaohou Fault and Lancangjiang Fault. Our results could contribute to better understanding of local seismic hazard evaluations in the vicinity of Yunlong area of Yunnan, China. [ABSTRACT FROM AUTHOR]

To study the seismogenic structure of the 7 October 2014 Ms 6.6 Jinggu earthquake, we use the cut-and-paste (CAP) method to obtain the focal mechanisms and depths of the mainshock and the two largest aftershocks with Ms > 5. Then, we take advantage of waveform cross-correlations to obtain precise time difference data and apply the double-difference method to relocate the aftershocks between October 7 and December 31. We relocate 2076 earthquakes (approximately 73.6% of the total) with an average horizontal accuracy of approximately 150 m and a depth uncertainty of approximately 700 m. The Ms 6.6 mainshock epicenter originated at 23.378°N, 100.475°E at a depth of 15.38 km. The Jinggu earthquake sequence exhibited a linearly concentrated distribution in the northwest-southeast direction with obvious segmentation features and, thus, it can be divided into four branches spatially and two stages temporally. The aftershocks first appeared around the Ms 6.6 mainshock and then extended on either side of the mainshock along the NW-SE direction (the NW branch). The earthquake rupture direction experienced a slight clockwise deflection at the NW end and rotated clockwise by approximately 90° toward the SW (the NE branch) at the SE end. Then, the rupture propagated a short distance along the SW direction and rotated counterclockwise by approximately 90° into an SSE direction (the NNW branch). There is a small angle between the NW and NNW branches. The depths of the whole sequence with vertical dip angles were shallower toward the NW and deeper with two seismogenic layers toward the SE. According to the distributions of the earthquakes and nearby fractures, it is highly possible that the Jinggu earthquake sequence occurred along a hidden fracture section of the Wuliangshan fault in the NW direction. Moreover, we can confirm that the three large earthquakes all occurred along right-lateral strike-slip faults. [ABSTRACT FROM AUTHOR]

Anomalous groundwater level and temperature changes are compared with ground deformation recorded before and after an earthquake of MW 5.4 and its foreshocks and aftershocks that occurred during 22-28 May 2006 in the Mexicali Valley, Baja California, Mexico. The coseismic groundwater level changes could be attributed to static volumetric strain changes caused by the mainshock, except for one well, where the groundwater level change may have been affected also by a triggered slip event at a nearby fault. Some of the coseismic temperature changes were attributed to increased convection and mixing of groundwater by seismic shaking. Modeling of groundwater level records allowed the estimation of hydraulic diffusivity. The observed ground tilt and groundwater level anomalies in the area close to the source fault before and after the mainshock and before the aftershocks occurrence are explainable by the dilatancy-diffusion theory, or possibly by assuming the occurrence of a slow slip events and/or fault permeability changes. [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]

Continental thrust faulting earthquakes pose severe threats to megacities across the world. Recent events show the possible control of fault structures on strong ground motions. The seismogenic structure of the 2008 Wenchuan earthquake is associated with high-angle listric reverse fault zones. Its peak ground accelerations (PGAs) show a prominent feature of fault zone amplification: the values within the 30- to 40-km-wide fault zone block are significantly larger than those on both the hanging wall and the footwall. The PGA values attenuate asymmetrically: they decay much more rapidly in the footwall than in the hanging wall. The hanging wall effects can be seen on both the vertical and horizontal components of the PGAs, with the former significantly more prominent than the latter. All these characteristics can be adequately interpreted by upward extrusion of the high-angle listric reverse fault zone block. Through comparison with a low-angle planar thrust fault associated with the 1999 Chi-Chi earthquake, we conclude that different fault structures might have controlled different patterns of strong ground motion, which should be taken into account in seismic design and construction. [ABSTRACT FROM AUTHOR]

The Xianshuihe fault zone consists of left-lateral, segmented strike-slip faults, which produce strong and relatively frequent earthquakes, and exposes millions of people to the risk of strong motion and earthquake-induced geologic hazards in Southwest China. Seismicity in this fault zone exhibits typical features of characteristic earthquakes. The stochastic finite-fault model was used to generate time-histories and peak values of strong ground motion at near-fault locations for the characteristic earthquakes. First, the source parameters were determined and verified by comparing them with the simulated time-histories and intensity distribution and observations from the 2014 Kangding earthquake (Mw 6.0). Then, scenario-based ground-motion hazard maps were produced from simulated ground motions of characteristic earthquakes. The scenario-based ground-motion hazard maps can be directly compared with historical and future earthquakes in the Xianshuihe fault zone. Scenario-based seismic hazard analysis also has other advantages. Our results show that current design ground motion for the Xianshuihe Fault area is not adequate. [ABSTRACT FROM AUTHOR]

We developed a synth esis approach to augment current techniques for seismic hazard evaluation by combining four previously unrelated subjects: the pattern informatics (PI), load/unload response ratio (LURR), state vector (SV), and accelerating moment release (AMR) methods. Since the PI is proposed in the premise that the change in the seismicity rate is a proxy for the change in the tectonic stress, this method is used to quantify localized changes surrounding the epicenters of large earthquakes to objectively quantify the anomalous areas (hot spots) of the upcoming events. On the short-to-intermediate-term estimation, we apply the LURR, SV, and AMR methods to examine the hazard regions derived from the PI hot spots. A predictive study of the 2014 earthquake tendency in Chinese mainland, using the seismic data from 1970-01-01 to 2014-10-01, shows that, during Jan 01 to Oct 31, 2014, most of the M > 5.0 earthquakes, especially the Feb 12 M7.3 Yutian, May 30 M6.1 Yingjiang, Aug. 03 M6.5 Ludian, and Oct 07 M6.6 earthquakes, occurred in the seismic hazard regions predicted. Comparing the predictions produced by the PI and combination approaches, it is clear that, by using the combination approach, we can screen out the false-alarm regions from the PI estimation, without reducing the hit rate, and therefore effectively augment the predictive power of current techniques. This provided evidence that the multi-method combination approach may be a useful tool to detect precursory information of future large earthquakes. [ABSTRACT FROM AUTHOR]

We analyzed the aftershock sequence of the 2008 Wenchuan earthquake from May 12, 2008 to May 12, 2013 using the earthquake catalog of the China Earthquake Networks Center (CENC). In the analysis performed, we took under consideration the temporary variation in the completeness of the earthquake catalog just after the Wenchuan mainshock. The cutoff completeness magnitude from May 12 to June 27, 2008 was above 3.0 due to the impact of the earthquake sequence on the seismological observatory practice. It was observed that the b value has an increasing trend from June 27, 2008 to late April 2009, while since May 2009, the b value has remained stable. If these characteristics were associated with the possible signature of fault healing, the 'apparent healing time' could be pinpointed by this measure as around 1 year. Due to two strong asperities present on the rupture of the Wenchuan mainshock, the aftershock zone can be divided into two segments, namely the north and the south segment. The b values of the two segments seem to show different trends of temporal variation. The main contribution of the increasing trend comes from the south segment, or the 'initiation segment' of the main rupture. [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]

We investigate the relationship between the impoundment and seismicity in the Longtan reservoir, southwestern China and find evidence that the seismicity was reservoir induced. After the reservoir impoundment, a pronounced increase in seismicity was observed in five clusters mainly concentrated in the areas where few earthquakes had occurred before the first filling. The observed induced seismicity shows a strong correlation with the filling cycles. The activity levels in the five clusters are different due to differences in the structures and permeabilities of the faults. Source parameters for 1,616 earthquakes with M 0.1-4.2 recorded by 24 fixed and temporary stations deployed around the reservoir were calculated after applying corrections for geometrical spreading, frequency-dependent Q, and site effects. The static stress drop and apparent stress in this area both appear to increase with increasing seismic moment over the entire magnitude range. Our results show that reservoir induced earthquakes have ten times lower average stress drop than natural tectonic earthquakes. These results may indicate that the reservoir induced seismicity can occur with a lower tectonic stress due to the high pore pressures of the underground medium, and that the effect of the water decreases the coefficient of friction. [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]

An Annual Consultation on the Likelihood of Earthquakes is regularly undertaken in continental China. It is a special kind of intermediate-term medium-range earthquake forecast and a practical service provided by seismological communities within the capability of modern seismology. One of the problems the Annual Consultation encounters is its false alarm rate, which has been higher than expected and has caused numerous controversies on the methodology and significance of the Annual Consultation. To tackle this problem we use the concept of reverse tracing of precursors (RTP) to analyze the long-term seismic activity in the alarm regions, or regions thought to have increased probability of earthquakes, as identified by the Annual Consultation. We apply the Pattern Informatics (PI) and relative intensity (RI) algorithms to the long-term estimation of seismic hazard in the RTP analysis. A retrospective study of the Sichuan-Yunnan region of southwest China, using the data from 1990 to 2003, shows that, by choosing the threshold proportion of overlapped areas between the long-term estimates and the Annual Consultation, the RTP analysis can correctly remove some of the false-alarm regions from the “black list’ and thus reduce the false-alarm rate of the Annual Consultation, without reducing the hit rate. Remarkably, the RTP approach, although originally proposed for short-term earthquake predictions, seems able to contribute to the Annual Consultation as well. [ABSTRACT FROM AUTHOR]

We systematically analyzed the Benioff strain release before 65 earthquakes with M S over 6.0 in China from 1978 to 2003 to investigate the generality of the widely discussed accelerating moment release (AMR) phenomenon before strong and intermediate-strength earthquakes. In this approach, a strong or intermediate-strength earthquake is selected as a ``target earthquake,'' and retrospective analysis of seismic activity before the ``target earthquake'' is performed. Simple searching area (three circular areas with different radius centered at the epicenter of the ``target earthquake'') and unified temporal range (8 years) are taken in the analysis. Justification of whether AMR exists is by both visual inspection and by power-law curve fitting. It is found that more than 3/5 of the earthquakes under consideration exhibit clear pre-shock AMR property, and 1/3 of the events seem to be sensitive to the searching area. AMR behavior shows apparent focal mechanism dependence: 15 out of 17 dip-slip earthquakes with stable moment release characteristics against the changing of searching areas exhibit AMR behavior, while 16 out of 25 strike-slip earthquakes with stable moment release characteristics exhibit AMR behavior. [ABSTRACT FROM AUTHOR]

We develop one-dimensional (1-D) path-specific velocity models in western China using new Rayleigh and Love wave group and phase velocity dispersion measurements for 20 events in the region. The earthquakes were grouped into three geographic clusters from which we compute the average phase and group velocity dispersion. We invert the average dispersion curves simultaneously for 1-D shear-velocity models appropriate for the three central Asian paths, using three previous shear-velocity models as initial models. The models are validated by forward modeling waveforms of recent events. The crustal thickness beneath western China in the vicinity of the Lop Nor test site is 50–60 km and our velocity models are consistent with major geologic features (e.g., basins and mountain ranges) and previous structural models for this region. [ABSTRACT FROM AUTHOR]

Western Sichuan is among the most seismically active regions in southwestern China and is characterized by frequent strong (M ≥ 6.5) earthquakes, mainly along the Xianshuihe fault zone. Historical and instrumental seismicity show a temporal pattern of active periods separated by inactive ones, while in space a remarkable epicenter migration has been observed. During the last active period starting in 1893, the sinistral strike–slip Xianshuihe fault of 350 km total length, was entirely broken with the epicenters of successive strong earthquakes migrating along its strike. This pattern is investigated by resolving changes of Coulomb failure function (ΔCFF) since 1893 and hence the evolution of the stress field in the area during the last 110 years. Coulomb stress changes were calculated assuming that earthquakes can be modeled as static dislocations in an elastic halfspace, and taking into account both the coseismic slip in strong (M ≥ 6.5) earthquakes and the slow tectonic stress buildup associated with major fault segments. The stress change calculations were performed for faults of strike, dip, and rake appropriate to the strong events. We evaluate whether these stress changes brought a given strong earthquake closer to, or sent it farther from, failure. It was found that all strong earthquakes, and moreover, the majority of smaller events for which reliable fault plane solutions are available, have occurred on stress–enhanced fault segments providing a convincing case in which Coulomb stress modeling gives insight into the temporal and spatial manifestation of seismic activity. We extend the stress calculations to the year 2025 and provide an assessment for future seismic hazard by identifying the fault segments that are possible sites of future strong earthquakes. [ABSTRACT FROM AUTHOR]

— Algorithms for the calculation of synthetic seismograms in laterally heterogeneous anelastic media have been applied to model the ground motion in Beijing City. The synthetic signals are compared with the few available seismic recordings (1998, Zhangbei earthquake) and with the distribution of observed macroseismic intensity (1976, Tangshan earthquake). The synthetic three-component seismograms have been computed for the Xiji area and Beijing City. The numerical results show that the thick Tertiary and Quaternary sediments are responsible for the severe amplification of the seismic ground motion. Such a result is well correlated with the abnormally high macroseismic intensity zone in the Xiji area associated with the 1976 Tangshan earthquake as well as with the ground motion recorded in Beijing city in the wake of the 1998 Zhangbei earthquake. [ABSTRACT FROM AUTHOR]

— For the realistic modeling of the seismic ground motion in lateral heterogeneous anelastic media, the database of 3-D geophysical structures for Beijing City has been built up to model the seismic ground motion in the City, caused by the 1976 Tangshan and the 1998 Zhangbei earthquakes. The hybrid method, which combines the modal summation and the finite-difference algorithms, is used in the simulation. The modeling of the seismic ground motion, for both the Tangshan and the Zhangbei earthquakes, shows that the thick Quaternary sedimentary cover amplifies the peak values and increases the duration of the seismic ground motion in the northwestern part of the City. Therefore the thickness of the Quaternary sediments in Beijing City is the key factor controling the local ground effects. Four zones are defined on the base of the different thickness of the Quaternary sediments. The response spectra for each zone are computed, indicating that peak spectral values as high as 0.1 g are compatible with past seismicity and can be well exceeded if an event similar to the 1697 Sanhe-Pinggu occurs. [ABSTRACT FROM AUTHOR]