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Space Electromagnetic Disturbances Induced by High-voltage Power Lines ZHANG Xue-min, QIAN Jia-dong, WU Ying-yan, ZHAO Shu-fan, LOU Wen-yu EARTHQUAKE    2019, 39 (1): 90-100.   Abstract （295）      PDF（pc） （4216KB）（583）       Knowledge map    With the fast development of global industrialization, high-voltage power lines have become one of the man-made interferences in electromagnetic environment monitoring. In this paper, recent achievements on power line radiations have been summarized, especially by using the satellite electromagnetic observations from DEMETER, such as power line harmonic radiation (PLHR), magnetospheric line radiation (MLR), ELF/VLF emissions, high energetic particle precipitation, etc. And then the coupling models including electromagnetic wave propagation and nonlinear wave-particle interaction have been introduced and discussed. It is aimed to provide more information for the data processing and analyzing techniques in the upcoming China Seismo-Electromagnetic Satellite (CSES-1) mission when the same PLHR signals are dealt with or the weak earthquake-related disturbances are distinguished.

The Seismic Application Progress in Electromagnetic Satellite and Future Development ZHANG Xue-min, QIAN Jia-dong, SHEN Xu-hui, LIU Jing, WANG Ya-lu, HUANG Jian-ping, ZHAO Shu-fan, OUYANG Xin-yan EARTHQUAKE    2020, 40 (2): 18-37.   DOI: 10.12196/j.issn.1000-3274.2020.02.002 Abstract （454）      PDF（pc） （6069KB）（552）       Knowledge map    DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) satellite, the first electromagnetic satellite specially aiming to earthquake monitoring in the world, was launched in 2004 by France, and ended in the end of 2010, with operating time of 6.5 years. The data along more than 30000 orbits were obtained, which provided a solid data foundation for the research in earthquake monitoring and ionospheric physics. Scientists in many countries carried out a number of earthquake application studies by using the data from this satellite, with hundreds of paper published, and pushed the research in seismo-electromagnetic satellite to a new peak. CSES (China Seismo-Electromagnetic Satellite), the first space satellite for geophysical field detection in China, was successfully launched on February 2, 2018. At present, its in-situ commission has been finished, and the satellite has been put into service, with the scientific data released to the public officially. Under this condition, it is important to summarize and retrospect the improvement and achievements in technology and science from DEMETER, in order to maximize the effectiveness of CSES, and transform the space electromagnetic detection to the operational run in earthquake investigation. The remarkable progresses from DEMETER satellite will be introduced in this paper, and the future development domains are suggested in space electromagnetic detection technology and scientific research combined with the characteristics in CSES satellite.

Recent Progress of Earthquake Prediction with Machine Learning YUAN Ai-jing, WANG Wei-jun, PENG Fei, YAN Kun, KOU Hua-dong EARTHQUAKE    2021, 41 (1): 51-66.   DOI: 10.12196/j.issn.1000-3274.2021.01.005 Abstract （674）      PDF（pc） （3494KB）（519）       Knowledge map    Machine learning (ML), especially deep learning (DL), has developed rapidly in recent years, which has made exciting progress in many applications such as data mining, computer vision, natural language processing, data feature extraction and prediction. Earthquake prediction is a complex, wide-ranging, immature, and controversial scientific issue. Its development is limited by unclear earthquake mechanisms and seismogenic structures, incomplete observation data, and unclear earthquake phenomena. However, machine learning may improve the mining and discovery of complex seismic data and promote the development of earthquake prediction science. This article reviews the application of machine learning in earthquake prediction, including the prediction of big earthquakes, big aftershocks and rock experimental fractures, finally looks forward to the research trends of machine learning in earthquake prediction.

Seismic Risk and Maximum Magnitudes of Potential Earthquakes for Active Faults in Hebei Province SUN Li-na,QI Yu-yan,JIN Xue-shen EARTHQUAKE    2017, 37 (2): 147-156.   Abstract （263）      PDF（pc） （3044KB）（512）       Knowledge map    Hebei province is one of the most active areas of seismic activity in north and even east mainland China, there is complex tectonic background and fault development. Along with the development of the province’s 11 urban active fault detection and seismic risk evaluation project, some scientific projects and the accumulation of the fault structural study data, late Pleistocene fault data is further updated. Then, there is an important question of how to assess the maximum potential earthquake magnitude and the risk of these active faults on long-term earthquake prediction. Using the maximum potential earthquake magnitude assessment model proposed by Wen Xue-ze, we first divided fault cell to the active faults in Hebei region, then formed the empirical relationship between the maximum magnitudes Mmax and the at/b values of the sub-areas' frequency-magnitude relationship in the Hebei area, and got the upper limit of the potential magnitude in fault cells by the formula. Furthermore, we calculated the seismogenic probability of partial fault area in the future strong earthquakes through the exponential relation with earthquake waiting time.

Daily Variation Ratio of Geomagnetic Z Component and its Relationship with Magnetic Storms and Earthquakes YUAN Gui-ping, LI Hong-yu, ZHANG Gui-xia, PAN Ying EARTHQUAKE    2018, 38 (1): 139-146.   Abstract （353）      PDF（pc） （2647KB）（509）       Knowledge map    Daily variation ratio of geomagnetic vertical component (Z) is important in the study of earthquake precursor analysis. The variation magnetic field makes an induced magnetic field because of the earth conductivity, and the induced magnetic field includes information from outer magnetic field and underground electrical conductivity, so the geomagnetic field Z component reflects more changes of underground activity than other components. We collected data of Jiangsu area since 1984 and got 29 events of anomalies with day by day ratio, and then carried out a statistical analysis on the relation between them by combining geomagnetic storm and the earthquake after the abnormal events. The study has found that the anomaly event of day by day ratio and earthquake have a good correlation without geomagnetic storm, with coefficient of 0.77, while the corresponding relationship drops to 0.25 with geomagnetic storm. Combining all of the abnormal events, we consider that, after the abnormal event of day by day ratio, the possibility of the abnormal event of day by day ratio being an earthquake precursor will be 0.8 if there is no geomagnetic storm on that day or the Dst index is smaller than that on the second day. Otherwise, the abnormality maybe be caused by geomagnetic storm rather than the influence of underground activity.

Analysis of the Anomaly Characteristics from Cross-fault Deformation Measurements LI Jie, TANG Ting-mei, JING Qiang, LOU Guan-shou, LIU Wen-yi EARTHQUAKE    2010, 30 (2): 100-111.   Abstract （65）      PDF（pc） （1260KB）（500）       Knowledge map    Based on the statistics of cross-fault deformation anomalies before strong earthquakes during the last forty years, this article analyses the characteristics of the time duration, spatial distribution, amplitude of the anomalies and the relationship of all the three factors. it disgusses the anomaly characteristics of the measurement of cross-fault deformation as well as the maximum spacing of the cross-fault sites and observation cycle of the monitoring of different magnitude of earthquakes. The results suggest that: The anomalies are mainly of medium term as well as short and medium terms, occur more frequently one year before the earthquakes. The time duration of the anomalies is directly proportional to the earthquake magnitude. The spatial distribution of the anomalies also has a phenomenon that it extends as the augment of the epicenter distance. The amplitude of the anomalies enlarges with the increase of time duration and reaches to higher level when the epicenter distance is within 160 to 350 km. The anomaly shape is devided into two main types:trend and mutant. The spacing of monitoring cross-fault sites of different earthquake magnitude can be different: The spacings for monitoring magnitude 7 earthquakes should be less than 450 km, and 300 km, 200 km, 100 km for magnitude 6, 5, 4 earthquakes respectively. The measurement cycle is supposed to be within three months.

A Review of Adjoint Tomography and Its Application in Earth’s Interior Imaging XIAO Zhuo, GAO Yuan EARTHQUAKE    2020, 40 (3): 52-64.   DOI: 10.12196/j.issn.1000-3274.2020.03.005 Abstract （556）      PDF（pc） （2947KB）（495）       Knowledge map    Numerical simulation techniques and adjoint method lead to the successful application of adjoint tomography in both regional and global full waveform tomography. Based on the spectral element method, adjoint tomography adopts full three-dimensional model as initial model for waveform modelling and calculates gradients efficiently through interaction between forward wavefield and adjoint wavefield. Owing to the power of high-performance computing, adjoint tomography utilizes full-wave tomography at large scale. Compared with traditional tomography techniques, adjoint tomography can describe the subsurface anomalies more detailed and comprehensively, so it is more favorable in deep dynamics research. Here we firstly introduce the basic theory of adjoint tomography, its workflow of implementation, and then we give a review of its worldwide applications, while finally a brief prospect of future developments is discussed at the end of this article.

Detection of Ionospheric TEC anomalies based on Prophet Time-series Forecasting Model ZHAI Du-lin, ZHANG Xue-min, XIONG Pan, SONG Rui EARTHQUAKE    2019, 39 (2): 46-62.   Abstract （349）      PDF（pc） （3354KB）（489）       Knowledge map    This paper proposed a new method for identification of ionospheric TEC anomalies using prophet forecasting model based on Facebook. First, we compared the precision of this new method with the traditional time series forecasting method (Autoregressive Integrated Moving Average, ARIMA models) and the identification method of the classical ionospheric TEC anomalies (Inter Quartile Range, IQR method), in predicting the background values of ionospheric TEC modeling. The results show that the precision of the former is obviously better than the latter two methods: about 2.55 times higher than that of the ARIMA models, and about 10.74 times higher than that of the IQR method. Meanwhile, when the best prediction modeling interval is established, the comparison of precision values is RMSEIQR=10.5841>RMSEARIMA=3.2780>RMSEProphet=0.846, indicating that the traditional detection methods have insufficiency in predicting modeling background values. Second, taking the August 8, 2017 Jiuzhaigou earthquake as example, we analyzed its ionosphere TEC anomalies and proved the effectiveness and accuracy of the new method. The results show that obvious ionosphere TEC negative anomalies appeared on the 10th and 2nd days before the earthquake, and obvious ionosphere TEC positive anomalies occurred on the 7th day before the earthquake. In addition, the comparative experiments show that the validity and accuracy of the Prophet forecasting model is significantly better than the IQR method

Micro-behavior of Well-water Temperature and its Mechanism CHE Yong-tai, LIU Cheng-long, YU Jin-zi EARTHQUAKE    2008, 28 (4): 20-28.   Abstract （65）      PDF（pc） （429KB）（483）       Knowledge map    In this paper, general monitoring conditions of water temperature in our country and micro-behavior phenomena such as solid tide, co-seismic effect and precursory anomaly before earthquakes is introduced. And its mechanism is analyzed. The authors propose that the study of mechanism of water behavior should be carried out from some aspects, such as heat systems and heat process, for example, from two geotemperature gradients, two heat convections, one conductivity and one heat diffusion and so on.

Evolution Characteristics of Water Level and Water Tem- perature in Zhao Gezhuang Well and Their Cause Analysis HAN Kong-yan, XING Cheng-qi, CUI Bo-wen, Kong Lai-shun, SUN Xiao-ru EARTHQUAKE    2019, 39 (3): 178-186.   Abstract （259）      PDF（pc） （2499KB）（482）       Knowledge map    The depth of Zhao Gezhuang well is 200 m. The observation aquifer is located in 182—200 m, which is a mixture of shallow cold water and deep hot water. Under the influence of mining and rainfall, the water level and water temperature have synchronous coordination changes in the long trend and annual variation. Due to groundwater exploitation, the ratio of cold water in the shaft reduces, the water level of the well decreases, and the water temperature raises. The rainfall infiltration recharge makes the cold water in wellbore increase, water level rise and water temperature drop. However, at the end of the rainy season, the inflow of cold water into the shaft decreases, and the water temperature rises gradually. The air pressure and the solid tide cause the diurnal variation of water movement between the wellbore and the aquifer, so that well water level has periodic fluctuation. This changes of the ratio of cold and hot water in the wellbore and causes the secondary effect of water temperature's periodic fluctuation. Both of them show synchronous and coordinated changes in diurnal variation. Different kind of interference factors causes different periodic change. It is necessary to choose different method and sampling period in order to eliminate the disturbance and extract the information of seismic anomaly.

Study on the Spatio-temporal Evolution Characteristics and Seismic Structure Environment of the 2019 M6.0 Changning Sichuan Earthquake Sequence GONG Yue, WANG Yu-xi, LIANG Ming-jian, LONG Feng, ZHAO Min EARTHQUAKE    2020, 40 (4): 90-102.   DOI: 10.12196/j.issn.1000-3274.2020.04.007 Abstract （217）      PDF（pc） （4852KB）（469）       Knowledge map    Features of seismic sequence can directly reflect the differences among tectonic stress field, seismotectonic and seismogenic environment. For example, mainshock-aftershock-type earthquakes mostly occur in a relatively uniform medium environment. However, foreshock-mainshock-aftershock-type earthquakes and swarms mainly occur in complex structure. On 17 June, 2019, the M6.0 an earthquake occurred in Changning County, Yibin City, Sichuan Province. Its aftershock totally distributed along a NW direction belt, bit in the northwest part of the belt, the aftershock distribution showed the cluster features. There is an obvious difference between the southeast part and northwestern part for aftershock activity. The southeast part can be considered as a mainshock-aftershock type with a fast decay. The northwestern part shows a feature of swarm, which decay is slowly and many aftershocks with M5 or more in the early stage. The M6.0 earthquake occurred in the Changning-Shuanghe anticline which is complicated and composed of several secondary fold structures and associated faults. The segmentation characteristics of the Changning M6.0 earthquake indicate that it is hardly to be produced by a single fault but a cascade fractures. Moreover, the aftershock focal depths in the northwestern part are more deeply, this means that the seismic activity in this area has been controlled by the Huaying Shan fault zone. Oppositely, the possible influence of the 2019 Changning M6.0 earthquake on Huaying Shan fault zone should be emphasized in the future.

Spatial and Temporal Variation of b value before and after the Changning MS6.0 Earthquake on June 17, 2019 ZENG Xian-wei, LONG Feng, REN Jia-qi, CAI Xin-hua, LI Wen-jun EARTHQUAKE    2020, 40 (3): 1-14.   DOI: 10.12196/j.issn.1000-3274.2020.03.001 Abstract （426）      PDF（pc） （4812KB）（465）       Knowledge map    Based on the earthquakes recorded in Yibin area (28.0°N~28.5°N, 104.6°E~105.1°E), Sichuan Province, from January 2014 to August 2019, we estimated the b values in the studied area by the maximum likelihood method and obtained their temporal and spatial characteristics. The results show that, firstly, the b value decreased rapidly five months before the Changning MS6.0 earthquake and recovered quickly after that. This phenomenon is likely to reflect the process of stress accumulation during earthquake preparation and stress release after the earthquake. Secondly, before the Changning earthquake, there was always a low b value anomaly (≤0.85) in the epicenter and its vicinity. Five months before the earthquake, a further decrease of b value occurred near the epicenter, especially in the northwest of Changning, where following three MS5 earthquakes taking place in Gongxian were just located in this abnormal region and its edge area. Thirdly, the spatial distribution of low b value anomalies indicates the risk area of medium and strong earthquakes in the future. And, the fast decrease region in b value can be used to determine the possible location of strong aftershocks. Fourthly, when analyzing the seismic risk, we should pay more attention to the b value decrease under the background of long-term low b value, which illustrates the increasing seismic risk in high stress concentration area.

Characteristics of Activity Periods for Shallow Earthquakes in Northeast China GAO Li-xin,DAI Yong EARTHQUAKE    2017, 37 (2): 115-125.   Abstract （202）      PDF（pc） （4210KB）（455）       Knowledge map    From the perspectives of energy of deep and shallow earthquakes and their energy release ratio as well as duration, the rhythm repetition of the end earthquakes of the fifth activity period and orderly activity image of moderate strong earthquake in the fifth activity period in northeastern China, we analyzed and compared characteristics with that of the former four periods. The results show that the energy release of the fifth activity period is far lower than other activity periods, energy release ratio of deep earthquakes and shallow earthquake is large, and the sustained time is long. The “closing door” earthquakes sustained the rhythm repetition of the former 4 activity periods. The properties of the “closing door” earthquakes include time and spatial clustering as well as earthquake swarm, seismic gap and banded orderly distribution image. The 7 earthauakes of MS≥5.0 in 2013 may be the “end” earthquakes of the fifth activity period.

Low Seismicity Anomaly and its Efficiency in Mid-term Earthquake Forecasting in Chinese Mainland ZHANG Guo-min, YIN Xiao-fei, WANG Peng, SHAO Zhi-gang EARTHQUAKE    2019, 39 (2): 1-10.   Abstract （303）      PDF（pc） （1206KB）（454）       Knowledge map    From the study of seismicity in Chinese mainland, we found that obvious low seismicity anomalies occur 1~2 years before some strong earthquakes. Using M≥5.0 seismic data in recent 100 years, in this paper the relations between low seismicity anomaly and future seismicity of Chinese mainland were analyzed. We established low seismicity indicator from annual frequency of M≥5.0 earthquakes, the maximum earthquake magnitude, and M≥6.0 seismic quiescence. Furthermore, the relations between low seismicity anomaly and future strong earthquakes were checked through probabilistic gain index β, predicting efficiency ratio α and R value for earthquake forecasting efficiency testing. Preliminary results indicate that some coefficients exist between low seismicity anomaly and future seismicity in Chinese mainland, mainly reflected in M≥7.8 huge earthquakes. However, the coefficients of M≥7.8 huge earthquakes are limited, and probabilistic gain index β and predicting efficiency ratio α are about 3, R value for earthquake forecasting efficiency testing is about 0.2. For M＜7.5 earthquakes, low seismicity anomaly is not exhibited, its probabilistic gain index β and predicting efficiency ratio α are near 0, which appear as random relations. The turning point at which some relations with low seismicity anomaly show is M7.5.

Study on Kunlunshan M8. 1 earthquake in 2001 and the trend of strong eqrthquakes MEN Ke-pei EARTHQUAKE    2002, 22 (3): 39-44.   Abstract （89）      PDF（pc） （68KB）（443）       Knowledge map    In this paper, the important significance of the 2001 Kunlunshan large earthquake with M= 8. 1, theorderly characteristics of the time and space of strong earthquake activity from 1996 to 2001 in western China and the correlation of strong events between western part of China's mainl and and Taiwan have been discussed. The trend of M≥ 7 events in future in Northern part of Qinghai-Xizang block has beenestimated by using the method of orderliness analysis.

Study on the Second Data Variation Characteristics of Geoelectric Field before and after Changning MS6.0 Earthquake XI Ji-lou, CHEN Min, DONG Lei, LIU Chao, GUAN Hua-ping EARTHQUAKE    2020, 40 (4): 129-143.   DOI: 10.12196/j.issn.1000-3274.2020.04.010 Abstract （178）      PDF（pc） （3641KB）（437）       Knowledge map    The geoelectric field is an important part of the earth electro-magnetic field. Using the traditional time series statistical analysis method, this paper studies and discusses the variation characteristics of the second sampling data of the geoelectric field observed from Xiannushan seismic station, which belongs to the Chongqing municipality. The results show that: ① before and after Changning MS6.0 earthquake, the anomalous change of the geoelectric field were recorded at Xiannushan seismic station, 390 km away from the epicenter; ② the average azimuth angle of the anomalous change was N77.55°E, approximately from the epicenter of Changning MS6.0 earthquake to Xiannushan seismic station; ③ the typical anomalous change of the geoelectric field was intermittent and non-periodic disturbance, which densely appeared 8 days before the main shock of Changning MS6.0 earthquake, lasted to the 4th day after the main shock, and then gradually transformed into the high-frequency disturbance changes; ④ the anomalous change of the geoelectric field appeared in lots of clusters, each of which is composed of multiple groups of step mutation with nonlinear attenuation. According to the comprehensive analysis, the anomalous change of the geoelectric field before and after Changning MS6.0 earthquake, may be related to the filtered electromotive force generated by the high-pressure migration of the underground fluid, during the change of the structural fracture and the process of the rock micro fracture.

Characteristics of Stress Field in Mainland China and Surrounding Areas TIAN Jian-hui, LUO Yan EARTHQUAKE    2019, 39 (2): 110-121.   Abstract （302）      PDF（pc） （5461KB）（436）       Knowledge map    In this paper, focal mechanism solutions of 4303 earthquakes occurred in and around the mainland of China (15°~55°N, 65°~125°E) from 1976 to 2018 are collected, and the focal mechanism solutions and the spatial distribution characteristics of the P, T axis are analyzed. Using these focal mechanism solutions, we obtained a 2-D tectonic stress field distribution. The results of stress field inversion show that the strike-slip stress is dominant in most of Yunnan, most of the Tibet Plateau and most of North and South China. The strong collision between the Indian plate and the Eurasian plate controls the western part of China. A large number of fault-type earthquakes are concentrated in the Tibet Plateau and the Tianshan area of active block in the western region. There are also normal fault type earthquakes in the Tibet Plateau interior, and the direction of the stress field changes greatly at 26°N. In the Yunnan-Myanmar active block located south of the eastern tectonic line of the Tibet Plateau, the direction of the maximum principal compressive stress changes from the direction of NNE to the direction of NNW. From the northeast block to the North China block and the South China block, the maximum principal compressive stress direction has a rotational tendency from NE to EW and NW.

Geochemical Characteristics of Soil Gas H2 and Rn in the Tangdong Active Fault HU Ning, MA Zhi-min, WANG Ming-liang, WANG Yu, LOU Lu-ling, XIA Xiu-jun, ZHANG Bao-shan, WANG Wen-jing, GOU De-ke EARTHQUAKE    2019, 39 (2): 174-182.   Abstract （284）      PDF（pc） （1552KB）（435）       Knowledge map    In order to study the geochemical characteristics of soil gas and the tectono-geochemical background reflected by fault gas in the Tong-Dong fault zone, the field monitoring method was used to analyze the concentration distribution of soil H2 and Rn in the two observation lines of Zhanghe village and Xinglizhuang village. The results show that the distributions of H2 and Rn concentration in Zhanghe village ranged from 0.24 to 174.7×10-6 and 13.3 to 69.8 kBq·m-3, respectively. The background values of H2 and Rn concentration are 14.26×10-6 and 24.8 kBq·m-3, respectively. The range of concentration distribution of H2 and Rn in Xinglizhuang observation line ranged from 11.8 to 67.06×10-6 and 43.6 to 72.6 kBq·m-3 respectively, with background values of 37.13×10-6 and 72.6 kBq·m-3, respectively. In the measure line of Zhanghe village, strong anomaly of H2 and Rn appeared at 90～105 m, but a higher anomaly occurred at 120～150 m, with anomalous values near the fault zone, which indicates the location of the fracture effectively. Integrated geological structure and physical geography, it is concluded that the high value anomaly of the gas composition in the survey line are mainly controlled by the tectonic conditions, and it is also affected by sediment properties and meteorological factors. Therefore, we should further track and monitor the gas composition in the soil layer of the target fault zone, and analyze the temporal and spatial variation of fault activity, and take gas isotope techniques to explore the source of the components, so as to enhance the important role of gas geochemical indicators for fault tectonics activity and to strengthen the efficiency of earthquake prevention.

Study on the Effective Elastic Thickness of Lithosphere and Mechanical Characteristics of Great Earthquake Tectonic Areas in the Chinese Mainland SHI Wen, CHEN Shi, HAN Jian-cheng, LI Hong-lei, LU Hong-yan EARTHQUAKE    2021, 41 (1): 1-12.   DOI: 10.12196/j.issn.1000-3274.2021.01.001 Abstract （447）      PDF（pc） （6138KB）（422）       Knowledge map    Studying the mechanical characteristics of the lithosphere in the areas where strong earthquakes have often happened are of significance for exploring the occurrence mechanisms of strong earthquakes. The lithosphere effective elastic thickness (Te) and initial loading ratio (F) are closely related to the mechanical characteristics of the continental lithosphere. We use a new joint inversion method integrated both admittance and coherence techniques to compute the effective elastic thickness and initial loading ratio in the Chinese mainland, with the WGM2012 gravity data, ETOPO1 topographic data, and the data of Moho depth and crustal density from CRUST1.0 model. Based on the estimated Te and F, we discuss that how the parameters of Te, F, and gradients of them affect the environment for the development of strong earthquake. We find the high-degree earthquake tectonic areas tend to low Te and high gradients of Te and F. These suggest that the regions with a relatively low lithosphere strength, and those at the belts with sharp changes of lithosphere strength and internal load can provide a positive environment for developing strong earthquakes.

Effectiveness Evaluation of Earthquake Activity Significantly Enhanced Prediction in North China JIA Luo-zhao, SONG Mei-qin, XIE Jian-jian, XING Kang, Gao Jia-yi EARTHQUAKE    2020, 40 (2): 38-48.   DOI: 10.12196/j.issn.1000-3274.2020.02.003 Abstract （275）      PDF（pc） （1956KB）（413）       Knowledge map    Research 13 typical earthquakes of magnitude 6 or higher in the North China block since 1970. Evaluating the effectiveness of full-time sweep detection of earthquake significantly enhanced anomaly index using Molchan and R values, research on the optimum prediction time and space parameters. Finally, the applicability of earthquake significantly enhanced anomaly index in North China Block is verified, it provides a practical basis for earthquake situation tracking using this method.

Study on Correlation Coefficient of Spectral Amplitude of Gaizhou Earthquake Swarms YANG Shi-chao, ZHANG Bo, CAO Feng-juan, WANG Liang, SHAO Yuan-yuan EARTHQUAKE    2019, 39 (3): 158-165.   Abstract （274）      PDF（pc） （2756KB）（407）       Knowledge map    The spectral amplitude correlation coefficient of the 2012 Qingshiling earthquake swarm and the 2014 Xihaiyu earthquake swarm in Gaizhou City were calculated by using digital seismic waveform data recorded in Liaoning Digital Seismic Network. The results show that the correlation coefficient of spectral amplitude of Qingshiling earthquake swarm is 0.72~0.90 and finally stabilizes at 0.75. The low value of the correlation coefficient of spectral amplitude indicates low consistency of focal mechanisms. The correlation coefficient of spectral amplitude of Xihaiyu earthquake swarm is 0.85~0.99 and finally stabilizes at 0.85. The high value of the correlation coefficient of spectral amplitude indicates high consistency of focal mechanisms. According to the analysis of the apparent stress in Gaizhou City, it is deemed that the variation of correlation coefficient of spectral amplitude of Gaizhou City is related to the change of stress level in this region.

Characteristics of Apparent Stresses of Small and Moderate Earthquakes in the Border Area of Shanxi, Hebei, Shandong and Henan Provinces ZHANG Li-xiao, YAN Jun-gang, LI Yan-e, ZHANG Shuang-feng, TAN Qing EARTHQUAKE    2018, 38 (1): 117-127.   Abstract （177）      PDF（pc） （4463KB）（403）       Knowledge map    Based on the seismic waveform data from 2005 to 2016 in the border area of Shanxi-Hebei-Shandong-Henan provinces recorded by Handan Seismic Network, apparent stress values of 302 small and moderate earthquakes (2.0≤ML<4.3) were calculated using near-surface Brune model and genetic algorithm. The range of apparent stresses of Shanxi-Hebei-Shandong-Henan border area is 0.01—3.26 MPa, with an average of 0.535 MPa. The scaling relationship between source parameters is discussed. The spatial and temporal characteristics of stresses are analyzed. The results show that there are some obvious high values of apparent stress and stress anomalies in many areas at the border area of Shanxi, Hebei, Shandong and Henan Provinces. The earthquakes mostly occur in the area of high apparent stress anomaly and its vicinity, and high apparent stress anomalies occurred before the majority of earthquakes. The results indicate that the abnormal high apparent stress give some indication to the prediction of the epicenters of moderate to strong earthquakes, which can be used as the basis of earthquake risk judgment at the border area of Shanxi, Hebei, Shandong and Henan.

Crustal Depth and S Wave Velocity Structure in Chenghai Fault Zone from Receiver Functions CHEN Jia, GAO Qiong, WANG Jun, DENG Jia-mei EARTHQUAKE    2019, 39 (1): 72-80.   Abstract （213）      PDF（pc） （6290KB）（402）       Knowledge map    We used teleseismic records from the temporary and fixed stations near the Chenghai fault zone. The total of the stations is 27.We get the P-wave receiver functions of every station using the teleseismic waveform. We get the crust thickness and shear velocity using the time domain linear inversion method.The results show the depth of Chenghai fault belt change from 42 km in the south to 54 km in the north. The depth of Moho in the south is more different from the north. The Binchuan and its north eastern area show obvious low-velocity layer from the depth profile. The lower layer is related to the thermal material. Then in the south area of Yongsheng, the vertical change of S wave velocity is more drastical. Low speed and high speed layer exist alternately, which could be the reason why this area has many earthquakes. At the same time, we give the preliminary contrast analysis about the receive functions which were calculated using broad band and short-period seismographs.

Neural networks of radial basis function (RBF) and it′s application to earthquake prediction WANG Wei, WU Geng-feng, ZHANG Bo-feng, WANG Yuan EARTHQUAKE    2005, 25 (2): 19-25.   Abstract （229）      PDF（pc） （89KB）（398）       Knowledge map    the principle and algorithm of neural networks of Radial Basis Function (R BF) and its application to the expert system for earthquake prediction (ESEP 3.0) are introduced in this paper. The actual application in earthquake forecast shows that the neutral networks can overcome some demerit of BP neural networks in leaning process, the constringency excessively depend on initial value and optimization constringency and often can′t appear. The RBF neural networks possess the rapid operation speed in learning and strong nonlinear mapping ability and very good efficiency.

Coseismic Ionosphere Disturbances of the 2008 Wenchuan Earthquake HE Jian-hui,ZHANG Xue-min,LIN Jian,WANG Min,SHEN Xu-hui EARTHQUAKE    2017, 37 (2): 126-134.   Abstract （251）      PDF（pc） （2938KB）（390）       Knowledge map    We use three ground GPS receiver stations at Xiaguan, Kunming and Luzhou in the CMONOC to study coseismic ionospheric disturbance (CID) for the 2008 Wenchuan earthquake. We retrieve high precise slant total electron content (STEC) through removing the DCB (Difference Code Bias) effect in the line of sight of GPS. Through preproccess of the GPS data and the STEC, we obtained the DTEC time series and the TEC traveling time plots among them. The results show that there exists two CID horizontal propagation speeds in this research. The first is the acoustic speed in the height of ionosphere, about 1.1 km/s, and the second is the secondary CID speed closed to 0.7 km/s, considered to belong to the gravity wave. Finally, using the ray-tracing technique, when the CID speed equals to the 1000 m/s, the standard deviation of the earthquake onset time can reach the minimum value 19.55s, and the origin of the CID is located at 30.8°N,103.15°E which is about 33.6 km southwest of the Wenchuan earthquake epicenter.

Using Parkinson Vector Analysis to Detect the Geomagnetic Changes in the Sichuan Changning 6.0 Earthquakesof June 17, 2019 AISA Yisimayili, CHEN Jie-hong, MAO Zhi-qiang EARTHQUAKE    2020, 40 (2): 91-99.   DOI: 10.12196/j.issn.1000-3274.2020.02.007 Abstract （316）      PDF（pc） （3476KB）（389）       Knowledge map    Seismo-magnetic anomalies induced from the existence of current and/or high-conductivity materials have been widely reported. The Parkinson vectors derived from geomagnetic data at 3 stations were obtained via the magnetic transfer function and discussed with respect to the location (104.9°E, 28.34°N) and the depth (19 km) of the Changning earthquake on June 17, 2019 in Sichuan province. Azimuth distribution constructed from the entire Parkinson vectors during the observation period is utilized to estimate the persistent background (i.e., underlying inhomogeneous tectonic structures) at each station. The normalized background distribution is subtracted from the normalized monitoring distributions computed using the azimuths of the Parkinson vectors within a 15-day moving window to determine the anomalous azimuths of high-conductivity materials. The analytical results show that high-conductivity materials appeared before 1~2 week and in areas about 15 km away from the epicenter reported by the China earthquake networks center.

Preliminary Study on the Traceability of the Observation and Measurement of Radon for Earthquake Monitoring HUANG Ren-gui, ZHAO Ying, LI Yu-ze, WANG Shi-xian, LUO Qi-bin, XIAO Jian EARTHQUAKE    2019, 39 (2): 183-190.   Abstract （314）      PDF（pc） （1133KB）（387）       Knowledge map    In this paper, the reliability of calibrating radon observation instruments using standard instruments is verified on the experimental results of radon chamber calibration and solid radon source calibration. The AlphaGUARD P2000Pro and AlphaGUARD P2000F radon measuring instrument of German Genitron Company, the classic measuring and transmitting instrument of radon measurement laboratory, are used as the source traceability instrument for the transmission source. The observation of water radon in Jiujiang Seismological Station FD-125 radon thorium chamber is calibrated by three calibration methods, including radon chamber calibration, solid radon source calibration and instrument calibration. The calibration of standard instruments and calibration of solid radon gas sources indicates that the deviation of the K value relative to the radon chamber calibration results is less than 6%, and they can meet the needs of the current radon observation and measurement. It can achieve the goal of unification with the national radon calibration scale.

Geochemical Characteristics of Soil Gas in the Xinbaoan—Shacheng Fault SHENG Yan-rui, ZHANG Zi-guang, ZHOU Xiao-cheng, DU Jian-guo, ZHOU Yue-ling, ZHANG Guan-ya, ZHAN Rui-xin, Liu Yong-mei, SUN Yu-tao, DING Zhi-hua EARTHQUAKE    2015, 35 (4): 90-98.   Abstract （134）      PDF（pc） （3654KB）（384）       Knowledge map    Measurement of soil gas concentration in fault zone is one of the important ways to monitoring fracture activity and seismic risk. We surveyed the soil gas concentrations (H2, He, CO2, Rn, Hg) and soil gas flux (CO2, Rn, Hg) of the Xinbaoan—Shacheng fault in Huailai in May, 2014. The results show that the ranges of concentration of H2, He, CO2, Rn, Hg are respectively (0.4~34.2)×10-6, (2.8~7)×10-6, (0.051~1.19)%, (0.31~18.22) kBq/m3, (2~54)ng/m3. Soil gases of H2 and Rn are effective parameters to reveal the fault location, which show significantly high value anomaly in the fault and scarp areas. We can preliminary confirm that there is higher gas effusion by the study results of soil gas concentrations and gas flux in Xinbaoan—Shacheng fault, which is related to seismic activity in this region.

Use of differential GPS in detecting active faults in cities ZHANG Jun-long, TIAN Qin-jian, LI Zhi-min, Ren Zhi-kun, HAO Kai EARTHQUAKE    2007, 27 (3): 74-82.   Abstract （57）      PDF（pc） （1442KB）（383）       Knowledge map    By using the method of differential GPS, on the basis of observing the features of the terraces in Huangshui basin, we have surveyed the parameters of the terraces in Huangshui basin, and primarily ascertained the characteristics of neo-tectonics in this region, and also found out the distribution and movement features of the active faults around Xining City. Through the research described above, we draw a conclusion as follows: by using the DGPS, the coordinate and elevation of the terraces can be quickly and accurately acquired; so the DGPS is a feasible way to find the positions and other features of weak active or concealed faults. T3, T4, T5 terraces is dislocated by Nan chuan river fault between 0.10 Ma B.P. and 0.05 Ma B.P. with the least velocity of 0.15 mm/a.

Seismogenic Structure and Seismic Activity Analysis of Minshan Block WAN Sen-lin, ZHANG Jun-long, LIU Ming-jun, HE Wei-Min, LI Hai-long, GUO Chang-bao, LI Zhi-min EARTHQUAKE    2020, 40 (2): 49-70.   DOI: 10.12196/j.issn.1000-3274.2020.02.004 Abstract （372）      PDF（pc） （4438KB）（382）       Knowledge map    The Minshan block is located in the middle of South-North Seismic Structural Belt in China with complex regional geological structures, numerous active faults and frequent strong earthquakes. Maowen fault, Tazang fault, Minjiang fault and Huya fault are the main active faults in different directions constitute the boundary of the Minshan block. From 638 to 2017, 11 powerful earthquakes of magnitude 6 or above occurred in this region, and the 2017 Jiuzhaigou MS7.0 earthquake is one of them. Based on the regional tectonic background, this paper summarizes the structural characteristics and seismicity characteristics of strong earthquakes occurring in Minshan block.and comprehensively analyses the seismogeological characteristics and seismic hazards in this area. It is concluded that: ① The spatial distribution of earthquakes is characterized by obvious zoning, the most destructive strong earthquake generating structures are the East-West boundary fault areas of Minshan block with strong activity, and the epicenter is located at the intersection or cutting position of two or more groups of active fault structures. ② the temporal distribution of earthquakes is characterized by migration and return and in-situ recurrence with the development of time. ③ The occurrence of destructive earthquakes along the East-West boundary of Minshan block has a certain time correlation. The seismic sequence of Huya fault in the east boundary from 1973 to 2017 is the seismic structural response of Minjiang fault in the west boundary from 1933 to 1960 about 40 years later. ④ Minshan block should be the potential danger area of strong earthquake in the future, and the potential dangerous area of strong earthquakes in the north-central section of Minjiang fault is the area worthy of further study in the near future.

Information Extraction of Damaged Buildings after Earthquake Based on Optimal Feature Space CHEN Jin, CHEN Wen-kai, DOU Ai-xia, LI Wen, SUN Yan-ping EARTHQUAKE    2019, 39 (3): 71-83.   Abstract （253）      PDF（pc） （5930KB）（379）       Knowledge map    This paper proposes an information extraction method which is based on traditional object-oriented method and the optimal feature space. In this method, images are segmented at an optimal scale by using ESP (estimate of scale parameter) tools. Then, distance matrix and minimum separation distance between various types of objects and ground are calculated, through the selected samples, so as to seek the optimal feature space. Finally, the post-earthquake images of damaged buildings are extracted according to the obtained optimal feature space. For the QuickBird image, the total precision of extraction is 83.1％ and the Kappa coefficient is 0.813. For the UAV(unmanned aerial vehicle) image, the total precision of extraction is 92.9％ and the Kappa coefficient is 0.940. Compared with the traditional object-oriented method, the precision and efficiency of the extraction method are greatly improved, which shows that this method has good popularization value in the information extraction of damaged buildings.

Study on loss assessment of construction earthquake damage based on remote sensing and GIS WANG Long, WANG Xiao-qing, DING Xiang, DOU Ai-Xia EARTHQUAKE    2007, 27 (4): 77-84.   Abstract （137）      PDF（pc） （1016KB）（377）       Knowledge map    A quick assessment method of earthquake damage loss based on Remote Sensing (RS) is introduced in the paper, which includes two parts, damage information acquisition and loss assessing. Damage information acquisition contains earthquake damage index mode and image classification mode. The former obtains macro earthquake damage of resident sites on ground through the relationship between damage index and intensity, and the latter uses digital image processing technique to gain the classified earthquake damage. The loss assessment is different according to the different modes of damage information acquisition. This method based on RS and GIS satisfies the actual demand, establishing a multi-person working mode and increasing the speed of earthquake damage assessment based on RS.

Monitoring Media V elocity Variations with Coda Wave Interferometry ZHANG Jin-chuan, WANG Qin-cai, XUE Bing, Ding Li-sha EARTHQUAKE    2014, 34 (3): 62-73.   Abstract （136）      PDF（pc） （576KB）（375）       Knowledge map    Multiply scattered waves are sensitive to media changes owing to the effect of re-peated sampling, superposition and amplification. Based on this characteristic, small medi-um changes could be detected by using coda wave interferometry. In recent years, coda wave interferometry is widely used in estimating velocity variation with high precision in areas such as seismology and non-destructive testing. This paper systematically presents the principle, method and research status of coda wave interferometry respectively, especially focusing on research advances of media velocity variations by using repeating earth-quake,artificial source, and ambient seismic noise. Applications of coda wave interferome try can contribute to the more subtle understanding of dynamic evolution process in the medium.

Present State and Prospect of Ambient Noise Tomography in the Study of Crust- mantle Structure WANG Qiong, GAO Yuan EARTHQUAKE    2012, 32 (1): 70-81.   Abstract （70）      PDF（pc） （1772KB）（374）       Knowledge map    Ambient noise tomography is a rapidly emerging field of seismological research. Applying ambient noise to earth structure research can avoid dependence of earthquake signals effectively, meanwhile, ambient noise method can obtain upper crust structure with higher resolution as well as the structure beneath urban area because ambient noise contains abundant short period information. This paper aims to analysis advantages and disadvantages using ambient noise tomography by showing its present state, process method and progress. Anisotropy inverted by a combination of ambient noise data, surface and body waves can accurately reveal crust-mantle structure and geodynamic characteristics of deep structure. Combining noise analysis and other active signal analysis techniques can further study variations of seismological parameter and physical properties before and after earthquake.

Analysis on the Characteristics of Time-varying Gravity Field Source Changes in Liaoning Area JIA Xiao-dong, ZHAI Li-na, CHEN Shi EARTHQUAKE    2021, 41 (1): 180-190.   DOI: 10.12196/j.issn.1000-3274.2021.01.014 Abstract （262）      PDF（pc） （3093KB）（373）       Knowledge map    Seismic gravity analysis can be used to obtain the physical properties of the earth by studying the change of the time-varying gravity. In this paper, the Bayesian gravity network adjustment method is used to process the mobile gravity observation data for a total of 7 periods of four years in Liaoning from 2011 to 2014, evaluate and analyze the overall monitoring capability of the gravity observation network in the study area,and employ the Euler deconvolution method to inverse field source parameters,before the lighthouse MS5.1 earthquake occurred in 2013. The results show that the gravity in the Shenyang-Liaoyang area changed greatly, forming a high-gradient zone, reflecting the increase in seismic activity in this area; while the depth of the underground medium field source inverted by Euler deconvolution is 10~40 km, It is consistent with the actual depth of the earthquake and is concentrated near the fault zone. The research results can further provide a certain reference for studying the characteristics of the deep seismogenic environment in Liaoning.

Analysis of Electromagnetic Disturbance Anomaly prior to the 2017 MS7.0 Jiuzhaigou Earthquake HUANG Ji-pan, WANG Xin-an, YONG Shan-shan, WANG Mo, LIU Zhong EARTHQUAKE    2019, 39 (3): 84-94.   Abstract （303）      PDF（pc） （5075KB）（372）       Knowledge map    Electromagnetic disturbance phenomena before earthquakes have been observed for many times, however the correlation should be further studied. We designed a multi-component seismic monitoring system-AETA, to monitor the electromagnetic disturbance. At present more than 200 AETA devices have been deployed in China under the support of the Chinese Earthquake Administration. On August 8, 2017, a large MS7.0 earthquake occurred in Jiuzhaigou county of Sichuan Province, China. There are 22 sets of devices installed at seismic stations within the 500 km range of the epicenter. We analyzed the observation data of 30 days before and after the earthquake using the sliding interquartile method and a 27-day window. The result shows that abnormal signal appeared at 11 stations. Among them, 4 out of 6 stations within 200 km around the epicenter have anomalies. And the positive anomaly is much more than the negative anomaly. Besides, most anomalies occurred during night time (20:00~6:00).

Numerical Simulation of the Cross-fault Baseline Anomalies of Trend Break and Annual Cycle Disappearance at the Tangshan Station LI Yuan, LIU Xi-kang, LIU Xia, DU Xue-song, WAN Yong-kui EARTHQUAKE    2019, 39 (1): 39-47.   Abstract （187）      PDF（pc） （3785KB）（372）       Knowledge map    There is no reasonable explanation for the abnormal phenomenon of the annual cycle disappearance and change of trend of the short baseline since 2012 at the Tangshan station. The potential interference factors are verified to be the construction of large buildings near the observation site. To analysis quantitatively the influence of building construction on the phenomena, this paper is based on many years of cross-fault data and uses a finite element method of 2-d linear elastic model to simulate the fault movement. The results show that nearby large building construction do cause a decrease in the tendency of the fault tensional movement and the starting point matches the observation in time. But it can't cause reverse to be compression. At same time, it can decrease the annual amplitude of fault-cross short baseline but can't lead the year cycle to disappear. So it can be considered that these abnormal phenomena have higher reliability and are related to the regional tectonic movement and stress field change. That means the tectonic compressive movement may have be strengthened by 2012 in north China.

Estimating the Equivalent Dipole of the 2008 Wenchuan MS8.0 Earthquake using Observed Electromagnetic Ground Signals LI Mei, WANG Zhong-ping, LU Jun, TAN Han-dong, ZHANG Xiao-tao EARTHQUAKE    2018, 38 (1): 49-60.   Abstract （200）      PDF（pc） （3573KB）（372）       Knowledge map    We use a relatively simple model of an underground current source co-located with the earthquake hypocenter to estimate the magnitude of the equivalent dipole required to produce observable ground signatures. The Wenchuan MS8.0 earthquake on May 12, 2008, is used as an example of a large typical inland event. Results show that for an observed 1.3 mV/m pulse at 1 Hz at Hebei Gaobeidian observing station, 1440 km away from the epicenter, during the abnormity climax, and a typical conductivity of 7.0×10-4 S/m, the expected equivalent dipole order is 1013 A·m, and that of the seismotelluric current is 108 A if the main fracture length 150 km is considered. The electromagnetic field 2D distribution on the ground of this dipole is of the characteristics of orientation or selectivity. There is near relationship between the orientation of the electric element and the electromagnetic field amplitude. At the same time, the electromagnetic fields attenuate rapidly as the observing distance increases. All these can give part evidence of the fact that electromagnetic abnormities observed related with earthquakes are of orientation or selectivity. The instalment may not observe a signal if it locates in weak field regions even though it is well within the detectable range. This result put some requests on how to select locations and layout when an earthquake observing network is in preparation.

Analysis on Changes of the Tectonic Strain in Survey Area Based on Multi-Component Borehole Straingauge ZHANG Xiao, QI Yu-yan, YUN Meng, LI Hui, SHE Ya-wen EARTHQUAKE    2019, 39 (4): 76-83.   Abstract （259）      PDF（pc） （3080KB）（372）       Knowledge map    According to the “Double Bushing” theoretical model and strain theory, the tectonic strain is calculated based on the observation data from the borehole straingaugeat Yixian Station. First, considering the inconsistent sensitivity of the components of borehole strain gauge, relative field calibration is applied to the data. The results show that the reliability increased from 0.7557 to 0.9344. Second, the theoretical solid tide method is used for absolute calibration of borehole strain to obtain the coupling coefficient. At last, the strain parameters of Yixian station observation point are obtained by strain conversion.The results show that the rates of the dilation strain εa and maximum shear strain εs are 2440 ns/a and 230 ns/a respectively. The main direction of strain is 138°. According to the above mentioned results, the tectonic strain near the Yixian Station is in a stable state of expansion.

Active State and Trend on Strong Earthquakes in North China XUE Yan, JIANG Xiang-hua, LIU Gui-ping EARTHQUAKE    2020, 40 (2): 1-17.   DOI: 10.12196/j.issn.1000-3274.2020.02.001 Abstract （521）      PDF（pc） （8768KB）（370）       Knowledge map    Historic strong earthquakes occurred frequently in North China, while the earthquakes with MS≥6.0 has been quiet for nearly 22 years since the 1998 Zhangbei MS6.2 earthquake. Scholars are very concerned about the activity trend of strong earthquakes and there are different views. This paper discusses the rhythmic characteristics of active and quiet periods of earthquakes with MS≥6.0, applies the technique of Morlet wavelet transform to quantitatively analyze the seismicity periodicities, and compares the seismicity features and duration time of the transition section from the active to quiescent period. It is studied that the spatial distribution of earthquakes in active periods, the comparison of strain release rates in active period, quiet period and quiet episode, statistical characteristics of the quiet episode duration time, the currently remarkable seismic quiescence of MS≥5.0 earthquakes, and regional seismicity features of MS≥5.0 earthquakes before the earthquakes with MS6.0~6.9 and with MS≥7.0 in North China. It is believed that the present situation is in the transition section or has been entered the quiet period.