Top Read Articles

Published in last 1 year |

In last 2 years |

In last 3 years |

All

Please wait a minute...


On the Relationship between Seismic Enhancement of the Eurasian Seismic Belt and the Occurrences of M≥7 Earthquakes in Mainland China CHEN Xue-zhong, LI Yan-e, WANG Heng-xin EARTHQUAKE    2014, 34 (1): 34-40.   Abstract （5712）      PDF（pc） （1705KB）（1957）       Knowledge map    According to the ratio of the seismic energy released by the M≥7 earthquakes in the Eurasian Seismic Belt to that released by the earthquakes with the same magnitude range in the whole world, we analyzed the relationship between the seismic enhancement of the Eurasian Seismic Belt and the occurrences of M≥7 earthquakes in the Chinese mainland based on the χ2 test of significance. The results show that when the ratio of the annually seismic energy released by the M≥7 earthquakes in the Eurasian Seismic Belt to that released by the M≥7 earthquakes in the whole world is above 50 percent and an M≥8 earthquake occurs in the Eurasian Seismic Belt, in the following three years there would be more than one M≥7 or M8 earthquakes occurring in the Chinese mainland. The test of significance under the significance level of 10 percent for this relationship can be passed.

Analysis of the 1604 Quanzhou offshore earthquake-tsunami effects HUANG Zhao, WANG Shan-xiong, WANG Xi-nian EARTHQUAKE    2006, 26 (4): 94-102.   Abstract （882）      PDF（pc） （727KB）（164）       Knowledge map    Whether the 1604 Quanzhou offshore earthquake generated tsunami is a contentious problem. Through the textual research and analysis of historic earthquake records, we conclude that Quanzhou offshore large earthquake did not cause obvious tsunami disaster. By analyzing related historic material and Taiwan Strait seismic structure, we determine the potential earthquake-tsunami source zones and their parameters, and make numerical simulation on the earthquake-tsunami source zones of Quanzhou offshore and Taiwan Strait southern shoal. In the numerical simulation process, we use the tsunami wave data of the 1994 Taiwan Strait earthquake to test the reliability of numerical model and routine. Based on Quanzhou offshore earthquake-tsunami zone and its parameters, the numerical simulation results show that the increase or decrease of water in Quanzhou bay induced by earthquake-tsunami waves cannot produce hazard effects. Our research supplies new evidence supporting that there was no tsunami hazard of the 1604 Quanzhou offshore large earthquake.

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 （693）      PDF（pc） （3494KB）（524）       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.

Research on Activity Characteristics of Strong Earthquakes in North China YIN Xiao-fei, ZHANG Guo-min, SHAO Zhi-gang, WANG Peng, SUN Xin-zhe EARTHQUAKE    2020, 40 (1): 11-33.   DOI: 10.12196/j.issn.1000-3274.2020.01.002 Abstract （595）      PDF（pc） （8180KB）（258）       Knowledge map    North China is the most central area for politics, economy and culture of our country, and also one of the earthquake-prone areas in China. The historical record for seismic data in North China is earlier and more continuous, and it is an ideal site for strong earthquake activity studying. This paper has selected the M≥6.0 earthquake catalogue in the third and fourth active periods as the basic data to study the activity characteristics of strong earthquakes in North China. Firstly, the relations of strong earthquake activity levels to active-tectonic blocks and boundaries in North China are discussed. Then, the recurrent phase and episodic characteristics of strong earthquake activities from time and space in North China are analyzed. Finally, the cumulative and conditional probabilities of the M≥6.0 earthquakes in North China are calculated to evaluate earthquake occurrence in this region after five years. The results suggest ① the M≥6.0 earthquakes are mainly concentrated in active-tectonic boundaries, the M≥7.0 earthquakes all happened in active-tectonic boundaries, and the linear relation between seismic strain-releasing rates and tectonic deformation velocities of active-tectonic boundaries in North China; ② Because energy releases of activity curtains in the fourth seismic active periods are lower than that of the third seismic active periods, it seems that M≥6.0 earthquakes will occur in North China in the future; ③ There are obviously different major regions of strong earthquakes between the third and fourth seismic active periods in North China, earthquake activities of the fourth seismic period migrate eastward compared with the third seismic period; ④ If the current quiet episode of the M≥6.0 earthquakes ends in the beginning of 2020, the accumulated seismic probability of the M≥6.0 earthquakes is about 80%; and if the current quiet episode of the M≥6.0 earthquakes ends by the end of 2022, the conditional seismic probability is 50%. This study can provide significant reference for the analysis of overall seismic trend and medium-to-long term earthquake hazard prediction in North China.

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 （562）      PDF（pc） （2947KB）（510）       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.

Study of the Activity Since Late Pleistocene of West Section of Cixian-Daming Faults Zone ZHANG Lu, XIE Xin-Sheng, GUO Hui EARTHQUAKE    2020, 40 (3): 83-98.   DOI: 10.12196/j.issn.1000-3274.2020.03.007 Abstract （556）      PDF（pc） （10260KB）（67）       Knowledge map    A M71/2 earthquake occurred in Cixian County, Hebei Province, in 1830, in the west section of the Cixian-Daming fault zone. Seismic rupture and the activity of this fault have been concerned by earthquake researchers. Previous studies focused on the surface rupture of the Cixian earthquake in 1830. The focus of this paper is on the fault activity since the late Pleistocene in the whole west section of the Cixian-Daming fault zone. The satellite interpretation, aerial photo interpretation, and field seismic geological surveys were applied to conduct researches, and trench excavation or exfoliation of field geological sections and sampling dating were performed at important locations, to determine the time of occurrence of ruptures in various sections of the fault. The western section of the fault is divided into three fault sections, in which F2 is the Cixian-Fengfeng section, F3 is the Dongtianjing-Taoquan section, and F4 is the Hanjiagou-Ganquan section. The F2 fault, an early-middle Pleistocene fault, is buried mostly. The eastern end of the F3 fault cuts off the 22 ka strata in the south of Dongtianjing Village, being late Pleistocene fault. The F3 fault section in the Nanshan Village, Gushan, is a Holocene fault, and the section is a suspected Holocene active fault from Zhangjialou Village to Taoquan Township. The main rupture in the F4 fault is the Holocene fault. The fault section of F4 is all located in the mountainous area of the bedrock, where many fault fractures such as bedrock sections, seismic trenches, and fault eyebrown ridges can be found. Lichens (Xanthoria) were developed on some of the ruptured surfaces. Lichen dating methods were used to determine these ruptured surfaces as the surface earthquake remnants of the Cixian earthquake in 1830. The Cixian-Daming fault zone ends at the western end of F4. A comprehensive analysis of the rupture events in each section of the fault zone was made to get the spatial and temporal distribution map of active events in the west section of the Cixian-Daming fault zone. It is estimated that the late Pleistocene earthquake recurrence period in the west section of the Cixian-Daming fault zone is about 6000 years.

Characteristics of Spatial and Temporal Distribution of Strong Earthquakes in Chinese Mainland and Trend after Maduo MS7.4 Earthquake WANG Peng, SHAO Zhi-gang, SHI Fu-qiang, YIN Xiao-fei EARTHQUAKE    2021, 41 (4): 1-14.   DOI: 10.12196/j.issn.1000-3274.2021.04.001 Abstract （544）      PDF（pc） （4092KB）（317）       Knowledge map    Analyzing characteristics of spatial and temporal distribution of strong earthquakes in Chinese mainland is benefit for determining trend of strong earthquakes in this region. Limited by completeness of catalogue, most analysis of strong earthquakes time intervals in Chinese mainland is on the basis of catalogue since 1900. Due to relative short duration of catalogue, it is difficult to exclude the possibility that current temporal characteristics of strong earthquakes are accidental, and it may cause over fitting which affects forecasting performance. To solve those problems, this paper analyzed synthetic catalogue based on the data from 2021—2030 key area for earthquake surveillance and protection in Chinese mainland. The results show that alternates clusters and quiescence is a common phenomenon for regional strong earthquakes. When supposed the active faults with quasi periodic recurrence behavior, temporal characteristics of synthetic catalogue are closest to the current catalogue. Based on understanding above, strong earthquake interval in Chinese mainland is fitted by the single parameter exponential distribution with wider application. Combined with structural correlation of adjacent strong earthquakes, trend of strong activity in Chinese mainland after the May 22, 2021 Maduo MS7.4 earthquake is analyzed. Results show that the next MS≥7.0 magnitude in Chinese mainland is likely to happen in next two years, the probability being 61.81% before the end of 2022. The probability with the next strong earthquake will occur in 2021 is 30.58%, and the most likely area is Bayankala block; The probability of the next strong earthquake within 2022 is 44.97%, and the middle-south section of the North-South seismic belt should be noticed.

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）（371）       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.

On Statistical Correlation and Causality: A Case Study of the Relation between Gasoline Price Rises in China and Global Large Earthquakes ZHUANG Jian-cang,LIU Jie,XUE Yan,HAN Peng EARTHQUAKE    2017, 37 (1): 1-9.   Abstract （511）      PDF（pc） （498KB）（322）       Knowledge map    Gasoline price rises in China show synchronization with the occurrence times of global M7.0+ earthquakes in recent years, attracting attentions from earthquake scientists and related personnel. Through statistical analysis of these two event sequences during 2003—2015, which are physically irrelevant, we found a significant correlation between them, which seems to be contrary to our common sense. The reason of this paradox is that these two sequences are pre-selected, if the population is sufficient, we can always find some samples highly-correlated with each other, even if these samples have no causal relation at all. The results imply that, some anomalies, which can pass statistical tests and are found retrospectively useful for earthquake prediction, may be not resulted from earthquakes, since they are pre-selected. In practical, such correlation between irrelevant processes can be easily found in the current big-data era, therefore, it is essential to investigate the physical mechanism behind and perform perspective forecasting tests in addition to doing correlation analysis.

Paleoearthquake Characteristics of the Eastern Segment of Yumen—Beidahe Fault in the Northern Margin of Qilian Shan LIU Xing-wang, YUAN Dao-yang, SHAO Yan-xiu, ZHANG Bo EARTHQUAKE    2019, 39 (3): 1-10.   Abstract （500）      PDF（pc） （7609KB）（136）       Knowledge map    Yumen—Beidahe fault is an important active fault at the south margin of Jiuxi Basin. The fault starts from qingcaowan at west, passes through Yumen, Qingtou Shan, Dahongquan, and ends at the east of Gutouquan. The fault is about 80 km long, strikes NWW , inclines south and dips 20°~60°. Yumen—Beidahe fault is an active thrust fault in Holocene. Earthquake surface ruptures are still preserved at the eastern segment of the fault. Based on the filed fault geomorphological investigation and trench excavation, it is revealed that the rupture zone was formed 1.7±0.3 ka ago. there had been another two paleoearthquakes occurring in (4.1±0.3)~(5.4±0.3) ka and 8.4±1.0 ka, and the magnitudes of the two paleoearthquakes were estimated to be about 7.0 by empirical formulas and existing earthquake cases.

The tress triggering of large aftershocks following the 1970 Tonghai great earthquake (M=7.7) HAO Ping, FU Zheng-xiang, TIAN Qin-jian, LIU Gui-ping, LIU Jie EARTHQUAKE    2004, 24 (2): 38-46.   Abstract （486）      PDF（pc） （1316KB）（221）       Knowledge map    The Tonghai great earthquake occurred on Jan. 5, 1970 in Yunnan Province. After the main shock, several large aftershocks (MS>5.0) occurred. Calculations of the change in Coulomb failure stress on aftershock failure plane reveal that 4 events among 5 large aftershocks occurred in areas with ΔCFS>0 (10-2~10-1 MPa); There are two contrary results for one aftershock due to two different focal mechanism, this aftershock occurred in areas with ΔCFS>0 and ΔCFS<0. It is concluded that the permanent fault displacement due to the main shock is the main causation of activity of large aftershocks.

Textual Research and Causative Structure of the Northern Xunwu Earthquake in Jiangxi Province on September 21, 1941 DENG Hui, DONG Fei-fei, XIE Bin EARTHQUAKE    2021, 41 (3): 104-113.   DOI: 10.12196/j.issn.1000-3274.2021.03.008 Abstract （470）      PDF（pc） （2684KB）（168）       Knowledge map    The epicentre location and isoseismic line of the 1941 M5¾ northern Xunwu earthquake in jiangxi province are not consistent in the seismic catalogue and investigation report of each version. On the basis of absorbing previous research results and supplementing new data, through detailed textual research of seismic survey data, we check the seismic intensity of each recorded point, review macro epicentre parameters of the earthquake, and redetermine its isoseismal range. Combined with the seismogeological investigation, the possible seismogenic structures of the 1941 AD northern Xunwu earthquake are studied comprehensively. According to the comprehensive analysis, the macroscopic epicentric parameters of the 1941 M5¾ northern Xunwu earthquake are 25.1°N and 115.7°E, and its isoseismal lines are distributed in the NW direction. Its seismogenic structure may be the huanggang-bijiashan fault, and its controlling structure may be the heyuan-shaowu fault.

Discussion on Filters in Earthquake Observation Instruments XUE Bing EARTHQUAKE    2021, 41 (1): 40-50.   DOI: 10.12196/j.issn.1000-3274.2021.01.004 Abstract （461）      PDF（pc） （3112KB）（216）       Knowledge map    The data output by earthquake observing instruments installed at fixed stations is a time series, which reflects the changes of the observed object over time. In this case, it is very important to understand the frequency response of the instrument. This article regards any signal processing process related to frequency response as filters, such as filters related to the frequency response of the sensor, anti-aliasing filters in the data acquisition process, etc., and discusses carefully. In some cases, the anti-aliasing filter is ignored, because the observation object changes slowly with time, and it is considered that there is almost no high-frequency component. However, this understanding is incorrect, and frequency aliasing interference is often found in actual observations. A simulation calculation example is used to illustrate the influence of frequency aliasing interference on the observation data, to explain the unreasonable phenomenon of the coseismic waveform in the component strain observation.

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 （457）      PDF（pc） （6069KB）（560）       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.

Geometric Distribution of Huaihe—Nvshan Lake Section of Anqiu—Juxian Fault in the Middle Part of Tanlu Fault Zone YANG Yuan-yuan, LI Peng-fei, FANG Liang-hao, LU Shuo, YAO Da-quan, ZHAO Peng, ZHENG Hai-gang, SHU Peng, ZHENG Ying-ping, PAN Hao-bo EARTHQUAKE    2022, 42 (1): 54-69.   DOI: 10.12196/j.issn.1000-3274.2022.01.004 Abstract （450）      PDF（pc） （9815KB）（71）       Knowledge map    The latest active Anqiu—Juxian fault named F5 fault in the middle section of the Tanlu fault zone is an important seismically active fault in the eastern China. The present studies have shown that the F5 fault has extended southward into the Huaihe—Nvshan Lake in Anhui province, however, the specific geometrical distribution of this segment still has two major unresolved problems. Firstly, does the eastern fault of the Ziyang mountain belongs to the branch of F5 fault? secondly, does the F5 fault extend south to the northern shore of Nvshan Lake? In order to solve these problems, based on the methods of remote sensing interpretation, geomorphological survey, trench excavation and dating of faulted strata, we conducted research on the faults on the eastern side of Ziyang mountain and the faults along the northern shore of Nvshan Lake. The results show that the eastern fault of the Ziyang mountain developed at an older age, and experienced a strong thrust compression movement in the early and middle Pleistocene. It did not active since the late Quaternary and does not belong to the F5 fault branch. The Tan-Lu fault zone faulted the Late Pleistocene stratum in the ShangZhan area on the northern shore of Nvshan Lake. The F5 fault has completely penetrated between the Huaihe River and Nvshan Lake, its trace is single and continuous, with a total length of about 20 km. It has been discussed that the F5 fault could terminated southward from Nvshan Lake to Mingguang City. The termination of the fault is controlled by the regional ancient structural pattern, which indicating that the fault is both new and inherited.

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 （449）      PDF（pc） （6138KB）（426）       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.

On seismological synthesis forecasting method taking Heze earthquake as a case ZHANG Bin, YANG Xuan-hui, LU Yuan-zhong EARTHQUAKE    2007, 27 (4): 27-35.   Abstract （435）      PDF（pc） （1916KB）（150）       Knowledge map    Abstract: Based on the previous earthquake prediction methods, we put forward a synthetical method of earthquake prediction. First, the dynamic image (including seismogenic gap and seismogenic belt) is used to confirm potential seismic dangerous zone approximately. Then a certain seismogenic zone is determined using coulomb stress infered from moderately strong earthquakes. Finally, ARM model and growing correlation length model are applied to judge whether the seismogenic zone is changed into critical state or not. In forecasting seismic three facts, the particular advantages of typical seismographic forecasting methods is exploited; in order to gain more credible forecasting result, the small correlated method has been intercompared and verified. This article studied Heze 5.9 earthquake, happened in 1983, using this synthetical method. The result shows that the forecasting result observed synthetical method is basically consistent to Heze earthquake.

Research on Amplitude Superposition Method of Airgun Signal YOU Xiu-zhen, LIN Bin-hua, LI Jun, SHAO Ping-rong, HU Shu-fang, WANG Shi-cheng EARTHQUAKE    2019, 39 (4): 1-12.   Abstract （431）      PDF（pc） （6837KB）（95）       Knowledge map    Because the source signal of airgun is weak, it is easy to be disturbed by external noise or earthquake, so its true amplitude is covered.If these interference records are directly involved in the superposition, they will easily lead to unreliable amplitude information and affect the superposition effect.In order to eliminate the interference effects, this paper proposes the methods of probability screening and noise model screening amplitude superposition. Based on the experimental data of airgun in Longmentan Reservoir and Shaxikou Reservoir in Fujian Province in June 2018, the application effects of the two methods are tested in terms of the ability of eliminating interference, waveform shape and amplitude, and the advantages and disadvantages of the two methods are compared.The results show that: ① the two screening methods can effectively remove the abnormal interference, and the waveform shape and maximum amplitude of the airgun signal after processing are basically consistent with the direct linear superposition; ② the fixed network generally has detailed information of instrument parameters, and the noise spectrum method can easily confirm the operation status of the station and screen out the abnormal station in time; for the mobile station with unknown information such as sensitivity, noise model screening method is limited in use, while the probability screening method is concise and applicable.

Wavelet Analysis of Barometric Pressure Effects on Groundwater Level YUAN Yong-dong,Zhou Rui,MO Pei-chan,XIANG Wei,FU Heng EARTHQUAKE    2017, 37 (4): 162-172.   Abstract （431）      PDF（pc） （903KB）（401）       Knowledge map    To investigate the main characteristics of the barometric pressure effects on groundwater level, we use groundwater level data and barometric pressure data in Nanning Shibu and Nanning Jiutang station to reveal period characteristics of both as well as their relations in time-frequency space by wavelet analysis, cross wavelet and wavelet coherence. Wavelet power spectrum shows that period band between 7.8 and 14.7 hours is the same significant period band for both groundwater level and barometric pressure. Another significant period band of barometric pressure is between 17.5 and 27.8 hours. Cross wavelet analysis indicates that the resonant period of groundwater level and barometric pressure is between 7.8 and 14.7 hours. The results of the wavelet coherence analysis show that groundwater level and barometric pressure have significant correlation in a wider period band, and the correlation coefficient of groundwater level and barometric pressure changes over period and time, and their relative phase angle also show differences due to difference of cycle.

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 （427）      PDF（pc） （4812KB）（478）       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.

Gravity Changes Before the 2019 Xiahe Gansu MS5.7 Earthquake ZHAO Yun-feng, ZHU Yi-qing, LIU Fang, XU Yun-ma, ZHANG Guo-qing, MAO Jing-lun, ZHU Hui EARTHQUAKE    2021, 41 (1): 67-77.   DOI: 10.12196/j.issn.1000-3274.2021.01.006 Abstract （418）      PDF（pc） （4024KB）（300）       Knowledge map    The relative gravity data were calculated by the of classic adjustment from 2017 to 2019 in the North-South seismic belt. We analyzed the precision of gravity value at sites in the study area of south-east of Gansu province, and studied the variation of the regional gravity field before Xiahe Gansu MS5.7 earthquake. The results show that ① Gravity value precision of 90% gravity sites is less than 10×10-8 m·s-2 after adjustment calculation in our study area, and the gravity value at absolute gravity sites is well accordance with absolute gravity observation. ② Between April 2017 and April 2018, gravity variation is positive in the south-west side of the Lintan-Dangchang fault, and it is negative in the north-east side of the fault. It is opposite to the gravity variation before Jiuzhaigou MS7.0 on August 8, 2017. There are violent difference gravity variation in the area near the Hezuo city and Xiahe county. ③ Between April 2018 and April 2019, gravity variation is negative in the south-west side of the Lintan-Dangchang fault, about -10×10-8～-30×10-8 m·s-2, and it is positive in the north-east side of the fault, about +20×10-8～+30×10-8 m·s-2. The gravity variation is not obvious near the epicenter of Xiahe MS5.7 earthquake, which indicated that the area near epicenter was possible to be in locked during the time. While there is a unconspicuous four quadrant distribution of gravity change centered on the junction of Xiahe county, Luqu county and Zeku county. ④ Strong earthquakes are prone to occur in four quadrant distribution center of gravity change of high gradient belt of positive and negative anomalies. We made a medium-term forecast about Xiahe MS5.7 earthquake based on relative gravity changes, especially forecasting localities of potential earthquake.

Full-waveform Based Focal Mechanism Inversion for Earthquakes of Small and Moderate Magnitude in the Capital Region DING Cheng, LI Jun-lun, WANG Xiao-shan, TAN Yu-yang, ZHANG Hai-jiang EARTHQUAKE    2020, 40 (4): 1-22.   DOI: 10.12196/j.issn.1000-3274.2020.04.001 Abstract （418）      PDF（pc） （10123KB）（163）       Knowledge map    Currently, the methods used in the study of the focal mechanism of small and moderate earthquakes in the capital region include the P-wave first motion polarity method, the amplitude ratio method and the waveform inversion method. The former two methods use only a small amount of information in the waveforms, and are limited by factors such as the station distribution, site effects etc. Similarly, the traditional waveform inversion method only uses part of the information of the waveform, and there are certain requirements for the magnitude and data quality, etc. To overcome the aforementioned limitations, this study attempts to use a new full waveform matching method, which uses comprehensive information mentioned above, to invert for the focal mechanism solution of earthquakes of small and moderate magnitude in the Capital Region, thereby improving the reliability of the solution. To test the reliability and applicability of the new full waveform matching method for the earthquakes in the capital region, we first perform a synthetic data test. The test results prove that the used full waveform matching method is stable and reliable. In early 2019, two recent M3+ earthquakes occurring in Beijing received extensive attention. We use the full waveform matching method to determine their focal mechanism solutions and analyze their occurrence in the background of regional active faults. Finally, we determine the focal mechanisms for 22 earthquakes (2.2≤M≤4.3) since 2015 in the capital region, and analyze the tectonic stress field in the capital region, which compares well with previous studies.

Statistical Analysis of Seismic Gap in North China WANG Xia, SONG Mei-qin, CHEN Hui EARTHQUAKE    2019, 39 (3): 187-195.   Abstract （409）      PDF（pc） （3357KB）（382）       Knowledge map    The seismic gaps in North China from 1970 to 2017 are analyzed using the unified identification criteria. The result shows that seismic gap before M≥5.0 earthquakes is 36.7% in North China. The relationship between the duration time of M≥3.0 earthquake has a certain linear positive correlation with the magnitude of main shock. However, the long axis scale, the initial magnitude and the main-shock magnitude don't have obvious linear relationship. The accuracy rate of seismic gap is 0.76, the false rate is 0.24, the missing rate is 0.60, and the R value is 0.32. R value is higher than R0 value with 97.5% confidence level. It indicates that the prediction method of seismic gap has certain forecast capability in North China.

Study on Seismogenic Structure of the Yutian MS6.4 Earthquake in Xinjiang in 2020 GENG Shuang, WANG Lin, TIAN Qin-jian, XU Yue-ren, LI Wen-qiao, YUAN Zhao-de EARTHQUAKE    2021, 41 (2): 1-13.   DOI: 10.12196/j.issn.1000-3274.2021.02.001 Abstract （381）      PDF（pc） （8874KB）（107）       Knowledge map    The Yutian MS6.4 earthquake, which occurred on 26 June 2020 in West Kunlun, Xinjiang, is another strong earthquake following the 2008 MS7.3 and 2014 MS7.3 earthquakes. Determination of the seismogenic structure of this earthquake is a basic problem to be solved for seismic anatomy. Based on GIS platform and technology, this paper fully integrates various data such as structure geology, high-resolution remote sensing, topography, seismology, GPS velocity field and focal mechanism. The dynamic and kinematic mechanisms related to earthquakes are studied, and the seismogenic structure is preliminarily determined. The Yutian earthquake may be the result of a further southwest rupture of the ruptured segment of the 2014 strong earthquake. The results of seismic relocation show that the epicenter is located near Ulugh Muztagh. The results of high-resolution remote sensing interpretation and tectonic geomorphology deformation analysis show that the epicentral area is a typical extensional basin-ridge tectonic area, and there are small faulted basins and basin-controlling normal faults. High resolution satellite images after the earthquake showed that no obvious surface rupture zone and secondary earthquake disasters were found in the earthquake area. This earthquake may be caused by the activity of the NE-trending tectonic system in the tectonic belt between the West Kunlun block and the Songpan-Ganzi block. Due to the oblique tension movement of the blocks on both sides of the structural belt, normal faults and strike-slip faults are successively formed and continuously and synchronously faulted in the structural belt. Normal faults are more active than strike-slip faults in the area. Normal faults and strike-slip faults can well adapt to and absorb the tensile pure shear component and the lateral simple shear component respectively, so that normal faults and strike-slip earthquakes occur frequently in the tectonic belt. There may be a multi-level extensional tectonic system in the crust from the surface to the deep, and there may be no obvious correlation between the various systems. This earthquake may have little relationship with the surface tensional structural system, and it is inferred that it is the result of the activity of deep-seated tensional structural system.

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）（399）       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.

Pre-, Co-, and Post-seismic Fault Movement Features of the 1966 Xingtai Strong Earthquake Swarm SHAO Zhi-gang, LI Yi-wen, WANG Peng EARTHQUAKE    2015, 35 (3): 1-9.   Abstract （357）      PDF（pc） （5510KB）（208）       Knowledge map    Based on the leveling observation data of the March 1966 earthquake swarm in Xingtai, this paper compared observed coseismic displacement and results from numerical simulation, thus inferred shallower Niujiaqiaoyang Fault and Yongfuzhuang Fault and a deeper NW oriented, NE trending fault as the causative faults of Xingtai earthquake swarm. Constrained by leveling data, this paper gave the spatial distribution of pre-, co-, and post-seismic movement of the faults. The results show that significant aseismic slip before the earthquake occurs mainly on the causative fault of March 8 MS6.8 earthquake, and also occurs on the segments in the causative fault of the March 20 Ningjin MS7.2 and 6.7 earthquakes with weak coseismic displacement. The after slip occurs mainly in the Niujiaqiaoyang Fault in the west of Shulu depression. From the spatial and temporal features of fault movement of the Xingtai earthquake swarm, we conclude that in the process of earthquake rupture nucleation, aseismic slip before the earthquake may occur in causative fault of foreshock, and also may occur in causative fault of mainshock. The distribution of afterslip shows a complementary spatial pattern with coseismic displacement. Whether the aseismic slip before the earthquake is the reason for some of pre-earthquake precursors is an issue worth further studying.

Characteristics of Focal Mechanism and Stress in the North-South Seismic Belt of China CUI Zi-jian, CHEN Zhang-li, WANG Qin-cai, LI Jun EARTHQUAKE    2019, 39 (1): 1-10.   Abstract （357）      PDF（pc） （8979KB）（94）       Knowledge map    Using the CAP method, the focal mechanisms of 466 M≥3.5 events that occurred in the North-South Seismic Belt from January 2009 to October 2017 have been obtained. Combining the results of 259 focal mechanisms (M≥4.5) from January 1976 to August 2017 from the GCMT, we investigated the characteristics of focal mechanisms and stress in the North-South Seismic Belt of China. The spatial distributions of focal mechanisms differ among different faults and blocks. It is consistent with active tectonics along the North-South Seismic Belt, mostly in eastern margin of the Tibetan Plateau. Under the complex dynamic environment in eastern margin of the Tibetan Plateau, the P axes directions vary much inside the North-South Seismic Belt. The P axes in the northern section of the North-South Seismic Belt are NE direction. In and surround the Longmenshan fault zone the P axes are nearly EW direction except the NE segment which are NW direction. Inside the Sichuan-Yunnan rhombic block the P axes are NNW direction, while in the west of the west boundary are NNE direction, in the east of the east boundary are NW direction. The stress direction transition bands correspond well with the Sichuan-Yunnan rhombic block boundary. Overall, the P axes in the North-South Seismic Belt and its neighbor area have a clockwise rotational pattern from north to south.

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 （356）      PDF（pc） （2647KB）（512）       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.

Distribution of Wave Velocity Ratio and Poisson′s Ratio in Jiangsu Area LI Ting-ting, LIU Li, HU Guang-wu, CHEN Fei EARTHQUAKE    2019, 39 (3): 149-157.   Abstract （354）      PDF（pc） （2670KB）（366）       Knowledge map    In this paper, we divided the Jiangsu area (30.5°N ~35.5°N, 116°E ~122°E) into 18 sections in which each section has the range of 1°×1°. We collected the phase data of Jiangsu Digital Seismic Network from January 1, 2009 to December 31, 2017. Using the multi-station methods, we calculated the velocity ratio and possion's ratio of the 18 sections. The results show that: ① In 18 sections, the mean velocity ratio ranges from 1.68 to 1.73, the correlation coefficients are above 0.99, the average velocity ratio value of the whole are is 1.71, which is lower than the average value of the global continental crust. ② The average poisson's ratio value is 0.24. This shows that there is no melting medium property in the study area, consistent with the crust medium which mainly consist of granite. ③ From the relevance of poisson's ratio and crust thickness, there is a negative correlation between the poisson's ratio and crust thickness in Jiangsu area, which is higher in the north and lower in the south, higher in the east and lower in the east. The Poisson's ratio of some sub-regions near 33°N, alternates high and low and changes complicatedly, which may be related to complex geological structure in the study area.

The Measure of the Magnitude of the Earthquake CHEN Zhang-li EARTHQUAKE    2020, 40 (1): 1-10.   DOI: 10.12196/j.issn.1000-3274.2020.01.001 Abstract （353）      PDF（pc） （393KB）（267）       Knowledge map    This paper aims at main problems in measuring earthquake size in China. On the basis of clarifying the physical meaning of earthquake size, we firstly points out that the traditional magnitude scale ML, mb(mB) and MS which are defined by the source radiation energy ER have some problems such as “overgeneralization”, “magnitude saturation” and “limitation” of ML magnitude scale, as well as the uninterchangeable between magnitudes of different scales. The seismic moment M0 derived from the “equivalent force” in the source area during the whole process of earthquake rupture is the most scientific measure of the earthquake size. In order to continue to use the term “magnitude” to describe the size of an earthquake, the moment magnitude scale MW defined by M0 not only solves problems in the traditional magnitude scale, but also applies to measure earthquakes with different sizes, different epicentral distances, and different focal depths. Therefore, it has been widely adopted by international seismology community in the past 20 years. Finally, we emphasize that promoting the measurement of earthquake size in line with international standards is an important basic work to advance the modernization of earthquake science and technology in China. It is not only conducive to the international communication and cooperation in earthquake science and technology, but also helpful to enhance the scientificity of earthquake prevention and disaster reduction.

The Method for Identify the Earthquake Precursor of Water RadonTaking the Water Radon Anomaly of Qingshui Hot Spring in Gansu Province As an Example SU He-jun, CAO Ling-ling, ZHANG Hui, LI Chen-hua, ZHOU Hui-ling EARTHQUAKE    2020, 40 (4): 198-213.   DOI: 10.12196/j.issn.1000-3274.2020.04.016 Abstract （352）      PDF（pc） （3274KB）（276）       Knowledge map    Correct judgements for anomaly features is the precondition for enhancing our ability to do the earthquake prediction. According to relative statistic, the true anomalies of earthquake are quite limited. It is important to study the relationship between the precursors and following earthquakes. The radon of Qingshui hot spring fluctuated drastically the 4th month before Jiuzhaigou MS7.0 earthquake on August 8, 2017. In order to identify the relationship between the radon anomaly and the earthquake, the cause and mechanism of this radon anomaly were studied deeply by pumping tests, analyzing isotopes and hydrochemistry components of Qingshui hot spring.The seismogenic structure of Jiuzhaigou earthquake and some other anomalies were also analyzed. The results showed that the test results are consistent with the actual observation. The water radon variation is positively correlated with water level variation but with water temperature.The proportion of fluid from deep crust did not increase according to composition of hydrogen and oxygen isotope and hydrochemistry. There seems to be little probability of seismogenic process of Jiuzhaigou earthquake caused rupture of Qingshui hot spring area.The radon anomalous of Qingshui hot spring is not the short-term anomaly for the 2017 Jiuzhaigou MS7.0 earthquake. It was caused by manual pumping. This study provides a more reliable method for identifying the anomalies of fluid before earthquakes.

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 （351）      PDF（pc） （3354KB）（501）       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

Earthquake Science on the Western Coast of South American (Chile)and Implications for Earthquake Prediction: An Overview SHI Fu-qiang, SHAO Zhi-gang, ZHU Lin, ZHANG Zhu-qi, SHAO Hui-cheng EARTHQUAKE    2019, 39 (1): 155-170.   Abstract （344）      PDF（pc） （3053KB）（362）       Knowledge map    The Chilean subduction is one of the highest seismic activity zone in the world, which has been attacked by three large earthquake of MW>8 since 2010. Based on related studies on seismic geology, historical earthquake, kinematic characterizes, etc., some interesting phenomenon that related to earthquake prediction and the relative research and cognition progress are summarized in this paper. ① Due to the well recorded historic earthquake and the comprehensive research on modern geodesy data-based interseismic fault locking, seismic gap and the high slip deficit locking zone have dominated several large earthquake in the recent years. ② Some seismogenic related precursors are found before the 2010 Maule MW8.8 and the 2014 Iquique MW8.1 earthquake. Different with the nesting of the two kinds of Mogi seismic gap before 2010 Maule MW8.8 earthquake, continuously decreasing of b-value, clustering of pre-shocks, suddenly changes of GPS transient signal, etc., were sprung up before the main shock of the 2014 Iquique MW8.1 earthquake. ③ The spatial distribution of coseismic slip and interseismic locking reveals the diversity of fault frictional properties. ④ Many cognitional debate on seismogenic physical mechanism and its complexity are still ongoing between different scientists and different methods. ⑤ After the combination of literature investigation and our daily work,some preliminary understanding and thinking are also discussed in this paper.

A Review of Researches on Land Mud Volcanoes in Northern Tianshan of Xinjiang and Southern Taiwan, China JIANG Yu-han, GAO Xiao-qi, WANG Yang-yang, ZHANG Lei EARTHQUAKE    2020, 40 (3): 65-82.   DOI: 10.12196/j.issn.1000-3274.2020.03.006 Abstract （341）      PDF（pc） （4723KB）（268）       Knowledge map    Based on the systematically introduction of the research progress, this paper comparatively analyses the geological characteristics of mud volcanoes between the southern Taiwan and the north Tianshan, Xinjiang province, including the eruption characteristics of the mud volcano in different states. The results show that the mud volcanoes in the study areas are all distributed along the fault zones, and mainly located in the anticlinal axis, which are mostly exposed to the mud-bearing layers. Besides, the geophysical characteristics show similarity in mineral compositions of the solid eruptions (quartz and montmorillonite etc.), the mud temperature of the liquid eruption, and the bubbling frequency between the aforementioned two study areas.The maximum bubble diameter and gas flow, in contrast, show obvious difference.Through comparatively analyzing the geochemical characteristics of liquid and gas eruption in the two regions, we find that the liquid eruption has the same characteristic of high salinity. Methane is the main content of the gas emissing from most of the mud volcanoes, but at volcanos carbon dioxide is the main content. The great difference in the eruptions from mud volcanoes in the two study areas, is considered to be the result of regional geological structures and climatic conditions. According to the current researches, the eruptions of mud volcanoes in both areas were caused by the increase of formation pressure. The geochemical mechanism of mud volcanoes is summarized and it has a good relationship with seismic activity, which shows that the geochemical parameters of mud volcanoes could be the potential indicators for the seismic activity.

Low-point Time Spatial Distribution Characteristics of Geomagnetic Vertical Component Diurnal Variation before the 2013 M6.6 Minxian—Zhangxian Earthquake DAI Yong, GAO Li-xin, YAO Li, ZHU Pei-yu, GE Gen, WANG Lei EARTHQUAKE    2019, 39 (3): 106-114.   Abstract （332）      PDF（pc） （3861KB）（309）       Knowledge map    The geomagnetic low-point displacement appeared on June 16th, 2013. In this paper, low-point time longitude effect is eliminated by the method of subtracting theoretical low-point time from measured low-point time. The isoline with low-point time of 0 h after eliminating the longitude effect is used as the boundary of low-point displacement. The epicenter of the M6.6 Minxian—Zhangxian earthquake is at the boundary of the geomagnetic low point displacement on June 16th. The diurnal variation of geomagnetic vertical components in mainland China during abnormal periods is statistically analyzed. There are significant zoning features. The diurnal variation pattern in the area with positive low-point time presents W type, while the diurnal variation pattern in the area with negative low-point time mainly presents V type characteristics. During the abnormal period, there are significant high gradient zones in the mainland of China. In this paper, the gradient value is used to quantitatively describe the spatial and temporal variation of low-point time. During the normal period of June 13th, there is no region in the mainland of China with a gradient value greater than 1.5 h /(°). During the abnormal period of June 16th, there is area with a gradient value greater than 1.5 h/(°). The epicenter of the 2013 M6.6 Minxian—Zhangxian Earthquake is located at the edge of the high gradient region.

Agenda Evolution of Earthquake Forecast/Prediction Research: Inspiration from Bibliometric Analysis ZHANG Yan, WU Zhong-liang, LI Jia-wei EARTHQUAKE    2019, 39 (2): 159-173.   Abstract （331）      PDF（pc） （4006KB）（375）       Knowledge map    In this paper, using Web of Science core database as the data resource, and with CiteSpace as the analysis tool, three issues are discussed based on bibiliometrics, which are ① the development process of earthquake forecast/prediction, from January 1, 1960 to December 31, 2017, ② the decade evolution of research agenda from January 1, 1968 to December 31, 2017, and ③ the main research agenda of earthquake forecast/prediction from January 1, 2008 to September 1, 2018. These analyses could provide references for research on earthquake forecast/prediction and strageties. Our results show that the processes of research on earthquake forecast/prediction have been in dynamic development. Especially, research agenda in each period of time gradually have more diversified growing trend, and tend towards more in-depth and detailed study stage promoted by important events.

Seismicity Characteristics of the 17 June 2019 MS6.0 Sichuan Changning Earthquake Sequence ZHAO Ce, ZUO Ke-zhen, ZHAO Cui-ping EARTHQUAKE    2020, 40 (3): 28-40.   DOI: 10.12196/j.issn.1000-3274.2020.03.003 Abstract （329）      PDF（pc） （7521KB）（137）       Knowledge map    On June 17, 2019, a MS6.0 earthquake occurred in Changning, Sichuan Province. Within four months after the earthquake, the seismic activity in the focal area presented features of high frequency, high intensity and slow attenuation. During the development and evolution of this earthquake swarm, tracking and studying the characteristics of aftershock activity, including the b-value that describes the proportional relation between large and small earthquakes and the change of stress during the development of the sequence, is of great significance to monitor and analyze the seismic risk. On the basis of accurate relocation of the seismic sequences by using the seismic catalogue before and after the earthquake in the focal area, the spatial and temporal distribution of the b-value were calculated. The spatial distribution of b-value shows that, before the earthquake, the b-values near the epicenter were significantly lower than its neighboring area; after the earthquake, the b-value of the sequence began to recover from southeast to northwest, and then its distribution was relatively even. The temporal variation of b-value indicates that, after the earthquake, the b-value decreased to an extremely low level in a short time and then began to rise; during this period, b-value oscillated many times, and most strong aftershocks occurred in the process of b-value decreasing; till the end of August 2019, the seismic activity of this sequence was still active.

Hydrogeochemical Characteristics of Gongyihai Hot Spring, in Shimian County, Sichuan Province SHI Hong-yu, WANG Wan-li, ZHOU Xiao-cheng, YAN Yu-cong, LI Peng-fei, JIANG Li, CHEN Zhi EARTHQUAKE    2021, 41 (1): 93-115.   DOI: 10.12196/j.issn.1000-3274.2021.01.008 Abstract （325）      PDF（pc） （4905KB）（291）       Knowledge map    It is of great significance to judge the short impending fluid anomaly of the moderate-strong earthquake.By using hydrogeochemical data, the hydrologic cycle model of hot springs was established to explore the relationship between hydrogeochemical changes and earthquakes in hot spring. The spatial-temporal variations of groundwater chemical types and their genesis were discussed by measuring ion concentration, trace element, hydrogen and oxygen isotopic compositions and Strontium isotope in the Gongyihai fault zone in Sichuan Province. From October 2008 to September 2019, 206 water samples were collected from Gongyihai hot spring in the Gongyihai Fault zone, and their hydrogeochemical characteristics were investigated. The results show that ① Hot spring water samples are Na-HCO3·Cl types. Stable isotope values (-108.67 ‰～-110.47 ‰ and -14.19 ‰～-14.83 ‰) distributed near the atmospheric precipitation line, indicating that the hot spring water mainly points to a meteoric origin; ② SiO2 (42.7 mg/L) values of the geothermal water indicated that those spring water was followed by interaction between water and rock during circulation with a probable mix of earth's surface water, and the circulation depth of hot spring was about 4.3 km; ③ Pre-earthquake anomaly, coseismic response and post earthquake anomaly in three MS5.0 earthquakes within the scale 300 km in hot spring fluids, through the mobile observation of the study area. Gongyihai hot spring is located at the intersection of Gongyihai fault zone and Anninghe fault zone, the surrounding earthquakes will influence the ion concentration changes of Gongyihai hot spring. Therefore, a hydrogeochemical model was proposed for the geochemical system on the basis of the geochemical data of hot springs combined with the geology and hydrogeology of the study area. These are of great significance to the short-term fluid anomaly judgment of future moderate and strong earthquakes around the Gongyihai fault zone.

Relocation and Focal Mechanism of the Songyuan Earthquake Swarm Sequence in 2013 LI Jun, WANG Qin-Cai EARTHQUAKE    2018, 38 (4): 62-73.   Abstract （324）      PDF（pc） （6531KB）（595）       Knowledge map    Double-difference location algorithm and the CAP method (Cut and Paste) were used for the precision mapping and inversion of the focal mechanism solution for the Songyuan earthquake swarm above M5 in 2013. The double-difference location results show that the epicenter distribution sequence of the Songyuan M5 earthquake swarm is NW—SE, with a length of about 10 km, width of about 5 km, and a major axis of about 317°. It is almost perpendicular to the Changling-Dashanzi fault, and the focal depth is mainly concentrated at 2~14 km. The results of the focal mechanism solution of 19 MS≥3.5 earthquakes indicate that the Songyuan M5 earthquake swarm is dominated by thrust, thrust and strike-slip earthquakes, and the dominant orientation of the focal plane solution I is NW—SE orientation. The depth of 19 earthquakes are focused on 4~6 km. The orientation of the epicentral distribution after the fine orientation is consistent with the dominant orientation of the focal mechanism solution plane I. The seismogenic structure of the Songyuan M5 swarm is an invisible fault that is almost perpendicular to the Changling—Dashanzi fault. The background stress field in the source area is affected not only by the push of the Pacific plate to the North East Asia plate, but also by the internal secondary fault zone of the Songliao basin, under the influence of deep seismic activity in the underground subduction zone of the Northeast China. The deep seismic activity has strengthened the disturbance of mantle material and further promoted the accumulation of stress in shallow medium. The junction of the secondary fault zone in Songliao basin is relatively weak, and when the stress accumulates to a certain extent, a moderate-strong earthquake will occur.

STUDY ON THE PRECURSORY CHARACTERISTICS OF YONGDENG EARTHQUAKE (MS=5.8) AND MEDIUM-AND SHORT-TERM PREDICTION OF TIANZHU-GULANG EARTHQUAKE (MS= 5.4) Mao Ke, Wang Zhenya, Shi Telin EARTHQUAKE    1998, 18 (2): 177-183.   Abstract （318）      PDF（pc） （107KB）（126）       Knowledge map    In this paper, the characteristics of temporal and spatial distribution of the precursory anomaly before Yongdeng earthquake have been analyzed by using synthetical method. The analytical results show that the precursors of Yongdeng earthquake (MS=5.8) are of the following features: large quantity, wide distribution, high density and obvious postseismic response. The temporal distribution is in groups, the spatial distribution is relatively stable, which may be related with such a pattern that the moderately strong earthquakes occurred in swarms in this area. This research result has been a pplied to them edium-term and short-term prediction of Tianzhu-Gulang earthquake (MS=5.4) in 1996.