Articles in press have been peer-reviewed and accepted, which are not yet assigned to volumes /issues, but are citable by Digital Object Identifier (DOI).
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Study on earthquake focal mechanism and seismogenic structure of the Santai MS4.7 earthquake in 2013
Liu Suihai, Lü Jinxiong, Zhao Xueqin, Zhang Gang, Wen Mingru
 doi: 10.11939/jass20200201
[Abstract](42) [FullText HTML](20) [PDF 1776KB](16)
Santai MS4.7 earthquake occurred in Mianyang city, Sichuan Province on February 19, 2013. The epicenter located in an intersection area which combined the basement fracture in central Sichuan basin, the Mianyang-Santai-Dazu fracture and the Pujiang-Santai-Bazhong fracture. Based on the earthquake catalogue, seismic phase report and waveform data, we relocated the earthquake sequence, and solved the focal mechanism of the main earthquake by joint inversion of local and teleseismic waveforms, and also studied the seismogenic structure of the Santai MS4.7 earthquake according to the field geological survey. The spatial distribution direction of the relocated aftershock sequence is NW-SE and it highly fitted with the nodal plane I of the focal mechanism, the seismogenic structure of the earthquake can be considered as strike NW-SE, dip NE, and rupture plane is nearly vertical, and the seismogenic fracture was dextral strike-slip dislocation by the proximately horizontal confining pressure in the direction of nearly NS. During the field survey, any fracture marks nor surface ruptures can be obviously found, hence the seismic structure is concluded as a buried fault. The focal depths are respectively 21.6 km and 19 km through the relocation and joint inversion of local and teleseismic woweforms. The focal depth reflects that the location of the source area is in the low-velocity layer which is in the bottom of the upper-crust. This earthquake is caused during the adjusted and changed process of the tectonic stress field caused by Wenchuan earthquake, and it is the result of the reactivation of the high-angle fault concealed in the Presinian crystalline substrate in middle-block of Sichuan basin.
Characteristics of Arias intensity and Newmark displacement of strong ground motion in Lushan earthquake
Li Xuejing, Xu Weijin, Gao Mengtan
 doi: 10.11939/jass.20200180
[Abstract](15) [FullText HTML](8) [PDF 2905KB](5)
The characteristics of spatial distribution, attenuation and correlation of ground motion parameters are important research contents in engineering seismology. In this paper, based on the ground motion records of Lushan earthquake, we study the spatial distribution and attenuation characteristics of Arias intensity and Newmark displacement as well as their correlation with other ground motion parameters, respectively. The results show that the spatial distribution of Arias intensity is related with the spatial distribution of seismic faults and the direction of earthquake rupture. Arias intensity has a good correlation with PGA. Furthermore, the site conditions have a significant effect on the correlation between the two: for the same PGA, the softer the site condition, the greater the Arias intensity. In addition, magnitude is also an important factor affecting the correlation between Arias intensity and PGA: with the same PGA, the greater the magnitude, the greater the Arias intensity. Newmark displacement has a good correlation with both PGA and Arias intensity, among which the correlation with Arias intensity is stronger, and the correlation coefficient can reach above 0.94. The research in this paper also shows that the existing models cannot describe the attenuation characteristics of Arias intensity and Newmark displacement of Lushan earthquake well, which indicates the particularity of Lushan earthquake in both the duration and rupture process. The particularity of Lushan earthquake reveals that the seismic geological and tectonic environment in Western China is significantly different from that in other regions. Therefore, the prediction equations of ground motion parameters suitable for earthquakes in Western China should be studied. The research results of this paper have important scientific significance and application value for us on both understanding the characteristics of ground motion and the prediction and prevention of earthquake disaster in China.
The conjunct effects of ISO and CLVD sources in underground explosions on the spectral null in Rg waves
Wang Xuliang, Jin Ping, Zhu Haofeng, Xu Henglei, Xu Xiong
 doi: 10.11939/jass.20200197
[Abstract](16) [FullText HTML](9) [PDF 1896KB](3)
The compensated liner vector dipole(CLVD)source is usually induced by underground explosions and could lead to a null in the Rg spectra. There is a theoretical scale between the null frequency and the depth of the CLVD source. Therefore we can estimate the depth of underground explosions with the null frequency. However, this relationship is based on simply considering the CLVD source while the conjunct effects of ISO and CLVD source are neglected. This study researches the conjunct effects of ISO and CLVD sources in underground explosions on the spectral null in Rg waves by numerical calculating the Rg spectra with seismology theory of surface waves. The results indicate that the null in mixed signals is quite different from the results of single CLVD source. Thus the null frequency of Rg waves is not simply corresponding to the theoretical value in practical underground explosions and it is improper to estimate the depth of explosions by directly applying the theoretical formula.
Empirical prediction models of time-averaged shear wave velocity vS20 and vS30 in Sichuan and Yunnan areas
Jia Lin, Xie Junju, Li Xiaojun, Wen Zengping, Chen Wenbin, Zhou Jian
 doi: 10.11939/jass.20200193
[Abstract](31) [FullText HTML](17) [PDF 3106KB](12)
The time-averaged shear wave velocity of overburden soil is an important parameter for site classification and reflecting site effects on ground motion, which is widely used in earthquake ground motion prediction models. Using the lithology and wave velocity profile data of 973 boreholes in Sichuan and Yunnan, we study the regional prediction model of the average shear wave velocity. Based on the bottom constant velocity (BCV) model, logarithmic linear model and Markov independent model, the empirical prediction models of vS20 and vS30 in this region were established. The BCV method has the largest prediction error. When the depth of the shear wave velocity is less than 10 m, this method will significantly underestimate the average wave velocity of the actual site. Based on the Boore method, we establish an empirical prediction model. By comparison, we find that the average wave speed prediction results in Sichuan and Yunnan are close to those in Beijing and California, and significantly lower than those in Japan. Through the comparative analysis of prediction error of three different extrapolation methods, we find that the prediction results based on Markov independence model have the smallest error at different depths, and it is preferred to use this method to set up regional prediction model.
Design and implementation of ionospheric multi-parameter anomaly monitoring system in Sichuan-Yunnan region
Liu Jiang, Xu Rui, Chen Cong, Rao Taiguo, Li Xingquan
 doi: 10.11939/jass.20210038
[Abstract](29) [FullText HTML](18) [PDF 0KB](3)
This paper introduced the design ideas and function implementation of ionospheric multi-parameter anomaly monitoring system in Sichuan-Yunnan region, and then applied the system to monitoring test of the MS6.0 earthquake on June 17, 2019 in Changning, Sichuan. The results show that the system realizes the real-time monitoring of abnormal changes such as global and China regional VTEC, site VTEC and foF2, which is helpful to carry out the demonstrative seismic-ionospheric anomaly monitoring. The graphic and data results can provide evidences for the identification of seismic-ionospheric anomalous disturbance, and ionospheric precursor information for earthquake monitoring and prediction in Sichuan-Yunnan region.
The anomaly characteristics of water temperature in the Eryuan well before the 2021 Yangbi MS6.4 earthquake in Yunnan,China
Ma Yuchuan, Yan Rui, Hu Xiaojing
 doi: 10.11939/jass.20210142
[Abstract](89) [FullText HTML](30) [PDF 0KB](41)
Interference characteristics of new energy power generation on electromagnetic observation environment:Taking the electromagnetic observation of Xuzhuangzi station of Tianjin as an example
Ma Yong, Li Ning, Xu Xuegong, Bi Jinmeng
 doi: 10.11939/jass.20210028
[Abstract](57) [FullText HTML](40) [PDF 0KB](11)
New energy power generation is an important measure taken by the countries to replace non-renewable energy sources to achieve sustainable utilization of power resources under the sustainable development strategy. Wind power and photovoltaic power generation are clearly defined as the key development fields of renewable energy. These big power generation facilities will have a great impact on the original seismic observation environment. Based on the electromagnetic observation project of the Xuzhuangzi station of Tianjin, aiming at the wind power and photovoltaic power generation facilities in the observation area around the station in recent years we analyzed the temporal and spatial changes of electromagnetic observation data in different observation environments by the field experimental measurement, and summarized the influence characteristics of the construction and operation of wind power generation and photovoltaic power generation on electromagnetic observation environment interference. The results show that the impact of wind turbine is significantly less than that of photovoltaic power generation equipment on the electromagnetic observation environment, which can be regarded as an interference point to regulate the distance between wind turbine and observation facilities, and in order to ensure that the photovoltaic power generation equipment does not affect the electromagnetic observation, it is necessary to treat each system as a whole and maintain a sufficiently large separation distance between them. This paper can provide a reference for the protection and evaluation of electromagnetic observation environment by building similar new energy power generation equipment in the seismic field, which is of important practical significance for protecting the observation environment of seismic stations.
Dynamic characteristics of fault hydrogen concentration in Aksu and its earthquake reflection efficiency
Zhong Jun, Wang Bo, Yan Wei, Ma Yuchuan
 doi: 10.11939/jass.20210007
[Abstract](55) [FullText HTML](15) [PDF 0KB](16)
This paper firstly analyzed the periodic components of the fault hydrogen concentration observation data in Aksu, and then explored the relationship between temperature, atmospheric pressure and the annual periodic components of hydrogen concentration using the linear regression and cross-correlation methods. At the same time, the Molchan error chart method was used to quantitatively verify the earthquake reflection efficiency of fault hydrogen in Aksu. The results show that: ① Fault hydrogen concentration in Aksu has good annual and semi-daily periodic components; ② There is a good positive correlation between the annual dynamic changes of fault hydrogen concentration and temperature, and a general correlation between the annual dynamic changes of hydrogen concentration and atmospheric pressure, indicating that the annual periodic changes of hydrogen concentration are mainly affected by temperature. The results from Molchan diagram method show that the fault hydrogen concentration anomaly in Aksu is more sensitive to moderate-strong earthquakes around the observation point, suggesting good earthquake reflection efficiency.
Structural characteristics of Yanyuan basin deduced from geophysical data and it dynamic implication
Zhang Pingchuan, Yu Changqing, Qu Chen, Qiu Longjun, Li Hengqiang
 doi: 10.11939/jass.20200119
[Abstract](348) [FullText HTML](177) [PDF 4138KB](52)
In this paper, an artificial seismic line and a short period natural seismic array covering the basin are set up. The seismic energy attribute is extracted from the artificial seismic data and the seismic velocity structure is obtained by seismic tomography. Meanwhile the S-wave velocity distribution at different depths is obtained by inverting the empirical Green’s functions retrieved from cross-correlation of the ambient noise data recorded by the short period seismic array. The results show that the Yanyuan basin is mainly divided into three layers by seismic reflection characteristics. The shallow layer is the Cenozoic sedimentary stratum with low velocity ranging from 1.0 km/s to 2.1 km/s, and it is characterized by good continuity and strong reflection. Cenozoic basin is thick in the south and thin in the north, where the sedimentary and structure are controlled by Yanyuan fault. The middle layer is medium-low velocity ranging from 3.5 km/s to 4.5 km/s, it is characterized by discontinuous reflection axis and weak reflection, which can be interpreted as Triassic strata. The deep layer is high velocity, characterized by chaotic seismic reflection and weak reflection energy, interpreted as Paleozoic strata. Furthermone, it is found that there is a detachment surface in the upper crust, which is the interface between sedimentary and basement, and a series of faults are developed from the detachment to the surface, and these faults are also an earthquake-prone area in Yanyuan basin. One of the faults is Jinhe-Qinghe fault, which is the boundary fault between Yanyuan basin and Kangdian block.
Tempo-spatial characteristics of repeating seismic events in the middle of Tianshan orogenic belt
Tang Lanlan, Zhang Yifeng, Yao Daoping
 doi: 10.11939/jass.20200192
[Abstract](66) [FullText HTML](30) [PDF 0KB](21)
Based on the seismic waveform data recorded in the stations of Xinjiang seismic network from 2009 to 2017, the repeating earthquakes in the middle of Tianshan orogenic belt and its periphery in Xinjiang were determined and relocated by using the waveform cross correlation technique and the master event approach. The results show that 11 618 of the 30 181 events are repeating events, which consist of 2395 groups of doublets and clusters, accounting for 38.5% of the total events. According to the statistical results of the distance between doublets before and after repeating events relocation, it is estimated that the system location error in the research area is about 5—10 km. In addition, combined with the latest source classification results in this area, the results show that repeating earthquakes of different source types have different spatial and temporal distribution characteristics. Repeating quarry blasts appear mostly as clusters, 93.6% of them occur during the daytime, and they also exhibit a seasonal pattern with more events in summers and fewer ones in winters. Tectonic earthquakes occurred in various thrust faults in the Tianshan orogenic belt, and occurred randomly at any time of the day, and the monthly frequency of tectonic events is relatively stable during the studied period. Repeating induced earthquake locations indicate that most of them are located near large gas/oil fields and water reservoirs, but some also geographically overlay tectonic earthquakes in some regions. The occurring time characteristics of induced earthquakes are similar to those of tectonic earthquakes, which appears as random distribution within 24 hours.
Ambient noise level of Sichuan region from seismic stations
Xie Jiangtao, Lin Liping, Zhao Min, Chen Liang
 doi: 10.11939/jass.20200148
[Abstract](121) [FullText HTML](33) [PDF 0KB](23)
Based on the three-component continuous waveform data observed by sixty permanent seismic stations in Sichuan seismic network recorded from January 1, 2015 to December 31, 2018, this paper calculated the noise power spectral densities and corresponding probability density functions, and then gave the statistical characteristics of noise power spectral density at different frequencies and the variations of the noise level at different regions and frequencies. The results show that the high-frequency seismic noises of most stations are affected by the human activities, production mode and lifestyle nearby, which has obvious seasonal and diurnal variations. The noise level increases during summer and decreases during winter, with the lowest level during the Spring Festival in the whole year; and the geographical spatial distribution is not obvious. At double-frequency microseisms, the noise level increases during winter and decreases during summer, and has obvious seasonal variation, with an average of 1−5 dB, which has obvious geographical spatial distribution characteristics. The average noise level in eastern Sichuan is the highest, followed by Panxi region, and the lowest in western Sichuan Plateau. The microseism peaks have different amplitudes and occur at different frequencies in summer and winter, with the peaks shifted by 1−2 s toward longer periods in the winter. Compared with the double-frequency microseism band, at primary microseism band the noise energy is weaker, the seasonal variation is not obvious, and the difference of noise level in geographical distribution is significantly reduced. While the long-period (>20 s) noise level has no obvious seasonal variation and no difference in geographical spatial distribution. In addition, installing seismographs in caves and borehole can effectively reduce the influence of noise sources, temperature and pressure on high-frequency band and long-period observations, and the noise level is lower than that of shallow installations.
Construction and verification of onsite ground motion prediction models for seismic intensity instrument
Peng Chaoyong, Zheng Yu, Xu Zhiqiang, Jiang Xudong, Yang Jiansi
 doi: 10.11939/jass.20210075
[Abstract](257) [FullText HTML](125) [PDF 2128KB](100)
Using the initial P-wave early warning parameters to construct onsite ground motion prediction models, so as to quickly release an alarm message when it reaches the predefined threshold, is a key issue of the onsite earthquake early warning system, which is directly related to the accuracy and timeliness of the early warning information. For Miscro-electro-mechanical-systems-based seismic intensity instrument with poor data quality, the obtained displacement record after two integrations has a large deviation, which will lead to more false and missed alarms. Therefore, for waveforms recorded by seismic intensity instrument, in this paper, we adopted Butterworth filters of different orders (1−4) to build several onsite ground motion prediction models based on the P-wave 3 seconds data and the whole P-wave window. These models are relationships between displacement amplitude PD and peak ground velocity PGV, PD and peak ground acceleration PGA, velocity amplitude PV and PGV, PV and PGA, acceleration amplitude PA and PGV, PA and PGA, respectively. The models are then verified using the collected Miscro-electro-mechanical-systems-based seismic event records from the Sichuan-Yunnan Demonstration Early Warning Network. The results show that for the seismic intensity instrument records, the two optimal onsite ground motion prediction models are the relationship between PV and PGV and the one between PA and PGA obtained by the first-order Butterworth filter processing and derived from the whole P-wave window. In specific applications, two or more statistical relationships should be simultaneously adopted to predict onsite ground motion, and observed ground motion values should be used as additional judgment conditions to reduce the probability of false and missed alarms.
Problems and suggestions on site classification
Chi Mingjie, Li Xiaojun, Chen Xueliang, Ma Shengjie
 doi: 10.11939/jass.20200152
[Abstract](16) [FullText HTML](11) [PDF 1260KB](5)
The physical meaning of site classification is not clear in the current seismic design code for buildings, at the same time, the boundary of site classification is easy to cause the divergence of design ground motion parameters. For the above problems and deficiencies, some suggestions are given. To solve the problem that the physical meaning of site classification is not clear, on the basis of the current site classification method, according to the site classification index such as the covering layer thickness and the equivalent shear wave velocity, the sites are classified by two-level: the first level classification is consistent with the current one, which classifies sites based on the fundamental period of the site and the thickness of the overburden layer; the second level classification further considers the degree of hardness of the geotechnical medium based on the first level classification, and sub-classification according to equivalent shear wave velocity. Based on the current research on seismic disaster and seismic motion characteristics of thick soft site, combined with the development of long-period constructions, the site classification is expanded from the original four categories to five categories, at the same time, the boundary of each classification, especially the boundary of class II, III and IV sites, is limited from the original open type, which can effectively avoid the problem of divergence of design ground motion parameters caused by site classification. The related research results can provide reference for site classification and determination of design ground motion parameters.
The dynamic mechanical response of the fault under different water injection schedules
Zhu Aiyu, Sun Zihan, Jiang Changshen, Chen Shi, Zhang Dongning, Cui Guanglei
 doi: 10.11939/jass.20210137
[Abstract](132) [FullText HTML](13) [PDF 1894KB](6)
Water injection used in industry can lead to the activation of existing faults and have induced many destructive earthquakes. Therefore, it is of great significance to study the dynamic response of faults under water injection to explore the mechanism of induced earthquakes. The poroelastic spring-slider model calculates the fault stability under three kinds of classical water injection schedules (ascending, rapidly ascending, descending and intermittent) using poroelastic coupling numerical simulation. The results show that, with the continuous injection of fluid, the pore pressure inside the fault will go through three stages: slow rise, rapid rise, and stable rise. For different water injection schedules, the three stages are not fully reflected, and the forms are different; under the same water injection schedule, the smaller the reservoir permeability is, the greater the pore pressure near the wellhead is, the smaller the pore pressure at fault is, and the greater the difference of pore pressure between the two is; the larger the value is, the easier the earthquake will be induced. The value is negatively correlated with the fluid pressure of injected reservoir fluid but positively correlated with the change rate of fluid pressure; the critical stiffness increases rapidly in the early stage due to the increase of the change rate of pore pressure and decreases in the later stage due to the influence of pore pressure. The rapid rising and falling water injection schedule greatly increase the possibility of inducing earthquake in the early stage of water injection. The intermittent water injection schedule causes a large change of necessary stiffness in the late stage of water injection, which increases the possibility of inducing an earthquake. This study can provide the quantitative scientific basis for the risk assessment of water injection-induced earthquakes and reduce the possibility of water injection-induced earthquakes.
The development in seismic application research for VLF/LF radio waves
Zhang Xuemin
 doi: 10.11939/jass.20210143
[Abstract](46) [FullText HTML](22) [PDF 0KB](15)
Radio waves from very low frequency and low frequency (VLF/LF) transmitters, as an active signal for communication and navigation purpose, show great advantages in ionospheric monitoring and application research with their long-distance propagation feature in the waveguide between surface and lower ionosphere. This paper summarized the developments in detecting technology of VLF/LF radio waves, their data analysis methods, case study and statistical research, coupling processes and channels in lithosphere-atmosphere-ionosphere. On the basis of the significant achievements of this technology in earthquake application, and the research in the origin of big disturbances in VLF/LF observations, the future development plan has been considered to build up a stereo-monitoring system in China by combining our long-history ground-based network and new satellite platform in electromagnetic field, to fully use of this technology to give the biggest contribution in earthquake research.
Relocation of earthquakes in Tangshan area in last decade
Guo Lei, Sun Lina, Zhou Yi, Wang Ning
 doi: 10.11939/jass.20210029
[Abstract](130) [FullText HTML](15) [PDF 0KB](17)
We relocated 4 874 earthquakes totally which were recorded by the Hebei Seismic Network and occurred in Tangshan area during the period between January 2010 and July 2020 by using the double-difference location method, the double-difference relocation method combined with waveform cross-correlation, and the double-difference tomography method combined with the waveform cross-correlation respectively. The relocation comparison of three methods suggests that the double-difference tomography method combined with the waveform cross-correlation could produce much higher resolution hypocentral parameters than those from the other two methods. As a result, the root mean square (RMS) residuals of the earthquake hypocenters were greatly reduced from 0.71 s to 0.27 s. In map view the relocated earthquakes are more concentrated on obvious strips around the faults, and the dominant distribution direction is NE, which is basically consistent with the fault trend in this area. The result is more reasonable in depth distribution with focal depth mainly concentrated in 5−15 km, and the distribution pattern appears as a nearly normal distribution. There is a new earthquake belt with steep dip angle in NNE direction on the east of the Tangshan−Guye fault through the spatial-temporal analysis of the plenty of consecutive small earthquakes. The analysis shows that the stress level is high and the tectonic activity is strong in this local area. Therefore it is speculated that there may be a hidden fault at the eastern end of the Tangshan-Guye fault, and the occurrence of earthquake in this region is related to its deep activities.
Anomalous characteristics of geomagnetic vertical strength polarization before the Milin MS6.9 earthquake in 2017
Li Xia, Feng Lili, Zhao Yuhong, Liu Lei, Gou Zhidong, Fan Wenjie, He Manqiu, Liao Xiaofeng, Aisa Yisimayili  
 doi: 10.11939/jass.20200196
[Abstract](275) [FullText HTML](128) [PDF 4945KB](21)
Based on the data of 65 geomagnetic observation stations in mainland China, the magnetic anomaly signals in the seismic source area are extracted by the method of geomagnetic vertical intensity polarization and the anomalous space-time scanning results are analyzed. The analysis shows that there was a large scale synchronous geomagnetic anomaly before the MS6.9 earthquake in Milin, Tibet. Since October 30, 2017, the calculation results showed a high value pattern of single peak or double peak, which lasted for 3 days. It reappeared two days later and lasted for four days, the abnormal area shows an evolutionary process of enlargement-shrinkage- disappearance -enlargement-disappearance. The high value abnormal repetition area is located in western China, mainly at the junction of the Bayan Hala block and the Qiangtang block on the Qinghai-Tibet Plateau. The abnormal process lasted for 9 days, 19 days after which a MS6.9 earthquake occurred in Milin, Tibet, with the epicenter located 5km from the threshold line of October 31, 2017.Comprehensive analysis shows that the abnormal high value of geomagnetic vertical intensity polarization has nothing to do with the external field, but reflects the underground electromagnetic signal, and this method has a certain indication significance for the moderate earthquakes in mainland China.
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Three-dimensional seismic velocity structure beneath the M6.4 Yangbi,Yunnan earthquake region
Du Guangbao, Wu Qingju, Zhang Xuemei
2021, 43(4): 397-409.   doi: 10.11939/jass.20210104
[Abstract](466) [FullText HTML](185) [PDF 44515KB](148)
This paper collected the seismic travel-time data both from temporary stations employed after Yangbi M6.4 earthquake and the seismic networks in Yangbi region and its vicinity from January of 2015 to 28 May, 2021 and performed the high-resolution inversion for three-dimensional velocity structure and accurate hypocentral locations by using double-difference seismic tomography method. The relocation results show that the sequence spread in the NW−SE direction along the Weixi-Qiaohou-Weishan fault. The focal depth in the area is generally in the range of 2−5 km with high dip angle of 80°. The three-dimensional velocity structure shows that the spatial distribution characteristics of the Yangbi M6.4 earthquake sequence are closely related to the velocity structure. The epicenter of the Yangbi M6.4 main shock was located near the P- and S-wave high-to-low-velocity anomaly transitional zones, which are favorable for occurrence of moderate-strong earthquakes, and the aftershocks are mainly distributed in the brittle region with low vP, high vS and low vP/vS. In addition, along the strike of Yangbi earthquake sequence, there are totally different velocity structures on both sides of main earthquake, and significant higher vP and lower vS anomalies are observed in the northwest of the Yangbi M6.4 main shock compared with the southeast part, which may obstruct the northwestward slipping of the seismogenic fault of Yangbi M6.4 earthquake, leading to the striking unilateral source rupture.
Study on Lg wave attenuation imaging in Yunnan
Liu Sen, Bian Yinju, Wang Tingting, Lu Zhinan
2021, 43(4): 410-426.   doi: 10.11939/jass.20200101
[Abstract](170) [FullText HTML](92) [PDF 4428KB](24)
In this paper, 470 broadband seismic records of natural earthquakes with M≥4.0 between May 2014 and May 2019 recorded by 121 fixed stations in and around Yunnan Province are collected. 6 976 high-quality vertical wave data is processed by using the reverse two-station method. The attenuation imaging of Lg wave at 1 Hz with spatial resolution less than 100 km in Yunnan area is inverted. The inversion results show that the Q0 value of Lg wave in Yunnan is in 60 to 300 range, and the whole is in low Q0 background, with significant changes in lateral heterogeneity. The distribution characteristics of low Q0 value in Yunnan area reflect the strong attenuation of Lg wave in Yunnan area. The Q0 value in the west side of Honghe fault is relatively low, in 50 to 160 range, and in the east side is relatively high, in 120 to 200 range. The distribution characteristics are consistent with the distribution of sedimentary layer thickness. Loose sedimentary layer may be the main cause of high attenuation in the east side. The Q0 value of Lg wave in Yunnan area shows a similar differential distribution with the distribution of surface heat flow, which may be related to frequent earthquakes, long-term strong tectonic movement and deep material upwelling with volcanic activity.
Research on seismic characteristics and identification of artificial explosion in different areas and natural earthquake
Wang Tingting, Bian Yinju, Yang Qianli, Ren Mengyi
2021, 43(4): 427-440.   doi: 10.11939/jass.20210169
[Abstract](343) [FullText HTML](196) [PDF 3538KB](63)
The differences of the seismic characteristics and frequency of the Huailai explosions, the Sanhe quarry explosions and the natural earthquakes with low magnitude are discussed. The results show that the two different area explosions have obviously different seismic characteristics and frequency distribution, Huailai explosion has stronger P wave energy than S wave and fast attenuation; The main frequencies of P wave and S wave in Sanhe quarry explosion are lower than that in Huailai explosion, S wave and surface wave are confused, and the low frequency developed obviously at different distances; While for natural earthquakes, the effective frequency band is wider and the frequency components are more complex than explosions. Pg/Sg spectral ratios in small-magnitude earthquakes and explosions were studied and cross-band spectral ratios were explored. Results obtained show that the high frequency (>5 Hz)Pg/Sg spectral ratio discriminants can completely distinguish explosions from low magnitude earthquakes; The spectral ratios of the cross-band related to low frequency (0−2 Hz) of Sg can effectively identify explosions in these two areas, Pg/Sg discriminants of the crossed frequency band can better reflect the difference characteristics of different types of events than that of the traditional single frequency band.
Gravity field characteristics and seismogenic model in North China
Xu Weimin, Shi Lei, Chen Shi, Lu Hongyan
2021, 43(4): 441-452.   doi: 10.11939/jass.20200150
[Abstract](130) [FullText HTML](84) [PDF 9244KB](33)
In this paper, we use a Bayesian principle-based gravity leveling method to uniformly process 16 periods of land-based mobile gravity observations from 2009-2017 in North China, and study the dynamic characteristics of the regional gravity field in conjunction with four earthquakes (M≥4.5) that have struck the studied area since 2009. Further, we study the characteristics of the isostatic gravity anomaly in North China, and analyze the relationship between regional gravity field changes and deep density structure based on the Bouguer gravity anomaly, sedimentary sequences gravity anomaly and Moho gravity anomaly in the studied area to characterize the three-dimensional density structure in North China. The results show that, the four earthquakes (M≥4.5) in the studied area in recent years have been located near the contours of the regional differential gravity field and the zero-value of the cumulative gravity field, the abnormally shifting gradient zones and the bends of the gradient zones, the unbalanced zones in the deep structure where the theoretical equilibrium thickness differs from theactual crustal thickness, and the high and low densities of the three-dimensional density structure inside the transition zone.
Characteristic analysis of the lithospheric magnetic anomaly before the Madoi MS7.4 earthquake on 22th May 2021
Dong Chao, Chen Bin, Yuan Jiehao, Wang Zhendong, Wang Can
2021, 43(4): 453-462.   doi: 10.11939/jass.20210115
[Abstract](361) [FullText HTML](149) [PDF 2006KB](53)
This paper analyzes and studies the magnetic anomaly characteristics of each component of the lithospheric magnetic field in the view of pre-earthquake changes of the lithospheric magnetic field near the epicenter of the Madoi MS7.4 earthquake using geomagnetic field vector data of the mainland of China in 2020 and 2019. The results show that before the Madoi MS7.4 earthquake, the lithospheric magnetic field components near the epicenter all changed to varying degrees. The Madoi MS7.4 earthquake epicenter is located at the weakly magnetic anomaly region, and near the zero-variation line of all the components. The Madoi MS7.4 earthquake epicenter is located between the high gradient belt and the low gradient belt of all the components. This paper confirms that the lithospheric magnetic anomaly will be changed before the earthquake, and summarizes characteristics of geomagnetic components magnetic anomaly, and provides a case for the future study of the seismo-magnetism, especially the earthquakes that magnitude larger than 7.0.
Classification of seismic events based on short-time Fourier transform and convolutional neural network
Zhang Fan, Yang Xiaozhong, Wu Lifei, Han Xiaoming, Wang Shubo
2021, 43(4): 463-473.   doi: 10.11939/jass.20200128
[Abstract](171) [FullText HTML](90) [PDF 7570KB](39)
With the increase of seismic observation data, the application of automatic processing technology in earthquake event classification, a basic work of seismic monitoring, is becoming more and more important. In this paper, 417 explosion events and 519 natural earthquake events are selected from the rich natural and non-natural seismic observation data of the Inner Mongolia Regional Seismological Network as the original data for the study. After preprocessing, such as interception and filtering, the original data is transformed into log amplitude spectrum in time-frequency domain by short-time Fourier transform, and convolution neural network with three convolution layers is used as classifier to distinguish earthquakes from explosion events. Five folds cross validation results show that the average accuracy of the algorithm used in this paper is 97.33%, and the accuracy of the test set is 98.03%. Our model has applied more original information in the classification of natural earthquake and explosion events, therefore can get a higher accuracy and better stability.
Random noise suppression of seismic data based on deep convolution neural network
Chen Tian, Yi Yuanyuan
2021, 43(4): 474-482.   doi: 10.11939/jass.20200135
[Abstract](155) [FullText HTML](83) [PDF 2557KB](24)
Random noise suppression of seismic data is essential in seismic data processing. Since the seismic data recorded by the geophone is usually noisy, this kind of noisy data can be regarded as a manifestation of low signal-to-noise ratio. Low SNR data will affect subsequent processing of seismic data, such as migration and imaging. In this paper, we aim to improve the imaging quality of seismic data and propose an intelligent noise reduction framework for convolutional neural network to adaptively learn seismic signals from noisy seismic data. In order to speed up network training and avoid gradient disappearance during training, we add residual learning and batch normalization methods to the network, and use ReLU activation function and Adam optimization algorithm to optimize the network. In addition, the two datasets, Marmousi and F3, are used to train and test the network. A fully trained network can not only retain weak features in learning, but also remove random noise. First, fully train the network, extract random noise from it, and retain the learned seismic data features, and then estimate the waveform features in the test set by reconstructing the seismic data. The processing results of synthetic records and field data show the potential of deep convolutional neural network in random noise suppression tasks, and experimental verification shows that the deep convolutional neural network framework has a good denoising effect.
Empirical relationship of stochastic uncertainty of source parameters in relative local area
Li Zongchao, Gao Mengtan, Sun Jize, Chen Xueliang, Zhang Bo
2021, 43(4): 483-497.   doi: 10.11939/jass.20200153
[Abstract](265) [FullText HTML](95) [PDF 7203KB](43)
In the numerical simulation of strong ground motion of future destructive earthquakes, the accuracy of source parameters selection has a great impact on the results of ground motion prediction. There are many uncertain factors in determining source parameters, including both random and cognitive uncertainties. Based on a large number of seismic events and literature researches, this paper focuses on statistical analysis of source parameters with random uncertainty characteristics by using statistical methods. Through regression analysis, a mathematical model is established to explain the randomness and uncertainty of source parameters in the form of empirical formula. In order to study the scaling relation characteristics of source parameters in local regions, we get more empirical relations which are more suitable for local seismic densely regions, especially those of the local regions including the Chinese mainland. This paper more than 1 700 seismic events with MW≥5.5 are selected from the global CMT catalogue. The empirical relationship of source parameters in earthquake intensive areas is studied by using statistical methods, including focal depth, magnitude, seismic moment, rupture area, etc. The number of seismic samples of asperity in a relatively large local range is increased, so as to obtain more suitable experience for local areas to calculate source parameters from the perspective of statistics relationship. The statistical results show that there are differences between the empirical relationship of source parameters obtained from local earthquake cases and those obtained from unlimited regional cases, especially when it comes to fault rupture area and asperity related parameters. The empirical relationship of source parameters obtained from local earthquake cases is more representative. When using the empirical formula obtained in this paper to calculate the focal parameters required for the strong ground motion of future destructive earthquakes, the ground motion prediction results will better reflect the real ground motion characteristics of the target area. It could improve the reliability of the ground motion prediction results.
Regularity research on the seismic response of characteristic parameters for ground motion peak to soil slope
Du Lurong, Zhang Jiangwei, Chi Mingjie, Chen Su
2021, 43(4): 498-507.   doi: 10.11939/jass.20200149
[Abstract](180) [FullText HTML](74) [PDF 2379KB](25)
We randomly selects 100 ground motion records with different ground motion peak characteristic parameters, and obtains the peak ground acceleration (PGA), peak ground velocity (PGV) and peak ground displacement (PGD) of each ground motion through baseline correction and integration. Based on finite element numerical simulation, the seismic response law of soil slopes is studied by comparing the characteristics of different peak characteristic parameters of the same observation point with the characteristics of the same peak characteristic parameters of different observation points, and the analysis of the characteristics of seismic peak characteristic parameters and the seismic response of soil slope correlation. The calculation results show that PGA, PGV and PGD have a good positive correlation with the seismic response of the soil slope, and the average correlation coefficients are 0.868, 0.981, 0.926, respectively. The correlation of PGV is better than that of PGA and PGD, while the correlation of PGD is slightly better than PGA. Therefore, it is recommended to use PGV as a parameter index in the evaluation of soil slope stability.
Research on application of focal mechanism and site conditions in judgment of Hebei earthquake influence field
Sun Lina, Qi Yuyan, Chen Ting, Wang Xiaoshan
2021, 43(4): 508-520.   doi: 10.11939/jass.20200133
[Abstract](147) [FullText HTML](96) [PDF 2673KB](24)
The determination of seismic influence field in post-earthquake work, a quickly gived reasonable map of seismic intensity distribution, was an important basis for emergency rescue after the earthquake and was important for the government to understand the disaster situation, deploy work and estimate the disaster loss. In this paper, the isoseismal maps of moderate strong earthquakes in Hebei Province were collected and sorted out, it was compared with the theoretical isotherm map generated by the regional earthquake intensity attenuation relationship based on the focal mechanism solution. The results show that, with the increase of magnitude, the similarity was higher between the theoretical isoseismal map and the actual isoseismal map in the high intensity area (≥Ⅶ), the theoretical isoseismal map was calculated by the attenuation relationship of seismic intensity with focal mechanism solution. In addition, according to the spatial variation of aftershock frequency within 24 hours after the earthquake, the theoretical isoseismal line in the polar region is modified, which is more consistent with the actual isoseismal line. That is to say, the theoretical calculated intensity is closer to the actual investigation intensity value. Finally, the grid of Hebei area was divided, and the bedrock PGA of the earthquake case on each grid center point was calculated according to the attenuation relationship of ground motion. Then, the site category attributes were extracted, considered site amplification factor, and the conversion of bedrock PGA to surface PGA was completed. The surface PGA was converted into intensity and compared with the actual earthquake isoseismal map. The results show that the similarity between the seismic influence field calculated by considering the site amplification effect and the actual isoseismal line was very high in the high intensity area, and the similarity is higher than the intensity attenuation relation method based on the focal mechanism solution.
Comparative analysis and transformation relations between China and the US site classification systems in building seismic code provisions
Zhou Jian, Li Xiaojun, Li Yaqi, Kang Chuanchuan
2021, 43(4): 521-532.   doi: 10.11939/jass.20200164
[Abstract](97) [FullText HTML](63) [PDF 2314KB](31)
In this study, based on 6 824 borehole profiles, we subdivide the site classes in GB 50011-2010 Code for Seismic Design of Buildings (Chinese code) into more homogeneous sub-classes by different values of the equivalent shear wave velocity (vSe) and site overlaying layers (D), and quantitatively analysis the effect of each parameters in the site classification schedule in the code. We build the relation between these sub-classes of the China code and classes of the US seismic design code National Earthquake Hazards Reduction Program Recommended Provisions for Seismic Regulations for New Buildings and Other Structures, carry out comparative analysis on two classification schedules, and build the probabilistic transformation relations for interconverting China site classes and the US site classes. The results show that: It is not appropriate to take the average shear wave velocity to a depth of 20 m (vS20) as the proxy for vSe in site classification of China code; for China site class Ⅱ and Ⅲ, different sub-classes have significantly different corresponding relations with the US site classes; the D effectively distinguishes the sites those velocity structures are similar at shallow layers while different at deeper layers; the main part of China site class Ⅱ and Ⅲ are both corresponding to the US site class D, the China site class Ⅱ leans to the US site class C, while the China site class Ⅲ leans to the US site class E; China site class Ⅳ is corresponding to the US site class E; most of the US site class C and D are both corresponding to China site class Ⅱ.It implies that the range of China site class Ⅱ is relatively vast.