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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Empirical relationship of stochastic uncertainty of source parameters in relative local area
Li Zongchao, Gao Mengtan, Sun Jize, Chen Xueliang, Zhang Bo
 doi: 10.11939/jass20200153
[Abstract](116) [FullText HTML](59) [PDF 7821KB](16)
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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 characteristic of the target area.
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
 doi: 10.11939/jass.20210115
[Abstract](130) [FullText HTML](92) [PDF 1541KB](20)
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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 bigger than 7.0.
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](72) [FullText HTML](24) [PDF 1707KB](39)
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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 MEMS-based seismic intensity instrument (SII) 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 SII, 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 Pd and PGV, Pd and peak ground motion acceleration (PGA), velocity amplitude (Pv) and PGV, Pv and PGA, acceleration amplitude (Pa) and PGV, Pa and PGA, respectively. The models is then verified using the collected MEMS-based seismic event records from the Sichuan-Yunnan Demonstration Early Warning Network. The results show that for the SII 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.
Three-dimensional seismic velocity structure beneath the M6.4 Yangbi,Yunnan earthquake region and its adjacent areas
Du Guangbao, Wu Qingju, Zhang Xuemei
 doi: 10.11939/jass.20210104
[Abstract](178) [FullText HTML](82) [PDF 2245KB](42)
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This paper collected the seismic travel-time data both from temporary stations employed after Yangbi M6.4 earthquake and the seismic networks from January 2015 to May 28, 2021 and perform 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 high-to-low-velocity anomaly transitional zones, which are favorable for moderate-strong earthquakes, and the aftershocks are mainly distributed in the brittle region with low vP, high vS and low vP/vS. In addition, significant higher vP and lower vS anomalies are observed in the northwest of the Yangbi M6.4 earthquake compared with the southeast part, which may obstruct the northwestward slip of the seismogenic fault of Yangbi M6.4 earthquake, leading to the striking unilateral source rupture.
Gravity field characteristics and seismogenic model in North China
Xu Weimin, Shi Lei, Chen Shi, Lu Hongyan
 doi: 10.11939/jass20200150
[Abstract](18) [FullText HTML](7) [PDF 0KB](2)
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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 4 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 4 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 the actual crustal thickness, and the high and low densities of the three-dimensional density structure inside the transition zone.
Study on Lg wave attenuation imaging in Yunnan
Liu Sen, Bian Yinju, Wang Tingting, Lu Zhinan
 doi: 10.11939/jass20200101
[Abstract](71) [FullText HTML](36) [PDF 4219KB](11)
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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.
Classification of seismic events based on short-time Fourier transform and convolutional neural network
Zhang Fan, Yang Xiaozhong, Wu Lifei, Han Xiaoming, Wang Shubo
 doi: 10.11939/jass.20200128
[Abstract](71) [FullText HTML](29) [PDF 7133KB](7)
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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.
Regularity research on the response of characteristic parameters for ground motion peak to soil slope seismic
Du Lurong, Zhang Jiangwei, Chi Mingjie, Chen Su
 doi: 10.11939/jass20200149
[Abstract](81) [FullText HTML](36) [PDF 2015KB](8)
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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.
Random noise suppression of seismic data based on deep convolution neural network
Chen Tian, Yi Yuanyuan
 doi: 10.11939/jass20200135
[Abstract](82) [FullText HTML](40) [PDF 2034KB](7)
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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.
Research on application of focal mechanism and site conditions in judgment of Hebei earthquake influence field
Sun Lina, Qi Yuyan, Chen Ting, Wang Xiaoshan
 doi: 10.11939/jiass20200133
[Abstract](80) [FullText HTML](43) [PDF 2358KB](9)
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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: 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
 doi: 10.11939/jass.20200164
[Abstract](20) [FullText HTML](8) [PDF 1806KB](4)
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In this study, based on 6 824 borehole profiles, we subdivide the site classes in Chinese building seismic design code provisions 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.
Research on seismic characteristics and identification of artificial explosion in different areas and natural earthquake
Wang Tingting, Bian Yinju, Yang Qianli, Ren Mengyi
 doi: 10.11939/jass.20210169
[Abstract](182) [FullText HTML](103) [PDF 3085KB](30)
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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 result showed 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 frequency of P wave and S wave in Sanhe explosion is 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 discriminants can completely distinguish explosions from earthquakes; The spectral ratios of the cross-band related to low frequency (0−2 Hz) of Sg can effectively identify explosions in these two different areas, Pg/Sg discriminants of the crossed frequency band can better reflect the difference characteristics of different types of events than the traditional single frequency band.
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](196) [FullText HTML](95) [PDF 4945KB](15)
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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.
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](232) [FullText HTML](118) [PDF 3414KB](31)
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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 inversion. 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 1000 m/s to 2100 m/s, and it is characterized by good continuity, strong reflection. The Cenozoic basin is thick in the south and thin in the north. The sedimentary and structure are controlled by Yanyuan fault. The middle layer is medium-low velocity ranging from 3500 m/s to 4500 m/s, it is characterized by that the reflection axis is discontinuous and the reflection is weak, 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. 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. One of the faults is Jinhe-Qinghe fault, which is the boundary fault between Yanyuan basin and Kangdian block. In addition, these faults are also an earthquake-prone area in Yanyuan basin.
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A preliminary study on the characteristics and mechanism of the May 2021 MS6.4 Yangbi earthquake sequence,Yunnan,China
Lei Xinglin, Wang Zhiwei, Ma Shengli, He Changrong
2021, 43(3): 261-286.   doi: 10.11939/jass.20210100
[Abstract](589) [FullText HTML](301) [PDF 5101KB](120)
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The MS6.4 (MW6.1) earthquake occurred on May 21, 2021 in Yangbi county, Yunnan, China is the main shock of a typical foreshock-mainshock-aftershock sequence. This research carried out a preliminary study focusing on tectonic background, double-difference hypocenter location, moment tensor and rupture directivity of major earthquakes, stress field and fault slip-tendency, as well as tidal effect. According to the results of moment tensor inversion and rupture directivity of the main shock and the distribution of aftershocks, it is determined that the source faults of the main shock has strike 137°, dip 75°, rake −167°. The centroid depth of the main shock is 6.0 km, and the fault ruptured unilaterally toward the south-east direction, showing pure double-couple mechanism with dominant right-lateral strike-slip and minor normal components. Relocated hypocenters show that the Yangbi earthquake sequence is located near, but significantly departs from the well-known Qiaohou-Weishan fault in the northern segment of the Honghe fault zone, demonstrating an unmapped NW-trending strike-slip fault (we named “Yangbi fault” in this paper) with some small scale conjugate faults of NE-trending. The hypocenters are distributed along the NW-trending major fault, but also exhibit clusters along the NE-trending faults. The strongest foreshocks and most of the major aftershocks were caused by rupture of NE-trending source faults. All major earthquakes show a unilateral rupture directivity. We have obtained reliable mechanism solutions of more than 20 events with MW>3.4 in the focused area (within 15 km of the center of the Yangbi earthquake sequence), which enabled us to be able to invert the mean stress field in the area. The principal stress shape ratio φ=(σ2σ3)/(σ1σ3) is 0.46±0.17; the (azimuth, plunge) of the maximum, intermediate, and minimum principal stress axes are (188.0°±9.0°, 12.4°±7.0°), (50°±45°, 72.1°±11.3°), and (280.3°±7.0°, 10.4°±12.0°), respectively. Through theoretical tidal strain and stress analysis, it is found that this seismic sequence is significantly affected by tidal modulation. The first major earthquakes of the foreshock clusters that began at 18:00−20:00 on May 18 and 19 and the main shock occurred near the peaks of tidal volumetric strain and Coulomb failure stress. Based on the focal mechanism solutions of the main earthquakes, the distributions of foreshocks and aftershocks, the facts of tidal modulation, the rupture directivity of major earthquakes, fault slip-tendency analysis, and the results of previous studies on similar seismic activities in northwestern Yunnan, we preliminarily suggest that the Yangbi earthquake sequence is significantly affected by the action of deep fluids. The first foreshock activity climax at 18:00 on 18 May, in a tensile fault step (should be permeable channel) area of the NW-trending fault, likely initiated along NE-trending faults (greater slip-tendency) by deep overpressure fluid, and then migrated to the northwest. The second climax of foreshock activity that began at night on the 19 May was concentrated near the hypocenter of the main shock. The triggering of these foreshocks and the action of deep fluid jointly promoted the activity of the NW-trending fault (smaller slip-tendency), but the main shock was mainly promoted by the action of deep fluid.
Crustal attenuation in the southern Tibetan Plateau by reverse two-station Lg-wave Q value tomography
Lu Zhinan, Bian Yinju, Wang Tingting, Liu Sen
2021, 43(3): 287-302.   doi: 10.11939/jass.20200051
[Abstract](402) [FullText HTML](185) [PDF 3289KB](33)
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Based on the seismic waveform data of 757 earthquakes recorded by 27 broadband stations of Tibet Autonomous Region seismic network from 2017 to 2019, it is for the first time that the reverse two-station method has been applied to 1 Hz Lg-wave Q value tomography study in the southern Tibetan Plateau. In this research, total 1 981 Lg-waves were intercepted from the velocity window of 3.5−2.4 km/s and the Q values of 13 543 paths were calculated. After testing the checkerboard recovery of 1°×1° and 0.5°×0.5° grids respectively, we got the tomography of the Lg-wave Q0 value of the southern Tibetan Plateau with 0.5°×0.5° resolution. The inversion result shows that there exhibits high attenuation and low Q values of Lg-wave in the southern Tibetan Plateau crust, which is highly consistent with the negative anomaly of P-wave velocity, the geothermal distribution and two rift valleys in the east of the Tibet. Therefore it is inferred that there may be widespread molten material in the crust of the southern Tibetan Plateau and two fluid-melting channels. The main channel is located between the Yadong-Gulu rift and the Sangri-Cona rift, and the secondary channel flows out along the Yarlung Zangbo suture zone. By analyzing the differences of molten material distribution on both sides of the Yadong-Gulu rift, it is considered that there are different dynamical evolution models in the front-end of collision between Indian Plate and Eurasian Plate, the dynamical evolution to the west of Yadong-Gulu rift is in accordance with the theory of shortening and thickening, and that to the east of Yadong-Gulu rift is consistent with the “pump” mode.
Variation characteristic of S-wave splitting on the 2019 Changning MS6.0 earthquake sequence,Sichuan
Huang Chunmei, Wu Peng, Li Dahu, Wang Yuhang, Lin Xiangdong
2021, 43(3): 303-320.   doi: 10.11939/jass.20200107
[Abstract](365) [FullText HTML](191) [PDF 3608KB](32)
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In this paper, the S-wave splitting parameters of the waveform data recorded at 10 stations in the source area of the 2019 Changning MS6.0 earthquake, Sichuan, from April 25, 2013 to July 31, 2019 were measured by the particle motion discriminant method combined with the polarization analysis method. More than four effective S-wave splitting parameters are obtained at nine stations. The results show that the S-wave splitting parameters at the stations in the studied region are characterized by partition in space and variation over time. The characteristics of fast wave polarization direction in space are as follows: the predominant polarization direction of fast S-wave at three stations in the southeastern source area of the Changning earthquake is in the direction of NE, which is consistent with direction of regional principal compressive stress in the southeastern source area. In the northwestern source area, the predominant polarization directions of fast S-wave, nearly EW, is consistent with the directions of regional principal compressive stress in the northwestern source area. Due to the combining effect of crustal stress and complex fault structure, the three stations CJW, GXA and LQS all have two predominant polarization directions of fast S-wave. The polarization directions of fast S-wave change with time as follows: After the main shock, the polarization directions of fast S-wave at each station gradually tended to be convergence after the dispersion increases; the polarization directions of fast S-waves at the station CJW changed three months before the main shock, indicating that with the accumulation of the stress during the seismogenic process, the anisotropic characteristics at the station CJW are controlled mainly by stress instead of structure. As for the temporal distribution, the average normalized delay time of slow S-wave at each station decreased as the distance increasing from the main shock and aftershock dense area to stations, reflecting the stronger accumulation and releasing of stress during seismogenic process in the aftershock dense area. In addition, the normalized delay time of slow S-wave at the station CNI decreased significantly about six months before the main shock, and increased rapidly after the main shock, suggesting the accumulation of stress before the earthquake and the abrupt release of stress after the earthquake lead to the change in geometry of the micro-cracks in upper crust.
Impact of the tsunami excited by the 2011 MW9.0 Japan earthquake on seismic ambient noises
Chen Fei, Xue Mei
2021, 43(3): 321-337.   doi: 10.11939/jass.20200176
[Abstract](330) [FullText HTML](188) [PDF 3359KB](15)
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The MW9.0 earthquake on March 11, 2011 occurred in the northeastern sea of Japan triggered a catastrophic tsunami, which had significant influences on the seismic ambient noises with ocean-lithosphere coupling. This study uses the continuous data recorded by seismic stations along the coast and inland of North America, combined with the seafloor pressure data recorded by the DART system nearby, as well as the predicted tidal data to analyze the impact of this tsunami on the seismic ambient noises by using time-frequency analysis and polarization analysis methods. The results show that this tsunami had little impact on the high-frequency noise (1.3−1.5 Hz) and short-period double-frequency microseisms (0.18−0.4 Hz), while it significantly enhanced the amplitudes of long-period double-frequency microseisms (0.1−0.15 Hz), single-frequency microseisms (0.05−0.08 Hz), as well as the Earth’s background free oscillations (0.004−0.007 Hz). Moreover, as the frequency of the ambient noise decreases, the amplitude enhancement becomes more pronounced and lasts longer. When the tsunami reaches the shore, it has an impact on the ambient noise of coastal stations nearby for all three frequency-bands of Earth’s background free oscillations, microseisms, and high-frequency noise and becomes the main energy source of seismic ambient noises at all three frequency bands. And the position of the dominant tsunami sources changes with time. All above-mentioned suggests that the influence of tsunami on seismic ambient noise is related to the propagation characteristics of tsunami, that is, due to the influence of water depth, reflections and diffractions of seafloor and inshore topography, the energy accumulation area changes with time, and the energy does not propagate uniformly to the coast, resulting in the changes of dominant polarization direction of seismic ambient noise in different frequency bands with time. By cross-disciplines of seismology and oceanography, this study is of significance for advancing studies on the coupling mechanism of ocean-lithosphere, identifying the characteristics of tsunami waves from the perspective of seismology, as well as exploring new tsunami warning mechanisms.
An automatic S phase picking algorithm for local earthquake events
Zhang Hongcai, Liao Shirong, Chen Zhiyong, Huang Lingzhu
2021, 43(3): 338-349.   doi: 10.11939/jass.20200112
[Abstract](73) [FullText HTML](15) [PDF 5356KB](19)
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Base on eigenvalue decomposition calculation, we discussed an automatic S phase picking algorithm suitable for local earthquake events. The algorithm needs few parameters, less computer resources and is easy to realize. By choosing seven time windows with different time length, it effectively reduce the S phase pick errors that caused by unreasonable time window selection. By taking 9 855 three-component records of Fujian seismic monitoring network, we test the applicability and accuracy of this algorithm. The results show that average S phase picking error by this method is (0.003±1.34) s, 79.6% of them are within 0.5 s, 4.1% of them are greater than 2.0 s, which indicates that the algorithm can meet the demands for daily S phase picking. All above-mentioned suggests that the quality of records is the most important factor that affects the accuracy of picking results, the S phase picking errors for high signal-noise ratio records are usually smaller than those for low signal-noise ratio records, and the accuracy of S phase picking for some low signal-noise ratio records will be improved after a band-pass filter preprocess.
Application of fractal interpolation method to geo-electric field interference data process
Wang Lanwei, Zhang Xingguo, Zhang Yu, Hu Zhe
2021, 43(3): 350-358.   doi: 10.11939/jass.20200137
[Abstract](261) [FullText HTML](121) [PDF 2092KB](15)
Abstract:
Geo-electric field and geo-electrical resistivity observation is one of the most important ways of earthquake monitoring. In recent years, geoelectric field observation has been subjected to more and more interference caused by subways, high-voltage direct current transmission, and electrical facilities, etc. Among all these interferences, there is a special type of known interference in the earthquake geo-electric field observation, which is so-called “interference from current” caused by the electric current in measuring geo-electrical resistivity if the geo-electric field and geo-electrical resistivity were observed at the same site. This kind of interference is characterized by short interference time, fixed interference waveform and fixed appearance time, and it will cause difficulties in identifying normal variation of geo-electric field and analyzing data. This paper deals with approaches of eliminating the interference data by using interpolation method. The fractal interpolation method and traditional Lagrange interpolation method were separately used. On the basis of introducing the principle of the two interpolation method, the processing result of the two methods on simulation data and actual data are compared, it demonstrates that fractal interpolation method has higher accuracy than that of Lagrange interpolation method. Then the fractal interpolation method was used in the actual data processing. The result shows that the method not only retrieves the section information effectively, but also preserves the overall original variation tendency of the observation data.
Spatio-temporal variation characteristic of the ultra-low frequency magnetic field prior to strong earthquakes of western Chinese mainland
Feng Lili, Feng Zhisheng, Fan Wenjie, Guan Yiliang, He Manqiu, Li Xia, He Chang, Liao Xiaofeng, Aisa Yisimayili, Yuan Wenxiu, Li Sha
2021, 43(3): 359-375.   doi: 10.11939/jass.20200093
[Abstract](296) [FullText HTML](179) [PDF 3517KB](21)
Abstract:
Based on the one second sampling data from fluxgate magnetometers in western Chinese mainland from 2015 to 2019, this paper carried out the vertical component polarization analysis of the frequency band between 5 s to 100 s, and then processed the analysis results by some mathematical methods. The results show that the high polarization value has no obvious shape and amplitude change in both meridional and zonal directions, and the high polarization value has nothing to do with geomagnetic field disturbance. On this basis, 18 high-value anomalies were screened out, and their spatial distribution map was obtained by interpolation method. The results show that within half a year after the synchronous appearance of multiple high-value anomalies of the vertical component polarization of geomagnetic field, the high-value region may have a strong earthquake with magnitude over M6.0. After the appearance of high value phenomenon, several high value regions are likely to have strong earthquakes; furthermore the magnitude of subsequent strong earthquake seems to be positively correlated with the area of the high-value zone.
A matching method of ground-motion response spectrum and the peak displacement based on the wavelet function
Wang Shan, Hao Minghui, Zhang Yushan, Zhao Fengxin
2021, 43(3): 376-386.   doi: 10.11939/jass.20200138
[Abstract](71) [FullText HTML](15) [PDF 3762KB](1)
Abstract:
When using numerical methods to synthesize ground motions, in addition to fitting the response spectrum, the fitting of peak displacements and the simulation of the non-stationary characteristics of natural ground motions also have important significance and engineering application prospects. Based on the wavelet function fitting method, this paper proposes a ground motion acceleration time history that can synthesize the target response spectrum and peak displacement at the same time. Numerical calculation examples show that this method has a faster rate of convergence, and can achieve a higher precision fitting of the target response spectrum and target peak displacement through less iterative calculations. Moreover, compared with other existing methods, the ground motion synthesized by this method can retain the non-stationary characteristics of natural ground motion, due to the local characteristics of wavelet function in time domain.
The centroid moment tensor solution of the 2021 MW7.5 Maduo,Qinghai,earthquake
Zhang Zhe, Xu Lisheng
2021, 43(3): 387-391.   doi: 10.11939/jass.20210079
[Abstract](1161) [FullText HTML](580) [PDF 4516KB](150)
Abstract:
The anomaly characteristics of well water temperature in Yushu seismic station before the 2021 Maduo MS7.4 earthquake
Su Weigang, Liu Lei, Yuan Fuquan, Zhao Yuhong, Sun Xihao
2021, 43(3): 392-396.   doi: 10.11939/jass.20210085
[Abstract](352) [FullText HTML](202) [PDF 2726KB](73)
Abstract: