2022 Vol. 44, No. 4

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2022, 44(4)
Joint inversion of the lithospheric structure of the central North China Craton from ambient noise and seismic surface wave
Huang Xiang, Ding Zhifeng, Ning Jieyuan, Xu Xiaoming
2022, 44(4): 539-554. doi: 10.11939/jass.20210042
Based on the observation data of the ChinArray Phase Ⅲ deployed in the central North China Craton, the Rayleigh surface wave dispersion with period range of 6 s to 140 s in the studied area is obtained using cross-correlation of ambient noise and seismic surface wave tomography. The high-resolution 3-D S-wave velocity structure of the lithosphere in the central North China Craton is further obtained with the Monte Carlo nonlinear inversion method. The results exhibit significant lateral differences in the lithospheric structure of different blocks of the North China Craton. The central part of the Ordos basin is characterized by high velocity overall, extending below 200 km, but there is a small range of low-velocity anomalies on the southeast margin. The North China basin in the east is characterized by low-velocity with thin crust and lithospheric thickness. Connected low-velocity zones at the northern and southern ends of the central orogenic belt and below the north-south gravity gradient line are observed, which extends below the North China basin. In the lower crust and uppermost mantle, the low-velocity zone in the Datong volcanic group area gradually shifts westward to the northeast corner of the Ordos basin. While in the upper mantle, the low-velocity anomalies in this area gradually fade off as the depth increased. And the low-velocity zone extended below the North China basin in the southeast. Based on the S-wave velocity model obtained in this study, we believe that the heart of the Ordos basin maintains the cratonic characteristics overall, but there is a local lithospheric modification at the southeast margin; the North China basin has experienced strong lithospheric destruction and thinning and crustal extensional deformation; the lithosphere at the northern and southern ends of the central orogenic belt and the north-south gravity gradient line has undergone partial modification and thinning. The mechanism may be the same and due to the upwelling of hot material in the mantle below the North China basin; the upwelling hot material below the Datong volcanic group intrudes into the lower crust below the northeast corner of the Ordos basin. Then it is blocked by the upper crust when rising in the crust and flows eastward to the bottom of the Datong volcanic group, forming the magmatic activity of the Datong volcanic group. The deep source may be related to the stagnant Pacific slab.
High-resolution crustal structure in the Songliao basin
Kuang Chunli, Zhang Ruiqing, Chen Chengfeng, Liu Jiadong
2022, 44(4): 555-566. doi: 10.11939/jass.20210108
High-resolution shallow crustal structure beneath the Songliao basin of Northeast (NE) China has obvious economic and scientific significance. To constrain the sediment and crustal structure of the Songliao basin, H-β grid search method based on wavefield downward continuation and decomposition is used with teleseismic data recorded from portable broadband seismic arrays in the NE China. The results show that the estimated sediment thickness is 0.2−2.5 km, and becomes thinner from the central depression toward the margin of the basin, with the thinnest sediment in the southwestern region. The crustal thickness varies from 24 km to 34 km, and its lateral variation correlates with the distribution of sedimentary thicknesses to a certain extent. The crustal stretching factor is calculated from the sedimentary and crustal thicknesses, with an average close to the lithospheric stretching estimation from previous receiver function studies. Thus, we infer that the thinning of the crust and lithosphere is dominated by pure shear mode during the extensional process of the Songliao basin. Moreover, the Songliao basin has a high crustal vP/vS ratio, indicating possible magmatic underplating during the lithospheric extension beneath the Songliao basin.
Structure of western Tibet from P wave teleseismic tomography
Fan Jie, Yang Wencai
2022, 44(4): 567-580. doi: 10.11939/jass.20200168
In this paper, the fast marching method (FMM) is used to calculate the theoretical travel time of the teleseismic P wave in our model. We inverted the relative travel-time residuals to obtain the relative velocity distribution of crust and upper mantle in western Tibet by subspace iterative algorithm. The results show that the high-velocity anomalies exhibit in the depth of lower crust of western Tibet, while in the depth of upper mantle, the range of the high-velocity anomaly gradually decreases from west to east. And there is an alternating distribution of high- and low-velocity anomalies in the east of our study area. Therefore it is considered that the Indian Plate subducted nearly horizontally within the Tibetan Plateau, and the subduction range in the west is larger. During the subduction process, the Indian Plate is being torn. Subsequently, the torn Indian Plate sank into the upper mantle, and the tearing gap affected the formation of Cenozoic rifts in western Tibet due to stress release.
Relocation and seismogenic structure analysis of the MS5.5 Ninglang earthquake sequence on January 2,2022
Wang Guangming, Wu Zhonghai, Liu Changwei, Zhang Tianyu, Peng Guanling
2022, 44(4): 581-593. doi: 10.11939/jass.20220017
On January 2, 2022, a MS5.5 earthquake occurred in the Ninglang County, Lijiang City, Yunnan Province. Using the P and S phase arrival data of this MS5.5 earthquake provided by the Seismic Catalogue System, the high-precision relative positions of 694 earthquakes in Ninglang MS5.5 earthquake sequence are obtained by using the double difference relocation algorithm. In general, the relocations reveal a 11 km-long, linear NNE−NS seismicity trend concentrating in the 4—11 km depth range, which is consistent with the NNE nodal plane (191°) of the mainshock focal mechanism solution. The mainshock is located in the southern segment of the earthquake sequence. The earthquake sequence shows two groups of active branches with different tendencies on the depth profiles, in which the east branch is consistent with the dip angle of the nodal plane Ⅱ (81°) of the mainshock focal mechanism solution. In addition, the earthquake may have triggered local fault activity in the adjacent area. According to the comprehensive analysis, the seismogenic structure of the MS5.5 Ninglang earthquake sequence should be a NNE−NS trending left-lateral strike-slip fault, with normal component, and the fault plane dips to the WNW at 81° angle. The properties of the seismogenic fault are not completely consistent with any mapped faults in this area. Although the MS5.5 Ninglang earthquake sequence is located to the north of the MS5.7 Ninglang-Yanyuan earthquake sequence in 2012, they have different seismogenic structures. The result of Coulomb failure stress shows that the MS5.7 Ninglang-Yanyuan earthquake in 2012 promoted the occurrence of the MS5.5 Ninglang earthquake.
Matching location for small events and seismogenic fault of Aohanqi earthquake swarm of Inner Mongolia
Zhang Ke, Zhang Fan, Zhang Hui, Wang Xin, Hao Meixian, Zhai Hao
2022, 44(4): 594-607. doi: 10.11939/jass.20210041
In Aohanqi area of Inner Mongolia, there occurred several clusters of small earthquakes during 2018−2019 and the waveforms of different earthquakes are overlapped with each other, which leads to the incompleteness of earthquake catalog. In order to solve this problem, we adopt the match and locate (M&L) method to identify, detect and locate the missing events in the catalogs, and then the focal mechanism solution of the largest event is analyzed by the CAP (cut and paste) method. The matched and located small earthquakes are used to fit parameters of seismogenic fault plane of the largest earthquake so as to determine the geometry of fault plane and seismogenic structure of Aohanqi earthquake swarm. The results show that by using the M&L method, we identified and located 405 small earthquake events, which are 5.4 times as much as the number of the original detected earthquakes, and the earthquake swarm extended predominately along the direction of NW−SE in the east of the intersection area between Hongshan-Balihan fault and Chifeng-Kaiyuan fault with focal depth mainly concentrating on 8−10 km. Besides, according to the fault fitting result of small earthquakes and the focal mechanism of the largest earthquake, it is concluded that the seismogenic structure of Aohanqi earthquake swarm is a concealed normal fault with sinistral strike-slip characteristics, which has a strike of 157° and a dip of 84°. Combined with the fault properties and activity characteristics of the Hongshan-Balihan fault and the Chifeng-Kaiyuan fault, it is deduced that the seismogenic fault of Aohanqi earthquake swarm may be formed by the interaction of the two deep and large faults in the continuous activities.
Forward modeling method of seismic multiple scattered waves
Zhang Bo, Wu Guochen, Li Qingyang, Yang Lingyun, Shan Junzhen
2022, 44(4): 608-618. doi: 10.11939/jass.20210053
When seismic waves pass through the underground scatterers, multi-order scattered waves will be generated, and the analysis of their seismic response characteristics is beneficial to infer the distribution and properties of the scatterers. Based on the two-dimensional scalar wave motion equation, combined with the seismic scattering theory and the Born approximation theory, the multi-order scattering wave equation is deduced. The numerical simulation of the two-point scatterer model and the complex scatterer model is carried out by using the high-order finite difference method, and the propagation law and wavefield characteristics of the multi-order scattered wave are analyzed. And then the single track records of multi-order scattering and each scattering are extracted and compared with the reference single track records, which verifies the accuracy of the scattering wave equation derived in this paper.
Joint iterative inversion of tectonic stress field and fault identification in Yingjiang area
Feng Bing, Zhu Liangyu, Hui Hang, Wang Wenqing, Chai Xuchao, Ji Dongjiao
2022, 44(4): 619-631. doi: 10.11939/jass.20210027
There has always been a problem in inversion of tectonic stress field by focal mechanism solution, it is impossible to determine which nodel plane is the correct seismogenic fault plane. The joint iterative stress inversion method can effectively avoid the error caused by incorrect fault selection by identifying the fault instability. In this paper, the focal mechanism solutions of five groups of earthquake sequences in Yingjiang and its adjacent areas are collected, and the tectonic stress field in this area is inversed. The results show that, in Yingjiang area, the main compressive stress is NNE, and the main tensile stress is ESE, which is basically consistent with the previous research results. However, the local stress field is not completely consistent. The strike of the principal stress axis along the Sudian fault extends from north to south, and the angle gradually shifts to the north. In the southwest of Yingjiang, the strike of the principal stress tends to the East, which may be related to the transverse extension of the Dayingjiang fault. In addition, the strike, dip angle, slip angle and friction coefficient of the main seismogenic fault nodal planes of the focal mechanism solutions of five groups of earthquake sequences are identified by stress field inversion. This provides a valuable reference for the future seismic and crustal dynamic changes research in this region.
Current state of tectonic stress in northwestern Yunnan and its relationship with earthquakes
Fan Wenjie, Cui Xiaofeng, Zhao Xiaoyan
2022, 44(4): 632-643. doi: 10.11939/jass.20210036
Based on collected the focal mechanism solutions of MS≥3.0 earthquakes from 2000 to 2018 in northwestern Yunnan, we analyze the current state of tectonic stress in northwestern Yunnan by Michael’s linear superposition stress inversion method, and further investigate the spatio-temporal distribution of stress tensor variance and its relationship with seismic activity. The results show that the focal mechanism solutions of earthquakes in northwestern Yunnan are complex in types, mainly strike-slip type (46%), followed by normal-faulting type (27%). Tectonic stress field is overall consistency and partial inhomogeneity. The tectonic stress field shows strike-slip faulting stress regime with NNSwards principal compressive stress and ENEwards principal tensile stress in the studied area. It suggests that the study area is subjected to horizontal compression from NNW direction, which plays a dominant role in the upper crustal movement and fault activities in this area. Regional grid stress inversion shows that the variance is mostly below 0.2 in northwestern Yunnan, which indicates that the stress field is in a uniform state except for some northern regions. According to the variation of variance with time and subsequent earthquakes, moderate to strong earthquakes in the studied area mostly occurred when the stress tensor variance was lower than 0.2. Most earthquakes mainly occurred during the process that the stress tensor variance decreased, that is, when the focal mechanism solutions tend to be consistent. And spatially these earthquakes basically occur in the low value zones of the variance or near the edge of the zones, which provides reference for judging the earthquake location and comprehending the regional stress concentration enhancement process in the future.
Paleoearthquakes and the latest active age of Jinghe segment of Bolokenu-Aqikekuduk fault
Yang Panxin, Hu Weihua, Hu Chaozhong, Sun Xinzhe, Huang Shuaitang, Guo Chunshan, Chen Zhihua, Ren Jinwei
2022, 44(4): 644-655. doi: 10.11939/jass.20210040
Bolokenu-Aqikekuduk fault is located at the northernmost end of the NW-trending dextral strike-slip fault system in the west Tianshan mountain, and is also the longest active fault extending in China. The latest active ages of both faults are determined to be Holocene based on the relation between the optically stimulated luminescence age of sediments and earthquake colluvial wedges. In this paper, two trenches were excavated on the latest surface deformation in the west of Aibi lake and southeast of Jinghe county. According to activity difference, the fault can be divided into the Aibi lake segment and the east Jinghe segment. The results show that the latest active times of the two segments are determined to be Holocene, and the latest earthquake events occurred on 3.7−4.86 ka BP respectively. According to the results of gully dislocation and pluvial fan dating, the activity rate in the east Jinghe segment is more than 4 mm/a. Furthermore, it is deduced that the Aibi Lake segment may be the seismogenic structure of M61/2 Jinghe earthquake in 1765, and its magnitude is likely to be underestimated. According to the rupture length of Aibi lake segment more than 60 km, the magnitude is likely to be more than M7.0.
Earthquake magnitude classification based on deep learning
Liu Tao, Dai Zhijun, Chen Su, Fu Lei
2022, 44(4): 656-664. doi: 10.11939/jass.20210046
In order to explore the magnitude information of the seismic acceleration time history recordings, we train a convolutional neural network to classify the seismic recordings based on the magnitude of the earthquakes. Nearly 120 000 earthquake recordings in K-NET and KiK-net are used as samples, and these acceleration time history recordings are used as inputs for model training after information screening and normalization. Taking the magnitude M5.5 as the classification standard, we train a deep learning model of convolutional neural network to classify large and small earthquakes. The results show that the model has an accuracy rate of 93.6% on the training set and 92.3% on the test set, which has a good classification effect. This suggests there are some fundamental differences between large earthquake recordings and small ones. Thus, earthquake magnitude information may be revealed from acceleration time history recordings of earthquakes.
Effect of soil layer structure with fluvial sedimentary facies on sand liquefaction
Wang Wei, Qi Yakun, Wang Haoyu, Li Jinyu, Zhang Xiaoqing, Shen Chao, Feng Weidong
2022, 44(4): 665-676. doi: 10.11939/jass.20210175
The sand liquefaction potential is evaluated with the in-situ test data of one single borehole in the relative codes, however, the real three-dimensional structure of the engineering site is very complex. It is helpful to increase the accuracy of the sand liquefaction evaluation by studying the effect of the soil layer structure on the liquefaction. By analyzing the distribution of the sites of the sand liquefaction manifestation caused in Songyuan MS5.7 earthquake on the 28 May, 2008 and the 2010−2011 Canterbury earthquake sequence, it is discovered that most of the sites are located on the inside bend of the meandering river. The dualstructure exists in the point bar formed by the lateral erosion of the outside bend and the deposition of the inside bend. The impermeable(including weakly permeable) clay layer is covered on top of the saturated fine sand, which is easy to cause the accumulation of the excess pore pressure. The discontinuous distribution of the impermeable clay layer is obvious in the braided fluvial facies. The simplified model is built for soil layer structures with the different fluvial sedimentary facies. The FLAC3D software is used to study the mechanism of the accumulation and dissipation of the pore pressure, and the seepage flow process. The distribution of sand liquefaction manifestation and the ground surface deformation is highly affected by the the soil layer structure with the fluvial sedimentary facies. It is necessary to consider the influence of the soil layer structure in the sand liquefaction evaluation methods on the basis of engineering geological zoning.
Numerical simulation of earthquake-induced loess landslides based on particle flow method
Jia Weilong, Chang Chaoyu, Li Peiru, Zhang Zhiwei, Xu Jiuhuan, Yang Jiyuan
2022, 44(4): 677-687. doi: 10.11939/jass.20210035
Research on the dynamic stability and sliding process of soil slopes based on particle flow theory is a new hot spot in landslide research in recent years. On the basis of field investigation and indoor experiment, the PFC2D program was used to simulate the instability failure movement process of the Xiamadazi landslide in Baowan village, Xingping township, Xiji county through the process of calibrating soil parameters, model establishment, power input, dynamic monitoring, etc., and the failure movement mechanism of the landslide is obtained. The following conclusions are obtained: ① The instability mechanism of the Xiamadazi landslide is that under the action of the earthquake, the leading edge of the slope is pulled and the trailing edge is pushed, causing the shoulder to be pulled and damaged. The larger velocity and displacement at the shoulder position after the instability is the main reason for the strong destructive force and the large disaster range of the earthquake landslide; ② The back wall of the earthquake-induced loess landslides is relatively flat, which is one of the important characteristics different from gravity landslides; ③ The relative altitude difference and length before and after the landslide obtained by particle flow simulation is more consistent with the actual situation. Therefore, the particle flow method can be used to predict the slip distance of earthquake landslides.
Uncertainties in probabilistic tsunami hazard assessment
Liu Ye, Ren Yefei, Wen Ruizhi, Wang Hongwei
2022, 44(4): 688-699. doi: 10.11939/jass.20210044
Regarding the extensive uncertainties result from in the probabilistic tsunami hazard analysis (PTHA), this study summarized the sources of these uncertainties and classified their categories. The methodologies based on logic-tree and event-tree approaches were proposed to quantify uncertainties in PTHA. And then, taking the potential tsunami source (PTS) of Manila trench as an example, both methodologies were performed to illustrate their effectiveness on quantifing the uncertainties derived from the magnitude upper-limit and rupture plane parameters. Some conclusions were drawn as follows: The variability of magnitude upper-limits of PTS affects remarkably the result of PTHA, suggesting a particular consideration that could be quantified effectively using the logic-tree approach. The dip, rake and rupture areas of PTS affect moderately the result of PTHA. The guarantee rate of tsunami hazard given by PTHA will be considerably higher than 20% and slightly lower than 80% when the uncertainties are quantified by an event-tree approach, meeting the requirements of tsunami-resilient structural design.
Research on the results of national public survey on the status of earthquake disaster mitigation services and the demand for earthquake early warning in 2020
Lian Weiping, Li Yumei, Liu Peixuan, Zhu Lin
2022, 44(4): 700-710. doi: 10.11939/jass.20210101
Earthquake information services require in-depth research on the public reach and feedback. Research on the public earthquake early warning needs and the acceptance of false alarms has recently become sincerely necessary for the earthquake early warning system is about to provide services to the public on a large scale due to the advancement of the national earthquake early warning project. This paper designs a survey index system including public reach rate and public satisfaction to quantitatively measure the public reach and satisfaction of earthquake disaster mitigation services and has achieved good results. The results of the nationwide public survey show that 80.7%, 56.2%, 29.5% and 26.7% of the public have contacted the four services including earthquake quick report service, earthquake knowledge popularization, earthquake resistance consulting service for self-built houses, and information portals of earthquake departments at all levels. The public contact of the services has obvious regional characteristics and group characteristics. The public satisfaction is generally high, but the timeliness satisfaction evaluation score of the earthquake quick report service is relatively low. The public lacks an intuitive experience of its timeliness improvement in recent years. Research on the public demand of earthquake early warning shows that 88.3% of the public believe that it is necessary, 56.8% of the public have a strong demand for it, and the public acceptance of false alarms has remained at a high level in the past ten years. In large cities and the earthquake-prone areas, the public demand for earthquake early warning and the acceptance of false alarms are visibly higher than the overall nationwide level.
Seismic dislocation theory of spherical Earth model and its application
Sun Wenke, Fu Guangyu, Zhou Xin, Xu Changyi, Tang He, Dong Jie, Zhou Jiangcun, Yang Junyan, Wang Wuxing, Liu Tai
2022, 44(4): 711-731. doi: 10.11939/jass.20210134
Seismic dislocation theory is the theory of studying the relationship between seismic fault slip and geophysical field change, and also it is the link between the source mechanism, the internal structure of the Earth, earthquake forecasting and other basic geophysical problems and geodetic-geophysical observation. The widely used dislocation theory of the semi-infinite medium model, due to the limitation of its geometric attribute, will riskily result in a certain degree of oversight and even fault in the application of seismic deformation and geodynamics analysis. In addition, modern geodesy technology can accurately observe seismic deformation on global and regional scales, and a suitable seismic dislocation theory born for global seismic deformation study is urgently required. For this purpose, our team has developed a new system of seismic dislocation theory based on the spherical Earth model through many years of systematic research. The establishment of such theory has promoted the study of global seismic deformation and geodynamic process, and expanded the study of earthquake-induced global geodynamic changes. This informative article briefly introduces the domestic development and application of seismic dislocation theory of spherical Earth model. The first section introduces the dislocation theory of elastic spherical Earth model, three-dimensional inhomogeneous Earth model and viscoelastic Earth model. The second section introduces the relevant applications of the dislocation theory of spherical Earth model in geodynamic change, fault and underground structure inversion and others in seismological geodesy. The seismic dislocation theory of the spherical Earth model has promoted the study of global seismic deformation and geodynamic changes. It is one of the important theoretical advances in the field of geophysics in recent years.