2022 Vol. 44, No. 3

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2022, 44(3)
Abstract:
Crustal thickness and Poisson’s ratio of orogenic belts in northern North China Craton using teleseismic receiver functions
Liu Jiadong, Ding Zhifeng, Wu Yan, Jiang Lei
2022, 44(3): 357-373. doi: 10.11939/jass.20210001
Abstract:
The thickness and Poisson’s ratio of crust of the North China Craton (NCC) are of great significance to the study of lithospheric evolution of the North China Craton. We collected receiver functions from 115 broadband seismic stations and six very broadband seismic stations on the Taihang-Yanshan orogenic belt and its adjacent areas in the northern North China Craton recorded from October 2006 to September 2009. First we used predictive deconvolution method to eliminate the influence of sedimentary on receiver function waveform. Then the effects of S wave azimuthal anisotropy and interfaces dipping were corrected by using H-κ-c stacking method. Finally, the thickness and Poisson’s ratio of research area were obtained. Our results are featured by lateral variation. The crust thickness in the research area is thick in the western block and thin in the eastern block, and is highly correlated to the topography, which is consistence with Airy isostasy. The low Poisson’s ratio of western block represent relative stability of the crust, the distribution of Poisson’s ratio in central orogenic belt and eastern block is inhomogeneous, suggests that the complex transformation process has been suffered in the crust. Combined with the previous research results, we speculate that there existed partial melting and mantle upwelling in the lower crust of Huailai-Yanqing basin and southern Tangshan, and lower crust detachment might have occurred on the north of Shijiazhuang, and the lower crust of Baoding-Fangshan may have been suffered mantle upwelling under the influence of extension after its detachment. The different crust structures of different areas result in the differences of crustal thickness and Poisson’s ratio distribution which are obtained by H-κ-c stacking as well as H-κ stacking.
Lithospheric velocity structure of Alaska revealed by double difference tomography
Zhou Shaoxian, Xue Mei
2022, 44(3): 374-387. doi: 10.11939/jass.20210122
Abstract:
Alaska region is formed by the northward accretions of terranes from different geological periods and has experienced extensive internal deformation and metamorphism, and the geological structure is complex. The Array Network Facility (ANF) website recently provides new observational data from the seismic network of USAarray, filling the observation gap in the west and north of Alaska. Based on P and S wave arrivals of 5 638 events recorded by 345 stations from ANF, this study relocates earthquakes and images the 3D lithospheric P-wave velocity structure beneath Alaska simultaneously by regional double difference tomography. The results reveal larger dip angle of subducting Pacific Plate and low-vP anomalies in the mantle wedge beneath western Alaska. These observations reflect the subduction process, during which the dehydration of the subduting Pacific Plate releases fluids into the mantle wedge, triggers partial melting, and generates melts, which was then transported to the surface by the upwelling flow so as to form Aleutian volcanic arc. In central Alaska, the coupling between the Yakutat terrane and the Pacific Plate reduces the subduction dip. On the one hand, the shallow subduction of the Yakutat terrane increases the compressive stress of the crust, causing the crustal thickening and uplifting of Chugach mountains. On the other hand, it cools the mantle wedge reducing magma generation, which are then combined with the closure of crust fractures resulted from the increase of the crustal stress, blocking the supply of melt to the surface, and finally leading to the formation of Denali volcanic gap. In addition, there is a clear boundary between Yakutat terrane and Wrangell volcanic field in the east, and the low velocity zone corresponding to magmatic activity in the region is concentrated in the northwest. The magma source may be related to upwelling of the toroidal mantle flow around the Pacific-Yakutat slab edge. These results suggest that the complex geodynamic processes in deep Alaska lead to the complex geological structure on the surface.
First arrival time picking algorithm of micro-seismic based on improved STA/LTA and adaptive VMD
Meng Juan, Wu Yanxiong, Li Yanan
2022, 44(3): 388-400. doi: 10.11939/jass.20200199
Abstract:
Accurate and reliable picking of the first arrival time is one of the critical steps in micro-seismic monitoring. Aiming at the problem of low accuracy of first arrival picking for micro-seisms under low signal-to-noise ratio, the traditional short term averaging/long term averaging algorithm is improved by introducing weight factor according to the change of signal amplitude to improve the accuracy of initial pickup. In order to further reduce the pickup error, variational mode decomposition (VMD) is optimized based on cross-correlation coefficient and permutation entropy criterion, and decomposition layers are determined adaptively. Then, the signals of 2−3 s before and after the initial pickup are decomposed by VMD, and the Kurtosis-Akaike information criterion (AIC) values of the decomposed intrinsic mode functions (IMF) are calculated to get the arrival time of each IMF, and the secondary arrival time is obtained by comprehensively weighting the picking results and energy ratios of each IMF. Simulation results show that the improved STA/LTA can reduce the initial picking error by more than 0.01 s at low SNR; compared with empirical mode decomposition (EMD) and wavelet packet decomposition, the adaptive VMD decomposition can reduce the picking error again, and the finalaverage picking error is less than 0.023 s. The first arrival time picking results of real micro-seismic signals show that the proposed algorithm can identify the first break of P-wave quickly and effectively, and the error is smaller than that of manual picking, which shows that the algorithm is effective and the picking accuracy is high.
Variation of b-value before and after Yangbi four MS≥5.0 earthquakes on May 21,2021
Zeng Xianwei, Zhao Xiaoyan, Li Mengya, Li Wenjun, Tang Hao, Yuan Yuan
2022, 44(3): 401-412. doi: 10.11939/jass.20210129
Abstract:
Four MS≥5.0 earthquakes occurred successively in Yunnan Yangbi from 21:21 to 22:31 on May 21, 2021, which are MS5.6, MS6.4, MS5.0 and MS5.2, respectively. Based on the earthquakes recorded in focal area of Yangbi earthquake and its vicinity from January 1, 2015 to June 4, 2021, we estimated the b-value by the maximum likelihood method. Then, we analyzed the spatial distribution of b-value before and after Yangbi earthquakes and got the views below. Firstly, an earthquake swarm occurred three days before the Yangbi earthquakes, then, the b-value near the focal area of Yangbi earthquake decreased rapidly after the earthquake swarm. It may indicate that the strength of crustal medium was close to the critical state of fracture. Secondly, the four MS≥5.0 earthquakes distribute along the edge of the abnormal area with low b-value. Thirdly, the b-value of the focal area increased obviously after the Yangbi earthquakes. It indicates that the regional stress has been released and the risk of strong earthquake is reduced in the short term. Fourthly, there are two b-value abnormal areas 40 km and 70 km northwest of the Yangbi earthquakes. It means that there is a risk of strong earthquakes in the abnormal areas in the future.
Modeling and applications on amplitude-magnitude-distance-depth of some teleseism and ultra-teleseism phases
Xue Fangzheng, Wang Hongchun, Zhu Haofeng, Xu Xiong
2022, 44(3): 413-426. doi: 10.11939/jass.20210023
Abstract:
The consistency analysis of the signal feature is an important method to estimate the relationship between the event and the signal in the detection of seismic event. The consistency of amplitude can be used for determination of association through the comparison of amplitude residuals with numerous signal features on time and frequency domain. Different phases comply with the different propagation and attenuation law of amplitude-distance-depth. In this paper, the distribution of sample size varying with the distance of teleseism and ultra-teleseism phases such as P, PcP, PKP, PKPab and PKPbc based on the IDC is made. The model of amplitude-magnitude- distance-depth is constructed by iterative regression based on the residual statistics. The model is estimated through the standard deviation and mean of residual of magnitude. The range of standard deviation of residual of magnitude is 0.30−0.36. It could satisfy the requirements of phase consistency. Besides the mean of residual of magnitude of PKPbc phase is greater than 0.03, the rest phases is about 0.01. It demonstrates that the system deviation of the model is so tiny that it could be neglected. The application research of model is carried out by three different cases such as comparison of predicted amplitude, detection of magnitude consistency and magnitude calculation of ultra-teleseism events. The application research demonstrates that these models could be applied to routine seismic monitoring.
Characteristics of surface deformation field of Changning shale gas block in southern Sichuan basin with InSAR data
Bao Yuxin, Sun Jianbao, Li Tao, Liang Cunren, Zhan Yan, Han Jing, Li Yongsheng, Zhang Jingfa
2022, 44(3): 427-451. doi: 10.11939/jass.20210064
Abstract:
In recent years, along with large-scale development of shale gas, the seismicity rate has increased dramatically, a series of microseismicity, felt earthquakes and even destructive earthquakes occurred in southern Sichuan basin, a relatively tectonic stable area. Some studies statistically infer whether these earthquakes were induced by industrial activities by using spatio-temporal correlations. This study, on the other hand, uses deformation measurements to analyze whether shale gas exploitation can produce detectable surface deformation, so as to analyze the relationship between deformation and shale gas exploitation, in an attempt to find an effective approach for shale gas exploitation monitoring. Long wavelength ALOS-2 satellite radar data has the potential for minimizing decorrelation effects of radar signals caused by vegetation, heavy water vapor and topographic relief in Sichuan basin. We used ALOS-2 InSAR data to measure surface deformation in Changning shale gas block in the past two or three years, found possible ground deformation caused by massive shale gas production and analyzed its basic characteristics. Meanwhile we also processed time-series of Sentinel-1 satellite radar data to measure the surface deformation during active periods of shale gas exploitation. Considering the errors and different observation geometries of the two datasets, the results from two databases are consistent in revealing the surface deformation. Furthermore, the meaured deformation field is in agreement with the spatial distribution of shale gas wells. Our observations show fast surface uplift during hydrofracture injection, also ground subsidence and horizontal motion in production period with fliud diffusion. We preliminarily reveal the non-steady deformation characteristics during shale gas production. Our study suggests that InSAR is an effective technique for shale gas production monitoring even in southern Sichuan basin where complex deformation occurs, and can provide insights supplementary for seismological observations.
Afterslip distribution of 2017 Iran MW7.3 earthquake and its triggering effects on the 2018 MW6.0 earthquake
Jiang Ziqin, Yang Yinghui, Chen Qiang, Xu Qian, Xu Lang, Huang Xiaomei
2022, 44(3): 452-466. doi: 10.11939/jass.20200140
Abstract:
In this study, a set of radar images acquired by the Sentinel-1 satellite that covers the interested seismically-effected area were collected. The time-series surface deformation of the 283-day time span after the 2017 Sarpol Zahab, Iran, MW7.3 earthquake was extracted by using small baseline subset technique, then the two-step procedure inversion is carried out to obtain the afterslip distribution. In order to analyze the triggering effects of the 2017 strong earthquake and its post-seismic faulting on the 2018 Javanrud MW6.0 earthquake, the coseismic deformation field covering the whole MW6.0 earthquake region was obtained by using differential interferometry technique, and the inversion results of seismogenic fault parameters were used as receiving fault parameters for stress calculation. The results show that the post-seismic deformation of the Sarpol Zahab earthquake is mainly dominated by the afterslip effect. 283 days after the earthquake, the accumulative slip of the after-slip model reaches up to 0.7 m. The coseismic source model of the Javanrud MW6.0 earthquake indicates that the seismogenic fault strike is 355.6°, the dip angle is 89.4°, and the rupture of coseismic fault is characterized by the right-lateral strike-slip together with some normal dip-slip component. Moreover, the calculated Coulomb stress change suggests that the MW7.3 earthquake and its afterslip have triggering effect on the subsequent Javanrud MW6.0 earthquake, and the occurrence of Javanrud earthquake could also be contributed by the regional plate activity.
Research on 1-D deep electrical structure in Hawaii
Liang Xuan, Tang Xingong, Yu Junhu, Xiong Bo
2022, 44(3): 467-475. doi: 10.11939/jass.20210047
Abstract:
Volcanic activity is closely related to deep magma transportation and material melting state. Long-term dynamic monitoring of volcanoes is helpful to master their deep structure and variation characteristics, and provides important geophysical evidence for predicting volcanic eruptions and volcanic earthquakes. We selecte the observation data from May 2018 to April 2019 for inversion, and the data come from a long-term magnetotelluric observation station set up by Phoenix Company in the Big Island, Hawaii. We obtain the deep electrical structure below the observation point and its time-varying characteristics, and compare the inversion results with the previous exploration results. The research results show that there is an obvious thin low-resistance layer at a depth of 2−3 km below the observation point, and its resistivity is about 20 Ω·m. It is speculated that it may be a magma chamber developed in the shallow part of the Earth’s surface. The range of resistivity at the depth of 100 km is 20−70 Ω·m. It is speculated that there may be an active complex magma reservoir at this depth. The inversion results are comparable with the previous exploration results in neighboring areas.
Optimization of local seismic network layout based on seismic monitoring capability
Qi Guoliang, Yuan Chuan, Yu Miao, Tang Lin
2022, 44(3): 476-488. doi: 10.11939/jass.20210019
Abstract:
In order to solve the problem of station location with constraints, the optimization theory of public service facility location is used for reference, and the constituent elements of seismic network monitoring capacity are deeply analyzed, the constraints such as terrain slope, environmental noise level and station layout are also added. Finally, the optimization model of station network layout based on the seismic detection capacity, the recording capacity and the positioning accuracy is established in this paper. Taking the seismic network in Chengdu as an example, the network layout optimization scheme that meets the seismic monitoring capacity requirements of focus and non-focus monitoring areas respectively are obtained by the use of simulated annealing algorithm. And the geographical location of new or newly-built monitoring stations is clearly given.
Spatial distribution characteristics of soil radon in the southern Tangyin graben
Hu Ning, Ma Zhimin, Lou Luling, Wang Yu, Zhang Baoshan, Wang Mingliang, Chen Meng, Guo Deke
2022, 44(3): 489-500. doi: 10.11939/jass.20200054
Abstract:
This paper discussed the spatial distribution characteristics of radon in the soil gas and their relationship with faults, geological structures, lithology, and sediment thickness based on the radon concentrations obtained by the field mobile measurement at the gridding layout observation points in the southern Tangyin graben. The measurements showed that the soil radon concentrations in the Tangyin graben varied from 3.09 to 78.54 kBq/m3 with a mean value of 27.22 kBq/m3, and the anomalous threshold was 48.40 kBq/m3. Spatially, the studied area was divided into two parts based on the contour of Quaternary system (50 m thickness), the distribution characteristics of soil gas presented that radon background concentrations were higher in western region than that in eastern evidently because of the difference of lithology units made up the local strata and the influence of human mining activity. Accordingly, the radon concentration anomalies of soil gas in western region were patchily scattered on the periphery of Tangxi fault belt besides of distributed along the fault belt itself. Nevertheless, in eastern region, the most of radon concentration anomalies mainly presented along Tangzhong and Tangdong fault belts. Similarly, the contours map of radon concentrations also indicated the azimuth of concentration anomalous belts were consistent with the strike of Tangzhong and Tangdong faults in east region, which implied the emanation of deep-seated source gas was controlled by fault structures. In addition, the radon concentrations contours map also suggested there was a radon anomalous band of NE strike that was almost parallel to contours of local Quaternary system thickness, by which we speculated there was a buried fault. Furthermore, in this studied area, though the release intensity of soil radon in the western part was significantly higher than that in the middle-eastern part, the radon concentrations anomalous extent showed a trend of increasing from west to east, which revealed that the Tangdong fault was more active than others. The comprehensive analysis indicated that the spatial distribution of soil radon concentrations was mainly controlled by fault structures, lithology formation, thickness of sedimentary layer, and human mining activities, and variations of radon concentrations were mainly dominated by the background tectonic activity of southern Tangyin graben. Our results imply that soil radon is an effective indicator for tectonic activity observation of Tangdong fault. While it is appiled to Tangxi fault which is located in the transition region between the uplift and the subsidence the influence of environmental background needs to be fully considered, because of the impact of bedrock cropping out partially and human mining activities.
Modification of fitting parameters in coherency model for spatial variation of seismic ground motion
Ding Haiping, Zhang Mingzhe
2022, 44(3): 501-511. doi: 10.11939/jass.20210006
Abstract:
In this study, the horizontal component of the 5th and the 45th seismic records of the SMART-1 array were selected. Firstly the lagged coherencies of seismic ground motion of station pairs with different separation distances were calculated. Then the influence of station distance on the fitting of parameters of the coherency function model was discussed, that is, there were obvious differences between the fitting results of the coherency function of a certain distance and the coherency functions of all different distances. In order to reduce this deviation, a method of quadratic regression on the fitting parameters of the coherency of different distances was proposed, and the Loh coherency function model was selected for verifying the method. Finally, the correction results of the fitting parameters based on the Loh coherency function model were given. The results show that the correction method proposed in this paper will greatly improve the fitting accuracy of the parameters in the coherence function model.
A method for seismic landslide hazard assessment using simplified Newmark displacement model based on modified strength parameters of rock mass
Chen Shuai, Miao Zelang, Wu Lixin
2022, 44(3): 512-527. doi: 10.11939/jass.20210008
Abstract:
Rapid assessment of seismic landslide hazard can provide a scientific basis fordecision-making aimed at post-earthquake emergency response. The Newmark displacement model can quickly assess the seismic landslide hazard after an earthquake without co-seismic landslide inventory. However, as one of the main parameters of the Newmark displacement model, physical and mechanical parameters of the rock mass assigned by traditional methods are too single to reflect the spatial differences of real rock mass strength under complex geological background. To tackle this issue, the distance to the fault, the elevation, and the distance to the river were selected as the evaluation indexes affecting the strength of rock mass, and the evaluation model of rock mass strength was established to obtain the regional rock mass strength modified coefficient, and then the critical acceleration obtained by the traditional method was modified. Combined with the instantaneous peak ground acceleration after an earthquake, the simplified Newmark empirical displacement model was used to calculate the slope cumulative displacement, and the rapid assessment of seismic landslide hazard was conducted. The Wenchuan MW7.9 earthquake was selected as the studied area to validate the performance of the presented method. Results show that the seismic landslide hazard area divided by the presented method is more consistent with the actual co-seismic landslide distribution compared to traditional method. The presented method in this paper can be used for rapid assessment of seismic landslide hazard, which has important reference value for guiding post-earthquake emergency rescue and land planning and also provides a new idea for the subsequent establishment of a basic geological spatial database.
H/V spectral ratio characteristics of hidden fault site based on ambient noise test
Hu Peng, Luo Yonghong, Song Zhibin, Nan Kai
2022, 44(3): 528-537. doi: 10.11939/jass.20210054
Abstract:
Ambient noise research has become a hot spot in geological exploration, but the research on ambient noise in alpine and gorge regions of Southwest China is still in its infancy. Based on more than 60 ambient noise tests conducted in the hidden fault crossing area of Anshun field in Shimian county, Sichuan, this paper explores the influence of hidden faults on the H/V spectral ratio characteristics of ambient noise. The results show that after excluding predominant-frequency areas that may be caused by the influence of rivers, the H/V spectral ratio curves are characterized by high frequency, low H/V spectrum ratio, and multi peak frequency on the fault zone. In addition, we estimated the thickness of overburden in this field by analyzing the predominant frequency of this test, and the calculation results of the overburden layer show thickness difference of 5−10 m in some strong weathering areas and high frequency areas of rivers. Moreover some areas with large changes in overburden thickness obtained by ambient noise array inversion are consistent with the trace distribution of the hidden faults. This study attempts to reveal the traces of hidden faults by using the ambient noise method, which provides a new reference basis for the exposure of hidden faults.