| Earthquake is a natural disaster which is difficult to forecast and does the greatest harm to the harmonious and stable development of human society.Under the background of vigorously promoting the development of earthquake science and technology in China,further researches on seismic anomaly perception and cognition based on satellite remote sensing is the actual demand for the development of multi-parameter intensive earthquake observation system,which is conducive to the scientific formulation of earthquake disaster monitoring and early warning policies.At present,passive microwave satellite remote sensing monitoring of tectonic activities and seismic anomalies is in the rise,and relevant reports at home and abroad are very active and developing rapidly.However,there are still some problems,such as unscientific selection of microwave frequency/polarization,unreliable perception methods,uncleaned abnormal results,and insufficient cognition of abnormal mechanism,which seriously restrict the seismic application research of passive microwave satellite remote sensing.In fact,the complete chain from passive microwave satellite remote sensing data to seismic reliable anomalies should at least include: microwave brightness temperature(MBT)data processing,MBT background field analysis,MBT anomaly perception,get rid of the fake and retain the genuine,cross verification,reliability evaluation and anomaly mechanism cognition,etc.The issues involved are complex,challenging and arduous.This research deeply summarizes and analyzes the problems in the current research,and carries out relevant research centering on the above scientific objectives.The main contents and innovations are as follows:(1)In order to solve the problem that the selection of frequency and polarization in seismic MBT anomalies research are diverse but lack of reliable basis,this research firstly built the multi-frequency and dualpolarization monthly mean MBT background over the Qinghai-Tibet Plateau and its surrounding areas,which was then divided into six sub-zone according to their spatial pattern.The influences of environmental factors,land cover and microwave channel(frequency/polarization)on spatial distribution and temporal variation characteristics of MBT backgrounds were revealed and analyzed.Accordingly,the multi-frequency and dualpolarization response characteristics of MBT background to a variety of natural but non-seismic(Nb NS)factors were further studied and analyzed,and the sensitive microwave channels of different Nb NS factors were obtained.Then,by comprehensively determining the optimal channels for seismic MBT anomaly research under the influence of different Nb NS factors in different land cover regions,the optimal channel selection strategy for seismic MBT anomaly study in different seasons and different locations in the Qinghai-Tibet Plateau and its surrounding areas was proposed.The above results not only provide a basis for the selection of microwave channels for studying seismic MBT anomalies in the investigate area of this research,but also provide a reference paradigm for the study of seismic MBT anomalies in other regions of the world.(2)In view of the insufficient reliability of the current method for precepting seismic MBT anomaly,this research proposed a spatiotemporally weighted two-step method(STW-TSM)for seismic MBT anomaly detection,which can effectively suppress the long-period nonseismic interference and short-period meteorological interference in the historical MBT data.The obtained MBT anomalies behaved more stronger correlations with the epicenters and tectonic structures.Then,the dynamic monthly mean background method(MMMB)was proposed in this research,which was capable of eliminating the persistent influence of Nb NS factors in the MBT data of earthquake year.Based on the above methods,the obtained MBT anomaly of the 2008 Wenchuan earthquake presented the evolution of ‘appearing before the earthquake—enhancing immediately preceding earthquake—peaking on coseismic day—migrating with aftershocks’,and the obtained MBT anomaly of the 2015 Nepal earthquake exhibited the characteristic phenomenon of ‘appearing before the earthquake—peaking on coseismic day—disappearing after the earthquake—repeating for the aftershock’,it was also found that striped MBT anomalies covering Bayan Har block appeared both before the Yushu earthquake in 2010 and Maduo earthquake in 2021.Furthermore,the characteristics of MBT anomalies associated with several typical strong earthquake in the middle section of Bayan Har block and the Longmenshan fault zone were compared and analyzed.The spatiotemporal commonness and individuality of different seismic MBT anomalies were analyzed and summarized,and the potential mechanical mechanism of MBT anomalies was initially explained from the macroscopic perspective of plate motion.(3)Aiming at the problem that coarse errors and pseudo-anomalies are not thoroughly eliminated in the abnormal results of the current research,this study firstly proposed a multi-frequency and multi-polarization compositing method for analyzing seismic MBT anomalies,which can carry out attribution analysis and geosphere determination for different MBT anomalies merely based on the differences in MBT anomalies of varied band and polarization.Then,a multi-parameter composite method for analyzing seismic MBT anomalies was proposed,which can further determine the reliable seismic MBT anomalies and eliminate the pseudoanomalies combined with multi-source heterogeneous auxiliary data.The validity of the above two analysis method is verified by studying the MBT anomalies of the Wenchuan earthquake,Nepal earthquake and other cases.Furthermore,a ‘3D’ method for verifying the reliability of seismic MBT anomaly combining DTS criterion,LCAI coupling paradigm and homologous physics was presented,and a case study based on the results of multi-geosphere anomalies of the Nepal earthquake in 2015 was carries out,which confirmed the reliability of the revealed MBT anomaly.Accordingly,the typical pseudo-anomalies and the uncertainty problems in this study are summarized and analyzed,and the composite chain of seismic MBT anomaly perception and cognition research was finally defined.(4)In view of the problem that the current understanding of the potential mechanism of seismic MBT anomalies is not deep,this research,based on the microwave radiative transfer model and microwave remote sensing physics,raised a discrimination method of seismic MBT anomalies.Combined with multi-source auxiliary data,the MBT anomalies related to the 2008 Wenchuan earthquake and 2015 Nepal earthquake are discriminated deeply.The main Nb NS factors such as vegetation,soil moisture and surface temperature are excluded,and the seismic MBT anomaly is determined to be caused by surface microwave dielectric change.Furthermore,combining with dielectric physics and P-hole theory,the influence of P-holes activated by rock loading on microwave dielectric of rock surface is analyzed from microcosmic perspective.Then,based on3 D crust stress simulation and regional geological structure,the potential physical and mechanical mechanism of seismic MBT anomaly in Quaternary strata of Wenchuan earthquake and high-altitude area of Himalayan mountains of Nepal earthquake is studied comprehensively.A response chain of ‘crust stress field alteration(CSFA)—activation and generation of P-holes—transmission of P-holes along stress gradient—surface/subsurface aggregation of P-holes—microwave dielectric decline—MBT rise’ is proposed,which provides a reasonable explanation for CSFA-induced seismic MBT anomalies from the perspective of dielectric physics and rock mechanics.61 figures,5 tables,238 references... |
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