The Multi-physics Abnormal Information Extraction And Analysis On Earthquake In Subduction Zones

As one of the sudden,unpredictable and destructive natural disasters,earthquake has always been the hot spot,key point and difficult point in the research of scholars all over the world.Subduction zones are regions with active tectonics,complex geological structures and frequent earthquakes in the world.In development process of earthquake,there are often gravity field,electromagnetic field thermal field and other geophysical field changes in subduction zones.It is the key to earthquake precursor study that how to extract accurately multi-physical field anomaly information before subduction zone earthquake from massive satellite remote sensing data and multi-source assimilation data.It also provides more theoretical support and method guidance for earthquake early warning.This paper takes the Chile subduction zone as the research object and the 8.8 magnitude earthquake in Chile on February 27,2010,the 8.2 magnitude earthquake in Chile on April 1,2014 and the 8.3 magnitude earthquake in Chile on September 16,2015 as the research earthquakes.The abnormal information of multi-parameters of thermal field and ionospheric TEC before three earthquakes are detected and analyzed by using different methods with multisource data.Firstly,by wavelet transform and cross wavelet transform to the surface latent heat flux(SLHF)and sea surface temperature(SST)two months before the three earthquakes in Chile,the results show that both SLHF and SST present high-power signal components.The signal period mainly distributes between 20-day period and 32-day period,and the high-power signal of SLHF appears slightly later than the SST.By comparing the wavelet power spectrum of SST and SLHF in different geographical locations,it shows that the high power signal only appears near the epicenter and has a good spatio-temporal correlation with the earthquake.According to upwelling index and chlorophyll concentration near the epicenter before the earthquake,upwelling brings cold water with lower temperature to the sea surface,which is not conducive to the growth of chlorophyll concentration theoretically.However,upwelling index and chlorophyll concentration around the epicenter both increase abnormally before the three earthquakes.Therefore,it believe preliminarily that the energy of the local thermal field anomaly on the ocean surface before the three earthquakes comes from the submarine structural heat source,which may be related to the following earthquakes.Then,in order to extract land surface tectonic thermal information,this paper use the in situ temperature field method to remove the large-scale atmospheric circulation anomalies and small scale of human activity influence and extract tectonic thermal information of three Chile earthquakes in MODIS land surface temperature product.The results show that the cold and hot anomalous belts appears alternately for many times before the three earthquakes.Moreover,the distribution of the anomalous belts is parallel to the structure of the subduction zone basically,which mainly distributes in the subduction orogenic belt.Finally,this paper attempts to construct a TEC non-seismic dynamic background field considering the influence of solar activity and geomagnetic activity.By comparing the TEC residues of the non-seismic dynamic background proposed in this paper with the traditional sliding window background,the results show that the TEC residues of the sliding window background method have obvious monthly and semi-annual cycles,which will have an important impact on the subsequent ionospheric anomaly detection.Meanwhile,the seismic ionospheric TEC anomalies of three Chile earthquakes are detected by using the non-seismic dynamic background.There are multiple abnormal perturbations detected in the 7 days before the three earthquakes.The anomalies of the magnitude 8.8 earthquake in Chile in 2010 and the magnitude 8.2 earthquake in Chile in 2014 is mainly positive abnormal perturbations accompanied by temporary negative abnormal perturbations.While it presents the negative abnormal perturbations before the magnitude 8.3 earthquake in Chile in 2015.The anomaly detected before the three earthquakes is shifted to the equatorial direction relative to the epicenter,and similar disturbance are detected in the magnetic conjugate region of the epicenter.