Study On Earthquake-related Anomalous Features Of Infrared Remote Sensing

Earthquake is an abrupt change in the complex Earth system, with high complexity and uncertainty. With the discovery of infrared radiation anomalies before earthquakes, people gradually began to use satellite remote sensing technology to study infrared anomalies before earthquakes. Infrared remote sensing observations have been widely used to extract infrared earthquake-related anomalies, because of the advantages in covering area widely, continuous distribution and updating database earlier.In this paper, Land Surface Temperature (LST) data from MODIS and Outgoing Longwave Radiation (OLR) data downloaded from NOAA web site were used to build the background fields of Mainland China. Based on removing background fields, LST and OLR data were applied in the research of 33 earthquakes occurred since 2000 with magnitude greater than 6, and multi-parameters of infrared remote sensing were carried out a comprehensive analysis in the typical earthquake cases (Pu'er earthquake, Wenchuan earthquake and Yushu earthquake). The main anomalous features of LST and OLR data related to the earthquakes were summed up. For different parameters and methods of infrared remote sensing, comprehensive consideration of the ability in reflecting earthquake, the data and processing methods were selected from the time scale and the study area. Combination of the analysis of infrared multi-parameters, the theory based on Earth-Atmosphere system radiation budget of infrared remote sensing earthquake-related information extraction using multi-parameters was preliminary discussed.The results are summarized as follows:(1) In 32 earthquake cases happened in Mainland China and magnitude greater than 6, there are 14 earthquakes with the phenomenon of LST increasing near the epicenters prior to earthquakes, with the ratio of reflecting earthquake ability to 43.7%. In 33 earthquake cases happened in Mainland China and magnitude greater than 6, there are 25 earthquakes with the phenomenon of OLR increasing near the epicenters prior to earthquakes, with the ratio of reflecting earthquake ability to 75.8%.(2) The main characteristics of LST and OLR anomalies before the earthquake are generally located within a radius of 4°of future earthquake epicenter, and the anomalies have a trend of migrating to the earthquake epicenter, mostly on the earthquake fault, showing a good correlation between infrared parameters and fault activity. The morphology of anomalies is isolated high values. OLR anomalies mainly appear 2 months before the earthquake to the month of earthquake in the monthly scale; the anomalies appear 15 days before the earthquake in the interdiurnal scale, and LST anomalies are almost concentrated in the seismogenic month. The evolution of the energy shows the seismic dynamic process, summarized as breeding (weak) - accumulation (strong) - accumulation (weak) - earthquake (disappeared). It is difficult to describe the magnitude of anomalies quantitatively, because the physical meaning of parameters, resolution and the accumulation time are different, so it is also difficult to determin the magnitude and focal depth of further earthquake by anomaly magnitude.(3) 1.0°OLR data are more suitable for the tracking of single point; it can better track the infrared radiation of a single point near the earthquake epicenter. 2.5°OLR data are more suitable for vorticity processing to extract information. For large-scale study area, it is usually analyzing the difference between the current month value and the average value of the month for many years. For small-scale study area, it is usually analyze the monthly changes and the vorticity analysis based on background fields. Strong radiation in the desert region makes the vorticity evolution always in isolated high value, thus, vorticity analysis is not suitable for such areas. MODIS retrieved land surface temperature data are suitable for carrying out monthly average difference method to track on a large study area.(4) The process of earthquake preparation accompanied by huge energy release and exchange, the radiation balance in this area is broken. It is specifically expressed in LST and OLR increasing, releasing more latent heat because of atmospheric convection enhancing, so the changes of the above parameters can reflect the process of earthquake preparation in some ways. During earthquake preparation, the energy accumulation reaches a certain level to cause the significant changes of surface temperature (or Brightness Temperature), so the time of LST or BT anomalies more likely happened on the earthquake month. OLR data measure the whole Earth-Atmosphere system in the radiation changes, including the radiation information of cloud top, land surface and atmospheric, so it can be the first earthquake-related anomalies. Compared to other infrared remote sensing parameters, Latent heat flux data anomalies usually appear at the latest. The relationship and characteristics in infrared remote sensing parameters make the extraction in infrared remote sensing earthquake-related anomalies by means of multi-parameters significant.