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Spectral and Thermal Anomalies as Earthquake Predictors- A Geomatic Approach
Eswar R Institute of Remote Sensing Anna University India eswar1204@gmail.com Yogesh D. Institute of Remote Sensing Anna University India geoyogesh@gmail.com Kodimalar T Institute of Remote Sensing Anna University India tkodimalar@gmail.com INTRODUCTION: An earthquake is the vibration of a part of the earth crust caused due to the internal and external stresses acting on the rocks in the crust. The tectonic kind of earthquakes is more prominent and cause more damage than the non-tectonic one. Unlike other natural hazards, an earthquake rattles the human beings since it comes without prior warning. Combined use of various technologies helps us to reach closer towards predicting earthquakes. Thermal sensors, GPS and other normal geophysical instruments can be used together for gaining more knowledge about the future earthquake. THERMAL ANOMALIES: Thermal Anomalies are the increase in emission of the land surface in TIR band. The enhanced emission gets recorded in the thermal sensors and it can be clearly delineated from the surroundings. It has been shown by many that thermal anomalies appear before major earthquakes and it can be traced from thermal sensors. Works of Tronin, Qig, Qinhuo, Zuij, Changgong, Saraf and others shows that thermal anomalies can be used as reliable precursor in predicting imminent earthquakes. But this requires constant monitoring of the region. GLOBAL POSITIONING SYSTEM: GPS is a well known technology for knowing the position of a point. Continuous GPS observations can help us to find out the relative movement of faults (Faults are the geological structures around which major earthquakes occur) can be found very precisely. Already USGS, Canada earthquake centre, UNAVCO and other agencies are using GPS for monitoring crustal plate motion. But in India this technology still needs to find its place in a huge manner. VARYING SPECTRAL REFLECTANCE AND THERMAL EMITTANCE: Each and every kind of object has its own spectral reflectance and thermal emittance. Hence the graph showing the spectral behavior of an object for different wavelengths of EM spectrum can known as spectral signature of the object. Works of Freund and others have shown that there is an increase in the infrared emission of rocks when they are subjected to stress. But we can infer from the work that the emission varies when the nature or magnitude or both of the stress varies. This can be also taken as a clue about the forces acting beneath the surface of the earth and how it can affect the rock bed. METHODOLOGY: The first step envisages a detailed seismic zoning and geologic mapping of the seismically active sites. After identifying the earthquake prone areas a detailed geologic survey should be conducted both by on field and remote sensing techniques. The rock types, attitude of the rocks, structures on rocks like folds, fractures if any should be identified and mapped. Using a hand held spectroradiometer and thermal radiometer the reflectance pattern of all the rock types found on field should be observed. The rock from which the observation to be made should be below the surface of the earth. The depth of observation can be selected based the nature and intense of weathering at a given place. This ensures that the rock is free from the agents of weathering and erosion that are operating on the surface; hence it is an intact rock; also the rock should not be disturbed manually. Necessary corrections are to be given to the observed data and reflectance curves are built. Samples of rocks are to be taken to the laboratory and the same observations should be carried out but the rocks were under the influence of applied artificial stresses. The applied forces are increased in small amounts till the rock fails. The various methods of applying stress in rock mechanics laboratory are followed to find the behavior for different kinds of stresses. Curves are to be obtained for varying stresses. Near the seismic zone high precision dual frequency GPS should be installed permanently at suitable points. Continuous data should be obtained and processed. This will yield the details about the movement of rock bed in the area. Campaigning mode GPS may not prove useful as it may have more uncertainty and the data would be rendered useless. Kirby (2008) in a paper noted that campaign mode GPS used to monitor tectonic activity in the Sichuan province of China had failed to note the sudden steepness of the topography and he recommends the use of continuous GPS monitoring in regions where tectonic activity is observed. Satellite data (thermal band) for the region under investigation is obtained regularly and it is analyzed for any thermal anomaly. Specific methods are available for extracting the Land surface temperature data from a thermal imagery. This requires finding out the combined emissivity of land cover features and meteorological data for giving necessary corrections. Higher earthquake magnitude and shallower focal depth are favorable conditions for the appearance of intense thermal anomaly with larger spatial extent and vice versa. (Saraf et al., 2008) By continuously analyzing the satellite data we can find out whether anomalies appear in the region under monitoring and also when combined with continuous GPS monitoring we can say whether there is any considerable plate movements and we can also find out in which direction the plates are moving by plotting velocity vectors over the regional map. Then on field observation of spectral and thermal behavior of different types of rocks in the region is to be carried out. As mentioned earlier the rock should be well below the surface and it must be intact. Detailed atmospheric corrections and correction for noise introduced by other factors have to be made. Then the obtained curves are compared with the curves in our library obtained in laboratory to find out which sort of force the rocks are subjected too and also we can get a little insight about the magnitude of force. This process is repeated daily and if the behavior indicates an increase in the force, we may come to a conclusion that stress fields are more likely going to rupture the rocks which may result in earthquake. From the combined information obtained from thermal anomaly observation, GPS monitoring and on field spectral and thermal observations we can come to a very strong conclusion about the earthquake to occur in near future. DATA ANALYSIS: In order to facilitate the analysis of data, a small application was developed. The developed GIS application which is named as Earthquake Analysis and Decision Support System (EADSS) can be used for analyzing geology of the area, fractures, fault zones, shear zones, data of previous earthquakes and thermal anomaly regions. We can also overlay GPS velocity vectors plot obtained from GPS measurements. In this case we have used the free data available from USGS and other resources. This application does not have any modules for comparing the spectral signature of rocks and it has to be done separately. This is a simple application which can be used even by a common man to get few basic details required for knowing about a region. Earth quake analysis system (EADSS) is developed using Oracle spatial Technology. This is a typical webGIS application which helps to analyze various data like thermal anomaly region obtained from thermal imagery, geology, GPS, and previous earthquakes data to know about earthquakes to happen in future Technology involved: Oracle spatial database Mapviewer API Oracle spatial database helps us to store both spatial like earthquake anomaly regions, fault zone and previous earthquake data. Map viewer API is used to develop the stand alone client application on java platform. Software description: The modules include Import/Export of different format data, Map Editing, Spatial Query Language support for combined attribute and map based queries. Vector based spatial data like thermal anomaly region and fault zones can be imported in to the database or exported to different formats. Query involves both the attribute and location based query of the previous earth quake data. Imported spatial data can be edited using the Editing module. To carry out standard tool module include basic map functions like zoom in, zoom out, paning. USER DOCUMENTATION:: It is a simple tool so that new users can also work with it without any difficulty. Step by step exercises are provided in the help module. Using the import and export module user can Import/Export vector files in various formats like shape files etc(Example shown in Figure 1).  Figure 1:Snap shot of the EADSS The methodology described in the paper can be combined with existing methods for monitoring seismic nature of a region like bore hole strain meters, tilt meters etc., and we can get a good insight about the occurrence of a forth coming earthquake. REFERENCES:
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