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Geomatics in Earthquake Mitigation

Geomatics in Damage Assessment
Disaster management consists of two main phases—disaster prevention and disaster preparedness (disaster relief, rehabilitation and reconstruction). In disaster prevention phase, GIS is used to manage the large volume of data needed for the hazard and risk assessment. In disaster preparedness phase, it is a tool for the planning of evacuation routes, for the design of centers for emergency operations, and for integration of satellite data with other relevant data in the design of disaster warning systems. High-resolution satellite imagery offers new possibilities for the earthquake damage assessment and thus multidisciplinary approach combining remote sensing techniques, spatial analysis and earthquake engineering can provide fast loss estimation. The information can be integrated into a GIS database and transferred via satellite networks or Internet to the rescue teams deployed on the affected zone. The results of a fast damage assessment received by the field operators could help the civil protection in order to co-ordinate the emergency operations (Chiroiu et al., 2001). Another disaster-based tool used in pre-disaster management is Vulnerability Mapping, which helps in possible mapping of liquefaction prone areas. Successful uses of remote sensing data have been made for damage assessment in the case of the 1995 Kobe, Japan and the 1999 Kocaeli, Turkey earthquakes (Matsuoka et al., 2000 & Estrada et al., 2000). Recently, military weather satellite DMSP of the U.S., using nighttime lights of the cities has been used to estimate the damaged areas (Kohiyama et al., 2000). Recently developed pseudo-colour transformation techniques (PCT) have been successfully evaluated on these same sets of pre-and post-earthquake datasets. The PCT image depicts liquefaction phenomenon in and around Ghandidham and Kandla that led to sinking of many buildings near Kandla port. Damage assessment of Bhuj earthquake has also been done using Landsat-7 Satellite images (Yusuf et.al., 2001). Even assessment or mapping of damages to homes and ground in water-affected regions during Bhuj quake using IRS-1C & 1D (PAN and LISS-III) pre-and post-earthquake datasets have also been attempted.

A new generation of high resolution optical satellites (IKONOS, TES, EROS etc) provide imagery with 1-meter resolution in panchromatic mode and 4 meters in multispectral. In the near future, less than 1m resolution of Quickbird satellite will be available for the civil applications (0.61 meters in panchromatic mode, 2.8 meters in multispectral). The high level of details makes possible reliable damage detection to the buildings or to other structures (Chiroiu et al., 2001). Figure 2 shows the use of remote sensing image for mapping of building damage due to earthquake (Chiroiu et al., 2001).

Fig 2. (a) Shows badly damaged buildings (red mark)
(c) Shows minor damages caused to buildings and apartments (yellow mark)
Role of Geomatics in Earthquake Forecasting
French micro-satellite DEMETER helps in detection of Electro-magnetic Emissions from earthquake regions, which can be used for earthquake prediction. It is known that the earth’s crust emits electromagnetic signals a few hours before an impending event, which affects the ionospheric electron density in turn. This can be detected may be in near future via the GSAT-2 satellite as it is proved that electromagnetic perturbations and seismic activity have a strong correlation with one another. Satellite thermal survey is a tool for investigations of seismoactive regions and earthquake predictions. The earth's surface images obtained in the thermal IR part of the spectrum are generated due to surface temperature and this is very relevant for studies in seismoactive regions. The NOAA/AVHRR-series satellite thermal images (STI) study have showed the presence of positive anomalies (of the order of 2-3°C) of the outgoing Earth radiation flux recorded at night-time and associated with the largest linear structures and fault systems of the crust (Tronin, 2000). The IR anomalies occur in the weakest and consequently the most 'sensitive' crustal zones i.e. in the point of intersection of major crust faults. These thermal anomalies start appearing prior to the earthquake (7-24 days before) and fade out within a day or two after the quake has occurred. A study of the Central Asian seismoactive region actually gave the idea that there was a statistically significant correlation between the activity of IR anomalies (mean value of area per year or month) and seismic activity. However, none of the above indicators have been established conclusively to be used as earthquake precursors.