Validation
Most of the field reports after the Gujarat earthquake present a disastrous situation of the city: "The old town of Bhuj, completely destroyed…" (AFPS 2001), or "several towns, like Bhuj (…) sustained widespread destructions" (EERI 2001). The spatial distribution of damages estimated by our study shows a high level of losses in the north side of the city, in the "old town". The dimensions of the damages in this part of the city are expressed clearly by some pictures taken after the earthquake (fig. 5, a and b).
One of the last official statistics of losses for the city of Bhuj are given by a UNDMT report of January 29 th , where the number of dead persons is 5,065 and of the injured persons is 10,925. After this date, the losses are quantified for the entire Katchch region, and there are no other statistics of losses only for the city of Bhuj. One of the last reports of losses gives a number of around 20,000dead persons and around 167,000 injured persons for the Kachch region, where cities like Anjar and Bachau (both with around 51,000 people) have suffered serious destructions.
The loss estimation performed in this work, in terms of human casualties, is not far from the last official statistics concerning the number of dead persons (4404 dead persons in this study vs. 5065 of the official statistics). A slight underestimation (lesser than 10%) may be due to the impossibility to recognize moderate and slight damage. The same constraint could explain the difference between the number of injured persons, which could be in reality between 5 and 10 times higher.
Conclusions
The high resolution satellite imagery offers new possibilities for the earthquake damage
assessment. A multidisciplinary approach combining remote sensing techniques, spatial analysis and earthquake engineering can provide a fast loss estimation. Photo interpretation techniques applied to 1 meter resolution images, in mono or multi temporal analysis, enable, for the case of Bhuj, a damage assessment with a high degree of accuracy. Losses can be quantified using a GIS, in terms of damaged area, and human casualties can be estimated applying computations based on simplified approaches.
Depending on the surface to be treated and the number of persons involved in the study, a near real time damage assessment could be possible. The feasibility of the application is conditioned by a fast imagery purchasing, which must be done immediately after the catastrophe and focused on the major urban zones; in the same time, the cloud coverage represent obviously an important factor constraining the acquisition. 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 better coordinate the emergency operations.
References
- Association Française de Génie Parasismique AFPS (2001). Le séisme de Bhuj (Gujarat, Inde) du 26 janvier 2001. Rapport de Mission, Paris, France.
- EDM (2000, b). The Bhuj Earthquake of January 26, 2001. Consequences and Futurs Challenges. Earthquake Disaster Mitigation Center; The Institute of Physical and Chimical Research (RIKEN). Miki, Hyako Prefecture, Japan;
www.edm.bosai.go.jp
- EERI (2001). Preliminary Observations on the Origin and Effects of the January 26, 2001 Bhuj (Gujarat, India) Earthquake. EERI Newslettres, Vol. 35, N°. 4; Oakland
- R. Eguchi et al (2000). Using Advanced Technologies to Conduct Earthquake Reconnaissance after the 1999 Marmara Earthquake; 2 nd Workshop on Advanced Technologies in Urban Earthquake Disaster Mitigation, DPRI, Kyoto University, Uji, Kyoto, Japan.
- NIBS (1999). HAZUS - Earthquake Loss Estimation Methodology. Technical Manual, Vol. III, Washington, D.C.
- M. Tralli (2001). Assessment of Advanced Technologies for Loss Estimation. Multidisciplinary Center for Earthquake Engineering Research; State University of New York at Buffalo Research Foundation, NY.
- United Nations Disaster Management Team (2001). India Earthquake Reports N° 1 - 21. www.reliefweb.org World Bank and Asian Development Bank (2001). Gujarat Earthquake Recovery Program; Assessment Report;
www.worldbank.org
TABLE 2. Loss estimation computation.
|
Damage Level
|
Density (people/km2)
|
Area (km2)
|
Affected People
|
Death Rate
|
Injury Rate
|
Injured Persons
|
Dead Persons
|
|
ED
|
28140
|
0.25
|
7 035
|
5%
|
60%
|
4221
|
352
|
|
CD
|
28140
|
0.18
|
5 065
|
80%
|
20%
|
1013
|
4052
|
| |
|
|
|
|
Total |
5234
|
4404 |