Application of GPS in crustal deformation studies: Some case studies


Fig.3 shows GPS network of 14 sites. Amongst these sites, 11 sites are located in the Kutch region. Both Trimble and Leica GPS receivers were used in GPS data collection. Fig.4 shows changes in East-West, North-south and vertical components of the baseline Lodai-Ratanpar ( which passes through the epicentral area) during 21-28 February,2001. During this time, though there were some after shock occurred, no displacement is seen in these components. However, a few days of GPS data analysis will not lead to any conclusion that there is no significant deformation taking place. Once enough data is collected at all the 14 sites, the data analysis will yield velocity distribution from which strain distribution can be estimated. This information can be supplemented by Interferometric Synthetic Aperture Radar (InSAR) (Reddy et al., 2000) results for better reliability on crustal deformation taking place the region


Fig. 4 East-West, North-South and vertical components of baseline Lodai-Ratanpar passing through the epicentral. The estimates are based on analysis of 6 hours data segments during 21-28 February 2001. The lower right corner graph shows the variations in baseline vector. Large errors are associated with the vertical component.

Niijima-Kozushima islands in Japan
Niijima – Kozushima islands in Izu peninsula, Japan started experiencing swarm type seismic activity starting from June 25, 2000. The Geographical Survey Institute (GSI), Japan has dense network of GPS sites around this region. 100 day of GPS data has been analyzed ( using GAMIT software ) at seven sites viz. Ohima, Toshima, Niiijima, Shikene, Kozushima, Miyake and Mikura. Fig. 5 and Fig.6 show the day to day variations of North-South, East-West and Up-down components starting from June 25, 2000 (corresponds to julian day 177) at Niijima the site which is close to the seismic activity and Ohima the site which is away from the activity. From the variations in the components of point position, it is clear that the variations are quite significant at Niijima and quite at Ohima (which is northern site much away from the activity). It is also clear from Fig.5 that, at Niijima there is about 70 mm displacement in the North-south component. This displacement occurred following an earthquake on July 1, 2000 (julian day 197). It is also clear that, it is not necessary that every earthquake cause displacement. The change in Niijima and Kozushima baseline (22 km) is about 80 cm and the linear strain is 37 microstrain. The large strain suggests that the source causing deformation is close to these Islands and the depth to the source is shallow.
Fig. 5 The North-South, East-West and Up-Down components of point position of the site Niijima island during 177-277 julian days of year 2000. The small open triangles on the lower most x-axis indicates the days on which the earthquakes occurred. Note the displacement of about 70 mm in North-South component following the earthquake on julian day 197.



Fig. 6 The North-South, East-West and Up-Down components of point position of the site ohima island during 177-277 julian days of year 2000. The small open triangles on the lower most x-axis indicates the days on which the earthquakes occurred. This site is away from the activity and no significant changes it the displacements.

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