Surface Deformation Caused By The 2004 Indian Ocean Tsunami Observed At Diego Garcia

The large mass of water move with tsunami, and its loading causes surface deformation. Several previous researches reports about this. Nawa et al. (2007) demonstrated loading effects of the 2004 Indian Ocean tsunami observed by broadband seismometers at Syowa station, Antarctica. Yuan et al. (2005) also showed loading effects of the tsunami by broadband seismometers installed along the coastal area around the Indian Ocean. Because detections of such surface deformation give data independent of tide gauge data, the detections are important for study on tsunami source mechanisms. We report the tsunami loading effect observed by broadband seismometer at Diego Garcia, British Indian Ocean Territory and compare with synthesis calculated from the model. In this study, we analyzed seismic records at the Diego Garcia (DGAR) seismic station operated by IRIS (Incorporated Research Institutions for Seismology). The velocity records were detrended and deconvolved with the instrumental response. After the deconvolution, we applied low-pass filtering with a cut-off frequency of 10-360secnd to remove short- and long-period noises. Focusing on STS-1 record around tsunami arrival time at DGAR, significant variation shoeing longer period than expected seismic wave is prominent. For confirmation of the detection of tsunami loading effect by the broadband seismometer records, we calculated tilt change expected from tsunami source proposed by Fujii and Satake (2007). The calculation is performed by taking a convolution of the Green"fs function and the sea level variation based on the tsunami propagation. Green"fs function for surface deformation caused by loading is given by Farrell (1972). When temporal-spatial resolution of sealevel data is 5min and 18.5km, the calculation and observation show good agreement. Using higher resolution data (1min, 0.74km), amplitude of calculation is closer to observation. But agreement of phase is get worse. As future works, we plan to evaluate accuracy of the calculation and present results.