ABSTRACT: Inverse analysis on the tsunami source of the 2011 off the Pacific coast of Tohoku Earthquake (Mw 9.0) was conducted on the basis of offshore sea-level observation near the source area. The effect of rupture process to a tsunami source inversion was investigated by a comparison between tsunami source models with assumptions of infinite and finite rupture velocity.
INTRODUCTION On 11 March, 2011, the 2011 off the Pacific coast of Tohoku Earthquake (the 2011 Tohoku earthquake, hereafter) occurred along the Japan Trench subduction zone. The Japan Meteorological Agency (2011) reported that the moment magnitude (Mw) of the earthquake was 9.0 and the epicenter was at N38º 6.2′, E142º 51.6′ and 24 km deep. Large tsunamis were generated by the earthquake, causing severe damage and loss of life over wide areas along the Pacific coast of Japan. These were successfully observed at offshore tsunami observation stations around Japan, such as GPS buoys (e.g., Kato et al., 2005) and cabled ocean-bottom pressure gauges (e.g., Meteorological Research Institute, 1980). Tsunami heights exceeded 5 m at offshore observatories near the tsunami source. For example, a water rise of 6.7 m was observed at the Central Iwate GPS buoy (Fig. 1). To reveal tsunami source is important for better understanding of the mechanism of tsunami genesis and improvement of the accuracy of tsunami forecast. In a case of tsunami generated by such a spatially and temporally large-scale tectonic deformation, not only the spatial distribution but also the temporal development of rupture motion may not be negligible. The objective of this paper is to develop a new inversion method of tsunami source including rupture processes with both spatial and temporal distribution and to evaluate it based on offshore observation data of the 2011 Tohoku Tsunami.