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Analysis of the Tsunami Generated by the Great 1977 Sumba Earthquake that Occurred in Indonesia

Institute of Seismology and Volcanology, Hokkaido University, Kita 10 Nishi 8 Kitaku, Sapporo 060-0810, Japan

Hiroyuki Matsumoto

Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima, Yokosura 237-0061, Japan

Sin-Iti Iwasaki

National Research Institute for Earth Science and Disaster Prevention, 3-1 Tennodai, Tsukuba 305-0006, Japan

The great outer-rise earthquake (M_w 8.3) occurred near the Sunda trench, Indonesia, on 19 August 1977. The earthquake has been previously studied using seismological data. The earthquake generated a large tsunami that caused severe damage in Sumbawa and Sumba Islands in Indonesia. The tsunami was also observed at tide gauges in Australia. We numerically computed a far-field tsunami, and we compared the observed tsunami waveforms on three tide gauges with the computed waveforms. We also numerically computed the tsunami inundation and compared the observed tsunami run-up of 8 m and tsunami inundation distance of 500 m in Lunyuk on Sumbawa Island with the computed ones. To explain the observed tsunami waveforms, tsunami run-up, and tsunami inundation distance, the slip amount is found to be 3 m on the assumed fault model (with a fault length of 200 km and fault width of 70 km). The rigidity is assumed to range between 6.0 and 6.8x10¹⁰ N m^-2, and the range of the total seismic moment is calculated to be between 2.5 and 2.9x10²¹ N m (M_w 8.2), which is similar to those estimated by the previous seismological studies. Additionally, we calculated the ratio between the observed tsunami run-up and the computed maximum tsunami height along the coastline of Lunyuk. This ratio, called the amplification factor, may possibly be used to roughly estimate the tsunami run-up from a tsunami numerical calculation result on a coarse grid system.