2:15 PM - 2:30 PM
[J09-1-04] Tsunami source of the 1979 Tumaco Earthquake estimated from historical tide gauge records and geodetic data
On December 12, 1979 an earthquake occurred in southern coast of Colombia , in front of Tumaco area (1.60N 79.36W, 07:59:03.300 UTC according to U.S. Geological Service). The surface-wave magnitude of this event was estimated as Ms7.7 (USGS), and its moment magnitude was calculated as Mw8.1 (GCMT Catalog). The epicenter was located 80 km southwest of Tumaco, offshore the Pacific coast of Colombia. This event generated a tsunami that killed more than 100 residents of San Juan Island, 60 km north of Tumaco. The observed coastal subsidence, due to the coseismic deformation, was approximately 0.50 m near Tumaco area (Herd et al., 1981).
This study aims to investigate the tsunami source of the 1979 Great Tumaco Earthquake using inversion of historical recorded tsunami waveform and geodetic data. We employ the tsunami signal recorded at three tide gauge stations (Esmeraldas and Santa Cruz in Ecuador, and Acujutla in El Salvador). To estimate the extent of the tsunami source and the slip distribution, we divide the tsunami source into 5 x 2 subfaults along the strike and dip directions, respectively. The assumed fault area covers the aftershock distribution during one month after the mainshock. The subfault size is 40 km x 40 km with top depths of 12.9 km and 24.0 km. The focal mechanisms for all the subfaults were taken form the GCMT solution of the mainshock.
The inversion result using only tsunami data, and the joint inversion of tsunami and geodetic data showed that the largest slip was located north the epicenter with an average slip of 5.4 m. The estimated moment magnitude from both inversion models was nearly identical Mw=8.03 (1.38E+21 N-m), which is slightly smaller than the published by GCMT (Mw=8.1, moment 1.60E+21 N-m). The estimated slip distribution suggested that the fault rupture started near the epicenter and propagated northeast, which is also supported by the aftershock distribution (Herd at al., 1981).
This study aims to investigate the tsunami source of the 1979 Great Tumaco Earthquake using inversion of historical recorded tsunami waveform and geodetic data. We employ the tsunami signal recorded at three tide gauge stations (Esmeraldas and Santa Cruz in Ecuador, and Acujutla in El Salvador). To estimate the extent of the tsunami source and the slip distribution, we divide the tsunami source into 5 x 2 subfaults along the strike and dip directions, respectively. The assumed fault area covers the aftershock distribution during one month after the mainshock. The subfault size is 40 km x 40 km with top depths of 12.9 km and 24.0 km. The focal mechanisms for all the subfaults were taken form the GCMT solution of the mainshock.
The inversion result using only tsunami data, and the joint inversion of tsunami and geodetic data showed that the largest slip was located north the epicenter with an average slip of 5.4 m. The estimated moment magnitude from both inversion models was nearly identical Mw=8.03 (1.38E+21 N-m), which is slightly smaller than the published by GCMT (Mw=8.1, moment 1.60E+21 N-m). The estimated slip distribution suggested that the fault rupture started near the epicenter and propagated northeast, which is also supported by the aftershock distribution (Herd at al., 1981).