Revising the seismic source of the 1979 Tumaco-Colombia earthquake (Mw = 8.1) for future tsunami hazard assessment

Abstract

The 1979 Great Tumaco earthquake occurred on 12 December and had a moment magnitude of Mw = 8.1. Its epicenter was located about 10 km offshore the Colombia-Ecuador Pacific border. This earthquake generated a catastrophic tsunami that destroyed several small communities on South America's Pacific coast. Several locations in Central America and in Hawaii also recorded tsunami waves with heights up to 50 cm. Thus, understanding this event's source characteristics and effects is vital for future tsunami hazard assessments in countries in the Pacific Ocean. This study revised the earthquake source using a joint inversion of tsunami waves and geodetic records. Further, this study also analyzed the tsunami propagation characteristics on the Pacific coast of North and South America using the revised earthquake source model.

The inversion results indicate that the earthquake source presented main slip asperities north of the epicenter, with a maximum slip of 3.40 m. It also presented a second large slip of 2.87 m, located south of the epicenter. The earthquake also generated a ground subsidence of up to 50 cm along the Ecuador-Colombia coastline. The uplifted zone was estimated beneath the sea, with the most significant displacement area north of the epicenter, with a maximum uplift of 1.16 m. The comparison between the observed and simulated tsunami waveforms of the 1979 Tumaco earthquake shows that, in general, there is a good correlation for the first period of the tsunami waveforms. The tsunami simulation results suggest a maximum coastal tsunami height of 3.5 m along the coast of Panama and Costa Rica, about 600 km from the earthquake source area.