Slip Distribution and Seismic Moment of the 2010 and 1960 Chilean Earthquakes Inferred from Tsunami Waveforms and Coastal Geodetic Data

Yushiro Fujii,Kenji Satake

doi:10.1007/s00024-012-0524-2

Abstract

The slip distribution and seismic moment of the 2010 and 1960 Chilean earthquakes were estimated from tsunami and coastal geodetic data. These two earthquakes generated transoceanic tsunamis, and the waveforms were recorded around the Pacific Ocean. In addition, coseismic coastal uplift and subsidence were measured around the source areas. For the 27 February 2010 Maule earthquake, inversion of the tsunami waveforms recorded at nearby coastal tide gauge and Deep Ocean Assessment and Reporting of Tsunamis (DART) stations combined with coastal geodetic data suggest two asperities: a northern one beneath the coast of Constitucion and a southern one around the Arauco Peninsula. The total fault length is approximately 400 km with seismic moment of 1.7 × 1022 Nm (Mw 8.8). The offshore DART tsunami waveforms require fault slips beneath the coasts, but the exact locations are better estimated by coastal geodetic data. The 22 May 1960 earthquake produced very large, ~30 m, slip off Valdivia. Joint inversion of tsunami waveforms, at tide gauge stations in South America, with coastal geodetic and leveling data shows total fault length of ~800 km and seismic moment of 7.2 × 1022 Nm (Mw 9.2). The seismic moment estimated from tsunami or joint inversion is similar to previous estimates from geodetic data, but much smaller than the results from seismic data analysis.

Highlights

Great (M [ 8) or giant (M [ 9) earthquakes have repeatedly occurred off the western coast of South America, where the Nazca Plate is subducting beneath the South American Plate with convergence speed of about 7.0 cm/year (ALTAMIMI et al, 2007)
Inversion of tsunami waveforms alone shows two large slip regions; the first one is in the central part of the source area around Constitucion, and the second one is to the south near the Arauco Peninsula (Fig. 6a; Table 1)
We examined the tsunami waveforms, or tsunami Green’s functions, at the coastal tide gauge and Deep Ocean Assessment and Reporting of Tsunamis (DART) stations from each subfault, and found that the tsunami waveforms from offshore subfaults arrive at the DART stations earlier than observed

Summary

Introduction

Great (M [ 8) or giant (M [ 9) earthquakes have repeatedly occurred off the western coast of South America, where the Nazca Plate is subducting beneath the South American Plate with convergence speed of about 7.0 cm/year (ALTAMIMI et al, 2007). Along the southern Chilean coast, where a giant earthquake (M 9.5) occurred around Valdivia in 1960, historical data show that great earthquakes have recurred with average interval of 120 years (LOMNITZ, 1970). The Maule earthquake occurred on 27 February 2010 [06:34:14 UTC, 35.931 S, 72.784 W, 35 km, M 8.8 according to the US Geological Survey (USGS)] and generated a tsunami that caused significant damage on the Chilean coast. Among them, VIGNY et al (2011) compiled the slip distributions from the aforementioned studies and compared them with the observed GPS data. While these models all show that there were two large slip patches, or asperities, their locations vary. Some models (LAY et al, 2010; VIGNY et al, 2011) show that both asperities are offshore, while others show a more coastal location (DELOUIS et al, 2010; LORITO et al, 2011)

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