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THE EARTHQUAKE AND TSUNAMI OF 27 FEBRUARY 2010 IN CHILE – Evaluation of Source Mechanism and of Near and Far-field Tsunami Effects

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Author(s): George Pararas-Carayannis

Journal: Science of Tsunami Hazards
ISSN 8755-6839

Volume: 29;
Issue: 2;
Start page: 96;
Date: 2010;
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Keywords: Tsunami | Chile | seismotectonics | Peru-Chile subduction | energy trapping.

ABSTRACT
The great earthquake of February 27, 2010 occurred as thrust-faulting along a highly stressed coastal segment of Chile's central seismic zone - extending from about 33oS to 37oS latitude - where active, oblique subduction of the Nazca tectonic plate below South America occurs at the high rate of up to 80 mm per year. It was the 5th most powerful earthquake in recorded history and the largest in the region since the extremely destructive May 22, 1960 magnitude Mw9.5 earthquake near Valdivia. The central segment south of Valparaiso from about 34o South to 36o South had been identified as a moderate seismic gap where no major or great, shallow earthquakes had occurred in the last 120 years, with the exception of a deeper focus, inland event in 1939. The tsunami that was generated by the 2010 earthquake was highest at Robinson Crusoe Island in the Juan Fernández archipelago as well as in Talchuano, Dichato, Pelluhue and elsewhere on the Chilean mainland, causing numerous deaths and destruction. Given the 2010 earthquake’s great moment magnitude of 8.8, shallow focal depth and coastal location, it would have been expected that the resulting tsunami would have had much greater Pacific-wide, far field effects similar to those of 1960, which originated from the same active seismotectonic zone. However, comparison of the characteristics of the two events indicates substantial differences in source mechanisms, energy release, ruptures, spatial clustering and distributions of aftershocks, as well as in geometry of subduction and extent of crustal displacements on land and in the ocean. Also, the San Bautista and the Juan Fernández Islands - ridges rising from the ocean floor – as well as the O’Higgins seamount/guyot may have trapped some of the tsunami energy, thus accounting for the smaller, far field tsunami effects observed elsewhere in the Pacific. Apparently, complex, localized structural anomalies and interactions of the Nazca tectonic plate with that of South America, can account for differences in the spatial distribution and clustering of shallow event hypocenters, as well as for seismic gaps where large tsunamigenic earthquakes could strike Chile’s Central Seismic zone in the future.
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