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Ground Motions of the Sumatra Earthquakes of 2004 and 2005

by Paul G. Somerville, Hong Kie Thio and Gene Ichinose

Somerville, Paul G., Hong Kie Thio and Gene Ichinose (2005). Ground Motions of the Sumatra Earthquakes of 2004 and 2005. SMIP05 Seminar on Utilization of Strong-Motion Data, p. 107 - 114.

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Abstract

The Sumatra earthquakes of December 26, 2004 (Mw 9.15) and March 28, 2005 (Mw 8.7) are the largest subduction earthquakes that have ever been recorded on modern digital instruments. Both earthquakes were caused by the subduction of the India–Australia plate beneath the Eurasian Plate. Although these earthquakes were not recorded on scale at close distances, they were recorded at regional distances. These regional recordings shown strong spatial variations in amplitude and duration that are consistent with rupture directivity effects. The duration of ground motion of the December event to the north in Thailand was about 600 seconds, while the duration in other directions, including Sumatra, was about 1,000 seconds.