October 25, 2010 Earthquake: Sumatra, Indonesia

Felt Reports

At least 445 people killed, 498 injured and 58 missing from the earthquake and a tsunami which had maximum wave heights of 7 meters on Pulau Pagai Utara, 3-5 meters on Pulau Pagai Selatan and 3 meters on Pulau Sipura. Felt (V) on Pulau Pagai Selatan. Felt (IV) at Padang and Pariaman; (III) at Bengkulu, Bukittinggi, Ketaun and Sungaipenuh; (II) at Kapahiang, Sumatra. Felt at Petaling Jaya, Malaysia

and (II) in Singapore. The following maximum tsunami

amplitudes were recorded on the these selected tide

gauges: 33 cm at Padang, 26 cm on Pulau Enggano and 23

cm on Pulau Tanahbala, Indonesia; 23 cm on Cocos

Island and 8 cm at Hillarys Boat Harbor, Australia; 7

cm on Diego Garcia; 11 cm at Male, Maldives; 40 cm at

Port Mathurin and 28 cm at Port Louis, Mauritius; 12

cm at Pointe Larue, Seychelles; 9 cm at Colombo, Sri

Lanka.

Tectonic Summary

The Pulau Pagai Selatan, Sumatra earthquake of October 25, 2010 occurred as a result of thrust faulting on or near the subduction interface plate boundary between the Australia and Sunda plates. At the location of this earthquake, the Australia Plate moves north-northeast with respect to the Sunda plate at a velocity of approximately 57-69 mm/yr. On the basis of the currently available fault mechanism information and earthquake depth it is likely that this earthquake occurred along the plate interface. The subduction zone adjacent to the region of this event last slipped during the Mw 8.5 and 7.9 earthquakes of September 2007, and today's event appears to have occurred near the rupture zones of those earthquakes. Today's earthquake is the latest in a sequence of large ruptures along the Sunda megathrust, including a M 9.1 earthquake that ruptured to within 800 km north of this earthquake in 2004; a M 8.6 700 km to the north between Nias and Simeulue in 2005; and a M 7.5 300 km to the north near Padang in 2009. Today's earthquake occurred near the southern edge of a Mw 8.7-8.9 rupture in 1797 and within the rupture area of a Mw 8.9-9.1 earthquake in 1833.

(above from reference #1053)

Based on information gathered from eyewitness interviews conducted during the survey, the earthquake was not strongly felt. Residents described it as a gentle, slow,

rocking earthquake that lasted for several minutes. These

accounts are consistent with seismological observations that

this earthquake was deficient in high-frequency energy and had a long rupture time, a defining feature of tsunami earthquakes. (reference #10265)