Magnitude | 8.6 - Richter scale |
---|---|
Depth | 22.9 km (14.2 miles) Km |
Location | OFF THE WEST COAST OF NORTHERN SUMATRA LAT 2.311, LON 93.063 |
Date-Time | Apr 11, 2012 08:38:37 UTC |
Source | USGS NEIC (WDCS-D) |
Event ID(s) | usc000905e |
Distances from major cities | |
---|---|
434 km (269 miles) SW of Banda Aceh, Sumatra, Indonesia |
The April 11, 2012, M8.6 and M8.2 earthquakes off the west coast of northern Sumatra, Indonesia, occurred as a result of strike-slip faulting within the oceanic lithosphere of the Indo-Australia plate. The quakes were located respectively 100 km and 200 km to the southwest of the major subduction zone that defines the plate boundary between the India/Australia and Sunda plates offshore Sumatra. At this location, the India/Australia plates move north-northeast with respect to the Sunda plate at a velocity of approximately 52 mm/yr.
Large strike-slip earthquakes are not unprecedented in the diffuse boundary region separating the India and Australia plates, southwest of the Sumatra subduction zone. Since the massive M 9.1 earthquake that ruptured a 1300 km long segment of the Sumatran megathrust plate boundary in December of 2004, three earlier large strike-slip events had occurred within 50 km of the first large April 11, 2012 event. These earthquakes occurred on April 19 2006 (Mw6.2), October 4 2007 (Mw6.2) and January 10, 2012 (Mw7.2). The focal-mechanisms of the three earlier earthquakes and the two great earthquakes of April 11, 2012, are consistent in implying that each earthquake could have occurred as the result of left-lateral slip on a north-northeast striking fault or right-lateral slip on a west-northwest striking fault. The two different orientations of strike-slip faulting are both possible under the same tectonic stress field; perpendicular strike-slip faults that are both compatible with the same stress field are called "conjugate faults". Possibly faults of both orientation have been involved in the recent earthquake activity.