Poster of the Java, Indonesia Earthquake of 02 September 2009 - Magnitude 7.0

Tectonic Summary

The Java earthquake of September 02, 2009, occurred at a depth of about 50 km as a result of reverse faulting. The tectonics of Java are dominated by the subduction of the Australia plate north-northeastward beneath the Sunda plate, with a relative velocity of 59 mm/year at the longitude of the earthquake. Although the September 02 shock's hypocenter would place it near the subduction interface between the Australia and Sunda plate, the orientation of the causative fault that is inferred from the seismic wave radiation-pattern is inconsistent with the shock occurring as interplate faulting on that interface. Instead, the earthquake likely occurred as the result of faulting within the subducting Australia plate.

The region of the plate boundary between the Australia plate and Sunda plate is seismically highly active, with past strong earthquakes having occurred within each of the Australia and Sunda plates as well as on the plate interface. The magnitude 7.8 earthquake of June 2, 1994 and the magnitude 7.7 earthquake of July 17, 2006, both of which occurred south of Java and both of which produced destructive tsunamis, occurred as the result of thrust faulting on the shallow plate interface near the Java trench. The devastating Yogyakarta earthquake of May 26, 2006, magnitude 6.3, occurred at shallow depth within the overriding Sunda plate. The magnitude 7.5 Java earthquake of August 28, 2007, occurred at a depth of about 290 km within the subducted Australia plate.