M 7.0 - 66 km SSW of Banjar, Indonesia

Tectonic Summary

The September 2, 2009, M 7.0 Java earthquake occurred at a depth of about 50 km as the result of reverse faulting near the boundary between the Australia and Sunda plates. Focal mechanism solutions indicate that rupture occurred on either a north-northeast- or south-striking, moderately dipping reverse fault. At the location of the earthquake, the Australia plate moves north-northeastward with respect to the Sunda plate at a velocity of about 59 mm/yr. Although the September 2nd event’s hypocenter would place it near the subduction interface between the Australia and Sunda plates, the orientation of the causative fault that is inferred from the seismic-wave radiation pattern is inconsistent with the earthquake occurring as interplate faulting on that interface. Instead, the earthquake likely occurred as the result of faulting within the subducting Australia plate. Slip on a fault aligned with either nodal plane of the focal mechanism solution is consistent with this intraplate setting.

The region of the plate boundary between the Australia plate and Sunda plate is highly seismically active, with past strong earthquakes having occurred within each of the Australia and Sunda plates as well as on the plate interface. The M 7.8 earthquake of June 2, 1994, and the M 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 Sunda-Java Trench. The devastating Yogyakarta earthquake of May 26, 2006, M 6.3, occurred at shallow depth within the overriding Sunda plate. The M 7.5 Java earthquake of August 28, 2007, occurred at a depth of about 290 km within the subducted Australia plate.

Hayes et al. (2016) Tectonic summaries of magnitude 7 and greater earthquakes from 2000 to 2015, USGS Open-File Report 2016-1192. (5.2 MB PDF)