M 7.7 - 226 km SSW of Singaparna, Indonesia

Tectonic Summary

The July 17, 2006, M 7.7 earthquake south of Java occurred as the result of shallow thrust faulting on or near the boundary between the Australia and Sunda plates, 50 km to the north of the Sunda-Java Trench that marks the sea-floor expression of this plate boundary. At the location of the earthquake, the Australia plate moves north-northwest relative to the Sunda plate, subducting at a velocity of about 59 mm/yr to progressively greater depths beneath Java and north of Java. The earthquake occurred on the shallow part of the plate boundary.

The region of the plate boundary between the Australia and Sunda plates is seismically highly active. From preliminary results, it appears that the July 17th earthquake is similar to the M 7.8 Java earthquake of June 2, 1994, which produced a tsunami that had a maximum run-up height of 13 m and resulted in more than 200 fatalities. That earthquake occurred south of Java about 600 km east-southeast of the July 17th earthquake, also as a result of thrust faulting on the shallow plate boundary. Events like these, which produce disproportionately large tsunamis given their moment magnitude, have been termed “tsunami earthquakes.” On August 20, 1977, a M 8.3 normal-fault earthquake occurred within the Australia plate about 1,200 km east-southeast of the July 17th earthquake, producing a tsunami that had a maximum run-up height of 15 m and resulted in nearly 200 fatalities. The M 6.3 Yogyakarta earthquake on May 26, 2006, a shallow rupture in the overriding Sunda plate near the Java coastline, 350 km northeast of the July 17, 2006, event, devastated the local population, causing more than 5,000 fatalities, nearly 40,000 injuries, and major damage.

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)