M 7.9 - 103 km S of Bengkulu, Indonesia

Tectonic Summary

The June 4, 2000, M 7.9 earthquake off southern Sumatra, one of the many islands in the large Indonesian Island Arc system, occurred as the result of complex, shallow, oblique-reverse faulting near the subduction zone plate boundary between the Australia and Sunda plates. Focal mechanism solutions for the earthquake indicate that rupture occurred on either a steeply dipping, south-southeast-striking reverse fault, or on a moderately dipping, east-striking reverse fault. Both nodal planes are oriented obliquely to the direction of subduction along this arc. Of these two possible fault orientations, finite-fault modeling of globally recorded seismic data is more consistent with slip on the southeast-striking fault. The location, depth, and focal mechanism solutions of the earthquake suggest this is likely an intraslab event, associated with the local subduction zone, but occurring within the downgoing slab rather than on the overlying plate boundary interface. At the location of the earthquake, the Australia plate moves northward beneath the Sunda plate at a velocity of about 60 mm/yr. The Australia plate is seismically active to a depth of about 650 km beneath Sumatra and Java.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Reverse-faulting events of the size of the June 4, 2000, earthquake are typically about 145x40 km (length x width); modeling of this earthquake implies similar dimensions, predominantly surrounding the hypocenter and to the northeast.

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)