Tectonic Summary

The January 21, 2007, M 7.5 Molucca Sea earthquake occurred as the result of shallow reverse faulting on or near the boundary between the Sunda plate and the Birds Head microplate, one of the many small microplates in the region of eastern Indonesia that together accommodate the relative convergence between the Australia, Sunda, Philippine Sea, and Pacific plates. Focal mechanism solutions indicate that rupture occurred on either a steeply dipping reverse fault or a shallowly dipping thrust fault. Of these two possible fault orientations, finite-fault modeling of globally recorded seismic data is more consistent with slip on the shallowly dipping fault. At this location, the Sunda and Philippine Sea plates are converging in an east-west direction at a rate of approximately 109 mm/yr.

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 May 3, 2006, earthquake are typically about 80x40 km (length x width); modeling of this earthquake implies dimensions of about 150x40 km, predominantly surrounding the hypocenter and to the northeast.

Frequent volcanic eruptions and earthquakes testify to the active tectonic processes that are currently in progress in response to the continued movement of the Australia, Sunda, and Pacific plates. The distribution of small ocean basins, continental fragments, remnants of ancient magmatic arcs, and numerous subduction complexes that make up the Indonesian region indicate that its history was equally tectonically active. Eleven earthquakes of M 7+ have occurred within 400 km of the January 21st event over the preceding 40 years. The largest of these earthquakes was a M 7.8 event in April 1990, roughly 350 km to the west, that resulted in at least 3 fatalities and 25 injuries.

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)

Event Details

Event Map

Tectonic Summary

Tectonic Summary

Historical Magnitude 4.5+ (100km)