M 7.0 - 156 km NW of Tobelo, Indonesia

Tectonic Summary

The January 18, 2023, M 7.0 earthquake northwest of the island of Halmahera, Indonesia, occurred at a depth of ~48 km in the very complex plate boundary region of eastern Indonesia, about 200 km to the southwest of the major plate boundary between the Sunda Plate and Philippine Sea Plate. Moment tensor solutions for the event indicate near-vertical strike-slip faulting, with slip either on a right-lateral fault striking to the northeast, or a left-lateral fault striking to the northwest. This event occurred near the boundary between the Halmahera slab and the Sunda Slab. The Halmahera slab is completely subducted and has no surface expression. Slip on a fault aligned with either nodal plane is consistent with the tectonic setting of this event.

Tectonics in eastern Indonesia are extremely complex and are dominated by the mostly convergent interactions of the Pacific, Australia, Philippine Sea, and Sunda plates, with some authors labeling the most proximate edge of the Pacific plate here as a separate tectonic block called the Caroline plate. The edges of the Sunda and Australia plates are also often subdivided into smaller tectonic blocks, including the Molucca Sea and Birds Head microplates. At the location of the January 18th earthquake, the Sunda and Philippine Sea plates are converging in north-south direction at a rate of approximately 78 mm/yr.

This area of the Molucca Sea frequently hosts moderate to large earthquakes. 18 M 7+ events have occurred within 250 km of the January 18th, 2023, earthquake over the past century. The largest was an estimated M 7.8 earthquake in April 1936. Despite the large number of events in the region, few have been damaging because of their oceanic setting.