Tectonic Summary

The Oct 10, 2021, M6.2 occurred as the result of oblique reverse faulting, at a depth of 35 km (22 miles). Earthquakes at this depth are likely mantle events associated with lithospheric flexure caused by the weight of the Hawaiian islands on the surrounding oceanic lithosphere. This earthquake is not associated with a swarm of deep earthquakes near Pahala on Hawaii's south-central coast, which has been ongoing for a few years.

The Island of Hawaii is the youngest island in a chain of volcanoes that stretches about 5,500 km across the northern Pacific Ocean. The island chain results from a magma source that originates deep beneath the crust. The ocean crust and lithosphere above the magma source, within the Pacific tectonic plate, move to the northwest with respect to the deep magma source. Over millions of years, new island volcanoes are formed, and older volcanoes are carried away from the magma source (towards the northwest), erode, and eventually subside beneath sea level.

Non-volcanic Hawaiian earthquakes reflect the long-term accumulation and release of lithospheric stresses, rather than short-term processes associated with the motion of magma before or during an eruption. The long-term stresses consist in part of stresses generated in the crust and mantle by the weight of the volcanic rock that composes the islands. In that sense, most Hawaiian earthquakes that are not directly associated with eruptions are nonetheless broadly related to volcanic activity.

Since 1990 there have been four M5-5.5 earthquakes in the offshore region south of Hawaii nearby the October 10, 2021 event at a similar depth. In the past century, there have been 63 earthquakes M5 or greater within 100 km of the October 10, 2021 event, including 15 earthquakes of M6 or larger. The largest event in the broader region was the Mw 7.7 Kalapana earthquake in 1975 that occurred 80 km to the northeast of the Oct 10th , 2021 earthquake. The 1975 Kalapana earthquake also generated a local tsunami that took 2 lives. Damage due to the 1975 earthquake and tsunami was estimated to total $4.1 million in Hawaii.

Event Details

Event Map