A swarm of 28 tectonic earthquakes rumbled below Mauna Kea yesterday

A swarm of about 28 tectonic earthquakes beneath the northeast side of Mauna Kea, in the Hāmākua region, was detected yesterday.

According to the U.S. Geological Survey (USGS) Hawaiian Volcano Observatory, these earthquakes mainly occurred at depths between 5 and 10 kilometers (3 and 6 miles) below the ground surface. The largest of these events were two magnitude-3 earthquakes, each with a couple of felt reports.

On Thursday, March 26, between 2 p.m. and 10 p.m. HST, the USGS Hawaiian Volcano Observatory recorded these earthquakes.

During the first few hours of the swarm, the earthquake rates were lower. Following the two magnitude-3 earthquakes, which occurred about one hour apart, the seismic activity stopped for about 90 minutes before resuming.

These tectonic events are not related to magma movement. Over the past 25 years, similar clusters of earthquakes in this region occurred in 2002, 2004, 2006, 2008, and 2010, along with a scattering of isolated earthquakes over time.

Maximum magnitudes have all been in the magnitude-3 range, with most earthquakes less than magnitude 2. The depth of these earthquakes places them beneath the Mauna Kea edifice and into the underlying Kohala volcano, whose rift zone extends to the submarine Hilo Ridge east of Mauna Kea.

These earthquakes appear to be related to the periodic release of stress in the elongated Kohala edifice. Stress gradually accumulates over time, likely due to the weight of the island. They do not appear to be directly related to the older submarine Laupāhoehoe slump or to flexural bending of the underlying oceanic lithosphere, according to the Hawaiian Volcano Observatory.

The Hawaiian Volcano Observatory will continue to closely track changes in seismic activity and monitor Hawaiian volcanoes for any changes.