Volcano Minute is a weekly audio activity or science update produced by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.

Although the earthquake looked like it happened on Mauna Loa based on its map location, it actually occurred beneath Mauna Loa and the Island of Hawaiʻi, in the Pacific Plate—about 14 miles below sea level. The earthquake was caused by the Pacific Plate bending under the immense weight of the Hawaiian Islands. These flexure earthquakes can be felt far and wide because the basaltic crust carries seismic energy extremely well in the Pacific Plate. 

Since 1950, there have been 12 earthquakes in Hawaii magnitude-6 or larger. Many of these earthquakes, including the damaging magnitude-6.7 Kīholo Bay earthquake in 2006, occurred because of the Pacific Plate flexing from the weight of the Hawaiian Islands. Others were due to flank movement within Kīlauea and Mauna Loa volcanoes, such as the magnitude-6.9 Kīlauea south flank earthquake in 2018 that occurred as magma was moving into the lower East Rift Zone of that volcano.  

Friday’s earthquake is a good reminder: Hawaii is one of the most seismically active places in the country. Earthquakes can strike without warning, so remember—Drop, Cover, and Hold On. And if you’re near the coast, be ready to move inland in case a tsunami is generated. 

Mahalo for listening, I’m Katie Mulliken and this was your weekly volcano minute brought to you by the USGS Hawaiian Volcano Observatory.