Why is Hawaii’s Pahala region shaking?

Update, January 17, 2023: They announced this week that there is probably a sill complex deep below the surface there!

Original post:

That’s one of Hawaii’s famous black-sand beaches. It’s located on the southern part of the Big Island in an area that has had increased seismicity for seven years.

This week, the USGS announced they will be part of a research team investigating the Pahala quakes in depth.

It is intriguing:

…Until 2015, an average of 7 earthquakes occurred deep beneath Pāhala each week. By 2015, the number of earthquakes had approximately quadrupled, with nearly 34 events happening per week. By the spring of 2019, the average number of weekly earthquakes identified in this region increased approximately 70-fold, relative to pre-2015 rates. This high rate of earthquake activity, with several hundred earthquakes occurring in an average week, has continued to the present.

Since August 2020, larger-magnitude earthquakes have also begun to occur deep beneath Pāhala. Eight magnitude-4.2-to-4.6 earthquakes, at depths of 31–34 km (19–21 miles) have been recorded. These larger events have been reported felt by people on the Island of Hawai’i as well as nearby Hawaiian Islands.

HVO, in collaboration with the University of Hawai’i at Mānoa (UHM), will begin an investigation this summer to learn more about the nature of these frequent, deep earthquakes beneath the southern part of the Island of Hawaiʻi.

Previous geophysical studies have theorized that deep earthquake activity beneath the Pāhala region may be related to hot spot magma transport and/or faulting in the brittle upper mantle beneath the island. Interestingly, the area of elevated seismicity is almost equidistant from the summits of the three most active volcanoes in Hawaiʻi: Kīlauea, Mauna Loa, and Kamaʻehuakanaloa (Lō‘ihi Seamount).

Whether this region has a possible connection to the shallower magma storage and transport systems of Kīlauea or Mauna Loa is unclear, but there are no obvious indicators of magma transport from this region to the surface…

This video was posted a year ago.

More on Lo’ihi, which is currently going under another name, here.

This study will be something to follow over the summer!

Featured image: Photo by Robert Linsdell, CC BY 2.0; Map, USGS, public domain

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