Hawaii Volcano Blog

Back-to-Back Quakes Shake Same Spot Under Mauna Loa Saturday

April 3, 2021, 1:27 PM HST
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Two moderate earthquakes struck the slopes of Mauna Loa Saturday, April 3, just before noon.

The US Geological Survey’s Hawaiian Volcano Observatory (HVO) recorded a magnitude-4.3 earthquake located beneath Mauna Loa’s south flank at 11:15 am, HST. This earthquake was preceded by a magnitude-3.9 at approximately the same location on 11:02 am, HST.

The magnitude-4.3 earthquake epicenter was three miles NW of Pāhala, near Wood Valley, with a depth of approximately five miles below sea level. The location can be found on the HVO website. More details are available at the National Earthquake Information Center website.

Weak to light shaking, with maximum Intensity of IV on the Modified Mercalli Intensity Scale, has been reported across the Island of Hawai‘i. At this intensity, significant damage to structures is not expected. The USGS “Did you feel it?” service (http://earthquake.usgs.gov/dyfi/) received over 130 felt reports within the first hour of the earthquake, including one report from Kaua‘i.

According to HVO Scientist-in-Charge Ken Hon, the earthquake had no apparent effect on Mauna Loa or Kīlauea volcanoes.

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“At this time, we have not observed any changes in activity at Mauna Loa or Kīlauea as a result of this earthquake,” Hon said. “Please be aware that aftershocks are possible and may be felt. HVO continues to monitor Kīlauea and other Hawaiian volcanoes for any changes.”

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Both the magnitude-4.3 and magnitude-3.9 earthquakes appear to be slip along vertical faults caused by southeast motion of Mauna Loa’s south flank. Today’s earthquakes are significantly shallower and west of the location of the ongoing seismic swarm under the Pāhala area that began in August 2019.

This does not represent a significant departure from the seismic activity observed over the past year and the Volcano Alert Level for Mauna Loa remains at ADVISORY. Other Mauna Loa monitoring data streams show no significant change in deformation rates or patterns that would indicate increased volcanic hazard at this time.

HVO continues to monitor Hawaiian volcanoes for any changes. The Alert Levels/Color Codes remain at WATCH/ORANGE for Kilauea and at ADVISORY/YELLOW for Mauna Loa at this time.

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For information on recent earthquakes in Hawai´i and eruption updates, visit the USGS Hawaiian Volcano Observatory website at https://www.usgs.gov/observatories/hawaiian-volcano-observatory.

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