“Volcano Watch” is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.
More than 7,000 people from throughout all Hawaiian Islands submitted “Did You Feel It?” reports to U.S. Geological Survey after a magnitude-6.0 earthquake that struck at 9:46 p.m. Friday, May 22, in the South Kona area on the west side of the Big Island.
Last week’s major quake set a new record for in the state for having the most “Felt Reports,” even including a report from Niʻihau.
But what caused this earthquake and how did responding agencies message about it?
The earthquake happened at a depth of 14 miles below sea level just south of Hōnaunau-Nāpōʻopoʻo. Its epicenter appeared to be on Mauna Loa volcano, when looking at a map.
However, the base of Mauna Loa sitting on top of the old oceanic crust is only 6 miles below sea level. The earthquake occurred deeper than the volcano — even deeper than the base of the ocean crust, which is bent downward by the weight of the Hawaiian Island chain.
These plate-bending, or lithospheric flexure, earthquakes happen within the upper lithospheric mantle within the Pacific Plate and are not directly related to volcanic activity.
The Pacific Plate is constantly readjusting to the weight of the islands through countless micro-earthquakes no one ever feels.
Bending of the plate generates larger, widely felt and often damaging earthquakes that can occur from Hawai‘i Island to Molokai‘i. These larger earthquakes are widely felt because they are deep — from 12 to 30 miles — and the lithospheric mantle efficiently transfers the earthquake waves.
Prior to the May 22 temblor, the most recent larger earthquakes were also caused by Pacific Plate adjustments: a magnitude-6.2 in 2021 south of the Big Island with about 3,500 felt reports and the damaging magnitude-6.7 Kīholo Bay earthquake in 2006 that had about 3,000 felt reports.
These “Did You Feel It?” responses are used to generate maps showing the intensity of shaking, which are helpful for emergency management agencies — such as Hawaiʻi County Civil Defense Agency — that respond to damage reports.
A few seconds after the May 22 earthquake started shaking the west side of the island, some Android phone users reported receiving alert notifications on their mobile devices: those near the epicenter were alerted that a quake happened near them; those farther away might have alerted about an earthquake nearby and to expect shaking.
These messages rely on the accelerometer and location of a cellphone, as well as accelerometers and locations of other Android phones; adjusting phone settings can enable you to turn those notifications on or off.
The Android Earthquake Alerts System is a proprietary feature developed by Google and is active throughout the United States for earthquakes of magnitude-4.5 or more, and differs from U.S. Geological Survey ShakeAlert Earthquake Early Warning System that is only available in California, Oregon and Washington state.
While the messages arrive quickly because they rely on the shaking detected by thousands of Android users, the official messages sent by U.S. Geological Survey and Pacific Tsunami Warning Center can take minutes or longer because they rely on instrumentation located across the landscape.
People need to verify the accuracy of the earthquake location and magnitude in some cases to ensure accurate earthquake and tsunami information before a message is sent .
Regional seismic networks compute the origin time and location for any given earthquake — to avoid confusion, only one set of earthquake information can be considered official.
The authoritative regional seismic network for Hawai’i is Hawaiian Volcano Observatory. National Oceanic and Atmospheric Administration’s Pacific Tsunami Warning Center is the authoritative agency for tsunami information and guidance.
Hawaiian Volcano Observatory staff started analyzing the May 22 earthquake data even before shaking stopped, as the earthquake rolled through the south and east sides of the island. The observatory’s automated software system rapidly sent out preliminary estimates of the earthquake origin time, location and magnitude.
Staff also posted immediately to the Hawaiian Volcano Observatory website and USGS Volcanoes social media accounts, acknowledging the earthquake and that staff were analyzing the data.
An initial earthquake message was sent to Earthquake Notification Service subscribers using a preliminary and automatically determined earthquake magnitude, location and depth. Shortly after, Pacific Tsunami Warning Center issued a statement saying no tsunami was generated.
Hawaiian Volcano Observatory released the reviewed earthquake timing, magnitude, location and depth within a few minutes following the quake.
Initially estimated as a magnitude-5.9 at 10 miles deep, those statistics later were increased when analysts determined the earthquake was larger and deeper.
The observatory then released an information statement with the accurate information, which interpreted the temblor being related to Pacific Plate flexure and not magma movement within Mauna Loa.
The May 22 earthquake is a reminder that Hawai’i is one of the most seismically active locations in the United States.
Earthquakes can affect large areas and happen with no warning. Don’t forget to “Drop, Cover and Hold On” during any earthquake. Immediately move inland if you’re near the coast in case a tsunami is generated.
VOLCANO ACTIVITY UPDATES
KĪLAUEA
VOLCANO ALERT LEVEL: Advisory
Kīlauea has erupted episodically since Dec. 23, 2024, within its summit caldera inside Hawai’i Volcanoes National Park. Episode 47 of summit lava fountaining happened for 9 hours May 14-15. No unusual activity is noted along Kīlauea’s East Rift or Southwest Rift zones.
WHAT’S NEXT: Summit region inflation since the end of Episode 47 indicates another fountaining episode is possible. Models indicate Episode 48 is most likely to begin between May 28 and May 30.
MAUNA LOA
VOLCANO ALERT LEVEL: Normal
Mauna Loa is not erupting. Read the latest information statement about the status of the volcano at the Mauna Loa web page on the Hawaiian Volcano Observatory website.
Hawaiian Volcano Observatory continues to closely monitor Kīlauea and Mauna Loa.
EARTHQUAKES
There were 10 earthquakes reported felt during the past week around the Big Island:
- MAGNITUDE-3.2 at 7:25 a.m. May 23 located south-southeast of of Hōlualoa at a depth of 23 miles.
- MAGNITUDE-2.9 at 2:41 a.m. May 23 located 4 miles south of Hōnaunau-Nāpōʻopoʻo at a depth of 8 miles.
- MAGNITUDE-4.0 at 12:56 a.m. May 23 located 7 miles south of Hōnaunau-Nāpōʻopoʻo at a depth of 14 miles.
- MAGNITUDE-2.4 at 12:02 a.m. May 23 located 6 miles south-southeast of Hōnaunau-Nāpōʻopoʻo at a depth of 13 miles.
- MAGNITUDE-2.6 at 10:50 p.m. May 22 located 6 miles south of Hōnaunau-Nāpōʻopoʻo at a depth of 10 miles.
- MAGNITUDE-2.1 at 10:22 p.m. May 22 located 9 miles south of Hōnaunau-Nāpōʻopoʻo at a depth of 13 miles.
- MAGNITUDE-2.3 at 10:01 p.m. May 22 located 8 miles south-southeast of Hōnaunau-Nāpōʻopoʻo at a depth of 2 miles.
- MAGNITUDE-3.2 at 9:52 p.m. May 22 located 6 miles south of Hōnaunau-Nāpōʻopoʻo at a depth of 13 miles.
- MAGNITUDE-6.0 at 9:46 p.m. May 22 located 8 miles south of Hōnaunau-Nāpōʻopoʻo and at a depth of 14 miles.
- MAGNITUDE-1.8 at 1:49 p.m. May 22 located 7 miles northeast of Pāhala at a depth of 19 miles.
Visit the Hawaiian Volcano Observatory website for past “Volcano Watch” articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake information and more. Email questions to askHVO@usgs.gov.
