Volcano Watch: A pupu platter of earthquakes

“Volcano Watch” is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.

A pupu platter is an assortment of appetizers commonly served at social gatherings in Hawaiʻi. During one week this month, Island of Hawaiʻi residents and visitors were treated to an assortment of earthquakes resulting from a variety of different geologic processes, like a pupu platter of earthquakes!

Thousands of earthquakes occur every year in Hawaiʻi. These earthquakes are monitored by the U.S. Geological Survey Hawaiian Volcano Observatory and fall into three main classes: volcanic, tectonic and mantle.

Volcanic earthquakes are associated with magma moving within, and erupting from, active volcanoes. Tectonic earthquakes are associated with slippage along faults within the volcanoes and along the décollement that separates the volcanoes from the underlying oceanic crust. Mantle earthquakes are associated with bending of the Earth’s crust and upper mantle because of the weight of the islands above.

The first earthquake in our pupu platter was a magnitude-5.1 event that occurred Dec. 4 at 5:54 p.m. It was located 9 miles southeast of Volcano at a depth of 1 mile below sea level. This was a tectonic earthquake related to shallow movement on the pali system of Kīlauea volcano’s south flank.

HVO received 1,180 felt reports from around the Island of Hawaiʻi and a handful from Maui, Oʻahu and even Kauaʻi. Fortunately, no damage was reported. A magnitude-3.1 aftershock occurred four minutes later.

A magnitude-4.4 event then occurred Dec 6 at 5:17 p.m. It was located 1 mile west-northwest of Volcano at a depth of 14 miles below sea level. It was likely a mantle earthquake related to flexing of the oceanic crust buried deep below the island. HVO received 383 felt reports for this event.

A magnitude-3.6 event then occurred Dec. 7 at 7:13 a.m. It was located east of Pāhala at a depth of 20 miles. The size, location and mechanism indicate that it likely was a mantle earthquake associated with the ongoing Pāhala seismic swarm. This event got 69 felt reports.

Two days later, two different earthquakes occurred within one minute of each other. A magnitude-3.6 event occurred Dec. 8 at 9:21 p.m. It was located 2 miles west-southwest of Hōlualoa at a depth of 8 miles below sea level. This was likely a tectonic earthquake associated with slippage on a fault within Hualālai volcano. HVO received 464 felt reports, primarily from the Kona side of the Island of Hawaiʻi.

One minute later, a magnitude-3.4 event occurred 12 miles north of Pāhala at a depth of 4 miles below sea level. This earthquake was likely a tectonic earthquake associated with slippage on the Ka‘ōiki fault system between Kīlauea and Mauna Loa volcanoes on the Island of Hawaiʻi. There were 44 felt reports for this event.

A magnitude-3.1 event occurred Dec. 11 at 3:08 p.m. It was located 13 miles southwest of Laupāhoehoe at a depth of 19 miles below sea level. It was likely a mantle earthquake related to flexing of the oceanic crust deep below Maunakea. This event had 29 felt reports.

In addition to the widely felt tectonic and mantle earthquakes above, more than 400 volcanic earthquakes occurred beneath the summit of Kīlauea from Dec. 4-11, with a peak of more than 200 events Dec. 7. While numerous, these earthquakes were small and not felt. All were below magnitude-3.0 and most were below magnitude-2.0. These events were associated with the intrusion of magma beneath Kīlauea summit.

This was a fascinating assortment of earthquakes from all around the Island of Hawaiʻi that, within the span of just one week, demonstrated different ways earthquakes can be generated in Hawaiʻi.

As always, HVO encourages you to submit a “Did You Feel It?” report if you feel an earthquake. Your felt reports contribute to earthquake intensity assessments generated by the USGS Earthquake Hazards Program and help us better understand the many processes that generate earthquakes in Hawaiʻi.

Volcano Activity Updates

Kīlauea is not erupting. Its USGS volcano alert level is advisory.

The unrest associated with the intrusion that began in early October southwest of Kīlauea’s summit continues. Earthquake activity in Kīlauea’s summit region during the past week remained relatively low. The Uēkahuna tiltmeter, located northwest of the caldera, showed little net tilt throughout the past week, as did the Sand Hill tiltmeter, located southwest of the caldera.

Unrest might continue to wax and wane with changes to the input of magma into the area and eruptive activity could occur in the near future with little or no warning.

The most recent sulfur dioxide (SO2) emission rate for the summit, approximately 70 tonnes per day, was measured Dec. 5.

Mauna Loa is not erupting. Its USGS volcano alert Level is at normal.

Webcams show no signs of activity on Mauna Loa. Summit seismicity has remained at low levels during the past month. Ground deformation indicates continuing slow inflation as magma replenishes the reservoir system following the 2022 eruption. SO2 emission rates are at background levels.

Two earthquakes were reported felt in the Hawaiian Islands during the past week: a magnitude-2.7 earthquake 1 mile south-southwest of Pāhala at 19 miles depth on Dec. 19 at 6:46 a.m. and a magnitude-3.0 earthquake 13 miles south-southeast of Pāhala at a depth of 20 miles Dec. 14 at 5:51 p.m.

HVO continues to closely monitor Kīlauea and Mauna Loa.

Visit HVO’s website for past “Volcano Watch” articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake information and more. Email questions to [email protected].