Earthquakes Increase from 60/Week to 600/Week on Hawaii Island
According to scientists at the USGS’ Hawaiian Volcano Observatory (HVO), earthquake activity near the city of Pahala has increased from about 60 earthquakes per week to 600 now over the past five years. Tucked between the volcanoes of Mauna Loa and Kilauea, Pahala is a small community with roots as a former sugar plantation. With a population of only about 1,400 residents, residents often feel the earthquakes under their feet – often several times a day.
In a 2015 study, USGS scientists located and classified the earthquakes that occur in this region into two camps: seismic tremors, often associated with deep magma movement, and volcanotectonic earthquakes, which indicate rock fractures beneath the surface.
The frequent earthquakes that occur here come from a region deep underground, about 12 to 25 miles deep. Scientists interpreted the seismic tremor as a migration of magma from the deep Hawaiian hotspot to shallower depths. Above this magma movement, the volcano-tectonic tremors appear from the quiver region deep below the Kilauea volcano. Based on the linear trend of this earthquake activity, USGS scientists believed that the distribution of the earthquakes marked a path of magma migration underground in the reservoir below Pahala to the summit of Kilauea.
A recently published study by seismologists at the California Institute of Technology (CalTech) sheds new light on the processes occurring deep beneath Pahala. These scientists have used newly developed machine learning to identify a large number of extremely small earthquakes occurring beneath the Pahala region that have not previously been cataloged by HVO. Such microseismicity is too small to be identified with automated methods typically used to detect earthquakes.
Many of these events are volcano-tectonic earthquakes that are within the zone of deep Pahala seismicity previously identified by USGS scientists. This large set of newly identified volcano-tectonic events outlines a region of horizontally stratified magma reservoirs deep beneath Pahala, termed the Rise Complex. To support this idea, long-period earthquakes occur in these sills, indicating the movement of fluids such as magma. Together, these observations show that the deep seismicity beneath Pahala is consistent with the migration and storage of magma within this threshold complex.
Based on the CalTech study, it is believed that the distribution of earthquakes could represent a possible magma pathway from the deep Pahala sill complex into the Kilauea magma reservoir. HVO warns that more evidence and studies are needed to support or refute such a hypothesis.
To better understand seismic and volcanic activity in the region, HVO 86 deployed temporary seismic instruments across Pahala to record earthquakes in the region over a three-month program. HVO has also proposed a temporary deployment of an additional 1,600 seismic instruments at the summit of Kilauea this summer to record seismic signals there over a period of 6 weeks.
HVO writes in their latest Volcano Watch update that “these dense, transient deployments will map seismic activity in the Kilauea and Pahala regions more accurately than HVO’s permanent instrument network. HVO seismologists will analyze this seismic data to understand if magma stored in Pahala’s active threshold complex is associated with Kilauea Volcano and therefore represents a source of magma.
HVO scientists continue to monitor not only the ongoing earthquakes in Hawaii, but also current volcanic activity.
The Kilauea volcano is about to erupt. Its summit eruption in Halema’uma’u Crater in Hawaii Volcanoes National Park is continuing, with vents erupting in the central-east portion of the crater floor. Summit Tilt has shown several deflation/inflation trends over the past week. Summit tremor activity remains low and eruptive tremors. On January 9, a sulfur dioxide emission rate of 3,500 tons per day was measured; These emissions are responsible for smog-like fog throughout the state of Aloha.
Mauna Loa, the world’s largest active volcano, is not currently erupting. According to HVO, webcams show no sign of activity on the volcano, which ended an eruption event last month. Mauna Loa. The seismicity remains low. Ground deformation rates and sulfur dioxide (SO2) emission rates are at background levels.
