USGS HVO Press Release — Magnitude 4.2 Earthquake Southwest of Moloka`i

The earthquake was located 55 km (34 mi) west-southwest of Maunaloa, Moloka‘i. A map showing the location of the earthquake is posted on the HVO website at http://hvo.wr.usgs.gov/seismic/volcweb/earthquakes/.

The depth of the earthquake was calculated to be shallow—about 6 km (4 mi). However, determining accurate earthquake locations and depths in this region can be difficult because of the sparse coverage of seismometers on Moloka‘i and adjacent islands. Earthquake locations are most accurate when seismometers surround the earthquake source, which is nearly impossible given the geography of the islands in the area. Often, the depths are the most uncertain in these situations. Therefore, subsequent and more sophisticated analysis will likely result in locating this earthquake at a greater depth in the mantle.

HVO's seismic records show that 3 earthquakes of magnitude 3 or larger have occurred in the same area in the past 25 years.

According to Wes Thelen, HVO's Seismic Network Manager, earthquakes outside of the Island of Hawai‘i are not uncommon and are typically caused by a structural adjustment of the mantle in response to the weight of the Hawaiian Islands. "This event is a good reminder that the Island of Hawai‘i is not the only Hawaiian island prone to earthquakes," he said.

Earthquake activity generally decreases northwest up the Hawaiian Island chain, but the potential for larger earthquakes still exists. Earthquakes with magnitudes greater than 6.0 occurred in the Moloka‘i region in 1870, 1871, 1895 and 1894.

"No aftershocks have been recorded, and aftershocks typically do not follow earthquakes at these depths in the mantle," Thelen added.

Today's earthquake was felt on several Hawaiian islands, from the Island of Hawai‘i to O‘ahu. The USGS "Did you feel it?" Web site (http://earthquake.usgs.gov/eqcenter/dyfi/) received more than 70 felt reports by 8:00 a.m., HST, ranging from weak to light shaking. Thus far, there have been no reports of damage, nor do we expect any given the location and size of the earthquake.

"The earthquake today caused no detectable changes on the active volcanoes on the Island of Hawai‘i," said Jim Kauahikaua, HVO's Scientist-in-Charge.

The magnitude was initially estimated at 4.0, but more detailed seismic analyses resulted in a final magnitude of 4.2.

The 2nd annual Great Hawaii Shakeout, scheduled for 10:16 a.m. on October 16, 2014, is an opportunity for all Hawaii residents to practice "Drop! Cover! Hold On!"—actions that are proven to reduce injury in an earthquake. For details, please visit shakeout.org/hawaii/.

For information on recent earthquakes in Hawaiʻi and eruption updates, visit the Hawaiian Volcano Observatory website at hvo.wr.usgs.gov.

Daily updates about ongoing eruptions, recent images and videos of summit and East Rift Zone volcanic activity, maps, and data about recent earthquakes in Hawaii are posted on the HVO website at https://volcanoes.usgs.gov/observatories/hvo. 

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