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Earthquake Swarm Occurs Near Kilauea Summit

Posted February 22, 2012, 05:31 PM HST
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The cluster of blue squares at lower left denotes the location of an earthquake swarm that was continuing this afternoon. Image from Hawaiian Volcano Observatory.

A swarm of earthquakes began early today at a fault marking the boundary between Kilauea and Mauna Loa, scientists at the Hawaiian Volcano Observatory said this afternoon.

Geologist Janet Babb said the shaking began at 1:17 a.m. and continued throughout the morning and afternoon. As of 3 p.m., more than 60 earthquakes had been detected along the Ka‘oiki Pali fault, including 14 which were greater than magnitude-2. The largest recorded at that point was a magnitude-3.2 tremor that occurred at 6:55 a.m.

The earthquakes have not been widely detected on the Big Island. Babb said the U.S. Geological Survey’s “Did you feel it?” website (http://earthquake.usgs.gov/eqcenter/dyfi/) received less than 10 reports in the first 12 hours of the swarm.

The Big Island is the site of thousands of earthquakes annually but most can be detected only by instruments.

Ka‘oiki Pali, which is located near the Namakanipaio campground about three miles north-northwest of Kilauea’s summit, was the site of previous earthquake swarms in 1990, 1993, 1997 and 2006. The swarms varied in length of activity, with the shortest being one day and the longest, the one in 2006, lasting several weeks.

The swarms, which are occurring at a depth of about three miles, rarely have produced tremors stronger than magnitude-4, Babb said.

After some of the previous swarms at Ka‘oiki geologists detected changes in the ongoing eruption in the east rift zone of Kilauea, one of the world’s most active volcanoes.

“With some swarms we have seen an influx of magma into Kilauea’s chamber,” said Wes Thelen, a seismologist at HVO. That influx is reflected by swelling of the volcano as detected by precise measurements using instruments linked to satellites.

Thelen said that has not been seen so far during this swarm.

That doesn’t mean that changes to Kilauea are not occurring, however.

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“We can see earthquakes long before we can see deformation of the surface,” he said.

Detecting changes in the volcano is further complicated by the fact that lately more magma has been detected moving into Kilauea.

“We are seeing inflation, but that’s been going on for weeks,” Thelen said.

The Ka‘oiki Pali area has been the site of increased seismicity since the occurrence of a magnitude-6.6 earthquake in November, 1983 – about 10 months after the current eruption of Kilauea began.

“We didn’t see seismic activity in this area until 1983, so there’s obviously a connection,” Babb said.

The 1983 earthquake was the second strongest at Kilauea in the past century, exceeded only by the 7.2 temblor that struck the volcano’s south flank in 1975. There have been two other quakes on the Big Island stronger than magnitude-6.6 during that period, including the magnitude-6.7 quake that struck along the Kohala coast on Oct. 15, 2006, and one measuring 6.9 that occurred in Kona in 1951.

The strongest earthquake known to have hit the Big Island occurred in 1868 along Mauna Loa’s south flank in the vicinity of Naalehu and Pahala. That shaker had an estimated magnitude of between 7.5 and 8.1, and was so powerful it stopped clocks in Honolulu.

 

 

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