Earthquake Swarm Picks Up with Sharp Tremors

Just when it looked like the swarm of earthquakes on Kilauea was quieting down, the volcano resumed its shaking Thursday night with several sharp jolts.

The swarm that began early Wednesday three miles northwest of Kilauea’s summit appeared to wane Thursday before coming back alive at 9:02 p.m. with a magnitude-4.1 earthquake.

That was followed by about a dozen smaller tremors, the biggest being magnitude 3.2, until a quake measuring 4.3 struck at 3:52 a.m. This one garnered more attention, with several residents of the Volcano Golf Course subdivision two miles from the swarm’s epicenter reporting items falling from shelves, said geologist Janet Babb with the Hawaiian Volcano Observatory.

She said the early-morning tremor also knocked some books off the shelves and dislodged small ceiling fixtures at HVO, the U.S. Geological Survey research facility located on the rim of Kilauea’s summit crater.

Six more temblors of at least 2.0 magnitude had occurred as of noon today, bringing the total to more than 100 since the swarm began Wednesday morning.

The earthquakes are originating at a depth of two to three miles below the surface in the area of the Ka‘oiki Pali, which can be seen above Highway 11 south of the access road to the golf course and in the vicinity of the Namakanipaio campground.

The swarm, like the magnitude-6.6 tremor that occurred in 1983, originate in a seismic zone which has produced Ka‘oiki Pali and a number of other surface features that have been covered by lava from Mauna Loa over the past thousand years and more.

While scientists say that changes in the amount of lava entering Kilauea’s plumbing system have been detected following some of the four previous Ka‘oiki swarms over the past 22 years, the two may not be directly related.

“We don’t have a real good sense of what’s happening there,” said HVO seismologist Wes Thelen.

The strong 1983 quake occurred at a depth of about six miles at an area known as the décollement (dei-COHL-ment) zone, which is where the mass of the island meets the oceanic plate below. Many of Kilauea’s stronger earthquakes – including the 7.2 tremor in 1975 – have occurred in that zone and geologists believe they may result from settling of the mountain above.

Thelen said while the swarms may be related to the ongoing eruption, changes to the eruption process, such as an inflation or tilt of the mountain, haven’t always followed.

“They could be related to the pressurization of the volcano, but then we’d expect to see changes to the tilt,” he said. “So far the volcano has acted like it doesn’t know they occurred.”