Friday, February 29, 2008

Mystery earthquake south of Hawai'i

A mysterious earthquake shook the seafloor between Hawai'i and the Marquesas Islands this morning, in a spot that's not known for temblors.
(Image: Image provided by Google Earth and USGS, annotated by the author.)

It wasn't a huge event, just a 5.4, but it was enough to set up a chatter between the folks at the U.S. Geological Survey who watch these things. They said there is no reason to believe it could presage another, bigger event.

The quake happened at 5:40 a.m. Hawai'i time on Friday, February 29, a little more than an hour before this posting.

The site was below the surface of the ocean floor, at 3.08 degrees north and 140.34 degrees west longitude. That's just northwest of the Marquesas and southeast of Hawai'i, a little north of the Equator.

It is an odd and unusual place for a quake, although such events are not unheard-of, said Barry Hirshorn, a geophysicist with the Pacific Tsunami Warning Center.

Most of the earthquakes around the Pacific occur at the edges of the vast Pacific Plate, one of the chunks of the earth's crust that are constantly in movement, shoving up against each other, rising up or slipping under each other, or sliding alongside each other. The perimeter of the Pacific Plate is familiarly known as the Ring of Fire, because of all the volcanic activity that is associated with the plate fringe.

There are also frequent quakes around Hawai'i, associated with both the activity of the volcanoes and the weight of the islands on the center of the plate.

But at the site of this morning's event, there are no islands, no volcanoes, no fault lines, and it's nowhere near the edge of the Pacific Plate. Hirshorn said he had discussed the event with folks at the Alaska warning center, who had also seen it on their instruments.

“You can have false readings, but this is a real quake. It's the middle of the plate. It's pretty rare to have that happen, but you can have residual areas of stress that build up” and cause an event, he said.

The quake was comparatively shallow, about 4 miles deep.

For information on the quake, see

© 2007 Jan W. TenBruggencate