Hawaii: The Cause of the Quake

Locals and tourists were mostly still asleep when an earthquake rocked the Hawaiian resort center of Kailua-Kona on Sunday morning. Authorities reported blackouts, landslides and widespread damage, but no deaths. A few hotels and at least one hospital had to be evacuated. Boulders dropped onto the Queen ka'ahamanu Highway, a main thoroughfare. While damage reports continued—and residents braced against aftershocks that could go on for days—NEWSWEEK spoke to Bruce Presgrave, a geophysicist with the United States Geological Survey's National Earthquake Information Center, in Golden, Colo.

NEWSWEEK: How big was the quake in Hawaii and where was the epicenter?

Bruce Presgrave: At 7:07 a.m. in Hawaii, we had an earthquake with a preliminary magnitude of 6.6. It occurred about six miles from Kona, Hawaii, along the west coast of the big island of Hawaii. It was followed about seven minutes later by a magnitude 5.8 aftershock. We've been continuing to see small aftershocks, mostly in the 3 range, since then.

Are earthquakes common in Hawaii?

Of all of the islands of Hawaii, it is the most active. The biggest one in recent years was an earthquake in 1975 that was a magnitude of 7.2. That was off the southeast coast of the big island. The last earthquake that occurred in this particular area was a magnitude 6.9 that occurred on August 21, 1951.

What's known so far about the damage in this quake?

So far we've seen reports about some structural damage. We're sort of monitoring the news media ourselves. We've definitely seen photos of landslides. We did hear a report of a house that was shifted off its foundation.

We think of earthquakes occur only where two tectonic plates meet, as in California. What's causing earthquakes in Hawaii?

The island of Hawaii is part of a chain of volcanoes. It's what's known as the Hawaiian hotspot. Gradually as the earth's crust moves over those volcanoes, it builds up islands and then gradually erodes them away. The island of Hawaii is the latest site over that hotspot. Because of the volcanic activity and the building of these islands, there [are] extra stresses on the [Pacific] plates.

Does that mean that the sheer weight of the islands is what caused the quake?

In a general sense, yes. There are technical details, but that's basically the idea. The buildup of the island is causing additional stresses.

Were the active volcanoes on the island a direct cause?

We consider this a tectonic event not a volcano-related event. It's basically caused by the stresses of the island-building process.

How long are the aftershocks likely to go on?

We would expect aftershocks to continue at least for a few hours or maybe a few days. It's always hard to tell. Sometimes aftershocks run on for many days or even months. But sometimes they stop pretty quickly.

Quakes on the coast sometimes produce tsunamis. What have you heard from the National Tsunami Center [in Honolulu]?

Fairly quickly the Tsunami Center put out a message saying first that the event didn't generate a Pacific-wide tsunami. Then they followed that up with a report just for the state of Hawaii saying that there was no local tsunami. As with any quake there would be the possibility that there would be some very slight sea level changes, but nothing destructive. Besides, if there'd been any from that earthquake it would already have happened.