Local Scientist Helps Unravel the Mystery of a Rare Earthquake
that Shook Hawaii
November 7, 2007
Dr. Patrick J. McGovern of the Lunar and Planetary Institute (LPI) recently completed a study on the October 15, 2006, earthquake that was felt as far away as Oahu.
At 7:07 a.m. on October 15, 2006, islanders were awakened by a 6.7-magnitude earthquake that was rupturing 24 miles beneath Kiholo Bay, just off the Hualalai volcano on the Big Island. Seven minutes later a 6.0-magnitude temblor occurred nearly 12 miles deep off Mahukona. Several hundred smaller aftershocks followed. This particular earthquake and aftershock was definitely a rarity. McGovern describes the two related events as fraternal twins, who are born minutes apart, but with different features.
According to McGovern, "It is unusual for aftershocks to have a different mechanism, but it's not unheard of.”
The weight of Hawaii's volcanos has always put a huge load on the Earth's lithosphere, which bends and creates stresses that cause earthquakes.
McGovern described two main types of earthquake mechanisms: one resulting from rocks being stretched and pulled apart (called extensional), and the other where blocks of rock are pushed together (called compressional). In this instance, the Kiholo Bay earthquake was extensional, deep in the Earth's mantle, and the shallower temblor, while still in the mantle, was compressional.
"It wasn't a surprise per se, but it said to me immediately this was something having to do with the lithosphere, the strong outer layer of Earth, responding to the load of volcanos," McGovern said.
In 1868 the Hawaiian Islands faced a series of severe earthquakes that reached 7.9 magnitude and were considered devastating to the island. Now that the island has become developed, the potential for damage and loss from a major eruption is astronomical.
McGovern is a LPI staff scientist who focuses his research on the evolution of terrestrial planet surfaces, lithospheres, and interiors, with emphasis on growth and development of large volcano-tectonic structures on Mars, Venus, and Earth.
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Last updated January 30, 2008