Scientists Say Recent Quakes Not Unusual

Officials Say Public Must Remain Aware Of Tsunami Alerts

 UPDATED 9:17 PM HST Oct 07, 2009
HONOLULU -

Scientists at the University of Hawaii Manoa said Wednesday's quakes near Vanuatu that prompted tsunami alerts in the islands are not unusual.

The 7.8-magnitude quake formed a small tsunami in Vanuatu, but the waves measured only about 24 inches. Vanuatu is about 1,000 miles west of Samoa, which was devastated by an earthquake and tsunamis last week.

"Earthquakes happen around the Pacific on a regular basis. The magnitude 8 in Vanuatu today was just another in a long cycle and it's quite typical," said geologist Brian Taylor, of the UH School of Ocean and Earth Science and Technology.

What is atypical? Back to back earthquakes measuring 7.1 and larger, scientists said. While one earthquake can trigger another one close by, scientists said it is hard to connect these recent quakes.

"Far away we don't understand the connections," Taylor said. "So the fact that we've had three or four of these large earthquakes in the last 10 days is kind of statistical randomness."

With three tectonic plates converging, the edges of the Pacific are the most active seismic zones on the planet.

So, scientists said we should not be alarmed at the number of quakes in the region. However, they stress that we should be aware of which ones cause a tsunami.

Deep, small quakes do not move the sea floor.

"But if you have an earthquake near the sea floor such as today's earthquake in Vanuatu, which is from a seduction zone event that literally moves the sea floor, when it bounces back and releases that stretch, that's when you get a tsunami," Taylor said.

Geophysicists at the Pacific Tsunami Warning Center said because Wednesday's quake was larger than 6.5 in magnitude they immediately sent out an advisory. It was later upgraded to a watch before they determined Hawaii was in the clear.

Pacific Tsunami Warning Center scientists said they wanted to err on the side of caution rather than wait for more measurements.

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