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Over forty earthquakes shake Northern Islands
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Posted on Aug 09 2005
More than 40 tremors shook the Northern Islands yesterday, as Anatahan experienced long-period earthquakes, which might indicate that volcanic eruptions are about to escalate.
The U.S. Geological Survey and the Emergency Management Office said the seismic station in Sarigan, Anatahan’s neighboring island in the north, recorded more than 40 temblors. Three of those quakes had magnitudes of around 4.
The seismic swarm began at around 1:52am and occurred over the next eight hours. At around 5:39am, a 4.2-intensity earthquake occurred, and the National Earthquake Information Center traced the event to about 40 miles northwest of Anatahan.
One of the seismic stations on Anatahan recorded fluctuating tremor levels, which ranged between 40- and 80-percent of the peak levels observed during the period June 17-26.
At 1:38pm on Monday, the USGS and the EMO said a long-period earthquake was recorded on Anatahan. Tremor levels later dropped and increased once again. Other long-period events occurred, with frequency ranging from several per minute to one every few minutes.
Long-period events are volcanic earthquakes that result from pressure changes during the unsteady transport of magma that inject into surrounding rock. When magma injection is sustained, a lot of earthquakes are produced. Those events indicate the possibility that a volcanic eruption is about to occur.
Tremor levels on Anatahan intensified rapidly early Monday morning, indicating another possibly strong eruption. Satellite imagery, however, could not detect the level of ash plume. Last Wednesday, volcanic activity escalated and ash emissions reached an altitude of about 42,000 feet.
Meanwhile, the Air Force Weather Agency’s satellite monitoring detected ash plume at 18,000 feet extending approximately 120 nautical miles northwest from the volcano’s summit at about 4:25am yesterday.
