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5.4 quake shakes Sarigan Island
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Posted on Aug 11 2005
A 5.4-intensity earthquake shook Sarigan Island, with the seismic swarm on the island escalating and recording some 360 temblors in a span of just three days.
The Emergency Management Office and the U.S. Geological Survey said the seismic swarm was recorded on Sarigan’s seismometer, while Anatahan’s volcanic activity continues. Sarigan is the island next to Anatahan in the north.
The agencies said the 5.4-strong quake occurred at about 1:10am yesterday, with the epicenter traced to about 30 kilometers west of Sarigan.
“Even though they are too small to be located, we believe that most of these earthquakes are occurring in the same area,” the agencies stated in a joint report.
On Anatahan, the seismic station recorded two “unusually strong” long-period earthquakes on Wednesday. One of them occurred at about 2:50pm and lasted 40 minutes, while an 8-minute event occurred at about 6:50pm.
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.
Generally, though, the agencies said tremor levels ranged between 40 and 60 percent of the peak levels recorded during the period of June 17-26.
Satellite monitoring by the Air Force Weather Agency detected an ash plume at 22,000 feet moving westerly and then curving to the northwest at about 10:16am yesterday.
The EMO and the USGS noted that the ash plume from the volcano extended approximately 90 miles to the west. They noted the presence of volcanic smog from 190 nautical miles west to about 225 nautical miles to the northwest of Anatahan extending above the eastern Philippine Sea.
