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140 quakes rattle Northern Islands
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Posted on Aug 10 2005
The swarm of earthquakes in the Northern Islands has become more frequent and has totaled more than 140 since Tuesday morning, according to two monitoring agencies.
The Emergency Management Office and the U.S. Geological Survey also said yesterday that Anatahan’s rumbling volcano remains in a state of continuous eruption. Long-period earthquakes have been occurring on Anatahan, a possible indication of stronger eruptions.
EMO geophysical seismic technician Ramon Chong said the exact location of most of the temblors could not be ascertained due to lack of equipment in the Northern Islands. The EMO recorded the seismic swarm through a seismometer on Sarigan Island, which is located next to Anatahan in the north. Four earthquakes had magnitudes of 4 and over.
In a joint report, the EMO and the U.S. Geological Survey said long-period earthquakes continue to occur on Anatahan, as recorded on the seismic station on the island.
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.
The agencies said, though, that tremor levels on Anatahan generally range from 40 and 70 percent of the peak levels recorded during the June 17-26 period.
Tremor levels on Anatahan intensified rapidly early Monday morning. On Wednesday last week, volcanic activity escalated and ash emissions reached an altitude of about 42,000 feet.
Yesterday, the agencies said ash plume rose to about 19,000 feet and moved northwesterly.
