5.8 quake shakes Maug, some 570 temblors noted on Sarigan

A 5.8 magnitude temblor shook Maug Island late Saturday afternoon, while government monitoring agencies tallied more than 570 quakes in the ongoing seismic swarm being recorded on Sarigan Island’s seismometer.

The Emergency Management Office and the U.S. Geological Survey also reported that tremor levels on Anatahan reached 90 percent of peak levels, but added that seismicity on the island continues to fluctuate.

The agencies said the quake occurred near Maug at about 5:37pm Saturday. The National Earthquake Information Center estimated the quake’s location at about 70 miles east-southeast of Farallon de Pajaros, the CNMI’s northernmost island, and about 340 miles north of Saipan.

Maug lies at the northern end of the Marianas chain, flanked to the north by Farallon de Pajaros and to the south by Asuncion Island. It used to be inhabited by a small population, but the CNMI Constitution declared the island uninhabited for purposes of wildlife conservation.

Maug comprises three steep-sided islets—North Island, East Island, and West Island—encircling a central lagoon. They represent the remains of a volcano that was believed to have collapsed following a massive and explosive eruption. The islets rise steeply from the sea, often as near vertical or undercut cliffs.

In 2003, federal and local scientists who were part of the National Oceanic and Atmospheric Administration’s Oscar Elton Sette mission reported the discovery of a submerged volcanic crater that was showing signs of activity. Marine monitoring conducted on the island at that time showed that volcanic vents were releasing warm water over 100-degrees Fahrenheit. Gas emissions were also prevalent underwater through gas bubbles.

The quake near Maug occurred as the seismic swarm recorded on Sarigan’s seismometer tallied at least 570 earthquakes beginning Tuesday last week. The EMO and the USGS said the events have been occurring at rates of up to 30 per hour.

The agencies said Anatahan’s volcanic eruption continues, and the island’s seismometer recorded tremors of up to 90 percent of peak levels. They added, though, that seismicity has been fluctuating and ranged between 45 and 90 percent of peak levels.

Citing satellite monitoring by the Air Force Weather Agency, they said an ash plume from Anatahan’s volcano was rising to an altitude of about 20,000 feet yesterday morning. They said the plume extended about 70 nautical miles southeast of Anatahan. An aircraft pilot approaching Guam at around 2:30pm Saturday also reported of a sulfury smell at 19,000 feet north of Anatahan.

The agencies have detected volcanic activity on Pagan during a 10-day mission to the island several weeks ago. The problem, though, is that no seismic equipment is currently stationed on Pagan to constantly monitor seismic activities on the inhabited island, according to EMO geophysical instrument specialist Ramon Chong, who admitted that his agency is handicapped in detecting when evacuation of people is needed.