‘Recent quakes may actually be favorable for the Marianas’

The recent earthquakes that jolted the Marianas could be related to the 9.9 magnitude quake off the coast of Sumatra that generated the disastrous tsunami experienced by about 22 countries but this has yet to be proven.

According to U.S. Geological Survey geologist Dr. Chris Waythomas, a quake as strong as the one in December may affect other parts of the world.

“It hits little faults under stress and loosens them up,” he said Tuesday.

Waythomas said the recent quakes in the Marianas may be positive in a way, citing that the frequent small earthquakes relieves the stress that builds up over time along the cracks of the Marianas Trench.

“Areas along trenches with no earthquakes for a long time…these are candidates for large earthquakes,” he said.

Waythomas, along with Dr. James E. Quick, are currently on Saipan doing presentations on tsunamis and Anatahan’s eruption.

During Tuesday’s presentation at the Governor’s conference room, Quick said the recent quakes are not directly related to the ongoing Anatahan eruption but indicated that both are part of the same subduction system, resulting from movements in the Pacific and Philippines plates under the seabed.

“As the Pacific plate passes down beneath the Marianas, melting magma comes up and makes a volcano; that same motion creates earthquakes,” he said.

Waythomas also explained that earthquakes “often come in clusters” and stressed that they remain “pretty unpredictable.”

He indicated, however, that the quakes may or may not be related to the Sumatran quake.

Quick said the activities are normal, considering the geologic setting of the islands.

“You’ve had a number of earthquakes, it’s normal for the geologic setting that you’re in. It’s only that you’ve had a little more than normal, but these things are statistical, so every 10 years or so, you’d expect in this area, based on your history, to have a magnitude of 6.0 or greater,” he said.

Another earthquake jolted the Marianas early Tuesday morning near Maug, registering 5.1 on the Richter scale, according to the USGS National Earthquake Information Center.

The quake occurred at about 4:41am and was located about 40 miles north-northwest of Agrihan, 85 miles north-northwest of Pagan, 280 miles north of Saipan, and 405 miles north of Guam. The quake occurred at a depth of 133.7 kilometers.

At least nine earthquakes shook the Mariana islands in less than two weeks, including Saturday’s temblor that measured 6.6 on the Richter scale.

Seven of those earthquakes transpired within four days beginning on Wednesday last week.

Anatahan unlikely to produce Marianas-wide tsunami

In his presentation, Quick also focused on the ongoing volcano eruption of Anatahan, indicating that the volcano continues to erupt with frequent explosions every minute.

The activity peaked on Feb. 1 and Feb. 5, with volcanic ash rising as high as 15,000 to 20,000 feet.

In his prognosis for the eruption, Quick indicated that the hazards of the eruption are limited to the island as well as local aviation. However, that situation can change quickly, he added..

Possible scenarios include larger explosions accompanied by pyroclastic flows. The flows entering the sea or flank landslides may generate a “small chance” of local tsunami but he said that very large explosions are unlikely because pressure is currently being released.

He added that the eruptions are not likely to be a major threat to aviation or generate a tsunami that would have Marianas-wide impact.

Quick noted that the Commonwealth is surrounded by many potential sources of tsunami, citing that earthquakes related to the Mariana Trench have produced tsunami, as well as landslides in the Hawaiian islands and elsewhere. The reef line is a plus but it could only slow down the wave.

With that, he said the Commonwealth needs an assessment of its tsunami run-up susceptibility to form the basis of a response plan and guide future development.

Waythomas said that, depending on how much time is spent on the assessment, results may take up to three years to be released. Assessment includes field study that would evaluate and identify major tsunami sources; collect data and get sea floor imagery for sea landslides; and sample flanks of the volcano to know how dense it is and how it may respond to shaking, among others.

“From there, you can better evaluate how it’s susceptible to failure,” he said.

USGS plans for the month include preparing a proposal to assess the tsunami run-up potential in the CNMI. In April, a workshop would be conducted on Saipan to develop a volcanic ash response plan, and in May, geologic mapping and hazard assessment of Pagan begins. The release of the Pagan geologic map is expected in September.

“Geologists would go out and do hazard assessment and try and understand how the volcano has behaved in the past, and that’s a good indicator of what it’s likely to do in the future,” Waythomas said.

“The plan is that each one of these volcanoes to the north will receive geologic mapping and hazard assessment,” Quick added. “That’s important because these volcanoes, they have personalities. Some volcanoes tend to explode a lot, others just make lava flows.”