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This comprehensive collection of seismic information will eventually replace the ANSS composite catalog hosted by the Northern California Data Center; however, historic regional seismic network catalogs have not yet been fully loaded.
M5.4 - 6km W of Iwai, Japan
36.047°N 139.832°E depth=37.5 km (23.3 mi)
2016-05-16 12:23:01 (UTC)
2016-05-16 07:23:01 (UTC-05:00) in your timezone
Times in other timezones
6.0 km (3.7 mi) W of Iwai, Japan
6.0 km (3.7 mi) SSE of Sakai, Japan
9.0 km (5.6 mi) E of Sugito, Japan
10.0 km (6.2 mi) NE of Kasukabe, Japan
41.0 km (25.5 mi) NNE of Tokyo, Japan
There is no cause for alarm, said Ian Madin with the Oregon Department of Geology & Mineral Industries. The quakes likely were caused by small movement in fault lines along the mountain.
There may have been as many as 100 small quakes, he said, some too small to detect. The Pacific Northwest Seismic Network recorded about 60 quakes in that time span.
"These appear to be related to small amounts of movement on unknown fault systems, not related to magma moving within the volcano," he told KGW. "And we get one of these every couple of years and they can get up to the mid fours. We expect to see more activity there in the future."
The recent earthquakes on Mount St. Helens to the north were related to magma movement and were not connected with the Hood quakes, he said. Madin also pointed out this was not the first time a swarm like this has happened on Mount Hood.
He believes these small faults likely make up one big one, capable of producing a magnitude 7 earthquake. He says the last time that happened was likely 10,000 years ago.
“They're just telling you there's a fault down there that's under tension. It’s being loaded up and sooner or later it’s going to go,” said Madin. But at this point, scientists don't know when that could happen.
“Is it every thousand years? Is it every 500 years? How often do we have big earthquakes up there?” Madin said.
Therefore, we conclude that, while earthquakes occur throughout the year at Mt. Hood, elevated seismicity levels along pre-existing faults south of Mt. Hood during summer months are hydrologically induced by a reduction in effective stress.