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MAP 2.1 2011/11/02 04:49:59 48.721 -122.899 13.2 23 km ( 14 mi) NNE of Friday Harbor, WA
MAP 2.1 2011/11/01 21:47:28 48.092 -121.933 0.0 3 km ( 2 mi) ENE of Granite Falls, WA
Thank you for the heads up!
There do seem to be some small local earthquakes on this record and we are looking at them more closely. Our coverage of Glacier Peak is pretty poor. We have only one station on the mountain and our system requires 3 or more stations to "trigger" on an event to get computer generated notifications. This would happen with a magnitude 2 or better but small M 1 earthquakes can slip by if not noticed. "Ice Quakes" can also look a lot like small earthquakes but usually have a different frequency content.
Our duty seismologists often review our subnet triggers with a particular eye for GPW events because of our poor coverage in the area but there are hundreds of these, usually wind noise, and interesting little events can get missed.
Thanks again for watching and taking the time to write. We will follow up and let you know what the volcano seismologists have to say about these once they have had a chance to review this "activity".
Director of Outreach & Information Services
University of Washington,
Pacific Northwest Seismic Network
Seattle, WA 98195-1310
On Nov 1, 2011, at 12:55 PM, tara XXXXXXX wrote:
Hello! I have been monitoring the cascade chain for sometime now and couldn't help but notice the recent activity at Glacier Peak. I live less than 50 miles from this volcano so have a vested interest in it! (My house sits on its last lahar) Looking at the most recent seismo:
....there most definitely seem to be some micro quakes, increasing in size over the past couple of days. Given the eruptive nature of this volcano, and the lack of monitoring equipment/isolation, it is one that makes me a bit nervous. I see that to date, none of these quakes have been listed. Are you aware of any changes or signs in addition to these micro quakes?
Thank you for your time-
The Seattle Fault (and the related Tacoma Fault) is not the only source of earthquake hazard in the Puget Lowland. Other faults in the near surface continental crust, such as the South Whidbey Island Fault (near Everett), and the yet to be studied Olympia Fault (near Olympia), though historically quiescent, are suspected of generating earthquakes of around magnitude 7. Others, such as the 2001 Nisqually earthquake, originate about 50 to 60 km below Puget Sound in the Benioff zone of the subducting Juan de Fuca plate; being so deep their energy is dissipated. And there are the infrequent but very powerful great subduction events, such as the magnitude 9 1700 Cascadia earthquake, where the entire Cascadia subduction zone, from Cape Mendocino to Vancouver Island, slips.
Many of these faults are inferred indirectly from gravity and magnetic surveys. There is evidence of recent movement on some of these faults. For example, in about 900 AD an earthquake is believed to have occurred on the Seattle Fault which raised Restoration point about 21 feet and Alki point at least 12 feet. These points are located just south of the Seattle Fault on either side of the Puget sound.
The motion on many of these faults is vertical. For example, vertical motion on the Seattle Fault and faults just to the north have caused the block of earth between faults H and I on the map to drop a total of more than 12,000 feet in the last 40 million years. The resulting basin has, of course, been filled with sediments.
Are the metallic sounding knocks the tree root sounds? How did whoever it was work out it was tree roots?