Don in Hollister Mon 22 Feb 2010, 8:30 pm
Hi Teresa. I contacted Aaron Wech about the tremors. Here is his reply. Take Care...Don
Don,
We can record and correlate VERY small vibrations across a network of seismographs to detect and pinpoint the location of these small tremors. Currently, we are limited in our ability to provide magnitudes, as both the behavior of these tremors and the resulting seismic signal observed are quite different from normal earthquakes. This makes it difficult to use standard earthquake magnitude estimation techniques. If a series of tremors is long enough in duration for GPS to see a signal, we can correlate their magnitudes with the overall amount of slip seen by GPS.
You are correct, California does have slow quakes and tremors. Some portions of the San Andreas fault seem to quietly creep; some seem to produce tremors. In fact, I have worked seismologists down there to help identify tremor activity during creep events in the San Juan Bautista area. This work has so far not been able to detect associated tremors with creep, despite tremors being observed in other portions along the SAF (such as Parkfield).
I hope this helps,
Aaron Wech
Yesterday it was quiet and now the tremors are occurring in Oregon. My current knowledge is about zip other than these are silent and related to plate movement. Thank you in advance.
