Yellowstone Monthly Update issued Oct 1, 2010

Seismic Summary: During the month of September 2010, 52 earthquakes were located in the Yellowstone National Park region. The largest event was a magnitude 2.4 on September 10 at 11:35 PM MDT, located about 8 miles northeast of Old Faithful. No earthquake swarms were recorded in September. Earthquake activity continues at background levels.

Beginning today (October 1, 2010), the University of Utah Seismograph Stations has reduced the magnitude threshold for public web posting of automated earthquake locations and magnitudes for the Yellowstone region. The new minimum magnitude threshold is M 1.5, reduced from the previous threshold of M 2.5. The new threshold value will allow more earthquake information to be rapidly released to the public and other users. This lower magnitude threshold will be tested during a trial period and may be increased again.

Small earthquakes are common in the Yellowstone region. With the reduced magnitude threshold for web posting of automated earthquake locations and magnitudes, it will no longer be practical for seismologists to continue the practice of reviewing all of this information immediately after posting. Users of these data should be aware that an unreviewed earthquake report can be significantly in error and might even be a false alarm, regardless of the reported magnitude. The University of Utah Seismograph Stations will continue its policy of including only reviewed events in its finalized earthquake catalog.

Ground Deformation Summary: Careful analysis of the Yellowstone GPS data shows that the period of accelerated Yellowstone caldera uplift, beginning in 2004, has decreased toward long-term background levels. A record of recent ground displacement can be found at:
http://pboweb.unavco.org/shared/scripts/stations/?checkkey=WLWY&sec=timeseries_plots&timeseries=raw