YELLOWSTONE VOLCANO OBSERVATORY MONTHLY UPDATE
Thursday, January 1, 2009 07:57 MST (Thursday, January 1, 2009 14:57 UTC)


YELLOWSTONE VOLCANO (CAVW#1205-01-)
44.43°N 110.67°W, Summit Elevation 9203 ft (2805 m)
Volcano Alert Level: NORMAL
Aviation Color Code: GREEN

December 2008 Yellowstone Earthquake And Ground Deformation Summary

Earthquake Summary:

Yellowstone seismicity increased significantly in December 2008 due to an energetic earthquake swarm that commenced on December 26. This swarm, a sequence of earthquakes clustered in space and time, is occurring beneath the northern part of Yellowstone Lake in Yellowstone National Park. As of this writing, the largest of these earthquakes was a magnitude 3.9 at 10:15 pm MST on Dec. 27. Through 5:00 pm MST on Dec. 31, the sequence had included 12 events of magnitude 3.0 to 3.9 and approximately 20 of magnitude 2.5 to 2.9, with a total of at least 400 events large enough to be located (magnitude ~1 or larger). National Park Service (NPS) employees and visitors have reported feeling the largest of these earthquakes in the area around Yellowstone Lake and at Old Faithful and Grant Village.

The hypocenters of the swarm events cluster along a north-south-trending zone that is about 7 km long. The vast majority of the focal depths are shallower than 5 km. It is not possible to identify a causative fault of other feature without further analysis.

Analysts are currently processing the backlog of seismic data from these events. The current analyst-processed catalog is believed to include all events of magnitude 2.5 and greater through Dec 31 at 5 pm MST, but hundreds of earthquakes remain to be processed. The total of more than 400 locatable events is based on automatically-determined locations and magnitudes for the swarm events.

The December 2008 earthquake sequence is the most intense in this area for some years. No damage has been reported within Yellowstone National Park, nor would any be expected from earthquakes of this size. The swarm is in a region of historical earthquake activity and is close to areas of Yellowstone famous hydrothermal activity. Similar earthquake swarms have occurred in the past in Yellowstone without triggering steam explosions or volcanic activity. Nevertheless, there is some potential for hydrothermal explosions and earthquakes may continue or increase in magnitude. There is a much lower potential for related volcanic activity.

The National Park Service in Yellowstone has been kept fully informed of the ongoing seismic activity via electronic means and by phone contacts with the University of Utah and the U.S. Geological Survey USGS). The Wyoming Office of Homeland Security is reviewing Earthquake Response Plans and monitoring seismic activity.

Earthquakes are a common occurrence in the Yellowstone National Park area, an active volcanic-tectonic area averaging 1,000 to 2,000 earthquakes a year. Yellowstone's 10,000 geysers and hot springs are the result of this geologic activity. A summary of Yellowstone's volcanic history is available on the Yellowstone Volcano Observatory web site (listed below).

The University of Utah operates a seismic network in Yellowstone National Park in conjunction with the National Park Service and the U.S. Geological Survey. These three institutions are partners in the Yellowstone Volcano Observatory. Seismic data from Yellowstone are transmitted to the University in real-time by radio and satellite links from a network of 28 seismographs in the Yellowstone area and are available on the web.

Seismologists continue to monitor and analyze data from this swarm of earthquakes and provide updates to the NPS and USGS and to the public via the following web pages.

Information on U.S. earthquake activity including Yellowstone can be viewed at the U.S. Geological Survey web site: http://earthquake.usgs.gov/eqcenter/recenteqsus/.

Information on earthquakes can also be viewed at the University of Utah
Seismograph Stations web site: http://www.seis.utah.edu/.

Seismographic recordings from Yellowstone seismograph stations can be
viewed online at: http://www.quake.utah.edu/helicorder...one/index.html.

An article on earthquake swarms at Yellowstone is available at the following: http://volcanoes.usgs.gov/yvo/public...apr04swarm.php

Persons who felt any of the earthquakes are encouraged to fill out a survey form on the USGS 'Did You Feel It?' web site: http://earthquake.usgs.gov/eqcenter/dyfi/.

Geologic information, maps, and monitoring information for Yellowstone can be found on the Yellowstone Volcano Observatory web site at:
http://volcanoes.usgs.gov/yvo/.


Ground Deformation Summary:

Through December 2008, continuous GPS data show that much of the Yellowstone caldera continued moving upward, though at a lower rate than the past few years. The maximum measured ground uplift over the past 53 months is ~23 cm at the White Lake GPS station, north of Fishing Bridge. An example can be found at:
http://pboweb.unavco.org/shared/scri...timeseries=raw.

The general uplift of the Yellowstone caldera is scientifically important and will continue to be monitored and studied closely by YVO staff.

A discussion of the current uplift episode at Yellowstone and long-term ground deformation at Yellowstone and elsewhere can be found at: http://volcanoes.usgs.gov/yvo/public...psanddowns.php.



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The Yellowstone Volcano Observatory (YVO) is a partnership of the U.S. Geological Survey (USGS), Yellowstone National Park, and University of Utah to strengthen the long-term monitoring of volcanic and earthquake unrest in the Yellowstone National Park region. Yellowstone is the site of the largest and most diverse collection of natural thermal features in the world and the first National Park. YVO is one of the five USGS Volcano Observatories that monitor volcanoes within the United States for science and public safety.