Increasing Quake Activity at Yellowstone Park

'Earthquake swarm' continues to rock Yellowstone
By Howard Pankratz
The Denver Post

Posted: 01/03/2009 05:27:26 PM MST
Updated: 01/03/2009 05:27:28 PM MST


At 11:32 this morning, a 3.5 magnitude earthquake was reported 38 miles east southeast of West Yellowstone, Mont., in Yellowstone National Park " the latest in a swarm of earthquakes that has hit the area in the past week.

The 3.5 tremor was followed this afternoon by a 3.2 magnitude quake at 12:40 p.m. and a 3.0 temblor at 1:15 p.m.

The swarm of more than 500 tremors is the largest series of back-to-back quakes to hit the area in years, according to scientists.

Today's quakes came on the heels of a series of tremors on New Year's Day, including a 3.0 at 6:30 p.m. and a 3.1 at 6:21 p.m.

"The December 2008 earthquake sequence is the most intense in this area for some years," said the Yellowstone Volcano Observatory. "No damage has been reported within Yellowstone National Park, nor would any be expected from earthquakes of this size."

According to the observatory, Yellowstone seismicity increased significantly in December because of what it described as an "energetic earthquake swarm" that began Dec. 27.

The swarm is occurring beneath the northern part of Yellowstone Lake in the park.

The largest of the quakes, according to the observatory, was a magnitude 3.9 at 10:15 p.m. on Dec. 27.

...

Professor Robert B. Smith, a geophysicist at the University of Utah and one of the leading experts on earthquake and volcanic activity at Yellowstone, said that the swarm is of keen interest to scientists.

"It's not business as usual," said Smith. "This is a large earthquake swarm, and we've recorded several hundred. We are paying careful attention. This is an important sequence."

Smith noted that beginning in 2004, there was "accelerated uplift of the Yellowstone Caldera" that covered the entire caldera.

In 2007, Smith and his University of Utah colleagues said the current rise in the caldera was "unprecedented" but concluded that because there were no major earthquakes or "earthquake swarms" accompanying the uplift, they found "little indication that the volcano is moving toward an eruption."

The last major earthquake swarm was in 1985 and lasted three months, Smith told The Denver Post.

The Yellowstone Plateau, which comprises Yellowstone National Park, is one of the largest super-volcanoes in the world and has gone through three volcanic cycles spanning two million years that included some of the world's largest-known eruptions.

Through 5 p.m. Dec. 31, the swarm had included 12 events of magnitude 3.0 to 3.9 and approximately 20 of 2.5 to 2.9, with a total of 400 quakes large enough to be located.

The observatory said similar swarms have occurred in the past without triggering steam explosions or volcanic activity. However, the observatory said there is some potential for explosions and that earthquakes may continue and increase in intensity.

Joe Moore, director of the Wyoming Office of Homeland Security, said his office is tracking the events at Yellowstone on a minute-by-minute basis.

"It's being followed very closely," said Moore.

He said his office has evaluated the emergency plans " which includes evacuations " developed by Teton County, where Jackson Hole is located, and Park County, where Cody is located.

Should a destructive earthquake or volcanic explosion occur, he said his agency would assist those counties as well as communities in Fremont County, which includes the Wind River Indian Reservation.

He said the Federal Emergency Management Agency in Denver is closely monitoring the seismic activity in Yellowstone.

"They are following it as much as we are," said Moore. "There has been an outstanding exchange of information" between local, state and federal agencies, he said.

Yellowstone is the site of the largest and most diverse collection of natural thermal features in the world.

The most devastating earthquake in recent history in the Yellowstone region occurred on Aug. 17, 1959, when a magnitude 7.1 earthquake hit. It was centered near Hebgen Lake, Mont., killed 28 people and caused more than $11 million in damage. Geysers in Yellowstone National park changed eruption times, and new ones began to erupt. On June 30, 1975, a magnitude 6.4 tremor hit the park.

Batesville is within the perimeters of the area that will have damage in the event there is another earthquake on the New Madrid fault.

“We’re concerned, given the historical evidence of what has happened in the past with the New Madrid Seismic Zone,” said Scott M. Ausbrooks, one of two guests at the Batesville Rotary Club meeting Monday. Ausbrooks is a geohazards and environmental geology supervisor for the Arkansas Geological Survey.

Earthquakes occur along faults, a fracture within the earth of which movement occurs. The release of strain along a fault plane causes an earthquake.

“If you have an earthquake, the waves propagate from the area of what we call the focus all the way to what we call the epicenter,” Ausbrooks, a professional geologist, said. “In the initial stage you have movement in different directions along the fault, strain accumulates and when it breaks that’s what releases the energy.”

Seismic activity on the New Madrid Fault at 2:15 a.m. on Dec. 16, 1811, registered as a 7.4-7.8 earthquake. The shaking was felt as far away as New England and Canada. Two more earthquakes followed " a 7.4-7.8 at 9 a.m. on Jan. 23, 1812, and a 7.6-8.0 at 3:45 a.m. on Feb. 7.

It was said the earthquakes caused the Mississippi River to run backwards, Lake Reelfoot to form in Tennessee and church bells to ring in the East. Hundreds of aftershocks were reported for over a year.

The University of Utah Seismograph Stations reports that as of 6 p.m. on January 2, seismicity of the ongoing Yellowstone earthquake swarm continues. Over 500 earthquakes, as large as M 3.9, have been recorded by an automated earthquake system since the inception of this unusual earthquake sequence that began Dec. 27, 2008. More than 300 of these events have been reviewed and evaluated by seismic analysts. Depths of the earthquakes range from ~ 1km to around 10 km. We note that the earthquakes extend northward from central Yellowstone Lake for ~10 km toward the Fishing Bridge area, with a migration of recent earthquakes toward the north. Some of the dozen M3+ earthquakes were felt in the Lake, Grant Village and Old Faithful areas. Personnel of the Yellowstone Volcano Observatory continue to evaluate this earthquake sequence and will provide information to the NPS, USGS and the public as it evolves.

This 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.

Is there a bulge beneath the lake? Mapping of the lake bottom has revealed a variety of faults, hot springs and craters beneath Yellowstone Lake. In a recent scientific report (Morgan et al., 2003), one feature was informally named the "inflated plain" by USGS researcher Lisa Morgan, who organized surveys of the lake beginning in 1999. In mapping the entire lake, she and her colleagues identified a region about 2,000 feet long that rises about 100 feet above the lake floor. The area is in the northern part of Yellowstone Lake, south-southwest of Storm Point. The area is home to many hot springs and the nearby sediments have undergone chemical changes due to the flow of thermal water.

Why was it called the inflated plain? Seismic images of the lake sediments in this area show that they were tilted, hinting that the region may have been pushed up or inflated. The amount of inflation would be much less than the 100-foot height of the feature, but is currently unknown. The images appear to indicate that the uplift is associated with accumulation of gas from Yellowstone's hydrothermal system. Similar inferred gas accumulations were also noted elsewhere within the lake. Future research will assess the amount of uplift and its origin, whether by gas buildup or other potential mechanisms.

Has the "inflated plain" been growing? At present, there is no evidence of recent growth of any features beneath the lake, and there is no indication that residents or visitors are in any danger. Temperature measurements from hydrothermal vents taken this year indicate no change in temperatures compared to those taken last year. The feature may have been there for decades or much longer.

So what's the big deal? There may be none. This region has active hydrothermal features, and possibly some uplift. It's possible that the area could host future hydrothermal explosions, but so could other areas beneath the lake and other areas within the Park.

What's a hydrothermal explosion? Hydrothermal explosions occur when water that feeds Yellowstone's geysers and hot springs is explosively flashed to steam, breaking rocks and throwing them into the air. Small hydrothermal explosion events occur every few years at Yellowstone, mostly in the geyser basins, and usually pose little hazard. There is geologic evidence for a few large hydrothermal explosions, some leaving craters thousands of feet across near Yellowstone Lake and in other areas of the park. Such large explosions have not occurred within the last several thousand years. Two classic papers discuss evidence for hydrothermal explosions at Yellowstone, both in the geyser basins (Muffler et al., 1971) and beneath Mary Bay in Yellowstone Lake (Wold et al., 1977).

Do any of the features beneath the lake relate to possible volcanic eruptions? It is very unlikely. All active features are related to faults and hot water (hydrothermal) vents. Identified craters were formed by collapse or as a result of old hydrothermal explosions. Many of the rocks beneath the lake are lava flows more than 100,000 years old.

Is there any possibility of a toxic gas emission from Lake Yellowstone as occurred in Africa some years ago? No. What occurred in Cameroon (Lake Nyos in 1986) resulted from CO2 buildup in the bottom waters of a tropical lake. In warm climates, lakes easily become stratified. In cold climates, however, the waters of lakes "turn over" once or twice per year. Cold water from melting ice sinks to the bottom of the lake. This creates a well-mixed lake with minimal potential for gas buildup. In addition, the CO2 at Lake Nyos was cold and not associated with thermal water. Waters and gases from the hot vents beneath Lake Yellowstone will tend to rise through the lake due to their low density.

Is anybody assessing the hazards from new hydrothermal explosions? A geologic hazard assessment of Yellowstone National Park is under way by YVO. The assessment will evaluate the known and potential hazards at Yellowstone from earthquakes, volcanic eruptions and hydrothermal explosions. Any new information on Yellowstone Lake will be made available to YNP officials and the general public.


References: Morgan, L.A., Shanks, W.C. III, Lovalvo, D.A., Johnson, S.J., Stephenson, W.J., Pierce, K.L., Harlan, S.S., Finn, C.A., Lee, G., Webring, M., Schulze, B., Duhn, J., Sweeney, R., Balistrieri, L., 2003, Exploration and discovery in Yellowstone Lake: results from high-resolution sonar imaging, seismic reflection profiling and submersible studies: Journal of Volcanology and Geothermal Research, v. 122, p. 221-242.

Morgan, L.A., Shanks, W.C., Lovalvo, D., Lee, G., Webring, M., Stephenson, W.J., and Johnson, S.Y., 2003, The Floor of Yellowstone Lake is Anything but Quiet: New Discoveries from High-Resolution Sonar Imaging, Seismic Reflection Profiling and Submersible Studies, In Morgan, L.A., ed., Integrated Geoscience Studies in the Greater Yellowstone Area: Volcanic, Hydrothermal and Tectonic Processes in the Yellowstone Geoecosystem, U.S. Geological Survey Professional Paper (in press). Also available in: Yellowstone Science, v. 11, no. 2 (Spring 2003), pp. 14-30. Article in two parts (2nd part is here).

Muffler, L.J.P., White, D.E., and Trusdell, A.H., 1971, Hydrothermal explosion craters in Yellowstone National Park: Geological Society of America Bulletin, v. 82, p. 723-740.

Wold, R. J., R. B. Smith, and M. A. Mayhew, 1977, Geophysical study of a hydrothermal explosion crater in Mary Bay, Yellowstone Lake, Wyoming, J. Geophys. Res., 82, p. 3733-3738.

New Year's Day 2009 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 p.m. MST on Dec. 27. Through 5 p.m. 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. There was 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 or 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 p.m. 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's 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.

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.

Series of earthquakes hit The Geysers
Written by Elizabeth Larson
Monday, 15 December 2008

THE GEYSERS " A series of small earthquakes punctuated by a temblor measuring 3.1 on the Richter scale shook the Cobb area Sunday evening.

The 3.1-magnitude earthquake occurred at 8:24 p.m. at a depth of 1.4 miles, as was centered two miles north of The Geysers, four miles west of Cobb and seven miles west northwest of Anderson Springs, according to the US Geological Survey.

A second earthquake, measuring 2.6 in magnitude, occurred 25 seconds later, to be followed by a third 10 seconds later that measured 1.8, US Geological Survey records showed.

Cobb resident Roger Kinney reported that the second earthquake felt near as big as the first and lasted longer.

Three more small quakes, two measuring 1.1 and one measuring 1.3, followed over the following three minutes. In all, 16 shakers followed the main one between 8:24 p.m. and midnight.

Besides several Cobb, the US Geological Survey reported that the 3.1-magnitude earthquake was reportedly felt in Kelseyville and as far away as Cloverdale.

Kinney said earthquakes in the seismically active area usually drop off in November and pick up again in April, so the quakes were a surprise, especially coming as closely apart as they did.

The last earthquake measuring 3.0 or above reported in Cobb, The Geysers or Anderson Springs took place Dec. 1 and measured 3.2 in magnitude.

The Geysers, a geothermal power field located 72 miles (116 km) north of San Francisco, California, is the largest geothermal development in the world. It is currently outputting over 750 MW. The Geysers consists of 22 separate power plants that utilize steam from more than 350 producing wells. [1] The Calpine Corporation operates and owns 19 of the 22 facilities. The other three facilities are operated by the Northern California Power Agency and the Western GeoPower Corporation.

The Geysers geothermal development spans an area of around 30 square miles (78 km²) in Sonoma and Lake counties in California, located in the Mayacamas Mountains. Power from The Geysers provides electricity to Sonoma, Lake, Mendocino, Marin, and Napa counties. It is estimated that the development meets 60 percent of the power demand for the coastal region between the Golden Gate Bridge and the Oregon state line.[1]

Steam used at the Geysers is produced from a greywacke sandstone reservoir, that is capped by a heterogeneous mix of low permeability rocks and underlaid by a Felsite intrusion.[2] Gravity and seismic studies suggest that the source of heat for the steam reservoir is a large magma chamber over 4 miles (7 km) beneath the ground, and greater than 8 miles (14 km) in diameter. [3]

Unlike most geothermal resources, the Geysers is a dry steam field, which means it mainly produces superheated steam. Because the power plant turbines require a vapor phase input, dry steam resources are generally preferable. Otherwise, a two-phase separator is required between the turbine and the geothermal wells to remove condensation that is produced with the steam.