Seismic Activity
The Yellowstone volcanic system is one of largest volcanic systems in the world and is a major area of seismicity, including a M7.5 earthquake in 1959, the largest historic event of the western U.S. interior. In 2002 alone, there were more than 2350 earthquakes at Yellowstone, including over 500 triggered by the Nov. 2002, M7.9 Denali earthquake.
Yellowstone Mountain
� © National Park Service
The Norris Geyser Basin is located at the
NW edge of the 640,000-year-old Yellowstone caldera and is in the vicinity of
several post-caldera rhyolite flows and at the intersection of large active
faults. Seismicity at the Norris area is characterized generally by swarms, but
includes a M 6.1 event in 1975. The caldera has a dynamic deformation history,
uplifting and subsiding up to 10 meters over decadal to millennial timescales.
Historically it rose 1 m between 1923 and 1985, then subsided ~25 cm to 1995,
and in the past ~7 years the NW caldera, including Norris, appears to uplifting.
Importantly, the recent uplift has been accompanied by expanding areas of
hydrothermal activity in Norris Geyser Basin, including the creation of hot
springs and fumaroles north of Norris and renewed activity of the Steamboat
geyser, the world's tallest. In July 2003, increased hydrothermal activity
required closure to visitors of parts of the Norris Back Basin. The relationship
between these diverse phenomena, however, remains unknown. The uplift itself may
be due to magma intrusion, release and expansion of hydrothermal fluids through
a permeability barrier, or some other mechanism.
The Yellowstone Volcano Observatory (YVO) operates under a cooperative agreement
between the USGS, the University of Utah (UU), and Yellowstone National Park to
monitor and evaluate volcanic and tectonic activity at Yellowstone, to assess
the accompanying geologic hazards, and to model the complex behavior of one of
the world's most dynamic magmatic systems.
In late July 2003, to investigate the recent anomalous hydrothermal activity, a
network of 7 broadband seismometers, and 5 GPS receivers were deployed in the
Norris Geyser basin, along with a series of thermal data loggers that recorded
the temperature of the ground surface and waters emerging from hot springs and
geysers. This allows quantification of thermal water flux on a minute-by-minute
basis. The seismic and the continuous recording GPS network was operated over a
~2 month period following the discovery of the thermal disturbance. The seismic
and GPS instrumentation along with the thermal monitoring allows the integration
of these various data for numerical modeling of the dynamics of the hydrothermal
system
Ideally, one can correlate between seismic and deformation signals with
the volume and temperatures of thermal water and/or gas that emerges from the
Norris Geyser Basin. This will enable scientists to investigate the relationship
between crustal strain, seismicity and hydrothermal activity.
- content provided by the United States Geological Survey
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