February 21, 2008 Wells, Nevada Earthquake Seen by EarthScope Observatories

Posted February 26, 2008

At 6:16 am (Pacific time) on February 21, 2008, a magnitude Mw=6.0 earthquake occurred near Wells, NV and was widely felt in Nevada, Idaho and Utah. This earthquake occurred in the midst of the EarthScope observatories designed to measure long-term ground deformation with GPS instruments (Plate Boundary Observatory) and rapid motion from seismic waves with seismometers (USArray). In addition to contributing to a faster, more accurate analysis of the earthquake location, size and fault orientation immediately after the event, as reported by the U.S. Geological Survey, data from these observatories will be used to test a new generation of models for how the Earth behaves in response to geologic forces. They will also be used to construct more accurate and detailed models of the speed with which seismic waves travel in the Earth, which will feed back into more accurate earthquake locations and may provide new insights into what triggers an earthquake.

Predicted horizontal ground motion model by W. Hammond and C. Kreemer (black arrows). Blue dots show the location of aftershocks that occurred within one day of the main shock as determined by Ken Smith of the Nevada Seismological Laboratory ; the size of the dot is proportional to earthquake magnitude. The red line shows the assumed fault trace at the surface. The black-and-white “beach ball” shows the fault plane solution as determined by D. Dreger at University of California, Berkeley.

The arrows overlain on this map of the topography near the earthquake hypocenter show a preliminary model of the direction and size of permanent ground displacement during the earthquake that is predicted by the source mechanism. These arrows show that some places may have moved almost 40 mm. Researchers can test these predictions by analyzing the GPS data recorded during the earthquake. Ongoing investigations near Wells will soon provide direct observations of surface rupture, if any occurred, which will be used to improve these models. Similar earthquakes, over thousands of years, have resulted in the distinctive topography of the Basin and Range province of the western United States.

Geologic cartoons from R. Lillie, Oregon State University, Corvallis OR, show how tectonic forces that pull the Earth's crust apart combine with gravity and buoyancy forces to thin the crust and form the alternating uplifted mountains and sediment-filled valleys characteristic of the Basin and Range province. This tectonic system is also responsible for the lava flows observed throughout this region; however, there is no reason to expect that this earthquake will generate a lava flow.

This graph shows seismic waves recorded by USArray seismic stations at increasing distance from the earthquake. This "record section" can be used to improve models of Earth structure.

Record section from C. Ammon, Penn State, University Park, Pennsylvania

Additional References:

Access to USArray seismograms from individual stations.
Access to ANF network maps, record sections and news links.
Access to PBO borehole strainmeter data