Global Positioning System constraints on crustal deformation before and during the 21 February 2008 Wells, Nevada M6.0 earthquake

Using Global Positioning System (GPS) data from permanent sites and U.S. Geological Survey (USGS) campaign data
we have estimated co-seismic displacements and secular background crustal deformation patterns associated with the 21
February 2008 Wells Nevada earthquake. Estimated displacements at nearby permanent GPS sites ELKO (84 km distant)
and GOSH (81 km distant) are 1.0±0.2 mm and 1.1±0.3 mm, respectively. The magnitude and direction are in agreement
with those predicted from a rupture model based on InSAR measurements of the near-field co-seismic surface
displacement. Analysis of long GPS time series (>10 years) from the permanent sites within 250 km of the epicenter
indicate the eastern Nevada Basin and Range undergoes steady tectonic transtension with rates on the order of 1 mm/year
over approximately 250 km. The azimuth of maximum horizontal crustal extension is consistent with the azimuth of the
Wells earthquake co-seismic slip vector. The orientation of crustal shear is consistent with deformation associated with
Pacific/North America plate boundary relative motion seen elsewhere in the Basin and Range. In response to the event, we
deployed a new GPS site with the capability to telemeter high rate, low latency data that will in the future allow for rapid
estimation of surface displacement should aftershocks or postseismic deformations occur. We estimated co-seismic
displacements using campaign GPS data collected before and after the event, however in most cases their uncertainties
were larger than the offsets. Better precision in co-seismic displacement could have been achieved for the campaign sites if
they had been surveyed more times or over a longer interval to better estimate their pre-event velocity.