InSAR Evidence for an active shallow thrust fault beneath the city of Spokane Washington, USA
Article first published online: 27 MAR 2013
©2013. American Geophysical Union. All Rights Reserved.
Journal of Geophysical Research: Solid Earth
Volume 118, Issue 3, pages 1268–1276, March 2013
How to Cite
2013), InSAR Evidence for an active shallow thrust fault beneath the city of Spokane Washington, USA, J. Geophys. Res. Solid Earth, 118, 1268–1276, doi:10.1002/jgrb.50118., , , and (
- Issue published online: 26 APR 2013
- Article first published online: 27 MAR 2013
- Accepted manuscript online: 15 FEB 2013 01:38PM EST
- Manuscript Accepted: 1 FEB 2013
- Manuscript Revised: 26 JAN 2013
- Manuscript Received: 19 OCT 2012
 In 2001, a nearly five month long sequence of shallow, mostly small magnitude earthquakes occurred beneath the city of Spokane, a city with a population of about 200,000, in the state of Washington. During most of the sequence, the earthquakes were not well located because seismic instrumentation was sparse. Despite poor-quality locations, the earthquake hypocenters were likely very shallow, because residents near the city center both heard and felt many of the earthquakes. The combination of poor earthquake locations and a lack of known surface faults with recent movement make assessing the seismic hazards related to the earthquake swarm difficult. However, the potential for destruction from a shallow moderate-sized earthquake is high, for example Christchurch New Zealand in 2011, so assessing the hazard potential of a seismic structure involved in the Spokane earthquake sequence is important. Using interferometric synthetic aperture radar (InSAR) data from the European Space Agency ERS2 and ENVISAT satellites and the Canadian Space Agency RADARSAT-1, satellite we are able to show that slip on a shallow previously unknown thrust fault, which we name the Spokane Fault, is the source of the earthquake sequence. The part of the Spokane Fault that slipped during the 2001 earthquake sequence underlies the north part of the city, and slip on the fault was concentrated between ~0.3 and 2 km depth. Projecting the buried fault plane to the surface gives a possible surface trace for the Spokane Fault that strikes northeast from the city center into north Spokane.