An earthquake swarm began early 2009 at Wooded Island on the Columbia River, located on the southeast border of the Hanford Site in Washington State. Hanford is located in the the desert of southeastern Washington in the Columbia Basin within the Columbia River flood basalt flows. The earthquakes are a great cause for concern in this area because Hanford is home to the most contaminated nuclear site in the United States and also stores 60% of the high-level radioactive waste in the U.S. (Department of Ecology).

In a previous study conducted by Wicks et al. (2011), approximately 1500 shallow (depth < 1 km) earthquakes ranging between magnitude -0.3 to 3 occurred near Wooded Island. They analyzed interferograms developed from SAR scenes spanning between February 2009 to October 2009 and found that the swarm was most likely caused by aseismic slip on a shallow thrust fault and a near-horizontal fault about 0.5 km below the surface.

Clustered shallow earthquakes continue to occur at Wooded Island. Since October of 2009, 294 earthquakes have contributed to the swarm. My project will focus primarily on the swarm activity between the date of the previous study and the end of 2011 when the highest magnitude earthquakes (M3.3 - M3.7) took place. I will use SAR data to produce interferograms of the swarm site to measure the ground deformation that has taken place since the end of Wicks’ study and to look for migration of the deformation toward areas of concern such as the Hanford nuclear site.

I will create interferograms from SAR scenes collected by ENVISAT (ENVI) and the European Remote Sensing satellite(ERS-2). ENVI scenes were collected along track 70 between January and July 2010. ERS-2 scenes along track 70 collected were in January and February of 2011. Additional ENVI scenes, collected along track 27 between June and December 2011, will be used to observe the deformation from the highest magnitude earthquakes in the swarm (M3.3 - M3.7). My intention is to produce a minimum of four interferograms spanning from January to June 2010, July 2010 to February 2011, January 2010 to February 2011, and June 2011 to December 2011. There was a limited amount of SAR data available for this site. Scenes along track 70 were only available through February 2011 so I will be unable to create an interferogram that spans all of 2010 and 2011.

Earthquake swarms at Wooded Island are cause for concern because they are shallow. Moderate magnitude, shallow earthquakes have the potential to cause damage because the hypocenters are located close to the surface (Wicks et al., 2013) where moderate shaking can easily be felt. Ground motion and deformation caused by the Wooded Island swarm should continue to be monitored because of its close proximity to the Hanford nuclear site. Continued deformation could increase the risk of radioactive contamination by compromising barriers containing toxic waste and allowing it leak into the groundwater.