1. Blakely, R. J. et al. Connecting the Yakima fold and thrust belt to active faults in the Puget Lowland, Washington. Journal of Geophysical Research 116, (2011).

Summary

Blakely et al. uses aeromagnetic evidence to suggest that faults within the Yakima Fold and Thrust Belt (YFTB) may extend all the way to Western Washington, merging with the active Seattle and Whidbey Island faults. If these connected faults are seismically active along their entire lengths then seismic hazards in Eastern Washington are potentially more dangerous and should be reassessed.

2. Blakely, R. J., Sherrod, B. L., Weaver, C. S., Rohay, A. C. & Wells, R. E. Tectonic Setting of the Wooded Island Earthquake Swarm, Eastern Washington. Bulletin of the Seismological Society of America 102, 1786–1795 (2012).

Summary

Blakely et al. used high-resolution aeromagnetic data to model the tectonic setting for the Wooded Island earthquake swarm. They came to the conclusion that regional tectonic forces (Yakima Fold and Thrust Belt) were the cause of the swarm though it may have been triggered by fluid pressure changes.

3. Chen, X., Shearer, P. M. & Abercrombie, R. E. Spatial migration of earthquakes within seismic clusters in Southern California: Evidence for fluid diffusion. Journal of Geophysical Research 117, (2012).

Summary

They studied 69 seismicity bursts to quantify their spatial migration and use a set of parameters to look for behavior differences between aftershock sequences and earthquake swarms.

tmax = timing of the largest event Δσquasi = ratio between total moment and radius μ = skew of the seismic moment release ds = measures the distance separation between the centers of the first half and the second half of each burst, normalized by the mean radius of the burst

After-shock sequences: low tmax, high Δσquasi, high μ, and low ds (no significant migration) Earthquake swarms: high tmax, low Δσquasi, low μ, and high ds (significant migration)

4. Gomberg, J., Sherrod, B., Trautman, M., Burns, E. & Snyder, D. Contemporary Seismicity in and around th e Yakima Fold-and-Thrust Belt in Eastern Washington. Bulletin of the Seismological Society of America 102, 309– 320 (2012).

Summary

Gomberg et al. examined the regional tectonic relationships and localized surface processes that create seismicity in eastern Washington. Evidence shows that earthquakes occurring within the Columbia River Basalt (CRB) exhibit more swarm like behavior than those beneath the CRB. They suggest that localized stress caused by fluids migrating through a crack network in the CRB is generating the earthquake swarms.

5. Shelly, D. R. et al. A fluid-driven earthquake swarm on the margin of the Yellowstone caldera: FLUID-DRIVEN YELLOWSTONE SWARM. Journal of Geophysical Research: Solid Earth 118, 4872–4886 (2013).

Summary

Shelly et al. used high-resolution earthquake detection and location techniques on the 2010 Madison Plateau swarm to study the relationship between pore fluid pressure and earthquake swarms. The Madison Plateau swarm displayed a rapid expansion of hypocenters over time, which suggests triggering by a fluid pressure pulse. They suggest that the swarms show a cyclic behavior: increase in fluid pressure causes faulting, faulting facilitates fluid flow, and fluids then cause resealing of the fault through mineralization.

6.Vidale, J. E. & Shearer, P. M. A survey of 71 earthquake bursts across southern California: Exploring the role of pore fluid pressure fluctuations and aseismic slip as drivers. Journal of Geophysical Research 111,(2006).

Summary

Vidale and Shearer studied 71 seismic bursts in southern California and found that shallow and normal faulting sequences are most likely to exhibit swarm like behavior. Many swarm hypocenters fall on a vertical plane and expand over time, which suggests increased fluid pressure. Aseismic slip or a combination of fluids and aseismic slip can also trigger earthquake swarms.

7. Wicks, C. et al. InSAR observations of aseismic slip associated with an earthquake swarm in the Columbia River flood basalts. Journal of Geophysical Research 116, (2011).

Summary

Wicks et al. studied the Wooded Island swarm from the beginning of 2009 until October 29. They used InSAR data of the swarm to create a model of a thrust fault and a nearly horizontal fault located between basalt beds. Evidence shows that swarm seismicity was most likely driven by fluid pore pressure and that aseismic slip may have been caused by seismicity or a pressure pulse stressing thixotopic (viscous materials that become less viscous under stress) interbed sediments.

8. Wicks, C., Weaver, C., Bodin, P. & Sherrod, B. InSAR Evidence for an active shallow thrust fault beneath the city of Spokane Washington, USA: THE SPOKANE FAULT. Journal of Geophysical Research: Solid Earth 118, 1268–1276 (2013).

Summary

Wicks et al. determined that a series of small magnitude, shallow earthquakes beneath Spokane, WA were caused by a previously unknown fault. The Wooded Island swarm could help determine the geology beneath Spokane since the geology beneath Hanford, WA is well known. Because of the potentially destructive behavior of shallow, moderate magnitude earthquakes (e.g. the 2011 Mw 6.2 Christchurch earthquake), further study of the Spokane fault is vitally important.