Dynamics and rapid migration of the energetic 2008-2009 Yellowstone Lake earthquake swarm

Yellowstone National Park experienced an unusual earthquake swarm in December January, 2008-2009 that included rapid northward migration of the activity at I km per day and shallowing of the maximum focal depths from 12 to 2 km beneath northern Yellowstone Lake. The swarm consisted of 811 earthquakes, 0.5 < M(W) < 4.1, aligned on a N-S 12-km-long vertical plane of hypocenters. The largest earthquake of the swarm had a 50% tensile crack-opening source determined by a full waveform inversion that we interpret as a magmatic expansion component. In addition, GPS data revealed F W crystal extension coincident with the swarm. Modeling of GPS and seismic data is consistent with E W opening of similar to 10 cm on a N S striking vertical dike. Our interpretation is that the swami was induced by magmatic fluid migration or propagation of a poroelastic stress pulse along a pre existing fracture zone. Citation: Farrell, J., R. B. Smith, T. Taira, W.-L. Chang, and C. M. Pashas (2010), Dynamics and rapid migration of the energetic 2008-2009 Yellowstone Lake earthquake swarm, Geophys. Res. Lett., 37,L19305, doi:10.1029/2010GL044605.