Triggered Seismicity Beneath the Katmai Volcanoes Following the December 6, 1999 Magnitude 7.0 Karluk Lake Earthquake, Alaska.
J.A. Power, S.C. Moran, S.R. McNutt, S.D. Stihler, and J.J. Sánchez.
U.S. Geological survey-Alaska Volcano Observatory (J.A. Power and S.C. Moran)
Geophysical Institute, University of Alaska Fairbanks (S.R. McNutt, S.D. Stihler, and J.J. Sánchez)
Abstract.A sudden increase in earthquake activity was observed beneath volcanoes in the Katami area on the Alaska Peninsula immediately following the December 6, 1999, magnitude (Mw) 7.0 Karluk Lake earthquake located beneath southern Kodiak Island, Alaska. The observed increase in earthquake activity consisted of small (ML $<$ 1.3), shallow (Z $<$ 5.0 km) events. These earthquakes were located beneath Mount Martin, Mount Mageik, Trident Volcano, and the Katmai caldera and began within the coda of the Karluk Lake mainshock. These earthquakes occurred in areas and magnitude ranges that are typical for the background seismicity observed in the Katmai area. Seismicity rates returned to background levels 8 to 13 hours after the Karluk Lake mainshock. The close temporal relationship with the Karluk Lake mainshock, the onset of activity within the mainshock coda, and the simultaneous increase beneath 4 separate volcanic centers suggest these earthquakes were remotely triggered. A similar but smaller increase in earthquake activity was observed beneath the Mount Martin and Katmai Caldera following a magnitude 6.5 aftershock that occurred on July 11, 2000. Modeling of the Coulomb stress changes from the mainshock for optimally oriented faults suggests negligible change in static stress beneath the Katmai volcanoes. This result thus favors models that involve dynamic stresses as the mechanism for triggered seismicity at Katmai..