Seismic Response of the Katmai Volcanoes to the 6 December 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 Katmai area on the Alaska peninsula immediately following
the 6 December 1999 magnitude (Mw) 7.0 Karluk lake earthquake 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. All
of 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
four separate volcanic centers all suggest these earthquakes were remotely
triggered. Modeling of the Coulomb stress changes from the mainshock for
optimally oriented faults suggests negligible change in static stress
beneath the Katmai volcanoes. This results favors models that involve
dynamic stresses as the mechanism for triggered seismicity at Katmai.