HR: 0800h
AN: T21A-0376    [Abstracts]
TI: Precursors to Great Earthquakes Along the Nankai Trough; Slow Earthquakes, Non-volcanic Deep Tremor and Slow Slip
AU: * Sacks, S
EM: sacks@dtm.ciw.edu
AF: Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015, United States
AU: Linde, A T
EM: linde@dtm.ciw.edu
AF: Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015, United States
AB: Just before (and during) the December 1944 Tonankai great earthquake, the Military Survey Institute of Japan carried out leveling surveys in the anticipated region of the earthquake. Mogi (1985) pointed out that large closure errors, for line segments measured on the day before and the morning of the earthquake, could be indicative of continuing tilting due to precursory slip. Before the 1946 Nankaido great earthquake there were level changes recorded by tide gauges and also large changes in water levels in wells. We have shown (Linde and Sacks 2002) that the pre-earthquake changes for both events are indicative of slow slip on the down-dip extension of the seismogenic zone, a region that can store strain energy but fails with slow slip. The coseismic slip for both earthquakes averages about 4 meters; the down-dip slow slip was determined to be about half the seismogenic value. In his most recent studies of the same area, Obara (2006) reports that small (~cm) slow slip events and non-volcanic tremor occur on the upper surface of the subducting plate. The locations for these events correspond rather closely to the areas we proposed as having slow slip precursory to the great earthquakes. Additionally the slip rate from Obara's work would result in about 2 meters being released in 100 years, the approximate return interval for the great earthquakes. This is consistent with the deficit being released as a large slow event just before those great earthquakes.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting