HR: 16:20h
AN: S34A-04 INVITED     [Abstracts]
TI: Triggering of Great Earthquakes
AU: * Sacks, I S
EM: sacks@dtm.ciw.edu
AU: Linde, A T
EM: linde@dtm.ciw.edu
AB: There have been many studies showing that of great earthquakes appear to be triggered by slow stress changes. In particular, stress changes due to strain diffusion from other large events in the region have been shown to be effective. Four centuries of earthquake occurrence data in Northeast Japan allowed a ~36 year lag time of subduction events after on-land earthquakes to be determined (Rydelek and Sacks, 1990). The elastic-viscoelastic model of the crust-lithosphere derived from geodetic observations over about 50 years can explain the time lag. The stress diffusion from the 1940's Nankai trough earthquakes, M ~8, slowly unloaded the normal stress clamping the Nojima fault over a 50 year period, resulting in the 1995 Kobe earthquake, m=6.9 (Pollitz and Sacks, 1997). From the earthquake record spanning about 12 centuries, the 1940's Nankai trough earthquakes were themselves advanced in time, the interval since the previous event of 1854 being clearly the shortest on record. Strain diffusion from the on-land great Nobi earthquake of 1891 explains not only the advance, but also the two year delay between the eastern (Tonankai) and western (Nankaido) events. The failure mechanism was modeled by Rydelek and Sacks, 2003. In the above examples, the strain diffusion has created stress changes of a fraction to a few bars at the fault so as to increase the Coulomb failure and modify the occurrence time by a significant amount, i.e. many years on a fault with recurrence interval of more than a century. Continuous GPS observations enable insight into much lower stress triggering of great events. It has long been recognized that most Nankai trough events (since 684) occur in the winter. A seasonal shortening of the continental plate (Heki, 2004) overlying the subducting Philippine sea plate, causes a reduction of stress on the thrust fault. Even though this stress change is less than 0.1 bar, and the yearly stress loading of the fault may be 0.5 to 1 bar, it seems to be sufficient to influence the failure time.
DE: 1208 Crustal movements--intraplate (8110)
DE: 7209 Earthquake dynamics and mechanics
DE: 7223 Seismic hazard assessment and prediction
DE: 7260 Theory and modeling
DE: 8164 Stresses--crust and lithosphere
SC: Seismology [S]
MN: 2005 Joint Assembly