HR: 1340h
AN: T33B-0543    [Abstracts]
TI: Do Old Faults Ever Die? Fault-Plane Orientations of Intraslab Earthquakes in the Tonga-Kermadec Subduction Zone
AU: * Hughes, A N
EM: hughesa@wlu.edu
AF: Department of Geology, Washington and Lee University, 116 N. Main Street, Lexington, VA 24450 United States
AU: Warren, L M
EM: warren@dtm.ciw.edu
AF: Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015 United States
AU: Silver, P G
EM: silver@dtm.ciw.edu
AF: Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015 United States
AB: One of the basic issues regarding the physical mechanism for deep earthquakes is the extent to which they occur on pre-existing faults: Do deep earthquakes reactivate faults that formed in the oceanic plate prior to subduction? A previous study of the Tonga subduction zone (Jiao et al., 2000) compared nodal plane distributions of outer-rise events to events as deep as 450 km and found them to be very similar. While this comparison provides some support for the pre-existing fault hypothesis, a more stringent test of the hypothesis is available by identifying the actual rupture planes of both the outer rise and deep events and comparing their orientations. Warren and Silver recently developed a semi-automated method to distinguish the fault plane from the auxiliary plane of the focal mechanism based on the directivity of the rupture, and we apply this method to the P waves of large earthquakes in the Tonga-Kermadec subduction zone. From 1994--2004, there were 74 earthquakes with M_W ≥6.0 and depth ≥100 km in the region, and we analyze them as well as the corresponding outer rise events. The focal mechanisms for most of the deep earthquakes contain a subvertical and a subhorizontal nodal plane. For earthquakes between 100--200 km depth, our preliminary results show that the ruptures tend to propagate subhorizontally, and that this rupture direction is often consistent only with the subhorizontal nodal plane. Below 450 km depth, earthquakes occur on both subhorizontal and subvertical planes.
DE: 7203 Body waves
DE: 7209 Earthquake dynamics (1242)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: Fall Meeting 2005