HR: 13:55h
AN: T13F-02    [Abstracts]
TI: Scaling Relationships for Slow Slip Events and Tremor in Subduction Zones
AU: * Schwartz, S Y
EM: sschwartz@pmc.ucsc.edu
AF: Earth and Planetary Sciences Department, University of California, Santa Cruz 1156 High Street, Santa Cruz, CA 95064, United States
AU: Rokosky, J M
EM: jrokosky@gmail.com
AF: Earth and Planetary Sciences Department, University of California, Santa Cruz 1156 High Street, Santa Cruz, CA 95064, United States
AU: Obara, K
EM: obara@bosai.go.jp
AF: Solid Earth Research Group, National Research Institute for Earth Sciences and Disaster Prevention, Tsukuba, AZ 85287, Japan
AB: Global compilations of faulting parameters for slow slip phenomena in subduction zones reveal that event duration is proportional to seismic moment rather than its cube-root, as for earthquakes (Schwartz and Rokosky, 2007; Ide et al., 2007). Ide et al. (2007) proposed two different models consistent with this scale dependent behavior that either assume direct proportionality between fault slip (d) and fault length (L), as observed for earthquakes or constant slip, independent of fault length. These two models predict different relationships between fault length and seismic moment, stress drop and rupture velocity that can be tested with available data. Combining data from 25 short-term slow slip events in Western Shikoku, the Kii Peninsula and Tokai, Japan with longer duration slow slip events globally reveals a nearly linear relationship between seismic moment (M_o) and fault length, inconsistent with the M_o α L³ and M_o α L² predictions of the two previously proposed models. The observed relationship implies that fault slip is proportional to the inverse of fault length, stress drop is proportional to the inverse of fault length squared and rupture velocity is constant. Although at present the scatter in most of these slow slip event parameters is still too large to confidently differentiate between trends, the relatively small range in slow slip propagation velocities over a large range in fault lengths is consistent with this new model. The direct proportionality between seismic moment and duration (τ) implies that slow slip phenomena have constant moment rate and therefore constant far-field-displacements as a function of time. We test this prediction by calculating reduced displacements for tremor episodes accompanying short-term slow slip events in SW Japan. Consistent with M_o α τ scaling, we find that reduced displacements are relatively constant throughout each 3-10 day slow slip episode. Average values of reduced displacement vary between the different slow slip episodes and show a decrease in reduced displacement with increasing cumulative slip in the accompanying slow slip event. We are investigating whether this, as well as other systematic tremor amplitude behavior, reflects regional variations and what it reveals about the mechanics of tremor and slow slip events.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1244 Standards and absolute measurements
DE: 7215 Earthquake source observations (1240)
DE: 7240 Subduction zones (1207, 1219, 1240)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting