HR: 1340h
AN: T23A-0571    [Abstracts]
TI: Dynamic Traction Evolution and Fracture Energy On Extended Faults Inferred From Kinematic Slip Models
AU: * Tinti, E
EM: tinti@ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Department of Seismology and Tectonophysics, via di Vigna Murata 605, Rome, 00143 Italy
AU: Spudich, P
EM: spudich@usgs.gov
AF: US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: Cocco, M
EM: cocco@ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Department of Seismology and Tectonophysics, via di Vigna Murata 605, Rome, 00143 Italy
AB: We estimate fracture energy density $(G)$ for moderate-to-large earthquakes by retrieving dynamic traction evolution at each point on the fault plane from slip history imaged by inverting ground motion waveforms. We use rupture models of the 1979 Imperial Valley, the 1992 Landers, the 1994 Northridge, 2000 Tottori, 1984 Morgan Hill, 1997 Colfiorito and the 1995 Kobe events. Our numerical approach uses slip velocity as a boundary condition on the fault in an elastic medium. We employ a 3-D finite difference algorithm to compute the dynamic traction evolution in the time domain during the earthquake rupture. We estimate fracture energy by calculating the scalar product between dynamic traction and slip velocity vectors. This approach does not require specifying a constitutive law and does not require the dynamic traction to be collinear with slip velocity. If these vectors are not collinear, the inferred fracture energy depends on the initial traction level. Fracture energy is taken to be the excess of work over the frictional work, where the kinetic friction (heat level) is assumed to be the minimum value of traction reached during slip. While the traction versus slip curves might be significantly degraded by poor resolution, other studies have shown that the inferred fracture energy might be more reliable. Our calculations reveal that the spatial distribution of $G$ is correlated with the total slip, the peak slip velocity and the rupture velocity $V_{r}$. For each heterogeneous slip model we compute the average of fracture energy density on the whole fault plane as well as for fault patches having slip exceeding various fractions of the maximum slip. Our estimates of average fracture energy density range between 1.4e6 and 2.e7 $J/m^2$ for earthquakes having moment magnitudes between $6.0$ and $7.3$, and are in agreement with the values proposed in the literature. We find that the total fracture energy $E_{g}(J)$ scales with seismic moment $Mo$ and, as a consequence, a similar scaling exists between average $G(J/m^2)$ and the average slip. The observed dependence of $G$ on $V_{r}$ is more complex than that expected from ruptures in 2D, and the dependence might be biased by slip heterogeneity.
DE: 7260 Theory and modeling
DE: 7209 Earthquake dynamics and mechanics
DE: 7215 Earthquake parameters
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting