HR: 0830h
AN: G31B-0709    [PDF]
TI: Transient rheology of the uppermost mantle in the epicentral region of the 1999 M7.1 Hector Mine earthquake, California
AU: * Pollitz, F F
EM: fpollitz@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., MS 977, Menlo Park, CA 94025 United States
AB: Elevated strain rates are often observed after large strike-slip earthquakes. A current challenge is to discriminate among models capable of explaining rapid postseismic deformation at various spatial scales: poroelastic rebound (e.g., Peltzer et al., 1998), afterslip (e.g., Hearn et al., 2002), and postseismic relaxation governed by a Maxwell rheology, nonlinear rheology or transient rheology (Ivins, 1996). At the small strains and timescales involved in postseismic relaxation, a transient response is expected (Minster and Anderson, 1981) . Observations of postseismic deformation following major earthquakes have high potential to constrain the properties of transient rheology because of the good time coverage and spatial sampling of geodetic measurements. Continuous GPS data from the Southern California Integrated GPS Network and campaign GPS data from the U.S. Geological Survey define the postseismic surface deformation field for the first 2.5 years following the 1999 M7.1 Hector Mine earthquake. We consider four classes of postseismic deformation models, including two transient rheology models represented by a Burgers body (a combination of Maxwell and Kelvin elements with viscosities ${\eta}_1$ and ${\eta}_2$, respectively) and conclude that the data are best explained with dominantly postseismic flow of the upper mantle governed by a a transient rheology. The upper mantle is characterized by two material relaxation times ~0.07 years and 2 years with associated viscosities ${\eta}_2 =1.7 \times 10^{17}$ Pa s and ${\eta}_1 = 4.6 \times 10^{18}$ Pa s. The Kelvin element is presumably one of several relaxation elements that compose an absorption band model of seismic wave attenuation. These results carry implications for the transition from anelastic to viscous behavior in Earth's upper mantle.
DE: 1208 Crustal movements--intraplate (8110)
DE: 1243 Space geodetic surveys
DE: 8162 Rheology--mantle
SC: Geodesy [G]
MN: 2003 Fall Meeting