HR: 0800h
AN: G21B-1283    [Abstracts]
TI: Poroelastic Deformation Due To the 2002 Mw 7.9 Denali Earthquake
AU: * Sil, S
EM: ftss@uaf.edu
AF: University Of Alaska Fairbanks, Geophysical Institute, UAF, 903 Koyukuk Drive, P.O. Box 757320, Fairbanks, AK 99775 United States
AU: Freymueller, J T
EM: jeff@giseis.alaska.edu
AF: University Of Alaska Fairbanks, Geophysical Institute, UAF, 903 Koyukuk Drive, P.O. Box 757320, Fairbanks, AK 99775 United States
AB: Coseismic water level changes due to the 2002 Mw 7.9 Denali earthquake were observed in Alaska. These water level changes show a linear relationship either with seismically induced volumetric strain or with a combined effect of volumetric strain and ground shaking. Water level recovery after the earthquake has been modeled by least squares technique, using an error function and a maximum decay time of one week. GPS observations also show very rapid deformation in the vicinity of the rupture zone during the first week following the earthquake. These two observations lead us to evaluate the importance of poroelastic deformation immediately after the earthquake. To determine the magnitude of poroelastic deformation we use the existing GPS derived slip model (Hreinsdottir et al, 2005) of the Denali earthquake. With the help of a dislocation model (Okada, 1985), undrained and drained deformation patterns are calculated using the Poisson's ratio values of 0.25 and 0.22 respectively. A poroelastic deformation model is derived from the difference between these two deformation patterns. The model suggests very small magnitude (less than 10 mm) horizontal deformation for all the far field continuous GPS sites. Only few sites near the junction of the Toutschunda and Denali fault show considerable horizontal deformation. The vertical poroelastic deformation predicted by the model is larger than the horizontal deformation for maximum sites. We modeled the three components of GPS time series from continuous GPS stations using the combination of an error function with a decay time of one week (for poroelastic deformation), a log function with a decay time of less than one month (for afterslip deformation) and an exponential function with a decay time of few years (for viscoelastic deformation) by the least squares technique. The magnitude of the error function is taken from the model of poroelastic deformation. The 2.5 years time series cannot distinguish between exponential relaxation time longer than 2 years; any model with a longer relaxation time can fit the time series about equally well. From this study we can conclude 1) postseismic deformation of Alaska after the November 2002 Denali earthquake cannot be modeled using a single deformation mechanism. 2) Poroelastic deformation played an important role only during the first week after the earthquake. 3) The magnitude of poroelastic deformation is considerably smaller for the Denali earthquake compared to recent earthquakes. 4) The time series is not sufficiently long to constrain the viscoelastic decay uniquely.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1209 Tectonic deformation (6924)
DE: 6924 Interferometry (1207, 1209, 1242)
DE: 6929 Ionospheric physics (1240, 2400)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Geodesy [G]
MN: Fall Meeting 2005