HR: 15:25h
AN: S42G-08    [PDF]
TI: Rupture process and near-source shaking from the 1965 Seattle-Tacoma and 2001 Nisqually intraslab earthquakes
AU: * Ichinose, G A
EM: gene_ichinose@urscorp.com
AF: URS Corporation, 566 El Dorado St. 2nd Floor, Pasadena, CA 91101-2560 United States
AU: Somerville, P G
EM: paul_somerville@urscorp.com
AF: URS Corporation, 566 El Dorado St. 2nd Floor, Pasadena, CA 91101-2560 United States
AU: Thio, H
EM: hong_kie_thio@urscorp.com
AF: URS Corporation, 566 El Dorado St. 2nd Floor, Pasadena, CA 91101-2560 United States
AB: The 2001 Nisqually intraslab earthquake produced moderate levels of ground motions below 30% g within the Puget Sound yet caused widespread damage and temporary disruption to buildings and transportation lifelines. The frequency of intraslab earthquakes (1949 M 7.1, 1965 $M_{w} 6.7$, and 2001 $M_{w} 6.8$) makes it important in understanding as much as possible about the source characteristics so that the hazards can be more reliably quantified. We inverted 0.05 to 0.5 $Hz$ strong ground motion, teleseismic, and geodetic data for the 2001 Nisqually earthquake to obtain a variable slip and rake model using the multiple time window method and Green's functions calculated from a regionally calibrated 1-D velocity model. The earthquake has a 12 $km^{2}$ sized asperity between 59 and 62 km depth with an average slip of 1.5 m ($M_{o}=1.59 \times 10^{26} dyne \times cm$; $M_{w}$ 6.74). We also inverted teleseismic P- and SH-waves digitized from WWSSN film records for the 1965 Seattle Tacoma earthquake slip and rake model. There are two asperities with areas of 4 and 8 $km^{2}$ near the hypocenter. Average slip for these asperities were 2 and 2.8 m ($M_{o}=9.43 \times 10^{25} dyne \times cm$; $M_{w}$ 6.63). Simulating near-source strong ground motions from historical and modern earthquake slip models adds more realism not possible with random or stochastic scenarios. We used a time domain approach to generate PGA and $S_{a}$ shake-maps for the 1965 and 2001 earthquakes. These shake-maps included the spatial and temporal evolution of slip estimated from the multiple time window inversion of seismic and geodetic data. We added a Kostrov source time function to improve the ground motion spectra at higher frequencies. The shake maps also included site and basin depth corrections based on California geology. The corrections helped reduce the bias in residuals between observed and simulated PGA and Sa but corrections that are more specific to the Puget Sound are needed to reduce the scatter. The patterns of strong ground shaking from the 1965 Seattle-Tacoma earthquake were very different from the 2001 Nisqually earthquake. Strong shaking in urban Seattle by the 1965 earthquake was twice as high (60% g) than by the 2001 earthquake. While retrofitting efforts help limit damages by the 2001 Nisqually earthquake, a future earthquake closer to urban Seattle or larger in magnitude may cause more widespread damage and disruption.
DE: 7209 Earthquake dynamics and mechanics
DE: 7212 Earthquake ground motions and engineering
DE: 7215 Earthquake parameters
DE: 7223 Seismic hazard assessment and prediction
SC: Seismology [S]
MN: 2003 Fall Meeting