Rupture process of the 1964 Prince William Sound, Alaska, earthquake from the combined inversion of seismic, tsunami, and geodetic data

Abstract

[1] Four great earthquakes (1952, 1960, 1964, and 2004) have occurred since seismic monitoring began and only two since the installation of a global seismic network. A reexamination of the 1964 (M 9.2) Prince William Sound (PWS), Alaska, earthquake is timely due to the 2004 Sumatra earthquake because it adds constraints to the potential range of source parameters for these types of infrequent events and aids in the ability to predict the ground motions for other subduction zone including Cascadia. We first measured the durations of high-frequency energy radiation from teleseismic P wave codas recorded by short-period World Wide Standardized Seismographic Network (WWSSN SP) instruments to put constraints on the earthquake rupture length. The durations ranged between 250 and 600 s and are shorter in time between azimuths of 190°and 260°. The fault length is estimated to range from 540 to 740 km, rupturing at average speeds of 1.4-2 km/s in a 220°-238°direction. We developed a multiple time window kinematic rupture model for the PWS earthquake from the least squares inversion of teleseismic P waves, tsunami tide gauge records, and geodetic leveling survey observations based on the Green's function technique. We assume three major fault segments for the subduction zone dipping 6-12°based on geologic data. The subfault size on the megathrust was set to 50 Â 50 km. The Patton Bay fault (PBF) imbricate thrust was assigned a 60 dip with a subfault size of 20 Â 20 km. We estimated a seismic moment of 5.52 Â 10 22 N m (M w 9.12). We identified three areas of major moment release, on the PWS segment near Montague and Middleton Islands extending out to the trench, beneath the Portlock anticline on the Cook segment between 58°N fracture zone and the Kodiak-Bowie seamount chain and finally on the Katmai segment off the coast of Kodiak Island extending to the trench. Our preferred rupture model has a peak slip of 14.9 m along the megathrust and 17.4 m along the PBF. The addition of the PBF resulted in an 8% improvement in residuals and also had a significant effect on the overall slip distribution. Moment release occurred as deep as 50 km depth slab contour near the 350°C isotherm and mantle fore-arc wedge, which is about 10-20 km deeper than previous coupling depths.

Tsunami hazard assessment in El Salvador, Central America, from seismic sources through flooding numerical models.

“…The source ruptures were characterized from inversions of geophysical and/or geodetical data (Barrientos and Ward, 1990;Hayes, 2009Hayes, , 2011, from observations of tsunami waves (Johnson and Satake, 1999) or from both (Ichinose et al, 2007). There are two particular sources that could be considered intermediate because of their proximity to El Salvador but whose features have been defined based on Álvarez-Gómez et al (2012), and the Nicaragua 1992 rupture area is taken from Piatanesi et al (1996); see text for further details on the rest of subduction interface ruptures.…”

Megathrust splay faults at the focus of the Prince William Sound asperity, Alaska

“…The Yakutat microplate is relatively buoyant, which results in a subduction angle of approximately 3°beneath PWS compared to the steeper 8°dip along the Kodiak segment [e.g., Brocher et al, 1994;Eberhart-Phillips et al, 2006;Doser and Veilleux, 2009]. The maximum slip from the 1964 earthquake was largely coincident with the southwestern edge of the subducted Yakutat terrane, which appears to be largely coupled to the underlying Pacific plate [Zweck et al, 2002;Doser et al, 2004;Eberhart-Phillips et al, 2006;Ichinose et al, 2007]. Geodetic measurements in the PWS area show movement at the Pacific-North America plate rate, which indicates a completely locked asperity [Zweck et al, 2002] with repeat times for large megathrust earthquakes of 330-900 years (summary in Carver and Plafker [2008]).…”

Extreme tsunami inundation in Hawai‘i from Aleutian–Alaska subduction zone earthquakes

“…Figure 9 also compares the inundation maps for Honolulu for two cases, confirming the effect. This result indicates that for the giant Aleutian earthquakes being considered, substantial variations of slip along the length of the fault (as observed in the 1964 Alaska earthquake source, e.g., Johnson et al 1996;Ichinose et al 2007) do not significantly influence the inundation pattern relative to the uniform-slip models at these tele-tsunami distances. Close to the source, such lateral variation will be magnified in proximity, but with Hawai'i at about 3500 km from the earthquake, the tsunami wave variations generated merge together and approximate the averaged case.…”

“…The 2011 Tohoku earthquake (Mw 9.1) was characterized by relatively short overall rupture and large 50-m shallow displacement near the trench (e.g., Lay et al 2011;Yamazaki et al 2011b, c). The 1964 Alaska earthquake (Mw 9.2) was notable in laterally varying slip characterized by alternating large and small displacement patches on the fault (e.g., Ichinose et al 2007), whereas the 1952 Kamchatka earthquake was characterized by small shallow displacement near the trench, increasing with depth (Johnson and Satake 1999). The large, deeper fault displacement characteristic of Kamchatka has smaller seafloor effects, and the resultant tsunami is smaller.…”