Combined Effects of Tectonic and Landslide-Generated Tsunami Runup at Seward, Alaska During the M W 9.2 1964 Earthquake

Abstract

We apply a recently developed and validated numerical model of tsunami propagation and runup to study the inundation of Resurrection Bay and the town of Seward by the 1964 Alaska tsunami. Seward was hit by both tectonic and landslide-generated tsunami waves during the M W 9.2 1964 megathrust earthquake. The earthquake triggered a series of submarine mass failures around the fjord, which resulted in landsliding of part of the coastline into the water, along with the loss of the port facilities. These submarine mass failures generated local waves in the bay within 5 min of the beginning of strong ground motion. Recent studies estimate the total volume of underwater slide material that moved in Resurrection Bay to be about 211 million m 3 (Haeussler et al. in Submarine mass movements and their consequences, pp [269][270][271][272][273][274][275][276][277][278] 2007). The first tectonic tsunami wave arrived in Resurrection Bay about 30 min after the main shock and was about the same height as the local landslide-generated waves. Our previous numerical study, which focused only on the local landslidegenerated waves in Resurrection Bay, demonstrated that they were produced by a number of different slope failures, and estimated relative contributions of different submarine slide complexes into tsunami amplitudes (Suleimani et al. in Pure Appl Geophys 166:131-152, 2009). This work extends the previous study by calculating tsunami inundation in Resurrection Bay caused by the combined impact of landslide-generated waves and the tectonic tsunami, and comparing the composite inundation area with observations. To simulate landslide tsunami runup in Seward, we use a viscous slide model of Jiang and LeBlond (J Phys Oceanogr 24(3):559-572, 1994) coupled with nonlinear shallow water equations. The input data set includes a high resolution multibeam bathymetry and LIDAR topography grid of Resurrection Bay, and an initial thickness of slide material based on pre-and post-earthquake bathymetry difference maps. For simulation of tectonic tsunami runup, we derive the 1964 coseismic deformations from detailed slip distribution in the rupture area, and use them as an initial condition for propagation of the tectonic tsunami. The numerical model employs nonlinear shallow water equations formulated for depth-averaged water fluxes, and calculates a temporal position of the shoreline using a free-surface moving boundary algorithm. We find that the calculated tsunami runup in Seward caused first by local submarine landslide-generated waves, and later by a tectonic tsunami, is in good agreement with observations of the inundation zone. The analysis of inundation caused by two different tsunami sources improves our understanding of their relative contributions, and supports tsunami risk mitigation in south-central Alaska. The record of the 1964 earthquake, tsunami, and submarine landslides, combined with the high-resolution topography and bathymetry of Resurrection Bay make it an ideal location for studying tectonic tsunamis in coastal region...

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

“…We interpret this growth fold to represent the along‐strike expression of the Bainbridge fault, a fault that parallels and is possibly related to the Contact fault system (Figure ) [ Helwig and Emmet , 1981; Dumoulin , ; Bol and Gibbons , ; Wilson and Hults , ]. Along the Junken Trough profile, this fold is likely rooted in a fault at depth, and a large seafloor scarp suggests this fault may pose a significant tsunami or ground‐shaking hazard to adjacent mainland communities and infrastructure, including Seward and other shallow waterways along the southern Kenai Peninsula [e.g., Plafker , 1969; Suleimani et al ., ].…”

“…Splay faults that extend across the western Gulf of Alaska shelf are consistent with the Plafker [] observations and the Suleimani et al . [] tsunami model, which showed that a source on the continental shelf is needed to produce the tsunami that arrived at Seward about 30 min after the earthquake. Plafker [] recognized that faults must have ruptured in the Gulf of Alaska during the 1964 earthquake to produce the footwall uplift along the south shore of Montague Island and to account for additional tsunami runups along the Kenai Peninsula; however, these hypothesized faults or fault extensions have not been identified.…”

Widespread deformation of basin-plain sediments in Aysén fjord (Chile) due to impact by earthquake-triggered, onshore-generated mass movements

“…They have been successfully correlated to historical earthquakes and were used to identify prehistorical events. Especially in fjords or bays, mass movements can be catastrophic (Syvitski and Schafer, 1996;Bøe et al, 2000;Urgeles et al, 2002) and potentially induce tsunamis (Tocher and Miller, 1959;Ward, 2001;L'Heureux et al, 2011;Suleimani et al, 2011). These, in turn, represent great hazards for coastal villages and harbors, which in many cases provide the best access to remote inland areas.…”

Source and progression of a submarine landslide and tsunami: The 1964 Great Alaska earthquake at Valdez

“…[] are able to reproduce observed runup at Valdez old town with a far‐traveled debris flow model. Here we investigate whether the simplest landslide scenarios can explain the observations; establishing the range of possible model fits is useful since quantitative landslide tsunami forecasts are becoming more prevalent [e.g., Masson et al ., ; ten Brink et al ., ; Suleimani et al ., ; Nicolsky et al ., ].…”