Assessment of the high-resolution paleoseismicity record from sediment gravity flows in Prince William Sound, Alaska

Abstract

Located along the Aleutian Megathrust Boundary, South-Central Alaska is one of the most seismically active areas in the world. Central to this region, Prince William Sound is a glacially carved basin that receives abundant sediment from multiple sources. Primary inputs include the Columbia Glacier and the Copper River, which have diagnostic signatures of Sr/Pb, Cu/Pb, K/Ca, Rb/Sr, and Rb/Ca. As a result, earthquake induced sediment gravity flows originating from different locations deposit event layers that have distinct provenance signatures. A previous study (Kuehl et al., 2017) identified five such event layers preserved in two cores from the southern part of the deep central channel of Prince William Sound that were attributed to large historical earthquakes. To better understand the spatial continuity of these event layers along the entire length of the central channel, seven new gravity cores were collected in a north-south transect. Sedimentation rates were determined by 210Pb, 137Cs, and 239,240Pu geochronology, and cores were assessed for variations in elemental content, grain size patterns, bulk organic and stable isotopic signatures (C/N, δ13C, δ15N). Based on a spatial analysis of these cores, local earthquakes of Mw < 7.0 deposit event layers in the central channel with signatures reflecting the epicenter location, and those of Mw > 7.0 (including an event layer from the 1964 great Alaskan earthquake) have mixed signatures resulting from the widespread generation of numerous flows throughout Prince William Sound. Complete gravity flow records are captured within deep ponded sediment basins and the area spanning the southern end of the central channel. Considering the thick (>100 m) late-Holocene sequence, the approach utilized in this study has the potential to provide a rich record of earthquake recurrence intervals to 4 ka.