Submarine Paleoseismology in Lake Tahoe, CA/NV and Puget Sound, WA

Submarine deposits record the tectonic, climatic, and volcanic history of the region. Through careful consideration of multiple lines of evidence, we should be able to distinguish between different signals and whether a system records past earthquake activity. Sediment coring and analyses in Lake Tahoe, CA/NV and Puget Sound, WA supplemented by seismic reflection profiling, sidescan swath imagery, and bathymetric data allow for a determination of causality. Five primary commonalities were identified between the two different tectonic regimes: 1. The body of water must be in close proximity to or underlain by active faults, 2. Slopes must be conducive to landslide activity, 3. Sedimentation in the body of water must be sufficient to allow the distinction between event deposits, 4. Multiple source areas and confluence of events is vital, and 5. Where possible, comparison to the existing paleoseismic record should be used as confirmation. Submarine landslides and associated debris flows and turbidites may be effective paleoseismic indicators, however, different trigger mechanisms may give rise to similar types of deposits. Thus, multiple lines of evidence must be used to determine causality. Also, every site may have unique characteristics that must be taken into account. In Lake Tahoe, event deposits are likely the result of strong shaking on faults within and in close proximity to the basin. Large and very large submarine landslides in Puget Sound are controlled by the crustal faults and local geology. The methods developed here may be used around the world to determine paleoseismicity and in many cases, extend the paleoseismic record beyond that of traditional methods.