Tsunamis in California

1. Large-scale Basement-involved Landslides, California Continental Borderland Article by Kammerling, M. J., M. R. Legg. 2003. Pure and Applied Geophysics. 160 (10-11): 2033-2051 Presented by Samuel W. Franklin, Geography major, GEOG 370, February 24, 2008 Tsunamis in California

2. Determining Possibility of a Landslide • Problem: Large seafloor relief, shallow metamorphic basement, and seismic activity in the California Continental Borderland combine to produce major submarine slides capable of generating local tsunamis. • Hypothesis: Measurements and analysis of slopes will determine the likelihood of a large-scale underwater slide.

3. Methods & Data Collection Slope Stability • Site: Off shore of Southern California and Baja California, Mexico • Used seafloor mapping by USGS to find possible problematic areas. • Used submersibles to get actual slopes, overhangs and rock type. • Quantified slope stability using Newmark’s dynamic slope stability analysis technique. • Then compared areas with large slopes to areas affected by seismic activity. • Used area of possible slide size vs. speed to determine the varying intensity of tsunami.

4. Results • In the Borderland Area researched there is an average relative seismic slope stability of moderate to unstable (scale used: Very Stable, High, Moderate, Low, Unstable). • Because major active faults lie along these large escarpments the potential for large scale, submarine landslides exists. • There are two specific areas found to be in danger and have been the cause of tsunami damage in the past.

5. Conclusion • Low stability slopes could be prone to catastrophic failure (large landslides) and tsunami generation. • Seismic activity greater than 6.5 on the Mercalli scale will result in a tsunami • Criticisms: Focused highly on probability. And there has not been a definitively destructive tsunami in seventy years.