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Landslide Risk Assessment in California's Continental Borderland

Investigating the potential for large underwater landslides in the California Continental Borderland region, considering factors such as seismic activity and subsea terrain to determine the risk of generating tsunamis.

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Landslide Risk Assessment in California's Continental Borderland

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  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.

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