Understanding Extreme Geohazards: The Science of the Disaster Risk Management Cycle European Science Foundation Conference November 28 to December 1, 2011, Sant Feliu de Guixols, Spain

Offshore Geohazards and Risk Onshore- How Science can Contribute to Coastal Disaster Risk Reduction

Brian McAdoo
Vassar College, Earth Sciences and Geography, Poughkeepsie, United States, brmcadoo@vassar.edu

Offshore geophysical hazards can pose significant risks to coastal communities and beyond. Tropical cyclones and major subduction zone earthquakes kill tens of thousands of people on average every year, and cause billions of dollars in economic losses that ripple across nations and can even spread globally. Submarine landslides, while not as deadly nor costly, remain an often overlooked hazard. Seafloor mapping technologies that emerged 20 years ago have resulted in an ever-growing catalog of seafloor maps, showing dramatic landslides that dwarf anything we see on land. Yet despite this influx of data, there is still many fundamental questions we have about these features- questions that lie at the core of understanding the risk offshore geohazards pose to onshore communities. One of the core contributions earth scientists can offer to disaster risk reduction efforts is the frequency and magnitude of hazards. Determining the magnitude of submarine landslides is easy when multibeam and side-scan sonar and seismic reflection data are available. The most critical challenge facing those interested in the risks posed by offshore landslides is their frequency of occurrence. Because diffusion rates underwater are orders of magnitude less than on land, very old (>10,000 years) landslides may look fresh, leading researchers to overestimate the risk they pose. Without efficient and cost-effective methods of dating offshore landslides to determine a the frequency and magnitude of occurrence, uninformed risk mitigation efforts can waste resources. Future research concerning the risk posed by offshore landslide must seek underutilized sources of frequency and magnitude data, primarily the offshore oil and submarine cable industries. These industries are impacted by these hazards, and must have these data to mitigate their risks. Coastal communities are also at risk from these hazards, not only because of potential disruption of services, but also from tsunami. Tsunamigenic landslides are rare, however they pose a set of unique challenges that makes mitigation difficult. Without the frequency-magnitude data, however, mitigation efforts can waste precious resources and possibly leave the system more vulnerable.