NEHRP Clearinghouse
- Title
- Local Tsunami Hazards in the Pacific Northwest from Cascadia Subduction Zone Earthquakes. (Earthquake Hazards of the Pacific Northwest Coastal and Marine Regions).
- File
- PB2006100047.pdf
- Author(s)
- Geist, E. L.
- Source
- January 2005, 26 p.
- Identifying Number(s)
- PP-1661-B
- Abstract
- Since the mid-1980s, there has been accumulating geologic evidence of large local tsunamis generated by earthquakes along the Cascadia subduction zone off the Pacific Northwest. Information from recent geophysical and geological investigations constrains the potential rupture-zone geometry and average repeat time of interplate thrust earthquakes. Based on this information, tsunami hazard maps have been prepared for coastal communities in the Pacific Northwest using sophisticated numerical models to simulate tsunami propagation and inundation. In this study, sources of uncertainty in tsunami hazard calculations are described and a probabilistic hazard analysis for tsunamis, similar to probabilistic seismic hazard analysis (PSHA), is outlined. Though probabilistic tsunami hazard analysis (PTHA) shares many similarities with PSHA, there are specific issues unique to tsunami hazards that need to be accounted for in the probability calculations. For example, the possibility of rupture along splay faults from the Cascadia interplate thrust have a large effect on tsunami generation, but a relatively small impact on peak ground accelerations onshore. The largest sources of uncertainty include the average slip and downdip extent of rupture. Also, it is demonstrated that significant variations in nearshore tsunami amplitude are caused by uncertainty in slip distribution patterns. Correct identification of uncertainties related to tsunami generation and propagation is critical in performing the probability calculations. PTHA has the potential to provide an improved technique for evaluating local tsunami hazards in the Pacific Northwest and elsewhere.
- Keywords
- Pacific northwest; Cascadia subduction zone; Probability; Hazard analysis; Seismology; Tsunamis; Calculations; Earthquakes