Climate-Driven Sea Level Rise Exacerbates Alaskan and Cascadian Tsunami Hazards in Southern California: Implications to Design Parameters

Tsunami hazards in Southern California are expected to be exacerbated by the climate change driven sea level rise (SLR). Two key questions are how relevant is this exacerbation and whether tsunami design parameters are significantly affected. We perform a non-stationary probabilistic tsunami hazard assessment (nPTHA) in the Southern California bays of San Pedro and San Diego, with consideration of tsunamis generated by earthquakes in the Alaska-Aleutians (ASZ) and Cascadia subduction zones (CSZ). We evaluate the changes of the maximum considered tsunami (MCT) design parameter, defined as a tsunami intensity that is exceeded with a 2% probability in 50 years. MCT elevation maps in the bays are calculated incorporating tides and SLR by means of a surrogate model. MCT elevations at assessed sites in San Pedro Bay and San Diego yield 2 m. The nPTHA shows that tsunamis generated in the ASZ zone are more hazardous in Southern California than those from the CSZ when evaluating MCT intensities. A comparison of scenarios with and without SLR also shows an increase of the MCT elevations of more than a foot in San Pedro Bay and San Diego, demonstrating that SLR causes a relevant impact, comparable to the influence of tides. The effect of SLR increasing MCT values is also comparable to the sensitivity of nPTHA results to some common earthquake epistemic uncertainties, such as the slip marginal distribution. Future tsunami hazard maps shall incorporate SLR when exposure times are long, as well as the uncertainty of tsunamigenic earthquake properties.