Abstract
This paper presents a framework for a probabilistic hazard assessment for the multi-hazard seismic and tsunami phenomena (PSTHA). For this work, we consider a full-rupture event along the Cascadia Subduction Zone and apply the methodology to the study area of Seaside, Oregon, along the US Pacific Northwest coast. In this work, we show that the annual exceedance probabilities (AEP) of the tsunami intensity measures (IM) are qualitatively dissimilar to the IMs of the seismic ground motion in the study area. Specifically, the spatial gradients for the tsunami IM are much stronger across the length scale of the city owing to the physical differences of energy dissipation of the two mechanisms. Example results of probabilistic seismic hazard analysis (PSHA) and probabilistic tsunami hazard analysis (PTHA) are shown for three observation points in the study area of Seaside. For the seismic hazard, the joint mean annual rate of exceedance shows similar trends for the three observation points, even though there is a large scatter between and . For the tsunami hazard, the joint AEP of hmax and (MF)max shows a high correlation between the two IMs in the study area. The joint AEP at each of the three observation points follows a particular Froude number (Fr) due to the local site-specific conditions locally rather than the distributions of fault slips. The joint probability distribution of hmax and (MF)max throughout the study region falls between 0.1 ≤ Fr < 1.0 (i.e., the flow is subcritical) regardless of return interval (500-, 1,000-, and 2,500-yr). However, the peak of the joint probability distribution with respect to hmax and (MF)max varies with the return interval, and the largest values of hmax and (MF)max were observed with the highest return intervals (2,500 yr) as would be expected. The results of the PSTHA can be the basis for a probabilistic multi-hazard damage assessment and help to understand the uncertainties of the multi-hazard assessments.
Highlights
Over the past decade and a half, megathrust earthquakes accompanied by near-field tsunamis have devastated coastal regions throughout the world, including the 2004 Indian Ocean tsunami (e.g., Jaffe et al, 2006; Rossetto et al, 2007), events in Chile in 2010 (e.g., Mas et al, 2012), and the 2011 Tohoku tsunami (e.g., Mori et al, 2013)
This paper presents a methodology for probabilistic hazard assessment for the multihazard seismic and tsunami phenomena [probabilistic seismic and tsunami hazard analysis (PSTHA)]
This paper marks one of the first attempts to provide a methodology for conducting a joint hazard analysis, which is termed as probabilistic seismic and tsunami hazard analysis (PSTHA), by combining probabilistic seismic hazard analysis (PSHA) with probabilistic tsunami hazard analysis (PTHA) based on a consistent process for concurrent earthquake occurrence and tsunami generation
Summary
Over the past decade and a half, megathrust earthquakes accompanied by near-field tsunamis have devastated coastal regions throughout the world, including the 2004 Indian Ocean tsunami (e.g., Jaffe et al, 2006; Rossetto et al, 2007), events in Chile in 2010 (e.g., Mas et al, 2012), and the 2011 Tohoku tsunami (e.g., Mori et al, 2013). While GMPEs are most often used for PSHA, it is worth noting that other methods for generating the IMs that involve the generation of synthetic ground motions have been recently proposed, all involving extremely computational intensive methods. These methods that could serve as alternatives to the GMPEs include kinematic earthquake models (e.g., Olsen et al, 2008; Frankel et al, 2014; Pulido et al, 2015; Iwaki et al, 2016), stochastic finite-fault ground-motion methods (e.g., Atkinson et al, 2009), or hybrid broadband ground-motion methods (e.g., Atkinson et al, 2011; Skarlatoudis et al, 2015)
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