Hyoungsu Park

Probabilistic Seismic and Tsunami Hazard Analysis Conditioned on a Megathrust Rupture of the Cascadia Subduction Zone

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.

Three-Dimensional Laboratory Experiments for Tsunami Inundation in a Coastal City

Laboratory experiments were conducted for tsunami inundation to an urban area with large building roughness. The waterfront portion of the city of Seaside which is located on the US Pacific Northwest coast, was replicated in 1/50 scale in the wave basin. Tsunami heights and velocities on the inundated land were measured at approximately 31 locations for one incident tsunami heights with an inundation height of approximately 10 m (prototype) near the shoreline. The inundation pattern and speed were more severe and faster in some areas due to the arrangement of the large buildings. Momentum fluxes along the roads were estimated using measure tsunami inundation heights and horizontal fluid velocities. As expected, the maximum momentum flux was near the shoreline and decreased landward. Inundation heights and momentum flux were slowly decreased through the road with buildings on each side. The results from this study showed that the horizontal inundation velocity is an important factor for the external force of coastal structures.