Probabilistic tsunami hazard assessment at Seaside, Oregon, for near‐ and far‐field seismic sources

TLDR

Probabilistic tsunami hazard assessment (PTHA) integrates tsunami inundation modeling with probabilistic seismic hazard assessment to quantify the likelihood and severity of tsunami events, enabling risk estimates when combined with vulnerability and exposure. The authors applied PTHA to Seaside, Oregon, producing spatial maps of 100‑year (1 % annual probability) and 500‑year (0.2 % annual probability) maximum tsunami amplitudes. The resulting maps show that 100‑year tsunamis are mainly from far‑field Alaska‑Aleutian sources with amplitudes below 4 m and limited inland reach, whereas 500‑year tsunamis are dominated by local Cascadia sources with amplitudes over 10 m and inland reach beyond 1 km, with key uncertainties arising from interevent times, sea‑level modeling, and bathymetric/topographic changes.

Abstract

The first probabilistic tsunami flooding maps have been developed. The methodology, called probabilistic tsunami hazard assessment (PTHA), integrates tsunami inundation modeling with methods of probabilistic seismic hazard assessment (PSHA). Application of the methodology to Seaside, Oregon, has yielded estimates of the spatial distribution of 100‐ and 500‐year maximum tsunami amplitudes, i.e., amplitudes with 1% and 0.2% annual probability of exceedance. The 100‐year tsunami is generated most frequently by far‐field sources in the Alaska‐Aleutian Subduction Zone and is characterized by maximum amplitudes that do not exceed 4 m, with an inland extent of less than 500 m. In contrast, the 500‐year tsunami is dominated by local sources in the Cascadia Subduction Zone and is characterized by maximum amplitudes in excess of 10 m and an inland extent of more than 1 km. The primary sources of uncertainty in these results include those associated with interevent time estimates, modeling of background sea level, and accounting for temporal changes in bathymetry and topography. Nonetheless, PTHA represents an important contribution to tsunami hazard assessment techniques; viewed in the broader context of risk analysis, PTHA provides a method for quantifying estimates of the likelihood and severity of the tsunami hazard, which can then be combined with vulnerability and exposure to yield estimates of tsunami risk.