Changing impacts of Alaska-Aleutian subduction zone tsunamis in California under future sea-level rise

Tina Dura,Alan R Nelson,Andra J Garner,Charles S Mueller,Robert Weiss,Robert C Witter,Richard W Briggs,Benjamin P Horton,Simon E Engelhart,Robert E Kopp

doi:10.1038/s41467-021-27445-8

Abstract

The amplification of coastal hazards such as distant-source tsunamis under future relative sea-level rise (RSLR) is poorly constrained. In southern California, the Alaska-Aleutian subduction zone has been identified as an earthquake source region of particular concern for a worst-case scenario distant-source tsunami. Here, we explore how RSLR over the next century will influence future maximum nearshore tsunami heights (MNTH) at the Ports of Los Angeles and Long Beach. Earthquake and tsunami modeling combined with local probabilistic RSLR projections show the increased potential for more frequent, relatively low magnitude earthquakes to produce distant-source tsunamis that exceed historically observed MNTH. By 2100, under RSLR projections for a high-emissions representative concentration pathway (RCP8.5), the earthquake magnitude required to produce >1 m MNTH falls from ~Mw9.1 (required today) to Mw8.0, a magnitude that is ~6.7 times more frequent along the Alaska-Aleutian subduction zone.

Highlights

The amplification of coastal hazards such as distant-source tsunamis under future relative sea-level rise (RSLR) is poorly constrained
We report the resultant distribution of maximum nearshore tsunami heights (MNTH) at the Ports of Los Angeles and Long Beach from our tsunami simulations as the maximum tsunami amplitude at our synthetic tide gauge 2 (TG2; located in the outer harbor at 17 m water depth) relative to mean sea level (MSL) (Fig. 1c, d)[20]
The U.S Geological Survey (USGS) Science Application for Risk Reduction (SAFRR) project modeled a Mw9.1 earthquake and its tsunami sourced along the Semidi section of the Alaska-Aleutian subdiction zone (Fig. 1b)

Summary

Introduction

The amplification of coastal hazards such as distant-source tsunamis under future relative sea-level rise (RSLR) is poorly constrained. To the more than one billion people worldwide living in the coastal zone below 10 m of elevation[1], the compound effects of relative sea-level rise (RSLR), tidal flooding[2], and storm surges[3–6] are of increasing concern. Other research shows increased extreme sea levels during coastal storms due to RSLR along coasts in California[6] as well as the contiguous United States[11]. Along coastlines affected by distant-source tsunamis, where potential tsunami amplitudes are generally on the order of or lower than projected twenty-first-century RSLR, rising baseline sea levels can significantly increase tsunami impacts[16,17]. At the low-lying, densely populated, and economically important Ports of Los Angeles and Long Beach, recent maximum tsunami amplitudes (defined as the absolute value of the difference between a particular peak or trough of the tsunami and the undisturbed sea level at the time) recorded at tide gauge 120

Methods

Results

Conclusion