TSUNAMISCurrent Models Underestimate Tsunami Threats

The 2004 Sumatra earthquake generated one of the most destructive tsunamis ever recorded, with 100-foot waves that killed nearly 230,000 and resulted in an estimated $10 billion in damage. It also ushered in a new understanding that potent tsunamis are triggered by shallow earthquake ruptures of underwater fault lines. Future tsunamis are likely to be just as severe, if not worse, potentially killing even more people and wiping out whole communities. Although current research points to rupture depth as a key factor in predicting tsunami severity, those models fail to explain why large tsunamis still occur following relatively small earthquakes.

Now, USC researchers have found a correlation between tsunami severity and the width of the outer wedge — the area between the continental shelf and deep trenches where large tsunamis emerge — that helps explain how underwater seismic events generate large tsunamis. Drawing insights from a survey of previous tsunamis, the authors analyzed the geophysical, seismic and bathymetric data of global subduction zones to identify and discuss potential tsunami hazards.

Their latest study revealed that current predictive models underestimate tsunami severity by as much as 100%. The work appears in the journal Earth-Science Reviews.

“Close to half of the human population is coastal, leaving our population and infrastructure vulnerable to seismic and tsunami hazards,” said USC’s Sylvain Barbot, associate professor of Earth sciences at USC Dornsife College of Letters, Arts and Sciences and co-author of the study. “To maintain our livelihoods and our economy, we need to protect ourselves from these very violent hazards that are relatively infrequent but still happen. We cannot stop this hazard, so we need to mitigate its effects.

“That means having evacuation plans for tsunamis and developing an urban development plan to avoid having schools and hospitals in inundation regions. There are preemptive measures we can take to protect ourselves against tsunamis and flooding long-term, and our study provides a description of how to define the area affected by these hazards.”

Tsunami Threat: Excitation Zone Width Highly Correlated with Severity
To develop their new model, Barbot and co-author Qiang Qiu, now at the South China Sea Institute of Oceanology under the Chinese Academy of Sciences, analyzed the structural and tectonic settings of nearly a dozen global earthquake-generated tsunamis. Varying in location and intensity, the analysis found that particularly large tsunamis emerge after horizontal movement is transferred to uplift in the outer wedge of sediment located between the continental shelf and the