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Geologists are searching for evidence of past tsunamis on the US West Coast as part of scientists' coordinated efforts to manage the risk of a future disaster in the region.

"Despite the fact that we have learned a significant amount about the earthquake sources for tsunamis, there are gaps in our understanding of past tsunamis, especially prehistoric tsunamis," Rick Wilson of the California Geological Survey told the Seismological Society of America's Annual Meeting in Reno, Nevada.

"If we can demonstrate when and where tsunamis occurred in the past, that information will give us a better understanding of the return periods in these areas, and that can go into the probabilistic analyses that help us understand our hazard and risk better."

The authorities in California, Oregon, Washington and Alaska set about preparing the plan following the 2011 Tohoku earthquake and tsunami that devastated northeastern Japan.

Scientists told the Reno meeting that evolving risk management plans included the development of tsunami hazard maps that guide the development of personal and community evacuation routes to detailed "playbooks" to help guide harbour and port officials.
Robert Witter of the US Geological Survey's Alaska Science Center assessed the evidence for frequent and large earthquakes and tsunamis occurring within the past 2,000 years in parts of the Eastern Aleutian Islands.

He told the meeting that earthquakes in the area could cause significant tsunami effects across the Pacific, especially in Hawaii and California.

Wilson said the playbooks developed in California had been put into use following a tsunami advisory after the September 2015 magnitude 8.3 Illapel earthquake in Chile.

Before this "there was very little consistency between communities in what they did", he said.

"Some evacuated their entire zone, some just evacuated their beaches."

The society also heard how new technologies could be deployed to increase tsunami preparedness. These include camera-bearing drones that send video messages of incoming waves to convince coastal dwellers to evacuate.

Souheil Ezzedine meanwhile warned that there was the remote possibility that the trigger for a tsunami might not come from an earthquake, but from an asteroid strike.

The Lawrence Livermore National Laboratory researcher showed data from a study that models the effects of an asteroid-generated tsunami, including the potential wave heights, on several coastline cities in the US.

Bill Condie is news editor of Cosmos.
https://cosmosmagazine.com/earth-sciences/scientists-work-survival-plans-us-west-coast-tsunami