Crossroads Lecture: Ready for a “Megathrust” Earthquake?

The San Juan Islands with suspected faults criss-crossing the islands. From Dave Halloran at SJ County Emergency Mgmt.

Sunday, April 7 at 2 p.m. at Orcas Center

From Crossroads Lecture Series

Tim Walsh, Chief Hazard Geologist of the Washington Department of Natural Resources, will discuss the risks and potential impacts of such a major earthquake, and the resulting tsunami, in the San Juan Islands at the next Crossroads Lecture.

Every 300 to 800 years, the Pacific Northwest experiences a powerful magnitude 9 Cascadia Earthquake. Based on physical evidence and Japanese tsunami records, the last one occurred in January 1700, which suggests that another such “megathrust” earthquake could occur soon, with devastating effects throughout the Pacific Northwest. In fact, recent studies by Oregon State University geologists put the odds of such an event occurring during the next 50 years at more than 10 percent.

Although we lie over a hundred miles from the offshore Cascadia fault, such a tremendous quake could still cause severe shaking in the islands, particularly in areas with loosely compacted soils. Our fair islands would also be vulnerable to the subsequent tsunami, which would probably arrive here about an hour afterwards and have major impacts in low-lying areas, especially at the ends of long bays.

“Are we ready for the next big one?” asks Walsh. “To paraphrase George Bernard Shaw, we learn from experience that we don’t learn from experience.” But he hopes that by publicizing the risks and effects of a megathrust earthquake, he can get people to heed warnings.

Walsh has performed extensive geologic mapping in all parts of the state, as well as, tsunami hazard mapping, active fault characterization, and landslide assessments. He has recently been heavily involved in the development of an updated tsunami simulation for Washington, the results of which he will present in his lecture.