Cascadia Fault Chatters and Pops with Little Quakes

Health & Safety - Mining, Environmental, & Cybersecurity

Date posted: 09/01/15

Sandi Doughton reports from Seattle that the initial results from a program to monitor the Cascadia Subduction Zone in unprecedented detail show that the fault off the Northwest coast is not as seismically quiet as it has long appeared. Seafloor seismometers deployed as part of the NSF Cascadia Initiative detected nearly 600 small earthquakes off central Oregon during their first year of operation, quakes that did not register on any land-based instruments. Though the subduction zone can unleash magnitude-9 megaquakes and tsunamis, there is no reason to think the small tremors are unusual or precursors to something bigger, seismologists say. There is still no way to predict when the fault will rupture, Schwartz said. Estimates of the average recurrence rate range between 250 and 500 years, but past quakes have struck at widely irregular intervals. Some data from the Japan 2011 megaquake hint that subduction zones may begin slipping in the weeks and days before a major quake, but it will take more intensive seafloor monitoring to find out if that is true. John Vidale, Director of the Pacific Northwest Seismic Network, explains how an early warning system could alert people before an earthquake hits. Both the U.S. and Canada have installed cabled networks of underwater instruments, including seismometers and pressure gauges, to continuously monitor small sections of the subduction zone. But scientists hope to greatly expand the networks in the future. Interest and panic around the coming Northwest megaquake spiked last month with the publication in The New Yorker of a dramatic account of the expected damage and death toll. There is a real hazard and people should understand that fear but turn it into positive action, making sure that they as prepared as they can be.