Last Friday the journal ScienceAdvances published the outcomes of recent research on the Cascadia Subduction Zone. Here is a summary paragraph from the report:
An important finding of our study is that a horizon interpreted as the plate interface transects the deep sediments of the inner wedge offshore of the Olympic peninsula… This décollement beneath the inner wedge extends downdip of the region of flattest TOC and has latitudinal extents that are aligned with the modeled high slip patch for the 1700 CE event… Incoming JdF plate basement relief is low and negligible faulting related to bending of the plate is detected seaward of the DF in this region… With the presence of the deeper slip surface in the sediment column, a smooth plate interface is inferred, which may also contribute to giant earthquake potential… The longer recurrence intervals estimated for this portion of the margin from offshore turbidite records… are also consistent with a larger amount of slip per event, related to larger rupture area. From these observations of plate interface geometry and properties, we infer that the south Vancouver Island through Washington region has greater potential than other sections of the margin for the largest earthquake ruptures. [Map below is from the report.]
Following is one translation of this careful scientific rhetoric:
[The study] has revealed that the fault splits into four segments instead of being one continuous strip like most fault lines. The discovery could prove more catastrophic because the tectonic plates can slide under each other, creating more pressure and more severe earthquakes The researchers concluded the Cascadia Subduction Zone has the potential to unleash a nine-plus magnitude quake… Cascadia’s four segments make it more dangerous than other major fault lines because they have different rock and sediment, with the most concerning section extending along northern Oregon, into Washington and southern British Columbia… This section of Cascadia is flatter and smoother than the other three sections, meaning it could cause the largest earthquakes, extending further into the US and impacting all of Washington’s coastal communities… Neither Oregon nor Washington state is sufficiently prepared for this type of disaster because of the limited information in the 1980s Cascadia model...
Here’s another translation from LiveScience. Here’s how the Seattle Times covered the report.
There is, of course, concern — considerable confidence — that a significant shift in this deep décollement (from the French décoller “to detach from”) will suddenly cause an extravagant range of surface-level detachments: bridges, dams, pipelines, water networks, piers from shores, bolts from welds, walls from foundations, roofs from walls, towers from anchors, rocks from mountainsides — undoing myriad intimacies on which we depend. The prospect of such detachment is so troubling that we often tend toward décollement of awareness from thinking, detachment of knowledge and action, desperately separating now from then.
