Oregon’s Newly Discovered Fault Lines Stretch for 34 Miles Along Two Flanks of Mount Hood

While most of the West Coast has been focusing on the prospect of a Cascadia subduction zone earthquake known as the Big One, geologists at Portland State University have been studying a completely different network of fault lines.

The four researchers—Ian Madin, William Burns, Lina Ma and Ashley Streig—recently published data on a network of fault lines on Mount Hood that could cause a 7.2 magnitude earthquake in the Portland area if triggered. They announced their findings Oct. 22.

In short: If the Big One doesn't decimate the city, the cracks on Mount Hood might.

"These faults are still poorly mapped, and we know little about their slip rates, earthquake history and recurrence levels," the researchers write.

Streig, one of the paper's co-authors and a PSU assistant professor of geology, acknowledges this is "back-of-the-envelope work," but "the possibility of one of these faults rupturing is very real."

So where exactly are the Mount Hood faults? Data provided to WW by Streig show the Mount Hood fault zone consists of four distinct fault segments that span 34 miles from Clear Lake north to the Columbia River. The longest of the four fault segments is the Blue Ridge Fault, which extends directly north of Mount Hood and traces Blue Ridge for three continuous miles.

Streig notes, however, that "if any fault sections were to rupture independently of each other, they could trigger a magnitude 7.7 earthquake."

A quake that size, the research paper notes, "may pose a threat to critical regional infrastructure including the city of Portland's Bull Run drinking water system, storage reservoirs operated by Portland General Electric, the highway and rail transportation corridors in the Columbia Gorge, and the U.S. Army Corps of Engineers power generation facilities at the Bonneville Dam."