The Most Recent Earthquake on the Mount Hood Fault Zone, Oregon: Implications for cascading earthquake, landslide, & flood multi-hazards in the Columbia River Gorge

  • 28 Mar 2023
  • 7:00 PM
  • Online and in-person at Bridge 99 Brewery

Scott Bennett

U.S. Geological Survey

Watch the recorded presentation

The Mount Hood fault zone is a N-trending, ~55 km-long zone of active faulting along the western margin of the High Cascades graben at the crest of the Oregon Cascade Range. Recent geologic mapping, fault scarp analysis, and a hand-dug paleoseismic trench on the Gate Creek fault, the northernmost segment of the Mount Hood fault zone, indicate the most recent earthquake occurred between AD 1363 and AD 1495. These dates overlap with tree-ring dates between AD 1446 and AD 1447 from trees drowned when the nearby Bonneville landslide blocked the Columbia River and impounded a lake 75 meters deep. The impounded lake then partly breached the landslide dam, causing downstream flooding in the Portland basin prior to AD 1479–1482.

Ground motion modeling of a magnitude ~7 earthquake along the Mount Hood fault zone suggests strong shaking at Table Mountain, the headscarp of the Bonneville landslide ~15 km west of the Mount Hood fault zone, could have initiated the landslide. Thus, it is possible that an earthquake in the 15th century along the Mount Hood fault zone could have triggered a cascade of hazards, including the earthquake itself, an earthquake-triggered landslide, and then a flood from breaching of the landslide dam.

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Central Oregon Geoscience Society

P.O. Box 2154,  Bend, Oregon 97709

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