INCIDENTAL DISCOVERY OF YOUNG FAULT FEATURES IN OREGON LIDAR CONSORTIUM LIDAR DATA (Invited Presentation)

Although most of the focus of earthquake resilience efforts in Oregon is on the Cascadia Subduction Zone and its potential for magnitude 9 earthquakes, local earthquakes on crustal faults remain a potential, but poorly understood, threat to the region. Few active crustal faults have been identified in Oregon, in part because of the thick forest that covers most of the state west of the crest of the Cascade Range. In recent years, the Oregon Department of Geology and Mineral Industries (DOGAMI) has collected high resolution (8 points per m²) lidar data over most of western Oregon, as well as significant areas of coverage east of the Cascades, with data collection funded by the Oregon Lidar Consortium. As part of the routine quality control procedures, DOGAMI geologists review all newly acquired lidar to find errors and artifacts. The data is reviewed in 2D and 3D hillshade and slopeshade visualizations at scales ranging from 1:8,000 to 1:24,000. In the course of this review we have identified dozens of previously unknown young fault features, typically fresh scarps from surface-rupturing earthquakes.

Major fault systems have been mapped near Mt. Hood, near the White Branch of the McKenzie River, in the upper Metolius River basin, South of Mt. Jefferson, in the La Pine graben, east of Crater Lake, and in the Klamath graben. Less extensive features have been mapped near the towns of Brookings, Bandon, Elgin, North Powder, and in the Summer Lake basin and the Summit Prairie area of Prairie City. DOGAMI has visited many of these features in the field on reconnaissance tours, but few have been studied in any detail. The majority of these newly mapped features do not coincide with previously mapped young faults from the USGS database, and few of those faults are evident where they are covered by lidar. These fault systems may pose significant hazards in many cases, and offer a wealth of opportunity for more detailed study which may help understand the tectonics of the Pacific Northwest.