Presentation
Testing the time dependence of slip on the West Klamath Lake fault zone
AGU Fall Meeting
(2016)
Abstract
Detailed inventories of fault slip over multiple time intervals are critical to our understanding of strain accumulation and release during the earthquake cycle, as well as for resolving potential variability in slip rates over time. Such variations are potentially associated with spatially or temporally clustered earthquakes and possible time-dependent changes in shear zone strength. The West Klamath Lake fault zone (WKLFZ) in southern Oregon provides an excellent opportunity to study incremental fault slip rates because it displaces multiple generations of datable landforms and has remarkable surface expression in airborne lidar imagery. There, we utilize these lidar data and new 3He cosmogenic exposure dating to reconstruct fault slip rates over intervals ranging from ~103 – 105 years. Our surficial geologic mapping along the northern extent of the WKLFZ reveals at least two generations of late-Pleistocene glacial landforms as well as several Holocene fan surfaces, all of which are progressively offset by an array of predominately down-to-the-east normal fault scarps. Dating of these features relies on 3He exposure dating of basaltic andesite boulders and depth profiles from glacial outwash terraces. Preliminary exposure dating of an offset moraine along Sevenmile Creek reveals ages consistent with the last glacial maximum (~15 – 25 ka), suggesting normal fault slip rates of ~0.1 mm/yr over this period. This estimate is consistent with slip rates determined from K-Ar dating of offset lava flows near Crater Lake, ~20 km to the north. Two dozen additional samples will focus on older glacial moraines and outwash surfaces, as well as debris-flow boulders on Holocene fans. These data will test the constancy of this preliminary slip rate over time. Taken together, our results will provide a detailed slip inventory for the WKLFZ over the last ~105 years, and elucidate the role of this structure in accommodating active deformation at the eastern edge of the Oregon Coast block.
Keywords
- Fault slip,
- Earthquake cycle,
- Geomorphology
Disciplines
Publication Date
December 15, 2016
Location
San Francisco, CA
Citation Information
Speth, G., C.B. Amos, W. Amidon, G. Balco, and A. Meigs (2016) Testing the time-dependence of slip on the Western Klamath Lake Fault Zone, Oregon, Eos Trans. AGU, Fall Meet. Suppl.