Distributed Active Faulting in High-Relief Volcanic Topography in Northeastern California

Session: Cryptic Faults: Assessing Seismic Hazard on Slow Slipping, Blind or Distributed Fault Systems [Poster]
Type: Poster
Date: 4/28/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Locating and characterizing distributed faulting in high-relief topography can be challenging due to vegetative cover and high rates of hillslope erosion that may mask surficial evidence of active faulting. Uncertainties in the activity and lengths of faults translate into higher uncertainties in seismic hazard assessments. Cryptic fault networks can be identified and characterized by integrating analyses of traditional geologic techniques with high-resolution topography, such as lidar and structure from motion models.

Our study is focused on the Pit River region in northern California, located between Mount Shasta and Lassen Peak. This is a tectonically complex area where the Klamath Mountains are juxtaposed against the Cascade Range backarc and overprinted by Basin and Range/Modoc Plateau/Walker Lane transtension. The region is characterized by distributed active faulting, such as the Hat Creek and Rocky Ledge fault systems. We concentrated north of these previously recognized fault zones in high-relief volcanic terrain using remote sensing and traditional geologic techniques. Our results reveal an active transtensional fault network in the high-relief volcanic topography north of the Pit River. This fault system appears to be a northward continuation of the Rocky Ledge and Hat Creek fault systems. This fault system trends NW-SE across the Mushroom Rock Ridge and vertically offsets the 4.9-6.3 Ma Bartle Gap volcanic unit through Quaternary deposits. Fault segments are generally short (1-4 km), discontinuous and display left- and right-stepping en echelon surficial patterns with <200 m between adjacent fault segments. Overall these faults form a through-going fault network. Quaternary to recent (Holocene) deposits are vertically offset between <1 to 30 m, indicating recent fault activity despite a lack of seismicity along many of the faults. These observations help explain the regional kinematics in the transition from the Walker Lane to Cascadia.

Presenting Author: Jessica A. T. Jobe

Authors