← Back to Sessions

Spatial Patterns of Tectonic Deformation at the Mendocino Triple Junction Inferred From River Terraces and Landscape Morphology

Description: 

At the Mendocino triple junction (MTJ), the Cascadia subduction zone, San Andreas Fault system, and Mendocino Fault meet in a complex deformation zone. In the immediate MTJ area, from roughly Ferndale to Shelter Cove, CA, previous investigation of the fault networks was primarily through bedrock mapping, with little differentiation between inactive and active faults, and few constraints on Quaternary deformation rates. Quantification of crustal deformation is limited to coastal uplift rates derived from emergent Holocene and Pleistocene marine terraces, and stream metrics and erosion rates from small coastal drainages within ~5 km of the coast. In this steep and densely vegetated environment, recognizing spatial variation of inland Quaternary crustal deformation rates could help identify the presence and location of active faults where there is little direct surface expression. We use lidar to map fluvial terraces and other geomorphic surfaces along river valleys in the MTJ area up to 30 km inland. Longitudinal profiles, height above river, and morphological characteristics are used to correlate terrace surfaces along the rivers. In the Mattole watershed, terraces with different vertical spacings occur along channel reaches having different gradients separated by distinct knickzones. These patterns may indicate spatially variable uplift rates. Complementary analysis of landscape morphology including hillslope steepness and relief, and river metrics such as channel steepness index expands the spatial extent of inferred deformation beyond the terraced river valleys. These analyses must consider apparent drainage area reduction due to drainage divide migration and stream capture, which itself provides additional insight into the landscape response to tectonic forcing. Spatial variation in apparent uplift rates indicate possible location and kinematics of crustal faults related to the San Andreas Fault and Cascadia subduction zone which are objectives for future study.

Session: Cryptic Faults: Advances in Characterizing Low Strain Rate and Environmentally Obscured Faults [Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Jessie

Student Presenter: No

Invited Presentation: 

Authors