← Back to Gallery

Analyzing Strain Partitioning in the Pacific Northwest with Block Models

At the Cascadia subduction zone, the Juan de Fuca plate (JdF) subducts obliquely under, and deforms, the North American plate (NA). Subduction deformation dominates deformation on land, as observed by geodetic measurements such as GNSS, limiting the resolution of surface faults on the overriding North American plate. The goal of this project is to better understand how oblique JdF-NA convergence is partitioned between surface faults in the Pacific Northwest region and the subduction zone using block models. Specifically, we apply an L₁ regularization known as Total Variation Regularization (TVR) to algorithmically select the most active faults from a dense block model. We constrain the subduction zone to accumulate dip-slip-only motion and test how many surface faults are involved in strain partitioning. We find a tradeoff between megathrust activity and surface fault activity: A dip-slip-only megathrust requires more active surface faults along with greater fault slip rates than a freely slipping (oblique) megathrust. However, even with a dip-slip-only megathrust, parallel strike-slip faults near the trench are neither active nor form a simple forearc sliver. Furthermore, geologic slip rates appear to be more consistent with estimated fault slip rates in models with a freely slipping subduction zone than in models with a constrained dip-slip subduction zone. In other words, near trench strike-slip faults are not required to explain onshore GNSS observations or geologic slip rates.

Presenting Author: Jeng Hann Chong

Student Presenter: Yes

Day: 4/22/2021

Time: 9:45 AM - 11:00 AM Pacific

Additional Authors