Mineral Physics Institute Summer Scholars Program

Beth Ann Bell University of S. Carolina Major: Geology Mentors: Bill Holt, Glenn Richard

Summer Project Description:

Title: Quantification of Past Tectonic Rates in Southern California

Southern California comprises one of the most tectonically active regions of the United States, with various styles
of deformation occurring here at the present time. Throughout the Cenozoic, the region has been characterized by
interaction between the North American plate and various plates underlying the Pacific Ocean. Today, the region is
primarily influenced by transpression (convergence at an oblique angle) between the North American and Pacific
plates, and the resulting deformation is complex, expressed in regions of uplift, major regional strike-slip faults,
and areas of local subsidence.

In order to better understand the complex deformation occurring in southern California, we will measure crustal
velocity fields in the region using both fault slip data and Global Positioning System (GPS) – based geodesy. We will
use these data and a computer program written by Bill Holt to construct models for the current states of velocity,
dilatational strain, and shear strain in the region. Using GPS information on the current crustal velocity field, we
will extrapolate backward in time at geologically short increments, calculating new velocity and strain solutions at
each step, for the past 3 million years of deformation in southern California. Our model should be able to predict
regions of uplift, subsidence, and rotation in the past 3 million years. We will also extrapolate our model forward in time,
to project ground movement in southern California for several million years into the future.

Given the large error likely in our extrapolation of past strain rates, we will search the literature for relevant studies in
southern California which will allow us to test our model’s predictions for uplift, subsidence, and rotation
in various regions of the study area against existing geological data. Low- temperature thermochronometric studies,
analyses of regional sedimentary basins, and studies of paleomagnetism in southern California may provide
constraints on the various parameters we are attempting to quantify, and will allow us to gauge our model’s efficacy
in determining past tectonic conditions.