Publication Date

2020

First Advisor

Jack P. Loveless

Document Type

Honors Project

Degree Name

Bachelor of Arts

Department

Geosciences

Keywords

Cascidia, Subductor zone, Earthquakes cycle, Uplift, Slow slip events, GPS, Pacific Northwest, Hazard, Elastic block model, MIDAS robust trend estimator

Abstract

The idealized earthquake cycle is characterized by strain accumulation during the interseismic period and its episodic release by the occurrence of earthquakes. The Cascadia Subduction Zone has not produced a megathrust earthquake since 1700. This lack of seismicity suggests that strain has been accumulating on the subduction interface with no form of release for over 300 years. However, slow slip events (SSEs), a form of aseismic strain release, have been detected on the subduction interface at depths of 40 to 50 km, deeper than strain has been thought to be able to accumulate according to previous studies of Cascadia. The presence of periodically recurring SSEs during the interseismic period of the earthquake cycle indicates that the interseismic period is not simply characterized by strain accumulation: there are periods of strain accumulation during inter-SSE periods, and periods of strain release during SSEs. This study uses GPS timeseries to calculate inter-SSE interseismic velocities and inverts them using an elastic block model to estimate the slip deficit distribution on the subduction interface. We question the assumption that slip deficit (a proxy for strain accumulation) is restricted to the shallow (< 30 km) portion of the subduction interface by allowing the downdip extent of slip deficit to extend down to 60 km depth. We superimpose estimates SSEs to visualize the spatial relationship between slip deficit and slow slip. By evaluating slip deficit and slow slip independently, we are able to examine SSEs’ effect on interseismic strain accumulation, as well as the effect of both inter-SSE slip deficit and slow slip on vertical deformation of the forearc. The spatial extent of interseismic slip deficit on the subduction interface and the ability of slow slip to release this accumulated slip deficit is directly related to the potential rupture area of a future megathrust earthquake. Gaining a better understanding of the interaction of these two processes, and specifically the role that SSEs play in the earthquake cycle, is crucial to understanding the hazard associated with the Cascadia Subduction Zone.

Rights

2020 Juliette Paule Saux. Access limited to the Smith College community and other researchers while on campus. Smith College community members also may access from off-campus using a Smith College log-in. Other off-campus researchers may request a copy through Interlibrary Loan for personal use.

Language

English

Comments

73 pages : color illustrations, map. Includes bibliographical references (pages 70-72) + Appendix with 14 items.

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