Title of Oral/Poster Presentation

Rocks can be scaly? A million years of damage in the southernmost San Andreas fault zone

Class

Article

College

College of Science

Faculty Mentor

Susanne Jänecke

Presentation Type

Poster Presentation

Abstract

We report preliminary results from a comprehensive analysis within the southern tip of the San Andreas fault (SAF) where many researchers predict nucleation of the next major M 7.8 earthquake to affect the Los Angeles basin. Better understanding the structural geology of the tip of the fault zone and the specific geometries that may give rise to future devastating earthquakes is vital. A major structural change occurs within the southern tip of the SAF and this study shows how the transpressional regime of the SAF gives way southward to the transtension that created the new ocean basin beneath Gulf of California. We name this transition between transpression and transtension, the Pope Transition Zone. In this critical zone we document a wide range of fault deformation: from slow, shallow creep with hairline fractures to highly-sheared zones with rounded block-in-matrix clasts in wide fault zones. Right-lateral slip across the San Andreas Fault Zone cuts progressively through middle Pleistocene to modern sediment, which makes it possible to characterize the structural differences between 1 yr, 1000 yrs, 50,000 yrs, 0.5 my and 1 my of plate motion. We separate the most active strands from the less active, and show how strain accumulated in the fault zone during the last one million years.

Location

The North Atrium

Start Date

4-12-2018 3:00 PM

End Date

4-12-2018 4:15 PM

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Apr 12th, 3:00 PM Apr 12th, 4:15 PM

Rocks can be scaly? A million years of damage in the southernmost San Andreas fault zone

The North Atrium

We report preliminary results from a comprehensive analysis within the southern tip of the San Andreas fault (SAF) where many researchers predict nucleation of the next major M 7.8 earthquake to affect the Los Angeles basin. Better understanding the structural geology of the tip of the fault zone and the specific geometries that may give rise to future devastating earthquakes is vital. A major structural change occurs within the southern tip of the SAF and this study shows how the transpressional regime of the SAF gives way southward to the transtension that created the new ocean basin beneath Gulf of California. We name this transition between transpression and transtension, the Pope Transition Zone. In this critical zone we document a wide range of fault deformation: from slow, shallow creep with hairline fractures to highly-sheared zones with rounded block-in-matrix clasts in wide fault zones. Right-lateral slip across the San Andreas Fault Zone cuts progressively through middle Pleistocene to modern sediment, which makes it possible to characterize the structural differences between 1 yr, 1000 yrs, 50,000 yrs, 0.5 my and 1 my of plate motion. We separate the most active strands from the less active, and show how strain accumulated in the fault zone during the last one million years.