A Cycle of Memory Creation, Erasure, and Solid to Fluid-Like State Transitions Encoded Within Granular Assemblages Sheared by Faults
A hallmark of many processes in Earth's subsurface [e.g., landslides, ground-rupturing earthquakes, liquefaction, and crystal-rich magmas] is the transitions in states that granular assemblages undergo, from structurally arrested to creeping to flowing. The frictional jamming and material memory theoretical frameworks argue that volume fraction and shear stress govern such transitions and that the material records the transitions. We use x-ray microtomography to determine if the three-dimensional re-arrangement and fracturing of grains within assemblages collected from two paleoseismic sites along the southern San Andreas fault record frictional jamming phenomenologies. Analyses reveal that fault zone granular assemblages transition between one or more interrelated but geometrically localized and mesoscopic deformation states that change assemblages' stability during the seismic cycle. These states include [1-2] bulk and localized grain re-arrangements, [3] individual grain fracturing, and [4] localized zones of grain fracturing. Grain re-arrangement is primarily a global phenomenon. Grain size and non-rattlers exert control over grain fracturing and re-arrangements. Coseismic shear erases anisotropic fabric memory developed during aseismic shear and introduces its own. Shear stress magnitude and elastoplasticity control memory creation and erasure and thus vary with distance from a fault strand. Our findings imply [1] that sheared fault zone sediments experience a cycle of memory creation and erasure accompanied by differing deformation phases and thus hold an invaluable record of how shallow faults move coseismically and aseismically, and [2] that frictional jamming and material memory remain promising unifying theories for granular flow, even considering naturally imposed disorder.
Session: From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments - IV
Type: Oral
Room: K’enakatnu 6
Date: 5/1/2024
Presentation Time: 05:00 PM (local time)
Presenting Author: Jhardel Dasent
Student Presenter: Yes
Additional Authors
Jhardel Dasent Presenting Author Corresponding Author jdasent@ucsd.edu University of California, San Diego |
Richard Kilburn rkilburn@ucsd.edu University of California, San Diego |
Vashan Wright vwright@ucsd.edu University of California, San Diego |
Katherine Scharer kscharer@usgs.gov U.S. Geological Survey |
Michael Manga manga@seismo.berkeley.edu University of California, Berkeley |
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A Cycle of Memory Creation, Erasure, and Solid to Fluid-Like State Transitions Encoded Within Granular Assemblages Sheared by Faults
Session
From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments
Description