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Abstract Episodic tremor and slow slip (ETS) downdip of the subduction seismogenic zone are poorly understood slip behaviors of the seismic cycle. Talc, a common metasomatic mineral at the subduction interface, is suggested to host slow slip but this hypothesis has not been tested in the rock record. We investigate actinolite microstructures from talc‐bearing and talc‐free rocks exhumed from the depths of modern ETS (Pimu'nga/Santa Catalina Island, California). Actinolite deformed by dissolution‐reprecipitation creep in the talc‐free rock and dislocation creep ± cataclasis in the talc‐bearing rock. This contrast results from stress amplification in the talc‐bearing rock produced by high strain rates in surrounding weak talc. We hypothesize that higher strain rates in the talc‐bearing sample represent episodic slow slip, while lower strain rates in the talc‐free sample represent intervening aseismic creep. This work highlights the need to consider fluid‐mediated chemical change in studies of subduction zone deformation and seismicity.
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SCENTAR: A High-Density Nodal Array to Study the Structure and Seismogenic Behavior of the Southern Cascadia Forearc
Abstract Tectonic and seismogenic variations in subduction forearcs can be linked through various processes associated with subduction. Along the Cascadia forearc, significant variations between different geologic expressions of subduction appear to correlate, such as episodic tremor-and-slip (ETS) recurrence interval, intraslab seismicity, slab dip, uplift and exhumation rates, and topography, which allows for the systematic study of the plausible controlling mechanisms behind these variations. Even though the southern Cascadia forearc has the broadest topographic expression and shortest ETS recurrence intervals along the margin, it has been relatively underinstrumented with modern seismic equipment. Therefore, better seismic images are needed before robust comparisons with other portions of the forearc can be made. In March 2020, we deployed the Southern Cascadia Earthquake and Tectonics Array throughout the southern Cascadia forearc. This array consisted of 60 continuously recording three-component nodal seismometers with an average station spacing of ∼15 km, and stations recorded ∼38 days of data on average. We will analyze this newly collected nodal dataset to better image the structural characteristics and constrain the seismogenic behavior of the southern Cascadia forearc. The main goals of this project are to (1) constrain the precise location of the plate interface through seismic imaging and the analysis of seismicity, (2) characterize the lower crustal architecture of the overriding forearc crust to understand the role that this plays in enabling the high nonvolcanic tremor density and short episodic slow-slip recurrence intervals in the region, and (3) attempt to decouple the contributions of subduction versus San Andreas–related deformation to uplift along this particularly elevated portion of the Cascadia forearc. The results of this project will shed light on the controlling mechanisms behind heterogeneous ETS behavior and variable forearc surficial responses to subduction in Cascadia, with implications for other analogous subduction margins.
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- Award ID(s):
- 2136391
- PAR ID:
- 10410508
- Date Published:
- Journal Name:
- Seismological Research Letters
- Volume:
- 94
- Issue:
- 1
- ISSN:
- 0895-0695
- Page Range / eLocation ID:
- 496 to 506
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1785/0220220251
