title: Monitoring transient changes within overpressured regions of subduction zones using ambient seismic noise.
abstract: In subduction zones, elevated pore fluid pressure, generally linked to metamorphic dehydration reactions, has a profound influence on the mechanical behavior of the plate interface and forearc crust through its control on effective stress. We use seismic noise-based monitoring to characterize seismic velocity variations following the 2012 Nicoya Peninsula, Costa Rica earthquake [M w (moment magnitude) 7.6] that we attribute to the presence of pressurized pore fluids. Our study reveals a strong velocity reduction (~0.6%) in a region where previous work identified high forearc pore fluid pressure. The depth of this velocity reduction is constrained to be below 5 km and therefore not the result of near-surface damage due to strong ground motions; rather, we posit that it is caused by fracturing of the fluid-pressurized weakened crust due to dynamic stresses. Although pressurized fluids have been implicated in causing coseismic velocity reductions beneath the Japanese volcanic arc, this is the first report of a similar phenomenon in a subduction zone setting. It demonstrates the potential to identify pressurized fluids in subduction zones using temporal variations of seismic velocity inferred from ambient seismic noise correlations.
authors.affiliation: Department of Earth and Planetary Sciences, University of California, Santa Cruz, Santa Cruz, CA 95064, USA.
authors.forename: Esteban J
authors.identifier: 0000-0002-5724-1513
authors.initials: EJ
authors.lastname: Chaves
authors.affiliation: Department of Earth and Planetary Sciences, University of California, Santa Cruz, Santa Cruz, CA 95064, USA.
authors.forename: Susan Y
authors.identifier: 0000-0002-1978-5392
authors.initials: SY
authors.lastname: Schwartz
mesh_terms: D003364:Costa Rica; D055866:Earthquakes; D004777:Environment; D004784:Environmental Monitoring / Q000379:methods*; D009038:Motion; D009622:Noise; D011312:Pressure; D018707:Volcanic Eruptions
keywords: Ambient seismic noise; Pore fluid pressure; Subduction zones
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