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Comparison of the stress-stimulated current of dry and fluid-saturated gabbro samples

Robert P. Dahlgren, Malcolm J. S. Johnston, Vern C. Vanderbilt and Rebecca N. Nakaba
Comparison of the stress-stimulated current of dry and fluid-saturated gabbro samples
Bulletin of the Seismological Society of America (December 2014) 104 (6): 2662-2672

Abstract

We investigate charge generation as a function of stress in fine-grained gabbro for both nominally dry samples and samples fully saturated with electrically conductive brine fluids similar to those observed in active earthquake fault zones. These experiments address a number of proposed and reported electrical precursory and coseismic phenomena associated with earthquakes. Compressive load was applied to one end of the sample in repetitive cycles using a pair of precision steel platens driven by a large hydraulic press. The samples were tested by cycling between constant low stress and constant high stress values with a 200-s periodicity. Net charge transport between the stressed and unstressed sample ends was monitored with a picoammeter. For the nominally dry samples, stress-stimulated current (SSC) transients on the order of 50-400 pA peak-to-peak were observed with a decay time constant approximately 10 s during stress loading and unloading. Under constant compressive loads of approximately 22 MPa, small negative polarity SSC of approximately 15 pA magnitude was observed as an offset from the baseline current at low load (5 MPa) conditions. For the fluid-saturated samples, neither transients nor SSCs were observed as a function of stress when the load was cycled, an observation that is consistent with more rapid internal self-discharge due to higher electrical conductivity of the sample. Because the Earth"s crust is fluid saturated, observation of significant electrical charge buildup is not expected during the observed slow stress accumulation prior to earthquakes or during any slow precursory stress release that may occur in the region of earthquake nucleation. However, observation of coseismic charge generation due to electrokinetic, triboelectric, and other processes may occur during earthquake stress drops, surface rupture, and seismic-wave arrivals from dynamic rupture.


ISSN: 0037-1106
EISSN: 1943-3573
Coden: BSSAAP
Serial Title: Bulletin of the Seismological Society of America
Serial Volume: 104
Serial Issue: 6
Title: Comparison of the stress-stimulated current of dry and fluid-saturated gabbro samples
Affiliation: NASA, Ames Research Center, Moffett Field, CA, United States
Pages: 2662-2672
Published: 201412
Text Language: English
Publisher: Seismological Society of America, Berkeley, CA, United States
References: 50
Accession Number: 2015-002536
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
Secondary Affiliation: U. S. Geological Survey, USA, United StatesWesleyan University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Seismological Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201502
Program Name: USGSOPNon-USGS publications with USGS authors
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