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Rate dependence of acoustic emissions generated during shear of simulated fault gouge Bulletin of the Seismological Society of America

Bulletin of the Seismological Society of America, 97(6): 1841-1849, 2007.
Authors: Karen Mair and Chris Marone and R. Paul Young
Description: ae in sheared granular
Tags: ae shearbib
Abstract: Earthquake systems are commonly described using rate and state dependent fault models; however, the connection between rate and state friction para meters and specific microprocesses remains a challenge. We present new laborator observations using modern ultrasonic techniques to reveal dynamic processes operat ing during frictional sliding. Granular layers were sheared under constant norma stress for a range of loading rates. During experiments, we monitored high-frequenc acoustic emissions (AE) generated by grain fracture and friction using an array o piezoelectric transducers surrounding the layers. Complete waveforms and event in formation were collected for thousands of microearthquakes. Perturbations in impose load point velocity (V) produced a friction response consistent with previous work For a given V, AE per sec decreased with accumulated slip, suggesting sensitivity t gouge layer evolution. Step increases in V led to immediate and sustained increases i AE per sec; the converse was true for V decreases. The positive rate dependence o AE per second is unsurprising because more slip is covered per unit time at highe V; however, AE per unit slip decreases with increasing V, indicating a deficit o acoustic activity at a faster slip rate. Assuming that AE result mainly from grain con tact sliding, acoustic activity is proportional to the real area of contact between slidin particles. Our results qualitatively agree with previous experiments carried out on bar rock surfaces and support ideas that the frictional contact junction area is reduce at increased sliding velocity. We highlight a new way to visualize micromechanica contact processes important in frictional mechanics and highly relevant to earth quake physics.
| BibTeX  
@article{mair07,
title = {Rate dependence of acoustic emissions generated during shear of simulated fault gouge Bulletin of the Seismological Society of America},
author = {Karen Mair and Chris Marone and R. Paul Young},
journal = {Bulletin of the Seismological Society of America},
note = {doi: 10. 1785 / 0120060242},
number = {6},
pages = {1841-1849},
volume = {97},
year = {2007},
description = {ae in sheared granular},
abstract = {Earthquake systems are commonly described using rate and state dependent fault models; however, the connection between rate and state friction para meters and specific microprocesses remains a challenge. We present new laborator observations using modern ultrasonic techniques to reveal dynamic processes operat ing during frictional sliding. Granular layers were sheared under constant norma stress for a range of loading rates. During experiments, we monitored high-frequenc acoustic emissions (AE) generated by grain fracture and friction using an array o piezoelectric transducers surrounding the layers. Complete waveforms and event in formation were collected for thousands of microearthquakes. Perturbations in impose load point velocity (V) produced a friction response consistent with previous work For a given V, AE per sec decreased with accumulated slip, suggesting sensitivity t gouge layer evolution. Step increases in V led to immediate and sustained increases i AE per sec; the converse was true for V decreases. The positive rate dependence o AE per second is unsurprising because more slip is covered per unit time at highe V; however, AE per unit slip decreases with increasing V, indicating a deficit o acoustic activity at a faster slip rate. Assuming that AE result mainly from grain con tact sliding, acoustic activity is proportional to the real area of contact between slidin particles. Our results qualitatively agree with previous experiments carried out on bar rock surfaces and support ideas that the frictional contact junction area is reduce at increased sliding velocity. We highlight a new way to visualize micromechanica contact processes important in frictional mechanics and highly relevant to earth quake physics. },
keywords = {ae shearbib }
}