Constructing constitutive relations for seismic and aseismic faulting and at high and low sliding speeds
| Cosa | seminari |
|---|---|
| Quando | 23/03/2010 da 14:30 al 16:30 |
| Dove | Sala Conferenze Roma via di Vigna Murata 605 |
| Persona di riferimento | Giulio Di Toro |
| Indirizzo e-mail per contatti | |
| Aggiungi l'evento al calendario |  vCal (Windows, Linux) iCal (Mac OS X) |
23 marzo 2010 ore 14.30 | Nicholas Beeler | Sala conferenze | Roma Sede Centrale
N. M. Beeler , Research Geophysicist, Cascades Observatory, US Geological Survey, Vancouver, Washington
also at USGS Earthquake Science Center, Menlo Park, California
and Dept of Geological Sciences, Brown University, Providence, Rhode Island
Abstract
In laboratory faulting experiments on bare quartzofeldspathic rock surfaces at low temperature and low slip, coseismic strength losses are typically less than 10% of the ambient stress and the maximum slip velocity is proportional to the fault strength loss approximately by twice the ratio of the shear wave speed to the shear modulus.
Results are consistent with typical natural earthquake properties: stress drops of a few tenths to a few MPa, low seismic efficiency, slip rates up to a few m/s and rupture propagation at rates approaching the shear wave speed. These earthquake-like properties of friction result from a second order, negative dependence of fault strength on the logarithm of slip velocity, sustained over many orders of magnitude sliding velocity at low normal stress, as well represented by rate and state variable constitutive equations.
However, where there are transitions in contact scale mechanisms, lab and natural faulting are not consistent with the above framework. Examples are the transition from rate weakening to rate strengthening at low slip speed (the brittle ductile transition) both at depth and near the earth's surface, strong rate weakening at high slip speeds (dynamic weakening), and from rate weakening to rate strengthening at intermediate speeds (the high speed cutoff). In this talk I present constitutive equations developed to model laboratory observed faulting that deviate significantly from standard rate and state friction - the examples are from low and high speed experiments, and are intended for both seismic and aseismic faulting.
also at USGS Earthquake Science Center, Menlo Park, California
and Dept of Geological Sciences, Brown University, Providence, Rhode Island
Abstract
In laboratory faulting experiments on bare quartzofeldspathic rock surfaces at low temperature and low slip, coseismic strength losses are typically less than 10% of the ambient stress and the maximum slip velocity is proportional to the fault strength loss approximately by twice the ratio of the shear wave speed to the shear modulus.
Results are consistent with typical natural earthquake properties: stress drops of a few tenths to a few MPa, low seismic efficiency, slip rates up to a few m/s and rupture propagation at rates approaching the shear wave speed. These earthquake-like properties of friction result from a second order, negative dependence of fault strength on the logarithm of slip velocity, sustained over many orders of magnitude sliding velocity at low normal stress, as well represented by rate and state variable constitutive equations.
However, where there are transitions in contact scale mechanisms, lab and natural faulting are not consistent with the above framework. Examples are the transition from rate weakening to rate strengthening at low slip speed (the brittle ductile transition) both at depth and near the earth's surface, strong rate weakening at high slip speeds (dynamic weakening), and from rate weakening to rate strengthening at intermediate speeds (the high speed cutoff). In this talk I present constitutive equations developed to model laboratory observed faulting that deviate significantly from standard rate and state friction - the examples are from low and high speed experiments, and are intended for both seismic and aseismic faulting.