SCEC Award Number 13012 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Spontaneous Rupture Propagation With Strong Dynamic Weakening
Investigator(s)
Name Organization
James Rice Harvard University
Other Participants John D. Platt, Harvard University
SCEC Priorities 3, 4, 6 SCEC Groups FARM, CS, DRCV
Report Due Date 03/15/2014 Date Report Submitted N/A
Project Abstract
 A companion SCEC 2013 study (Thermally Driven Shear Localization in Fault Zones, Project 13011) focused on identifying physical mechanisms controlling the thermal weakening and related localization of rapid shear in fault gouge. The goal in this work was to see the implications, for dynamic rupture propagation, of those new views of how the histories of slip and stress on a fault are related to one-another - such being an essential input for analysis of
spontaneous dynamic rupture. The studies have also been partly supported, starting 1 July 2013, by a 3-year NSF grant, NSFEAR Geophysics Program Grant EAR-1315447: "Materials physics of rapidly sheared faults and
consequences for earthquake rupture dynamics". The main contributions in this phase of the work are being made by John D. Platt, as a part of his Ph.D. thesis in preparation. His work is being summarized in a manuscript "Steadily propagating slip pulses driven by thermal decomposition" in preparation by Platt, in combination
with Robert C. Viesca (a former Ph.D. student in our group, now at Tufts University) and Dmitry I. Garagash (a former sabbatical visitor to our group, from Dalhousie Univ.), to be submitted to J. Geophys. Res. That work seems to be the first modeling of propagating dynamic rupture in cases for which thermal decomposition is a part of the process, it being assumed to follow a preliminary phase of frictional heating and related weakening by thermal pressurization of native ground fluids. Previously, Garagash [2012] has presented such an analysis of propagating slip pulses for the case of fault weakening solely by thermal pressurization of native fluids. Their approach is to solve for self-healing slip pulses propagating at a constant rupture velocity. Results show that for fixed fault properties there are two ways to propagate a slip pulse.
One is a pulse with small slip that never triggers thermal decomposition and the other is a pulse with large slip and significant weakening due to thermal decomposition. Thermal decomposition leads to a distinctive along-fault slip rate profile, with peak slip rates coinciding with the onset of
the reaction. The study establishes how the total slip and rupture velocity vary for slip pulses with and without thermal decomposition. Before submitting the manuscript, Platt plans to add a results section showing how model outcomes like total slip, rupture velocity, etc. vary with the reaction parameters (e.g., with Er, Pr, A, md and Q) in the equation set within the report).
Intellectual Merit This figure, from Platt, Viesca and Garagash [2014] (in preparation; see reference list) shows the
distribution of sliding velocity V along a propagating rupture in the form of a self-healing slip
pulse, of length L, which is advancing steadily, at propagation speed Vr, along a planar fault
under plane strain conditions. The case of weakening by thermal pressurization of native ground
water (in blue) is contrasted with that of an initially dry fault zone (in red) in which a fluid phase
is introduced, as a volatile component, by thermal decomposition of the fault zone material.
Broader Impacts An impact, not yet fully realized, is that this level of understanding of the faulting process will
help us to interpret, and understand the significance in terms of causative processes, of fault zone
observations in the field and in laboratory specimens. The work also takes steps towards
understanding how the materials physics of fault zone processes interact with rupture dynamics.
Exemplary Figure This is Figure 3 from the report (which is given in enlarged format in the final report section, EXEMPLARY FIGURE). This figure is from John D. Platt, Robert C. Viesca and Dmitry I. Garagash (2014 paper in preparation; see reference list). It shows the distribution of sliding velocity V along a propagating rupture in the form of a self-healing slip pulse, of length L, which is advancing steadily, at propagation speed Vr, along a planar fault
under plane strain conditions. The case of weakening by thermal pressurization of native ground water (in blue) is contrasted with that of an initially dry fault zone (in red) in which a fluid phase is introduced, as a volatile component, by thermal decomposition of the fault zone material.