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    Seismic precursors linked to super-critical fluids at oceanic transform faults (2014)
    Nature Publishing Group
    In:  Nature Geoscience, 7 (10). pp. 757-761.
    Details
    Publication Date: 2015-07-24
    Description: Large earthquakes on mid-ocean ridge transform faults are commonly preceded by foreshocks1, 2, 3 and changes in the seismic properties of the fault zone3. These seismic precursors could be linked to fluid-related processes2, 3. Hydrothermal fluids within young, hot crust near the intersection of oceanic transform faults are probably in a supercritical condition4. At constant temperature, supercritical fluids become significantly more compressible with decreasing pressure, with potential impacts on fault behaviour. Here we use a theoretical model to show that oceanic transform faults can switch from dilatant and progressive deformation to rupture in response to fluid-related processes. We assume that the fault core material behaves according to a Cam-clay-type5 constitutive law, which is commonly used to account for the behaviour of clays. According to our model, we find that the fault is initially stable, with stresses gradually increasing over a timescale of years in response to tectonic loading. The fault evolves into a metastable phase, lasting a few days, during which the fault rocks dilate and pore pressures decrease, causing the compressibility of the supercritical fluids to increase. This in turn triggers fault-slip instability that creates foreshock swarms. In the final phase, the fault fails in the mainshock rupture. Our results imply that seismic precursors are caused by changes in fluid pressure which result in variations in fluid compressibility, in response to rock deformation just before rupture.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/NGEO2244
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    A Bayesian Framework to Rank and Combine Candidate Recurrence Models for Specific Faults (2012)
    Seismological Society of America (SSA)
    Details
    Publication Date: 2012-06-01
    Description: We propose a probabilistic framework in which different types of information pertaining to the recurrence of large earthquakes on a fault can be combined in order to constrain the parameter space of candidate recurrence models and provide the best combination of models knowing the chosen data set and priors.We use Bayesian inference for parameter and error estimation, graphical models (Bayesian networks) for modeling, and stochastic modeling to link cumulative offsets (CO) to coseismic slip. The cumulative offset-based Bayesian approach (COBBRA) method (Fitzenz et al., 2010) was initially developed to use CO data to further constrain and discriminate between recurrence models built from historical and archaeological catalogs of large earthquakes (CLE). We discuss this method and present an extension of it that incorporates trench data (TD). For our case study, the Jordan Valley fault (JVF), the relative evidence of each model slightly favors the Brownian passage time (BPT) and lognormal models.We emphasize that (1) the time variability of fault slip rate is critical to constrain recurrence models; (2) the shape of the probability density functions (PDF) of paleoseismic events is very important, in most cases not Gaussian, and should be reported in its complexity; (3) renewal models are in terms of intervals between consecutive earthquakes, not dates, and the algorithms should account for that fact; and (4) maximum-likelihood methods are inadequate for parameter uncertainty evaluation and model combination or ranking. Finally, more work is needed to define proper priors and to model the relationship between cumulative slip and coseismic slip, in particular, when the fault behavior is more complex.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
    Published by Seismological Society of America (SSA)
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