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Miller, Stephen Andrew

Nom
Miller, Stephen Andrew
Affiliation principale
Fonction
Professeur ordinaire
Email
stephen.miller@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/940

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  • Publication
    Métadonnées seulement
    Coupling of full two-dimensional and depth-averaged models for granular flows
    (2013)
    Domnik, Birte
    ;
    Pudasaini, Shiva P.
    ;
    Katzenbach, Rolf
    ;
    Miller, Stephen Andrew 
  • Publication
    Métadonnées seulement
    Earthquake scaling and the strength of seismogenic faults
    (2002)
    Miller, Stephen Andrew 
    [1] Two important and unresolved issues in tectonics and earthquake mechanics are the strength of seismogenic faults, and scaling relationships between the seismic moment of an earthquake and the area or length of the rupture. These two issues, usually treated separately, are shown here to be fundamentally related. It is shown that the reported scatter in moment-area and moment-length data of strike-slip and dip-slip earthquakes is not scatter, but instead reflects the strength of the fault that failed. Relationships that exhibit continuous scaling between small and large earthquakes are derived, and demonstrate that fault zone pore pressure is the scaling parameter that collapses the combined catalogs of strike-slip and dip-slip earthquakes to a single function. It is shown that for large earthquakes overpressures vary continuously between hydrostatic and near-lithostatic above about 15 km, with evidence for a clear transition to near-lithostatic pore pressures below this depth. These results have significant implications for plate tectonics, earthquake source physics, and mechanistic seismic hazard assessment.
  • Publication
    Métadonnées seulement
  • Publication
    Métadonnées seulement
    Note on rain-triggered earthquakes and their dependence on karst geology
    (2008)
    Miller, Stephen Andrew 
    Recently reported rain-triggered seismicity from three separate storms occurred exclusively in karst geology. In this paper, I discuss how the hydrogeology of karst controls rain-triggered seismicity by channeling of the watershed after intense rainfall directly into the karst network. Such channeling results in very large increases in hydraulic head, and more importantly, substantially increases the vertical stress acting on the underlying pore-elastic media. Rapid loading upon a pore-elastic media induces seismicity by increasing pore pressure at depth in a manner similar to that observed from reservoir impounding. Using a simple 1-D model of a pore-elastic medium, it is shown that the instantaneous fluid pressure increase at depth is a substantial fraction of the pressure step applied at the boundary, followed by time-dependent pore pressure increases associated with the typical linear diffusion problem. These results have implications for the change in fluid pressure necessary to trigger earthquakes, and leads to the following hypothesis to be tested: Unambiguous rain-triggered seismicity will only occur in karst regions.
  • Publication
    Métadonnées seulement
  • Publication
    Métadonnées seulement
    New insights on stress rotations from a forward regional model of the San Andreas fault system near its Big Bend in southern California
    (2004)
    Fitzenz, D. D.
    ;
    Miller, Stephen Andrew 
    Understanding the stress field surrounding and driving active fault systems is an important component of mechanistic seismic hazard assessment. We develop and present results from a time-forward three-dimensional (3-D) model of the San Andreas fault system near its Big Bend in southern California. The model boundary conditions are assessed by comparing model and observed tectonic regimes. The model of earthquake generation along two fault segments is used to target measurable properties (e.g., stress orientations, heat flow) that may allow inferences on the stress state on the faults. It is a quasi-static model, where GPS-constrained tectonic loading drives faults modeled as mostly sealed viscoelastic bodies embedded in an elastic half-space subjected to compaction and shear creep. A transpressive tectonic regime develops southwest of the model bend as a result of the tectonic loading and migrates toward the bend because of fault slip. The strength of the model faults is assessed on the basis of stress orientations, stress drop, and overpressures, showing a departure in the behavior of 3-D finite faults compared to models of 1-D or homogeneous infinite faults. At a smaller scale, stress transfers from fault slip transiently induce significant perturbations in the local stress tensors (where the slip profile is very heterogeneous). These stress rotations disappear when subsequent model earthquakes smooth the slip profile. Maps of maximum absolute shear stress emphasize both that (1) future models should include a more continuous representation of the faults and (2) that hydrostatically pressured intact rock is very difficult to break when no material weakness is considered.
  • Publication
    Métadonnées seulement
    Stability regimes of a dilatant, fluid-infiltrated fault plane in a three-dimensional elastic solid
    (2006)
    Hillers, Gregor
    ;
    Miller, Stephen Andrew 
    [ 1] We investigate in a systematic parameter space study dilatant effects on slip evolution of a fluid-infiltrated fault in the continuum limit. The fault is governed by rate-and state-dependent friction and an empirical law for porosity evolution. We focus on the response of systems as a function of fluid-related parameters, such as the degree of overpressurization, dilatancy and diffusivity. This study emphasizes the exploration of the parameter space for homogeneous along-strike properties to investigate the evolution of spatiotemporal slip depending on hydromechanical processes. Three types of responses emerge. First, system-wide unstable stick-slip develops for drained conditions, and for undrained conditions if mechanisms leading to an increase in pore space are less effective. The critical stiffness depends on hydraulic diffusivity and dilatancy, which is shown to correspond with interevent times of simulated stick-slip events. During instabilities the evolution of hydraulic variables differ significantly between drained and undrained conditions. Second, stable creep is a result of dilatant processes. Third, systems situated in transitional stability regimes develop nonuniform slip pattern in space and time, revealing a possible explanation for rupture termination and observed stable afterslip. Although these patterns are produced by models located in transition zones of the parameter space, the occurrence of heterogeneous slip evolution is persistent for an extensive range of parameter values. Since transition zones contain an broad range of plausible conditions in the crust, they do not represent extreme cases.
  • Publication
    Métadonnées seulement
    Earthquakes as a coupled shear stress high pore pressure dynamical system
    (1996)
    Miller, Stephen Andrew 
    ;
    Nur, Amos
    ;
    Olgaard, David L.
    The migration, coalescence and localization of slip, seismicity, and zones of high pore pressure are modeled using a porosity reduction mechanism to drive pore pressure within a fault zone in excess of hydrostatic. Increased pore pressure in discrete cells creates zones of low effective stress, which induces slip that may propagate to surrounding cells depending on the local state of stress. At slip, stress is transferred using the solution for a rectangular dislocation in an elastic half-space, and pore pressures are redistributed by conserving fluid mass. Using simple assumptions about fault rheology and permeability, it is shown that the interaction between shear stress and effective stress evolves to a state of earthquake clustering with repeated events, locked zones, and large variations in fault strength. The model evolves from a uniform shear stress state on a strong fault, to a heterogeneous shear stress state on a weak fault.
  • Publication
    Accès libre
    Fault anatomy of the La Sarraz strike-slip fault system
    (2015-10-26)
    Schmitt, Nicole
    ;
    Grassi, R.
    ;
    Miller, Stephen Andrew 
    ;
    Perrochet, L.
    ;
    Valley, Benoît 
    ;
    Mosar, Jon
  • Publication
    Métadonnées seulement
    Aftershocks driven by a high-pressure CO2 source at depth
    (2004)
    Miller, Stephen Andrew 
    ;
    Collettini, Cristiano
    ;
    Chiaraluce, Lauro
    ;
    Cocco, Massimo
    ;
    Barchi, Massimiliano
    ;
    Kaus, Boris J. P.
    In northern Italy in 1997, two earthquakes of magnitudes 5.7 and 6 (separated by nine hours) marked the beginning of a sequence that lasted more than 30 days, with thousands of aftershocks including four additional events with magnitudes between 5 and 6. This normal-faulting sequence is not well explained with models of elastic stress transfer(1,2), particularly the persistence of hanging-wall seismicity(3) that included two events with magnitudes greater than 5. Here we show that this sequence may have been driven by a fluid pressure pulse generated from the coseismic release of a known deep source(4) of trapped high-pressure carbon dioxide (CO2). We find a strong correlation between the high-pressure front and the aftershock hypocentres over a two-week period, using precise hypocentre locations(5) and a simple model of nonlinear diffusion. The triggering amplitude (10-20 MPa) of the pressure pulse overwhelms the typical (0.1-0.2 MPa) range from stress changes in the usual stress triggering models(1,6). We propose that aftershocks of large earthquakes in such geologic environments may be driven by the coseismic release of trapped, high-pressure fluids propagating through damaged zones created by the mainshock. This may provide a link between earthquakes, aftershocks, crust/mantle degassing and earthquake-triggered large-scale fluid flow.