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Yann Klinger - One of the best experts on this subject based on the ideXlab platform.
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Relation between continental strike‐slip Earthquake segmentation and thickness of the crust
Journal of Geophysical Research, 2010Co-Authors: Yann KlingerAbstract:[1] High-resolution maps of large continental strike-slip Earthquake surface ruptures show that they are formed of fault segments. These segments are bounded by fault bends, step overs, or combinations of the two. The lowest limit in size for such segments may not be relevant in the understanding of Earthquake Mechanics, as it pertains to the granular properties of fault zones. The maximum limit in segment length, however, is important as it is directly relates to the maximum extent of seismic rupture. To measure the length of the segments, a new quantitative method based on piecewise linear fitting is developed and is used to automatically retrieve segments from Earthquake rupture maps. Next, this approach is tested against a set of ten continental strike-slip Earthquake ruptures derived from similar, high quality maps. The test suggests that segments have a maximum length of ∼18 km, independent of regional tectonic setting. Slip-inversions for Earthquakes, based on seismological and/or geodetic data, most often are not unique and can show some variability even for one particular event. Some basic characteristics, however, such as total moment release or general source geometry, seem to persist that are relevant to Earthquake Mechanics. Measurements of the maximum horizontal extent of individual slip-patches derived from seismic source inversion for strike-slip ruptures show that their strike dimension does not increase infinitely with magnitude, but instead reaches a maximum value of ∼25 km. These two independent lines of observations, complemented by earlier data and analog experiments, suggest that it is the thickness of the seismogenic crust that controls the structural scaling of the length of seismic segments, and that it is independent of the ultimate size of individual Earthquakes.
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Relation between continental strike-slip Earthquake segmentation and thickness of the crust
Journal of Geophysical Research: Solid Earth, 2010Co-Authors: Yann KlingerAbstract:High-resolution maps of large continental strike-slip Earthquake surface ruptures show that they are formed of fault segments. These segments are bounded by fault bends, step overs, or combinations of the two. The lowest limit in size for such segments may not be relevant in the understanding of Earthquake Mechanics, as it pertains to the granular properties of fault zones. The maximum limit in segment length, however, is important as it is directly relates to the maximum extent of seismic rupture. To measure the length of the segments, a new quantitative method based on piecewise linear fitting is developed and is used to automatically retrieve segments from Earthquake rupture maps. Next, this approach is tested against a set of ten continental strike-slip Earthquake ruptures derived from similar, high quality maps. The test suggests that segments have a maximum length of similar to 18 km, independent of regional tectonic setting. Slip-inversions for Earthquakes, based on seismological and/or geodetic data, most often are not unique and can show some variability even for one particular event. Some basic characteristics, however, such as total moment release or general source geometry, seem to persist that are relevant to Earthquake Mechanics. Measurements of the maximum horizontal extent of individual slip-patches derived from seismic source inversion for strike-slip ruptures show that their strike dimension does not increase infinitely with magnitude, but instead reaches a maximum value of similar to 25 km. These two independent lines of observations, complemented by earlier data and analog experiments, suggest that it is the thickness of the seismogenic crust that controls the structural scaling of the length of seismic segments, and that it is independent of the ultimate size of individual Earthquakes.
Ruth A. Harris - One of the best experts on this subject based on the ideXlab platform.
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The SCEC/USGS Dynamic Earthquake Rupture Code Verification Exercise
Seismological Research Letters, 2009Co-Authors: Ruth A. Harris, Michael Barall, Ralph J. Archuleta, Eric M. Dunham, Brad T. Aagaard, Jean-paul Ampuero, Harsha S. Bhat, Víctor M. Cruz-atienza, Luis A. Dalguer, Phillip DawsonAbstract:Numerical simulations of Earthquake rupture dynamics are now common, yet it has been difficult to test the validity of thesesimulations because there have been few field observations and no analytic solutions with which to compare the results. This paper describes the Southern California Earthquake Center/U.S. Geological Surve(SCEC/USGS) Dynamic Earthquake Rupture Code Verification Exercise, where codes that simulate spontaneous rupture dynamics in three dimensions are evaluated and the results produced by these codes are compared using Web-based tools. This is the first time that a broad and rigorous examination of numerous spontaneous rupture codes has been performed—a significant advance in this science. The automated process developed to attain this achievement provides for a future where testing of codes is easily accomplished. Scientists who use computer simulations to understand Earthquakes utilize a range of techniques. Most of these assume that Earthquakes are caused by slip at depth on faults in the Earth, but hereafter the strategies vary. Among the methods used in Earthquake Mechanics studies are kinematic approaches and dynamic approaches. The kinematic approach uses a computer code that prescribes the spatial and temporal evolution of slip on the causative fault (or faults). These types of simulations are very helpful, especially since they can be used in seismic data inversions to relate the ground motions recorded in the field to slip on the fault(s) at depth. However, these kinematic solutions generally provide no insight into the physics driving the fault slip or information about why the involved fault(s) slipped that much (or that little). In other words, these kinematic solutions may lack information about the physical dynamics of Earthquake rupture that will be most helpful in forecasting future events. To help address this issue, some researchers use computer codes to numerically simulate Earthquakes and construct dynamic, spontaneous rupture (hereafter called “spontaneous rupture”) solutions. For these types of numerical simulations, rather than prescribing the slip function at each location on the fault(s), just the friction constitutive properties and initial stress conditions are prescribed. The subsequent stresses and fault slip spontaneously evolve over time as part of the elasto-dynamic solution. Therefore, spontaneous rupture computer simulations of Earthquakes allow us to include everything that we know, or think that we know, about Earthquake dynamics and to test these ideas against Earthquake observations.
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Earthquake stress triggers, stress shadows, and seismic hazard
Current Science, 2000Co-Authors: Ruth A. HarrisAbstract:Many aspects of Earthquake Mechanics remain an enigma at the beginning of the twenty-first century. One potential bright spot is the realization that simple calculations of stress changes may explain some Earthquake interactions, just as previous and ongoing studies of stress changes have begun to explain humaninduced seismicity. This paper, which is an update of Harris, reviews many published works and presents a compilation of quantitative Earthquake-interaction studies from a stress change perspective. This synthesis supplies some clues about certain aspects of Earthquake Mechanics. It also demonstrates that much work remains to be done before we have a complete story of how Earthquakes work.
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Dynamic 3D simulations of Earthquakes on En Echelon Faults
Geophysical Research Letters, 1999Co-Authors: Ruth A. HarrisAbstract:One of the mysteries of Earthquake Mechanics is why Earthquakes stop. This process determines the difference between small and devastating ruptures. One possibility is that fault geometry controls Earthquake size. We test this hypothesis using a numerical algorithm that simulates spontaneous rupture propagation in a three-dimensional medium and apply our knowledge to two California fault zones. We find that the size difference between the 1934 and 1966 Parkfield, California, Earthquakes may be the product of a stepover at the southern end of the 1934 Earthquake and show how the 1992 Landers, California, Earthquake followed physically reasonable expectations when it jumped across en echelon faults to become a large event. If there are no linking structures, such as transfer faults, then strike-slip Earthquakes are unlikely to propagate through stepover s >5 km wide.
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introduction to special section stress triggers stress shadows and implications for seismic hazard
Journal of Geophysical Research, 1998Co-Authors: Ruth A. HarrisAbstract:Many aspects of Earthquake Mechanics remain an enigma as we enter the closing years of the twentieth century. One potential bright spot is the realization that simple calculations of stress changes may explain some Earthquake interactions, just as previous and on going studies of stress changes have begun to explain human-induced seismicity. This paper, which introduces the special section “Stress Triggers, Stress Shadows, and Implications for Seismic Hazard,” reviews many published works and presents a compilation of quantitative Earthquake interaction studies from a stress change perspective. This synthesis supplies some clues about certain aspects of Earthquake Mechanics. It also demonstrates that much work remains before we can understand the complete story of how Earthquakes work.
Toshihiko Shimamoto - One of the best experts on this subject based on the ideXlab platform.
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Earthquakes: Radiated Energy and the Physics of Faulting - Relating high-velocity rock-friction experiments to coseismic slip in the presence of melts
Geophysical monograph, 2013Co-Authors: Giulio Di Toro, Stefan Nielsen, Takehiro Hirose, Toshihiko ShimamotoAbstract:The dynamic strength (τ f ) of faults during coseismic slip is a major unknown in Earthquake Mechanics, though it has crucial influence on rupture properties, dynamic stress drop, radiated energy and heat produced during slip. In order to provide constraints on τ f , High-Velocity Rock Friction Experiments (HVRFE) are conducted on natural rocks with rotary shear apparatuses, reproducing slip (several meters) and slip rate (0.1-3 m s -1 ) typical of large Earthquakes. Among the various weakening mechanisms possibly activated during seismic slip, we focus on melt lubrication. Solidified, friction-induced melts (pseudotachylytes) decorate some exhumed seismic faults, showing that melt can occur on natural faults, though its frequency is still a matter of debate. In the presence of melt, τ f undergoes an initial strengthening stage, followed by a dramatic weakening stage (thermal runaway). Field estimates based on pseudotachylyte thickness and experimental measures of τ f suggest large stress drops once thermal runaway is achieved. These estimates of τ f are compatible with large dynamic stress drops and high radiation efficiency, as observed for some Earthquakes. Moreover, the threshold for the onset of thermal runaway might explain differences between the Mechanics of small (M < 4) and large Earthquakes. A simple mathematical model coupling melting, extrusion and thermal diffusion reproduces some observed experimental features such as the duration of the weakening stage and the convergence to a steady-state.
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Earthquakes in the Lab
Science, 2012Co-Authors: Toshihiko Shimamoto, Tetsuhiro TogoAbstract:Understanding how Earthquakes of different sizes occur is one of the most challenging questions in fault and Earthquake Mechanics. On page 101 of this issue, Chang et al. ( 1 ) report the results of a carefully conducted experiment using a spinning flywheel attached to a high-velocity frictional testing machine to produce what they term an Earthquake-like slip event. By changing the rate of revolution of the flywheel, the amount of kinetic energy transferred to the simulated fault in Sierra White granite or Kasota dolomite could be varied by about six orders of magnitude and could produce a series of frictional slips ranging from 0.003 to 4.6 m, corresponding to a moment magnitude range of M w = 4 to 8 with respect to the range of fault displacements. The power relationship between energy input and displacement is similar to that found for natural Earthquakes. Also, the slip produced by the flywheel is characterized by very rapid initial acceleration followed by gradual deceleration, somewhat similar to slip history recognized for natural Earthquakes ( 2 ). Such experiments will arouse discussions about whether they are realistic proxies of natural Earthquakes.
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Fault lubrication during Earthquakes
Nature, 2011Co-Authors: G. Di Toro, Stefan Nielsen, Takehiro Hirose, N. De Paola, Kazuo Mizoguchi, Francesca Ferri, Massimo Cocco, Toshihiko ShimamotoAbstract:A review of about 300 published and unpublished rock friction experiments that reproduce seismic slip conditions suggests that a significant decrease in friction occurs at high slip rate. Extrapolating the experimental data to conditions that are typical of Earthquake nucleation depths, the authors conclude that faults are lubricated during Earthquakes, irrespective of the fault rock composition or specific weakening mechanism involved. This study reviews a large set of fault friction experiments and finds that a significant decrease in friction occurs at high slip rate. Extrapolating the experimental data to conditions typical of Earthquake nucleation depths, it is concluded that faults are lubricated during Earthquakes, irrespective of the fault rock composition or specific weakening mechanism involved. The determination of rock friction at seismic slip rates (about 1 m s−1) is of paramount importance in Earthquake Mechanics, as fault friction controls the stress drop, the mechanical work and the frictional heat generated during slip1. Given the difficulty in determining friction by seismological methods1, elucidating constraints are derived from experimental studies2,3,4,5,6,7,8,9. Here we review a large set of published and unpublished experiments (∼300) performed in rotary shear apparatus at slip rates of 0.1–2.6 m s−1. The experiments indicate a significant decrease in friction (of up to one order of magnitude), which we term fault lubrication, both for cohesive (silicate-built4,5,6, quartz-built3 and carbonate-built7,8) rocks and non-cohesive rocks (clay-rich9, anhydrite, gypsum and dolomite10 gouges) typical of crustal seismogenic sources. The available mechanical work and the associated temperature rise in the slipping zone trigger11,12 a number of physicochemical processes (gelification, decarbonation and dehydration reactions, melting and so on) whose products are responsible for fault lubrication. The similarity between (1) experimental and natural fault products and (2) mechanical work measures resulting from these laboratory experiments and seismological estimates13,14 suggests that it is reasonable to extrapolate experimental data to conditions typical of Earthquake nucleation depths (7–15 km). It seems that faults are lubricated during Earthquakes, irrespective of the fault rock composition and of the specific weakening mechanism involved.
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Frictional melting of peridotite and seismic slip
Journal of Geophysical Research, 2009Co-Authors: P. Del Gaudio, Stefan Nielsen, G. Di Toro, Toshihiko Shimamoto, Takehiro Hirose, Andrea CavalloAbstract:[1] The evolution of the frictional strength along a fault at seismic slip rates (about 1 m/s) is a key factor controlling Earthquake Mechanics. At mantle depths, friction-induced melting and melt lubrication may influence Earthquake slip and seismological data. We report on laboratory experiments designed to investigate dynamic fault strength and frictional melting processes in mantle rocks. We performed 20 experiments with Balmuccia peridotite in a high-velocity rotary shear apparatus and cylindrical samples (21.8 mm in diameter) over a wide range of normal stresses (5.4–16.1 MPa), slip rates (0.23–1.14 m/s), and displacements (1.5–71 m). During the experiments, shear stress evolved with cumulative displacement in five main stages (stages 1–5). In stage 1 (first strengthening), the coefficient of friction μ increased up to 0.4–0.7 (first peak in friction). In stage 2 (abrupt first weakening), μ decreased to about 0.25–0.40. In stage 3 (gradual second strengthening), shear stress increased toward a second peak in friction (μ = 0.30–0.40). In stage 4 (gradual second weakening), the shear stress decreased toward a steady state value (stage 5) with μ = 0.15. Stages 1 and 2 are of too short duration to be investigated in detail with the current experimental configuration. By interrupting the experiments during stages 3, 4, and 5, microstructural (Field Emission Scanning Electron Microscope) and geochemical (Electron Probe Micro-Analyzer and Energy Dispersive X-Ray Spectroscopy) analysis of the slipping zone suggest that second strengthening (stage 3) is associated with the production of a grain-supported melt-poor layer, while second weakening (stage 4) and steady state (stage 5) are associated with the formation of a continuous melt-rich layer with an estimated temperature up to 1780°C. Microstructures formed during the experiments were very similar to those found in natural ultramafic pseudotachylytes. By performing experiments at different normal stresses and slip rates, (1) the “thermal” (as it includes the thermally activated first and second weakening) slip distance to achieve steady state from the first peak in strength decreased with increasing normal stress and slip rate and (2) the steady state shear stress slightly increased with increasing normal stress and, for a given normal stress, decreased with increasing slip rate. The ratio of shear stress versus normal stress was about 0.15, well below the typical friction coefficient of rocks (0.6–0.8). The dependence of steady state shear stress with normal stress was described by means of a constitutive equation for melt lubrication. The presence of microstructures similar to those found in natural pseudotachylytes and the determination of a constitutive equation that describes the experimental data allows extrapolation of the experimental observations to natural conditions and to the study of rupture dynamics in mantle rocks.
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high velocity frictional properties of a clay bearing fault gouge and implications for Earthquake Mechanics
Journal of Geophysical Research, 2008Co-Authors: Nicolas Brantut, Alexandre Schubnel, J N Rouzaud, Fabrice Brunet, Toshihiko ShimamotoAbstract:[1] Frictional properties of natural kaolinite-bearing gouge samples from the Median Tectonic Line (SW Japan) have been studied using a high-velocity rotary shear apparatus, and deformed samples have been observed with optical and electron (scanning and transmission) microscopy. For a slip velocity of 1 m s−1 and normal stresses from 0.3 to 1.3 MPa, a dramatic slip-weakening behavior was observed. X-ray diffraction analysis of deformed samples and additional high-velocity friction experiments on pure kaolinite indicate kaolinite dehydration during slip. The critical slip-weakening distance Dc is of the order of 1 to 10 m. These values are extrapolated to higher normal stresses, assuming that Dc is rather a thermal parameter than a parameter related to a true characteristic length. The calculation shows that dimensionally, Dc ∝ 1/σn2, where σn is the normal stress applied on the fault. The inferred Dc values range from a few centimeters at 10 MPa normal stress to a few hundreds of microns at 100 MPa normal stress. Microscopic observations show partial amorphization and dramatic grain size reduction (down to the nanometer scale) localized in a narrow zone of about 1 to 10 μm thickness. Fracture energy Gc is calculated from the mechanical curves and compared to surface energy due to grain size reduction, and energies of mineralogic transformations. We show that most of the fracture energy is either converted into heat or radiated energy. The geophysical consequences of thermal dehydration of bonded water during seismic slip are then commented in the light of mineralogical and poromechanical data of several fault zones, which tend to show that this phenomenon has to be taken into account in most of subsurface faults and in hydrous rocks of subducted oceanic crust.
Linda M Warren - One of the best experts on this subject based on the ideXlab platform.
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Earthquake Mechanics and deformation in the Tonga‐Kermadec subduction zone from fault plane orientations of intermediate‐ and deep‐focus Earthquakes
Journal of Geophysical Research, 2007Co-Authors: Linda M Warren, Amanda N Hughes, Paul G SilverAbstract:[1] We make use of rupture directivity to analyze 82 deep Earthquakes (≥100 km depth) in the Tonga-Kermadec subduction zone. Identifying the fault planes for 25 of them, we are able to place new constraints on both the physical mechanism of intermediate- and deep-focus Earthquakes and deformation within the subducting slab. We find that half of deep Earthquakes with MW ≥ 6 have detectable directivity. We compare the obtained fault orientations with those expected for the reactivation of outer-rise normal faults and with those expected for the creation of new faults in response to the ambient stress field. Earthquakes >300 km depth match the patterns expected for the creation of a new system of faults: we observe both subhorizontal and subvertical fault planes consistent with a downdip-compressional stress field. Slip along these faults causes the slab to thicken. Rupture propagation shows no systematic directional pattern. In contrast, at intermediate depths (100–300 km), all ruptures propagate subhorizontally and all identified fault planes, whether in the upper or lower region of the double seismic zone, are subhorizontal. Rupture propagation tends to be directed away from the top surface of the slab. After accounting for the angle of subduction, the subhorizontal fault plane orientation is inconsistent with the orientation of outer-rise normal faults, allowing us to rule out mechanisms that require the reactivation of these large surface faults. Subhorizontal faults are consistent with only one of the two failure planes expected from the slab stress field, suggesting that isobaric rupture processes or preexisting slab structures may also influence the fault plane orientation. If all deformation takes place on these subhorizontal faults, it would cause the slab to thin. Assuming the slab is incompressible, this implies that the slab is also lengthening and suggests that slab pull rather than unbending is the primary force controlling slab seismicity at intermediate depths.
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Earthquake Mechanics and deformation in the tonga kermadec subduction zone from fault plane orientations of intermediate and deep focus Earthquakes
Journal of Geophysical Research, 2007Co-Authors: Linda M Warren, Amanda N Hughes, Paul G SilverAbstract:[1] We make use of rupture directivity to analyze 82 deep Earthquakes (≥100 km depth) in the Tonga-Kermadec subduction zone. Identifying the fault planes for 25 of them, we are able to place new constraints on both the physical mechanism of intermediate- and deep-focus Earthquakes and deformation within the subducting slab. We find that half of deep Earthquakes with MW ≥ 6 have detectable directivity. We compare the obtained fault orientations with those expected for the reactivation of outer-rise normal faults and with those expected for the creation of new faults in response to the ambient stress field. Earthquakes >300 km depth match the patterns expected for the creation of a new system of faults: we observe both subhorizontal and subvertical fault planes consistent with a downdip-compressional stress field. Slip along these faults causes the slab to thicken. Rupture propagation shows no systematic directional pattern. In contrast, at intermediate depths (100–300 km), all ruptures propagate subhorizontally and all identified fault planes, whether in the upper or lower region of the double seismic zone, are subhorizontal. Rupture propagation tends to be directed away from the top surface of the slab. After accounting for the angle of subduction, the subhorizontal fault plane orientation is inconsistent with the orientation of outer-rise normal faults, allowing us to rule out mechanisms that require the reactivation of these large surface faults. Subhorizontal faults are consistent with only one of the two failure planes expected from the slab stress field, suggesting that isobaric rupture processes or preexisting slab structures may also influence the fault plane orientation. If all deformation takes place on these subhorizontal faults, it would cause the slab to thin. Assuming the slab is incompressible, this implies that the slab is also lengthening and suggests that slab pull rather than unbending is the primary force controlling slab seismicity at intermediate depths.
Paul G Silver - One of the best experts on this subject based on the ideXlab platform.
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Earthquake Mechanics and deformation in the Tonga‐Kermadec subduction zone from fault plane orientations of intermediate‐ and deep‐focus Earthquakes
Journal of Geophysical Research, 2007Co-Authors: Linda M Warren, Amanda N Hughes, Paul G SilverAbstract:[1] We make use of rupture directivity to analyze 82 deep Earthquakes (≥100 km depth) in the Tonga-Kermadec subduction zone. Identifying the fault planes for 25 of them, we are able to place new constraints on both the physical mechanism of intermediate- and deep-focus Earthquakes and deformation within the subducting slab. We find that half of deep Earthquakes with MW ≥ 6 have detectable directivity. We compare the obtained fault orientations with those expected for the reactivation of outer-rise normal faults and with those expected for the creation of new faults in response to the ambient stress field. Earthquakes >300 km depth match the patterns expected for the creation of a new system of faults: we observe both subhorizontal and subvertical fault planes consistent with a downdip-compressional stress field. Slip along these faults causes the slab to thicken. Rupture propagation shows no systematic directional pattern. In contrast, at intermediate depths (100–300 km), all ruptures propagate subhorizontally and all identified fault planes, whether in the upper or lower region of the double seismic zone, are subhorizontal. Rupture propagation tends to be directed away from the top surface of the slab. After accounting for the angle of subduction, the subhorizontal fault plane orientation is inconsistent with the orientation of outer-rise normal faults, allowing us to rule out mechanisms that require the reactivation of these large surface faults. Subhorizontal faults are consistent with only one of the two failure planes expected from the slab stress field, suggesting that isobaric rupture processes or preexisting slab structures may also influence the fault plane orientation. If all deformation takes place on these subhorizontal faults, it would cause the slab to thin. Assuming the slab is incompressible, this implies that the slab is also lengthening and suggests that slab pull rather than unbending is the primary force controlling slab seismicity at intermediate depths.
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Earthquake Mechanics and deformation in the tonga kermadec subduction zone from fault plane orientations of intermediate and deep focus Earthquakes
Journal of Geophysical Research, 2007Co-Authors: Linda M Warren, Amanda N Hughes, Paul G SilverAbstract:[1] We make use of rupture directivity to analyze 82 deep Earthquakes (≥100 km depth) in the Tonga-Kermadec subduction zone. Identifying the fault planes for 25 of them, we are able to place new constraints on both the physical mechanism of intermediate- and deep-focus Earthquakes and deformation within the subducting slab. We find that half of deep Earthquakes with MW ≥ 6 have detectable directivity. We compare the obtained fault orientations with those expected for the reactivation of outer-rise normal faults and with those expected for the creation of new faults in response to the ambient stress field. Earthquakes >300 km depth match the patterns expected for the creation of a new system of faults: we observe both subhorizontal and subvertical fault planes consistent with a downdip-compressional stress field. Slip along these faults causes the slab to thicken. Rupture propagation shows no systematic directional pattern. In contrast, at intermediate depths (100–300 km), all ruptures propagate subhorizontally and all identified fault planes, whether in the upper or lower region of the double seismic zone, are subhorizontal. Rupture propagation tends to be directed away from the top surface of the slab. After accounting for the angle of subduction, the subhorizontal fault plane orientation is inconsistent with the orientation of outer-rise normal faults, allowing us to rule out mechanisms that require the reactivation of these large surface faults. Subhorizontal faults are consistent with only one of the two failure planes expected from the slab stress field, suggesting that isobaric rupture processes or preexisting slab structures may also influence the fault plane orientation. If all deformation takes place on these subhorizontal faults, it would cause the slab to thin. Assuming the slab is incompressible, this implies that the slab is also lengthening and suggests that slab pull rather than unbending is the primary force controlling slab seismicity at intermediate depths.
