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  • 1
    Publication Date: 2016-07-13
    Description: The travel lengths of rockfalls and rockslides can be difficult to predict due to complex interactions of numerous physical processes, such as fragmentation of the rock mass and its effect on the energy dissipation through basal and internal friction. Previous studies have shown that the front of the rockslide deposits travels farther with increased fragmentation. However, little is known about the displacement of the center of mass, which is the relevant parameter for studying the energy budget, leaving open the question whether fragmentation acts as an effective sink or source of energy. Taking advantage of a newly developed rock analogue material, we perform a total of 109 experiments to study the effect of fragmentation on the displacement of the center of mass and the energy budget of experimental rockslides. To determine the degree of fragmentation, we define a characteristic fragment size from the total mass of the experimental sample and the mass of the largest fragment. The degree of fragmentation is seen to depend linearly on the aspect ratio of the experimental sample, and as a power law on its cohesion. Similar to the previous studies, our results show that the travel distance of the front of the deposits increases with the degree of fragmentation. In contrast, displacement of the center of mass is reduced with the degree of fragmentation, suggesting increased energy consumption, consistent with the assumption that fragmentation acts effectively as an energy sink.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
    Publication Date: 2015-05-30
    Description: Viscoelastic effects potentially play an important role during all phases of the earthquake cycle in subduction zones. However, most current models neglect such effects in the interseismic deformation pattern. Here we use Finite Element Method (FEM) models to investigate the control of viscoelasticity on interseismic deformation, and to highlight the pitfalls of interpreting the data with purely elastic models for both the forward and inverse problems. Our results confirm that elastic models are prone to overestimating the interseismic locking depth, a crucial parameter for estimating the maximum possible earthquake magnitude. The application of the viscoelastic model improves the fit to the interseismic deformation, especially in the inland area. Additionally, we construct 3-D FEM models constrained by geophysical and GPS data and apply our methodology to the Peru - North Chile subduction zone. Our results indicate that viscoelastic effects contribute significantly to the observed GPS data. The signals interpreted as back-arc shortening in the elastic model can be alternatively explained by viscoelastic deformation, which, in turn, dramatically refines the interseismic locking pattern in both dip and strike directions. Our viscoelastic locking map exhibits excellent correlation with the slip distributions of previous earthquakes, especially the recent 2014 Mw 8.1 Iquique earthquake. The incorrect elastic assumptions affect the analysis of interseismic deformation with respect to slip deficit calculations. Our results thus suggest that it is necessary to thoroughly re-evaluate existing locking models that are based on purely elastic models, some of which attribute viscoelastic deformation to different sources such as microplate sliver motions.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
    Publication Date: 2016-08-30
    Description: Analog sandbox experiments are an important tool to understand brittle tectonic deformation. To date, most experiments are interpreted kinematically only. With the advent of reliable, small scale force sensors, however, their dynamic evolution becomes available for analysis, offering new insights into the transient evolution of tectonic systems. Both rock and granular materials show an evolution of strain hardening and weakening during loading in the brittle-plastic regime, but so far this similarity has only been appreciated qualitatively. As strain weakening is a vital parameter controlling fault reactivation and lifetime, it requires proper scaling. We therefore measured and analyzed two common granular analog model materials (quartz sand and glass micro beads) using ring-shear tests at a range of normal loads typical for analog experiments. We find two different modes of strain weakening as a function of normal load: Strain weakening at normal loads 〈1kPa is due to partial loss of extrapolated cohesion, while at normal loads 〉1kPa it is controlled by reduction of internal friction, which is consistent with previous measurements in this range. We show that this introduces a scale-dependence into the scaling and restricts the possible use of the tested materials to crustal scale models with a length scaling factor of . For these we quantitatively compare the model materials' transient strength evolution to that known from natural rock and the earth' crust.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
    Publication Date: 2014-01-14
    Description: [1]  We have investigated the influence that megathrust earthquake slip has on the activation of splay faults using a 2D Finite Element Method (FEM), taking into account the effects of gravity and variations in the frictional strength properties of splay faults. We simulated both landward-dipping and seaward-dipping splay fault geometries, and imposed depth-variable slip distributions of subduction events. Our results indicate that the two types of splay fault exhibit a similar behavior, with variations in frictional properties along the faults affecting only the seismic magnitude. The triggering process is controlled by a critical depth. Megathrust slip concentrated at depths shallower than the critical depth will favor normal displacement, while megathrust slip concentrated at depths deeper than the critical depth is likely to result in reverse motion. Our results thus provide a useful tool for predicting the activation of secondary faults and may have direct implications for tsunami hazard research.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
    Publication Date: 2019
    Description: Abstract The magnitude of great subduction megathrust earthquakes is controlled mainly by the number of adjacent asperities failing synchronously and the resulting rupture length. Here we investigate experimentally the long‐term recurrence behavior of a pair of asperities coupled by static stress transfer over hundreds of seismic cycles. We statistically analyze long (c. 500 ka) time‐series of M8‐9 analogue earthquakes simulated using a seismotectonic scale model approach with two aims: First, to constrain probabilistic measures (frequency‐size distribution, variability) useful for hazard assessment and, second, to relate them with geometric observables (coseismic slip pattern, locking pattern). We find that the number of synchronized asperity failures relative to the number of individual asperity failures as well as the coefficients of variation of recurrence intervals and seismic moment scale with the logarithm of stress coupling between the asperities. Accordingly, tighter packed asperities tend to recur more periodically and with a more characteristic magnitude while more distant asperities show clustering of more variable sized events. The probability of synchronized failures seems to be controlled to first order by geometrical relations (i.e. spacing and offset of asperities. The effects of rheological properties are evident but it remains to be explored to which extent they vary in nature and how sensitive the system is to those.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Publication Date: 2017-08-04
    Description: The majority of the largest subduction megathrust earthquakes share the common characteristic of rupturing more than one asperity along strike of the margin. Understanding the factors that control coseismic failure of multiple asperities, and thus maximum magnitude, is central for seismic hazard assessment. To investigate the role of asperities size and spacing on maximum magnitude, seismicity rate and percentage of synchronized ruptures, we use analog models simulating along-strike rupture behavior of megathrust earthquakes. We found negative correlations between the barrier-to-asperity length ratio Db/Da and maximum magnitude and seismicity rate. Db/Da also controls the process of asperities synchronization along the megathrust. A permanent barrier behavior is observed for Db/Da 〉0.5. Comparing our experimental results to the Nankai Trough historical seismicity, we propose that the distribution of megathrust frictional heterogeneities likely explains the diversity of earthquakes which occurred there.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
    Publication Date: 2017-02-19
    Description: Postseismic surface deformation associated with great subduction earthquakes is controlled by asthenosphere rheology, frictional properties of the fault, and structural complexity. Here, by modeling GPS displacements in the six years following the 2010 Mw 8.8 Maule earthquake in Chile, we investigate the impact of heterogeneous viscosity distribution in the South American sub-continental asthenosphere on the 3-D postseismic deformation pattern. The observed postseismic deformation is characterized by flexure of the South America plate with peak uplift in the Andean mountain range and subsidence in the hinterland. We find that, at the timescale of observation, over two orders of magnitude gradual increase in asthenosphere viscosity from the arc area towards the cratonic hinterland is needed to jointly explain horizontal and vertical displacements. Our findings present an efficient method to estimate spatial variations of viscosity, which clearly improves the fitting to the vertical signal of deformation. Lateral changes in asthenosphere viscosity can be correlated with the thermomechanical transition from weak sub-volcanic arc mantle to strong sub-cratonic mantle thus suggesting a stationary heterogeneous viscosity structure. However, we cannot rule out a transient viscosity structure (e.g. power law rheology) with the short time span of observation.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
    Publication Date: 2017-12-15
    Description: Analog sandbox experiments are a widely used method to investigate tectonic processes that cannot be resolved from natural data alone, such as strain localization and the formation of fault zones. Despite this, it is still unclear, to which extent the dynamics of strain localization and fault zone formation seen in sandbox experiments can be extrapolated to a natural prototype. Of paramount importance for dynamic similarity is the proper scaling of the work required to create the fault system, W prop . Using analog sandbox experiments of strike-slip deformation, we show W prop to scale approximately with the square of the fault system length, l , which is consistent with the theory of fault growth in nature. Through quantitative measurements of both W prop and strain distribution we are able to show that W prop is mainly spent on diffuse deformation prior to localization, which we therefore regard as analogous to distributed deformation on small-scale faults below seismic resolution in natural fault networks. Finally, we compare our data to estimates of the work consumed by natural fault zones to verify that analog sandbox experiments scale properly with respect to energy, i.e. that they scale truly dynamically.
    Print ISSN: 0278-7407
    Electronic ISSN: 1944-9194
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
    Publication Date: 2022-02-16
    Description: Abstract
    Description: This dataset includes particle image correlation data from 26 experiments performed with Foamquake, a novel analog seismotectonic model reproducing the megathrust seismic cycle. The seismotectonic model has been monitored by the means of a high-resolution top-view monitoring camera. The dataset presented here represents the particle image velocimetry surface velocity field extracted during the experimental model through the cross-correlation between consecutive images. This dataset is supplementary to Mastella et al. (2021) where detailed descriptions of models and experimental results can be found.
    Description: Methods
    Description: Foamquake is a scaled seismotectonic model that reproduces the key features of a generic natural megathrust. The experimental setup is composed of a Plexiglass box where a flat-topped elastic foam rubber wedge with a dimension of 145x90x20 cm^3 (the overriding plate analog) overlaying a planar, 10° dipping rigid plate (the subducting plate analog). The model is free to move laterally for 5 cm within the Plexiglass box. Thus, it is not affected by friction acting at the two sides of the foam wedge. Instead, the rear (i.e., the thickest side) of the vertical wedge is confined by a rigid vertical backstop. The interface between the foam and the lower plate mimics the megathrust interface. Along the rigid subducting plate, a plastic conveyor belt moves downward at the constant velocity of 0.01 cm/s reproducing a steady trench-orthogonal subduction. Along the plate interface a 1 cm layer of granular material (i.e., rice) mimics a seismic asperity surrounded by sand reproducing the heterogeneous frictional configuration of the analog fault zone. Due to the physical properties of granular materials placed along the analog megathrust, Foamquake experiences stick-slip behavior. This behavior, can be described in the rate and state framework, results in the quasi-periodic spontaneous nucleation of frictional instabilities within the rice layer, named foamquakes. The rice is characterized by a velocity weakening frictional behavior while the sand is characterized by velocity neutral behavior. As a consequence, analog earthquakes nucleate within the granular seismic asperity, while the sand tends to inhibit the rupture propagation. Given the 3D nature of the setup, models with more than one asperity can be performed with Foamquake. This dataset includes data from 22 models with a single-asperity configuration. Those models differ from each other by a variation of the normal load applied above the asperity and of the along trench asperity length. This repository also includes data derived from 4 models characterized by the presence of two asperities divided by a barrier.
    Keywords: subduction megathrust earthquakes ; asperities ; multi-scale laboratories ; EPOS ; Analog modelling results ; deformation ; geologic process ; tectonic process ; subduction ; Particle Image Velocimetry (PIV) ; analogue models of geological processes ; MatPIV ; Earthquake simulator ; earthquake ; seismic activity ; geological process ; seismic activity ; thrust fault ; subduction zones ; plate margin setting ; Wedge simulator ; EARTH SCIENCE 〉 SOLID EARTH 〉 TECTONICS 〉 EARTHQUAKES ; EARTH SCIENCE 〉 SOLID EARTH 〉 TECTONICS 〉 PLATE TECTONICS 〉 PLATE BOUNDARIES ; EARTH SCIENCE SERVICES 〉 MODELS 〉 GEOLOGIC/TECTONIC/PALEOCLIMATE MODELS ; EARTH SCIENCE SERVICES 〉 MODELS 〉 PHYSICAL/LABORATORY MODELS ; geological process 〉 seismic activity 〉 earthquake ; lithosphere 〉 earth's crust 〉 fault
    Type: Dataset , Dataset
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