Signature of transition to supershear rupture speed in the coseismic off-fault damage zone

Most earthquake ruptures propagate at speeds below the shear wave velocity within the crust, but in some rare cases, ruptures reach supershear speeds. The physics underlying the transition of natural subshear earthquakes to supershear ones is currently not fully understood. Most observational studies of supershear earthquakes have focused on determining which fault segments sustain fully grown supershear ruptures. Experimentally cross-validated numerical models have identified some of the key ingredients required to trigger a transition to supershear speed. However, the conditions for such a transition in nature are still unclear, including the precise location of this transition. In this work, we provide theoretical and numerical insights to identify the precise location of such a transition in nature. We use fracture mechanics arguments with multiple numerical models to identify the signature of supershear transition in coseismic off-fault damage. We then cross-validate this signature with high-resolution observations of fault zone width and early aftershock distributions. We confirm that the location of the transition from subshear to supershear speed is characterized by a decrease in the width of the coseismic off-fault damage zone. We thus help refine the precise location of such a transition for natural supershear earthquakes.

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Episodic fluid flow in an active fault

Geology ◽

10.1130/g46254.1 ◽

2019 ◽

Vol 47 (10) ◽

pp. 938-942 ◽

Cited By ~ 8

Author(s):

Sarah Louis ◽

Elco Luijendijk ◽

István Dunkl ◽

Mark Person

Keyword(s):

Fluid Flow ◽

Numerical Models ◽

Damage Zone ◽

Normal Fault ◽

Geothermal Gradient ◽

Hydrothermal Activity ◽

The Past ◽

Discharge Rates ◽

Fault Damage Zone ◽

Wide Zone

Abstract We present a reconstruction of episodic fluid flow over the past ∼250 k.y. along the Malpais normal fault, which hosts the Beowawe hydrothermal system (Nevada, USA), using a novel combination of the apatite (U-Th)/He (AHe) thermochronometer and a model of the thermal effects of fluid flow. Samples show partial resetting of the AHe thermochronometer in a 40-m-wide zone around the fault. Numerical models using current fluid temperatures and discharge rates indicate that fluid flow events lasting 2 k.y. or more lead to fully reset samples. Episodic fluid pulses lasting 1 k.y. result in partially reset samples, with 30–40 individual fluid pulses required to match the data. Episodic fluid flow is also supported by an overturned geothermal gradient in a borehole that crosses the fault, and by breaks in stable isotope trends in hydrothermal sinter deposits that coincide with two independently dated earthquakes in the past 20 k.y. This suggests a system where fluid flow is triggered by repeated seismic activity, and that seals itself over ∼1 k.y. due to the formation of clays and silicates in the fault damage zone. Hydrothermal activity is younger than the 6–10 Ma age of the fault, which means that deep (∼5 km) fluid flow was initiated only after a large part of the 230 m of fault offset had taken place.

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Thermochronology and REE analyses as new tools to track thermal anomaly and fluid flow along a crustal scale fault (Têt fault, French Pyrenees)

10.5194/egusphere-egu2020-8850 ◽

2020 ◽

Author(s):

Gaétan Milesi ◽

Monié Patrick ◽

Philippe Münch ◽

Roger Soliva ◽

Sylvain Mayolle ◽

...

Keyword(s):

Numerical Modelling ◽

Hot Springs ◽

Hot Spring ◽

Numerical Models ◽

Hanging Wall ◽

Damage Zone ◽

Thermal Anomaly ◽

Geothermal Gradient ◽

Fault Damage Zone ◽

Hydrothermal Flow

The T&#234;t fault is a crustal scale major fault in the eastern Pyrenees that displays about 30 hot springs along its surface trace with temperatures between 29&#176;C and 73&#176;C. The regional process of fluid circulation at depth has previously been highlighted by thermal numerical modelling supported by hydrochemical analyses and tectonic study. Numerical modelling suggests the presence of a strong subsurface anomaly of temperature along-fault (locally > 90&#176;C/km), governed by topography-driven meteoric fluid upflow through the fault damage zone (advection). On the basis of this modelling, we focused our thermochronological study on 30 samples collected close and between two hot spring clusters in both the hanging wall and the footwall of the T&#234;t fault, where the most important thermal anomaly is recorded by models. We analysed apatite using (U-Th)/He (AHe) dating combined with REE analyses on the same dated grains.Along the fault, AHe ages are in a range of 26 to 8 Ma in the footwall and 43 and 18 Ma in the hanging wall, and only few apatite grains have been impacted by hydrothermalism near the St-Thomas hot spring cluster. By contrast, particularly young AHe ages below 6 Ma, correlated to REE depletion, are found around the Thu&#232;s-les-bains hot spring cluster. These very young ages are therefore interpreted as thermal resetting due to an important hydrothermal activity. A thermal anomaly can be mapped and appears restricted to 1 km around this cluster of hot springs, i.e. more restricted than the size of the anomaly predicted by numerical models. These results reveal that AHe dating and REE analyses can be used to highlight neo- or paleo-hydrothermal anomaly recorded by rocks along faults.This study brings new elements to discuss the onset of the hydrothermal circulations and consequences on AHe and REE mobilisation, and suggest a strong heterogeneity of the hydrothermal flow pattern into the fault damage zone. Moreover, this study suggests that crustal scale faults adjacent to reliefs can localise narrow high hydrothermal flow and important geothermal gradient.&#160;&#160;Besides these results, this study provides new constraints for geothermal exploration around crustal faults, as well as a discussion on the use of thermochronometers into fault damage zones.&#160;

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Probabilistic multiscale modeling of fracture in heterogeneous materials and structures

Industrial laboratory Diagnostics of materials ◽

10.26896/1028-6861-2020-86-7-45-54 ◽

2020 ◽

Vol 86 (7) ◽

pp. 45-54

Author(s):

A. M. Lepikhin ◽

N. A. Makhutov ◽

Yu. I. Shokin

Keyword(s):

Monte Carlo ◽

Monte Carlo Method ◽

Fracture Mechanics ◽

Multiscale Modeling ◽

Virtual Work ◽

Numerical Models ◽

Heterogeneous Materials ◽

Heterogeneous Structure ◽

Generalized Coordinates ◽

Heterogeneous Structures

The probabilistic aspects of multiscale modeling of the fracture of heterogeneous structures are considered. An approach combining homogenization methods with phenomenological and numerical models of fracture mechanics is proposed to solve the problems of assessing the probabilities of destruction of structurally heterogeneous materials. A model of a generalized heterogeneous structure consisting of heterogeneous materials and regions of different scales containing cracks and crack-like defects is formulated. Linking of scales is carried out using kinematic conditions and multiscale principle of virtual forces. The probability of destruction is formulated as the conditional probability of successive nested fracture events of different scales. Cracks and crack-like defects are considered the main sources of fracture. The distribution of defects is represented in the form of Poisson ensembles. Critical stresses at the tops of cracks are described by the Weibull model. Analytical expressions for the fracture probabilities of multiscale heterogeneous structures with multilevel limit states are obtained. An approach based on a modified Monte Carlo method of statistical modeling is proposed to assess the fracture probabilities taking into account the real morphology of heterogeneous structures. A feature of the proposed method is the use of a three-level fracture scheme with numerical solution of the problems at the micro, meso and macro scales. The main variables are generalized forces of the crack propagation and crack growth resistance. Crack sizes are considered generalized coordinates. To reduce the dimensionality, the problem of fracture mechanics is reformulated into the problem of stability of a heterogeneous structure under load with variations of generalized coordinates and analysis of the virtual work of generalized forces. Expressions for estimating the fracture probabilities using a modified Monte Carlo method for multiscale heterogeneous structures are obtained. The prospects of using the developed approaches to assess the fracture probabilities and address the problems of risk analysis of heterogeneous structures are shown.

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Fault controls on spatial variation of fracture density and rock mass strength within the Yarlung Tsangpo Fault damage zone (southeastern Tibet)

Engineering Geology ◽

10.1016/j.enggeo.2021.106238 ◽

2021 ◽

pp. 106238

Author(s):

Xueliang Wang ◽

Giovanni Battista Crosta ◽

John J. Clague ◽

Douglas Stead ◽

Juanjuan Sun ◽

...

Keyword(s):

Rock Mass ◽

Spatial Variation ◽

Damage Zone ◽

Fracture Density ◽

Rock Mass Strength ◽

Fault Damage Zone ◽

Yarlung Tsangpo ◽

Southeastern Tibet

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Probing Be star disks: new insights from Hα spectroscopy and detailed numerical models

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311010908 ◽

2010 ◽

Vol 6 (S272) ◽

pp. 398-399 ◽

Cited By ~ 1

Author(s):

Carol E. Jones ◽

Christopher Tycner ◽

Jessie Silaj ◽

Ashly Smith ◽

T. A. Aaron Sigut

Keyword(s):

High Resolution ◽

Numerical Models ◽

Analytical Tool ◽

High Resolution Spectroscopy ◽

Be Stars ◽

Line Shapes ◽

Physical Conditions ◽

Temperature Distributions ◽

Inclination Angles ◽

Be Star

AbstractHα high resolution spectroscopy combined with detailed numerical models is used to probe the physical conditions, such as density, temperature, and velocity of Be star disks. Models have been constructed for Be stars over a range in spectral types and inclination angles. We find that a variety of line shapes can be obtained by keeping the inclination fixed and changing density alone. This is due to the fact that our models account for disk temperature distributions self-consistently from the requirement of radiative equilibrium. A new analytical tool, called the variability ratio, was developed to identify emission-line stars at particular stages of variability. It is used in this work to quantify changes in the Hα equivalent widths for our observed spectra.

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Modelling of interactions between dykes, inclined sheets and faults at Santorini volcano

10.5194/egusphere-egu21-6309 ◽

2021 ◽

Author(s):

Kyriaki Drymoni ◽

John Browning ◽

Agust Gudmundsson

Keyword(s):

Tensile Strength ◽

Fault Zone ◽

Numerical Models ◽

Damage Zone ◽

Sheet Thickness ◽

Analytical Models ◽

Energy Conditions ◽

Dyke Swarm ◽

Normal Faults ◽

Santorini Volcano

Dykes and inclined sheets are known occasionally to exploit faults as parts of their paths, but the conditions that allow this to happen are still not fully understood. Here we report field observations from a well-exposed dyke swarm of the Santorini volcano, Greece, that show dykes and inclined sheets deflected into faults and the results of analytical and numerical models to explain the conditions for deflection. The deflected dykes and sheets belong to a local swarm of 91 dyke/sheet segments that was emplaced in a highly heterogeneous and anisotropic host rock and partially cut by some regional faults and a series of historic caldera collapses, the caldera walls providing, excellent exposures of the structures. The numerical models focus on a normal-fault dipping 65&#176; with a damage zone composed of parallel layers or zones of progressively more compliant rocks with increasing distance from the fault rupture plane. We model sheet-intrusions dipping from 0&#730; to 90&#730; and with overpressures of alternatively 1 MPa and 5 MPa, approaching the fault. We further tested the effects of changing (1) the sheet thickness, (2) the fault-zone thickness, (3) the fault-zone dip-dimension (height), and (4) the loading by, alternatively, regional extension and compression. We find that the stiffness of the fault core, where a compliant core characterises recently active fault zones, has pronounced effects on the orientation and magnitudes of the local stresses and, thereby, on the likelihood of dyke/sheet deflection into the fault zone. Similarly, the analytical models, focusing on the fault-zone tensile strength and energy conditions for dyke/sheet deflection, indicate that dykes/sheets are most likely to be deflected into and use steeply dipping recently active (zero tensile-strength) normal faults as parts of their paths.

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High Resolution 3‐D Shear Wave Velocity Model of Northern Taiwan via Bayesian Joint Inversion of Rayleigh Wave Ellipticity and Phase Velocity with Formosa Array

Journal of Geophysical Research Solid Earth ◽

10.1029/2020jb021610 ◽

2021 ◽

Author(s):

Cheng‐Nan Liu ◽

Fan‐Chi Lin ◽

Hsin‐Hua Huang ◽

Yu Wang ◽

Elizabeth M. Berg ◽

...

Keyword(s):

High Resolution ◽

Phase Velocity ◽

Rayleigh Wave ◽

Shear Wave ◽

Wave Velocity ◽

Shear Wave Velocity ◽

Joint Inversion ◽

Velocity Model ◽

Northern Taiwan

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The South Georgia Wave Experiment: A Means for Improved Analysis of Gravity Waves and Low-Level Wind Impacts Generated from Mountainous Islands

Bulletin of the American Meteorological Society ◽

10.1175/bams-d-16-0151.1 ◽

2018 ◽

Vol 99 (5) ◽

pp. 1027-1040 ◽

Cited By ~ 7

Author(s):

D. R. Jackson ◽

A. Gadian ◽

N. P. Hindley ◽

L. Hoffmann ◽

J. Hughes ◽

...

Keyword(s):

High Resolution ◽

Gravity Waves ◽

Numerical Models ◽

Small Island ◽

Small Scale ◽

The South ◽

South Georgia ◽

Low Level ◽

Wave Experiment ◽

Realistic Representation

AbstractGravity waves (GWs) play an important role in many atmospheric processes. However, the observation-based understanding of GWs is limited, and representing them in numerical models is difficult. Recent studies show that small islands can be intense sources of GWs, with climatologically significant effects on the atmospheric circulation. South Georgia, in the South Atlantic, is a notable source of such “small island” waves. GWs are usually too small scale to be resolved by current models, so their effects are represented approximately using resolved model fields (parameterization). However, the small-island waves are not well represented by such parameterizations, and the explicit representation of GWs in very-high-resolution models is still in its infancy. Steep islands such as South Georgia are also known to generate low-level wakes, affecting the flow hundreds of kilometers downwind. These wakes are also poorly represented in models.We present results from the South Georgia Wave Experiment (SG-WEX) for 5 July 2015. Analysis of GWs from satellite observations is augmented by radiosonde observations made from South Georgia. Simulations were also made using high-resolution configurations of the Met Office Unified Model (UM). Comparison with observations indicates that the UM performs well for this case, with realistic representation of GW patterns and low-level wakes. Examination of a longer simulation period suggests that the wakes generally are well represented by the model. The realism of these simulations suggests they can be used to develop parameterizations for use at coarser model resolutions.

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A Microphysical Bulk Formulation Based on Scaling Normalization of the Particle Size Distribution. Part I: Description

Journal of the Atmospheric Sciences ◽

10.1175/jas3620.1 ◽

2005 ◽

Vol 62 (12) ◽

pp. 4206-4221 ◽

Cited By ~ 27

Author(s):

Wanda Szyrmer ◽

Stéphane Laroche ◽

Isztar Zawadzki

Keyword(s):

Particle Size ◽

High Resolution ◽

Particle Size Distribution ◽

Size Distribution ◽

Numerical Models ◽

Radar Data ◽

Retrieval Algorithm ◽

Microphysical Processes ◽

The Moment ◽

Microphysical Parameterization

Abstract The authors address the problem of optimization of the microphysical information extracted from a simulation system composed of high-resolution numerical models and multiparameter radar data or other available measurements. As a tool in the exploration of this question, a bulk microphysical scheme based on the general approach of scaling normalization of particle size distribution (PSD) is proposed. This approach does not rely on a particular functional form imposed on the PSD and naturally leads to power-law relationships between the PSD moments providing an accurate and compact PSD representation. To take into account the possible evolution of the shape/curvature of the distribution, ignored within standard one- and two-moment microphysical schemes, a new three-moment scheme based on the two-moment scaling normalization is proposed. The methodology of the moment retrieval included in the three-moment scheme can also be useful as a retrieval algorithm combining different remote sensing observations. The developed bulk microphysical scheme presents a unified formulation for microphysical parameterization using one, two, or three independent moments, suitable in the context of data assimilation. The effectiveness of the scheme with different combinations of independent moments is evaluated by comparison with a very high resolution spectral model within a 1D framework on representative microphysical processes: rain sedimentation and evaporation.

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