Inverse Modeling of Earthquake Source Properties Constrained by Pseudotachylite Surface Roughness

2021 ◽  
Author(s):  
Donglai Yang ◽  
Phillip Resor
Keyword(s):  
Shear Stress ◽  
Shear Zone ◽  
Stress Drop ◽  
Scaling Laws ◽  
Moving Boundary ◽  
Internal Heat ◽  
Bayesian Optimization ◽  
Rock Surface ◽  
Kinematic Parameters ◽  
Topographic Relief

<p>Under high rates of coseismic slip, frictional melt may be generated at the shear zone potentially altering the dynamics and rendering classical rate-and-state friction laws ineffective. Pseudotachylytes (solidified frictional melt) created in laboratories and found in natural fault zones thus provide thermal and mechanical information critical to the study of dynamic shear zone processes, including thermal runaway, stress drop, and viscous braking. While extensive geochemical and mineralogical evidence has suggested the occurrence of disequilibrium melting during pseudotachylite generation, few studies have leveraged it to resolve the kinematics of co-seismic slip.</p><p>In this study, we optimize the kinematic parameters of the regularized Yoffe source function using the topographic relief of a pseudotachylyte/wall rock surface in combination with a one-dimensional fluid-mechanical-thermal finite element model. The model consists of solving a two-phase moving boundary problem with an internal heat source constrained by the slip kinematics of the Yoffe function in tandem with the Couette flow problem as an approximation to the shearing of the viscous melt. The topographic relief data come from a pseudotachylyte-bearing fault within the Gole Larghe fault zone, Italy measured using high-resolution X-ray tomography. On this fault surface, biotites are ~260 (±100) micron lower than the mean surface height as a result of preferential melting associated with a lower fusion temperature than quartz or feldspar. Using Monte Carlo sampling of the relief data distribution and Bayesian optimization, we optimize the kinematic parameters of the regularized Yoffe functions and resolve the statistics of shear stress evolution.</p><p>Our preliminary results show that the displacement-averaged shear stress in frictional melt ranges from 2 to 7 MPa with a mean value of 5.5 MPa. This is much smaller than estimates based on pseudotachylyte thickness and laboratory experiments, indicating a more complete stress drop than previously thought. The optimal Yoffe source functions have a mean total rise time of ~4 seconds, which is longer than that inferred from scaling laws. Simulations are ongoing and we look forward to interpreting the results in the context of source properties, source models, and energy partitioning for pseudotachylyte-bearing faults.</p>

Rotation of the principal stress directions due to earthquake faulting and its seismological implications

1995 ◽  
Vol 85 (5) ◽  
pp. 1513-1517
Author(s):  
Z.-M. Yin ◽  
G. C. Rogers
Keyword(s):  
Shear Stress ◽  
Normal Stress ◽  
Principal Stress ◽  
Stress Drop ◽  
Rotation Angle ◽  
Overburden Pressure ◽  
Rupture Area ◽  
Earthquake Faulting ◽  
Stress Directions ◽  
Before And After

Abstract Earthquake faulting results in stress drop over the rupture area. Because the stress drop is only in the shear stress and there is no or little stress drop in the normal stress on the fault, the principal stress directions must rotate to adapt such a change of the state of stress. Using two constraints, i.e., the normal stress on the fault and the vertical stress (the overburden pressure), which do not change before and after the earthquake, we derive simple expressions for the rotation angle in the σ1 axis. For a dip-slip earthquake, the rotation angle is only a function of the stress-drop ratio (defined as the ratio of the stress drop to the initial shear stress) and the angle between the σ1 axis and the fault plane, but for a strike-slip earthquake the rotation angle is also a function of the stress ratio. Depending on the faulting regimes, the σ1 axis can either rotate toward the direction of fault normal or rotate away from the direction of fault normal. The rotation of the stress field has several important seismological implications. It may play a significant role in the generation of heterogeneous stresses and in the occurrence and distribution of aftershocks. The rotation angle can be used to estimate the stress-drop ratio, which has been a long-lasting topic of debate in seismology.

scholarly journals Ice Stream C, Antarctica, sticky spots detected by microearthquake monitoring

1994 ◽  
Vol 20 ◽  
pp. 183-186 ◽  
Author(s):  
S. Anandakrishnan ◽  
R. B. Alley
Keyword(s):  
Shear Stress ◽  
Stress Drop ◽  
Fast Moving ◽  
Fault Plane ◽  
Spatial Density ◽  
Ice Stream ◽  
Slow Moving ◽  
Ice Stream B ◽  
Basal Shear ◽  
Plane Area

Microearthquakes at the base of slow-moving Ice Stream C occur many times more frequently than at the base of fast-moving Ice Stream B. We suggest that the microearthquake source sites are so-called “sticky spots”, defined as limited zones of stronger Subglacial material interspersed within a weaker matrix. The fault-plane area of the microearthquakes (O(102m2)) is therefore a measure of the size of the sticky spots. The spatial density of the microearthquakes (O(10 km-2)) is a measure of the distribution of sticky spots.The average stress drop associated with these microearthquakes is consistent with an ice-stream bed model of weak subglacial till interspersed with stronger zones that support much or all of the basal shear stress. We infer a weak inter-sticky-spot material by the large distances (O(103m)), relative to fault radius, to which the microearthquake stress change is transmitted.

scholarly journals Convection in an internally heated stratified heterogeneous reservoir

2019 ◽  
Vol 870 ◽  
pp. 67-105 ◽  
Author(s):  
Angela Limare ◽  
Claude Jaupart ◽  
Edouard Kaminski ◽  
Loic Fourel ◽  
Cinzia G. Farnetani
Keyword(s):  
Heat Source ◽  
Scaling Laws ◽  
Lower Layer ◽  
Thermal Structure ◽  
Internal Heat ◽  
Source Distribution ◽  
Heat Sources ◽  
Homogeneous Fluid ◽  
Earth’S Mantle ◽  
Lower Fluid

The Earth’s mantle is chemically heterogeneous and probably includes primordial material that has not been affected by melting and attendant depletion of heat-producing radioactive elements. One consequence is that mantle internal heat sources are not distributed uniformly. Convection induces mixing, such that the flow pattern, the heat source distribution and the thermal structure are continuously evolving. These phenomena are studied in the laboratory using a novel microwave-based experimental set-up for convection in internally heated systems. We follow the development of convection and mixing in an initially stratified fluid made of two layers with different physical properties and heat source concentrations lying above an adiabatic base. For relevance to the Earth’s mantle, the upper layer is thicker and depleted in heat sources compared to the lower one. The thermal structure tends towards that of a homogeneous fluid with a well-defined time constant that scales with $Ra_{H}^{-1/4}$, where $Ra_{H}$ is the Rayleigh–Roberts number for the homogenized fluid. We identified two convection regimes. In the dome regime, large domes of lower fluid protrude into the upper layer and remain stable for long time intervals. In the stratified regime, cusp-like upwellings develop at the edges of large basins in the lower layer. Due to mixing, the volume of lower fluid decreases to zero over a finite time. Empirical scaling laws for the duration of mixing and for the peak temperature difference between the two fluids are derived and allow extrapolation to planetary mantles.

scholarly journals The Deep Structure and Rheology of a Plate Boundary-Scale Shear Zone: Constraints from an Exhumed Caledonian Shear Zone, NW Scotland

Lithosphere ◽  
2020 ◽  
Vol 2020 (1) ◽  
Author(s):  
Alexander D. J. Lusk ◽  
John P. Platt
Keyword(s):  
Shear Stress ◽  
Internal Structure ◽  
Shear Zone ◽  
Deep Structure ◽  
Plate Boundary ◽  
Seismogenic Zone ◽  
Differential Stress ◽  
Peak Shear Stress ◽  
Thrust Zone ◽  
Crustal Strength

Abstract Below the seismogenic zone, faults are expressed as zones of distributed ductile strain in which minerals deform chiefly by crystal plastic and diffusional processes. We present a case study from the Caledonian frontal thrust system in northwest Scotland to better constrain the geometry, internal structure, and rheology of a major zone of reverse-sense shear below the brittle-to-ductile transition (BDT). Rocks now exposed at the surface preserve a range of shear zone conditions reflecting progressive exhumation of the shear zone during deformation. Field-based measurements of structural distance normal to the Moine Thrust Zone, which marks the approximate base of the shear zone, together with microstructural observations of active slip systems and the mechanisms of deformation and recrystallization in quartz, are paired with quantitative estimates of differential stress, deformation temperature, and pressure. These are used to reconstruct the internal structure and geometry of the Scandian shear zone from ~10 to 20 km depth. We document a shear zone that localizes upwards from a thickness of >2.5 km to <200 m with temperature ranging from ~450–350°C and differential stress from 15–225 MPa. We use estimates of deformation conditions in conjunction with independently calculated strain rates to compare between experimentally derived constitutive relationships and conditions observed in naturally-deformed rocks. Lastly, pressure and converted shear stress are used to construct a crustal strength profile through this contractional orogen. We calculate a peak shear stress of ~130 MPa in the shallowest rocks which were deformed at the BDT, decreasing to <10 MPa at depths of ~20 km. Our results are broadly consistent with previous studies which find that the BDT is the strongest region of the crust.

SECONDARY FAULTING: II. GEOLOGICAL ASPECTS

1966 ◽  
Vol 3 (2) ◽  
pp. 175-190 ◽  
Author(s):  
M. A. Chinnery
Keyword(s):  
Shear Stress ◽  
Shear Zone ◽  
Direct Result ◽  
End Effect ◽  
The Past ◽  
Fault Systems ◽  
San Andreas ◽  
Transcurrent Fault ◽  
Secondary Fault

A secondary fault is defined as a fracture which arises as a direct result of movement on a master transcurrent fault. Some previous approaches to the study of secondary faulting are discussed, and fallacies in the arguments of McKinstry (1953) and Moody and Hill (1956) are pointed out. The effect of movement on a fault is to reduce the initial shear stress everywhere except in the vicinity of the ends of the fault, where it causes complex additional stresses (see first paper in this series on the theoretical aspects of secondary faulting). Thus it is proposed that secondary faulting is an end effect of a master shear movement, and on this basis six major modes of secondary faulting, labelled types A to F, are described. The usefulness of these results in the analysis of fault systems is illustrated by applying them to the Alpine, San Andreas, and Mac Donald faults. In each case it is possible to predict or explain the curvature, location, and sense of the secondary faults in the area. In addition, the development of the master fault may be traced by locating the ends of the shear zone at various times in the past.

Simulation of Open Channel Turbulent Flow Over Bridge Decks and Formation of Scour Hole Beneath the Bridge Under Flooding Conditions

2009 ◽  
Author(s):  
Bishwadipa Adhikary ◽  
Pradip Majumdar ◽  
Milivoje Kostic ◽  
Steven A. Lottes
Keyword(s):  
Shear Stress ◽  
Turbulent Flow ◽  
Open Channel ◽  
Moving Boundary ◽  
Bridge Decks ◽  
Critical Shear Stress ◽  
Navier Stokes ◽  
Scour Hole ◽  
Scour Holes ◽  
Bed Roughness

This study is focused on the simulation of open channel turbulent flow over flooded laboratory scale bridge decks and formation of scour holes under various flooding conditions. Solutions for turbulent flow field are based on Reynolds Averaged Navier-Stokes (RANS) equations and turbulence closure models using the STAR-CD commercial computational fluid dynamics (CFD) software. An iterative computational methodology is developed for predicting equilibrium scour profiles using the single-phase flow model with a moving boundary formulation. The methodology relies on an empirical correlation for critical bed shear stress that is used to characterize the condition for onset of sediment motion and an effective bed roughness that is a function of sediment particle size. The computational model and iterative methodology were stable and converged to an equilibrium scour hole shape and size that compares reasonably well with experiment using a constant critical shear stress value.

scholarly journals Pressure and shear stress caused by raindrop impact at the soil surface: Scaling laws depending on the water depth

2016 ◽  
Vol 41 (9) ◽  
pp. 1199-1210 ◽  
Author(s):  
Amina Nouhou Bako ◽  
Frédéric Darboux ◽  
François James ◽  
Christophe Josserand ◽  
Carine Lucas
Keyword(s):  
Shear Stress ◽  
Water Depth ◽  
Scaling Laws ◽  
Soil Surface ◽  
Surface Scaling ◽  
Raindrop Impact

Shape dynamics and scaling laws for a body dissolving in fluid flow

2015 ◽  
Vol 765 ◽  
Author(s):  
Jinzi Mac Huang ◽  
M. Nicholas J. Moore ◽  
Leif Ristroph
Keyword(s):  
High Speed ◽  
Scaling Laws ◽  
Moving Boundary ◽  
Fluid Flows ◽  
Solute Concentration ◽  
Flow Speed ◽  
The Body ◽  
Body Volume ◽  
Flow State ◽  
Terminal Form

AbstractWhile fluid flows are known to promote dissolution of materials, such processes are poorly understood due to the coupled dynamics of the flow and the receding surface. We study this moving boundary problem through experiments in which hard candy bodies dissolve in laminar high-speed water flows. We find that different initial geometries are sculpted into a similar terminal form before ultimately vanishing, suggesting convergence to a stable shape–flow state. A model linking the flow and solute concentration shows how uniform boundary-layer thickness leads to uniform dissolution, allowing us to obtain an analytical expression for the terminal geometry. Newly derived scaling laws predict that the dissolution rate increases with the square root of the flow speed and that the body volume vanishes quadratically in time, both of which are confirmed by experimental measurements.

Crustal melt granites and migmatites along the Himalaya: melt source, segregation, transport and granite emplacement mechanisms

2009 ◽  
Vol 100 (1-2) ◽  
pp. 219-233 ◽  
Author(s):  
M. P. Searle ◽  
J. M. Cottle ◽  
M. J. Streule ◽  
D. J. Waters
Keyword(s):  
Partial Melting ◽  
Shear Zone ◽  
Internal Heat ◽  
Shear Zones ◽  
Source Rocks ◽  
Crustal Thickening ◽  
Main Central Thrust ◽  
Crustal Layer ◽  
Middle Crust ◽  
The Himalaya

ABSTRACTIndia–Asia collision resulted in crustal thickening and shortening, metamorphism and partial melting along the 2200 km-long Himalayan range. In the core of the Greater Himalaya, widespread in situ partial melting in sillimanite+K-feldspar gneisses resulted in formation of migmatites and Ms+Bt+Grt+Tur±Crd±Sil leucogranites, mainly by muscovite dehydration melting. Melting occurred at shallow depths (4–6 kbar; 15–20 km depth) in the middle crust, but not in the lower crust. 87Sr/86Sr ratios of leucogranites are very high (0·74–0·79) and heterogeneous, indicating a 100 crustal protolith. Melts were sourced from fertile muscovite-bearing pelites and quartzo-feldspathic gneisses of the Neo-Proterozoic Haimanta–Cheka Formations. Melting was induced through a combination of thermal relaxation due to crustal thickening and from high internal heat production rates within the Proterozoic source rocks in the middle crust. Himalayan granites have highly radiogenic Pb isotopes and extremely high uranium concentrations. Little or no heat was derived either from the mantle or from shear heating along thrust faults. Mid-crustal melting triggered southward ductile extrusion (channel flow) of a mid-crustal layer bounded by a crustal-scale thrust fault and shear zone (Main Central Thrust; MCT) along the base, and a low-angle ductile shear zone and normal fault (South Tibetan Detachment; STD) along the top. Multi-system thermochronology (U–Pb, Sm–Nd, 40Ar–39Ar and fission track dating) show that partial melting spanned ̃24–15 Ma and triggered mid-crustal flow between the simultaneously active shear zones of the MCT and STD. Granite melting was restricted in both time (Early Miocene) and space (middle crust) along the entire length of the Himalaya. Melts were channelled up via hydraulic fracturing into sheeted sill complexes from the underthrust Indian plate source beneath southern Tibet, and intruded for up to 100 km parallel to the foliation in the host sillimanite gneisses. Crystallisation of the leucogranites was immediately followed by rapid exhumation, cooling and enhanced erosion during the Early–Middle Miocene.

Allometric scaling of wall shear stress from mice to humans: quantification using cine phase-contrast MRI and computational fluid dynamics

2006 ◽  
Vol 291 (4) ◽  
pp. H1700-H1708 ◽  
Author(s):  
Joan M. Greve ◽  
Andrea S. Les ◽  
Beverly T. Tang ◽  
Mary T. Draney Blomme ◽  
Nathan M. Wilson ◽  
...  
Keyword(s):  
Shear Stress ◽  
Magnetic Resonance ◽  
Wall Shear Stress ◽  
Cardiovascular System ◽  
Phase Contrast ◽  
Scaling Laws ◽  
Allometric Scaling ◽  
Scaling Exponent ◽  
Infrarenal Aorta ◽  
Wall Shear

Allometric scaling laws relate structure or function between species of vastly different sizes. They have rarely been derived for hemodynamic parameters known to affect the cardiovascular system, e.g., wall shear stress (WSS). This work describes noninvasive methods to quantify and determine a scaling law for WSS. Geometry and blood flow velocities in the infrarenal aorta of mice and rats under isoflurane anesthesia were quantified using two-dimensional magnetic resonance angiography and phase-contrast magnetic resonance imaging at 4.7 tesla. Three-dimensional models constructed from anatomic data were discretized and used for computational fluid dynamic simulations using phase-contrast velocity imaging data as inlet boundary conditions. WSS was calculated along the infrarenal aorta and compared between species to formulate an allometric equation for WSS. Mean WSS along the infrarenal aorta was significantly greater in mice and rats compared with humans (87.6, 70.5, and 4.8 dyn/cm2, P < 0.01), and a scaling exponent of −0.38 ( R2 = 0.92) was determined. Manipulation of the murine genome has made small animal models standard surrogates for better understanding the healthy and diseased human cardiovascular system. It has therefore become increasingly important to understand how results scale from mouse to human. This noninvasive methodology provides the opportunity to serially quantify changes in WSS during disease progression and/or therapeutic intervention.

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