scholarly journals Scaling seismic fault thickness from the laboratory to the field

2021 ◽  
Author(s):  
Thomas P. Ferrand ◽  
Stefan Nielsen ◽  
Loïc Labrousse ◽  
Alexandre Schubnel
Keyword(s):  
Energy Balance ◽  
Fault Plane ◽  
Relative Displacement ◽  
Seismic Fault ◽  
First Approximation ◽  
Scaling Relationship ◽  
Suspension Viscosity ◽  
Solid Suspension ◽  
Shear Heating ◽  
Heating Up

<p>Pseudotachylytes originate from the solidification of frictional melt, which transiently forms and lubricates the fault plane during an earthquake. Here we observe how the pseudotachylyte thickness <em>a</em> scales with the relative displacement <em>D</em> both at the laboratory and field scales, for measured slip varying from microns to meters, over six orders of magnitude. Considering all the data jointly, a bend appears in the scaling relationship when slip and thickness reach ∼1 mm and 100 µm, respectively, i.e. <em>M</em><sub>W</sub> > 1. This bend can be attributed to the melt thickness reaching a steady‐state value due to melting dynamics under shear heating, as is suggested by the solution of a Stefan problem with a migrating boundary. Each increment of fault is heating up due to fast shearing near the rupture tip and starting cooling by thermal diffusion upon rupture. The building and sustainability of a connected melt layer depends on this energy balance. For plurimillimetric thicknesses (<em>a</em> > 1 mm), melt thickness growth reflects in first approximation the rate of shear heating which appears to decay in <em>D</em><sup>−1/2</sup> to <em>D</em><sup>−1</sup>, likely due to melt lubrication controlled by melt + solid suspension viscosity and mobility. The pseudotachylyte thickness scales with moment <em>M</em><sub>0</sub> and magnitude <em>M</em><sub>W</sub>; therefore, thickness alone may be used to estimate magnitude on fossil faults in the field in the absence of displacement markers within a reasonable error margin.</p>

Computer program for a fault-plane solution

1963 ◽  
Vol 53 (1) ◽  
pp. 1-13
Author(s):  
Keichi Kasahara
Keyword(s):  
Probability Function ◽  
Fault Plane ◽  
Successive Approximations ◽  
Standard Errors ◽  
Machine Time ◽  
The Past ◽  
First Approximation ◽  
Plane Solution ◽  
Earthquake Mechanism ◽  
Time Required

Abstract In its earthquake mechanism studies the Dominion Observatory has been producing solutions graphically, but a program based on a probability function defined by Knopoff has been written for the IBM 1620 which permits the best solution to be obtained by a series of successive approximations from a given first approximation. The program prints out the strike and dip of the two nodal planes, their standard errors, the azimuth and plunge of their line of intersection, and a list of the stations producing inconsistent data. Weights can be assigned to each station; in practice these weights would depend on the past reliablity of the station. The machine time required depends on the number of stations used, the accuracy of the first approximation and other factors; in general 20 to 30 minutes is required for a solution involving 30-40 stations.

Fault-plane solution for the Tango, Japan, earthquake of March 7, 1927*

1955 ◽  
Vol 45 (1) ◽  
pp. 37-41
Author(s):  
John H. Hodgson
Keyword(s):  
Fault Plane ◽  
Independent Solution ◽  
Relative Displacement ◽  
Fault Plane Solution ◽  
First Motion ◽  
Plane Solution

Abstract In an attempt to obtain confirmation of the fault-plane methods in use by the Dominion Observatory by comparison with an observed fault, a solution has been attempted for the Tango, Japan, earthquake of March 7, 1927. The direction of first motion was read from seismograms, accumulated for an earlier study by E. A. Hodgson, and filed at Ottawa. The data derived from the records are not sufficient to allow an independent solution that is very closely defined, but it is shown that they do satisfy the known strike, dip, and relative displacement very well.

Seismic fault attribute estimation using a local fault model

Geophysics ◽  
2019 ◽  
Vol 84 (4) ◽  
pp. O73-O80 ◽  
Author(s):  
Yihuai Lou ◽  
Bo Zhang ◽  
Ruiqi Wang ◽  
Tengfei Lin ◽  
Danping Cao
Keyword(s):  
Seismic Data ◽  
Fault Plane ◽  
3D Seismic ◽  
Seismic Amplitude ◽  
Seismic Fault ◽  
Analysis Window ◽  
Full Analysis ◽  
Fault Interpretation ◽  
Analysis Point ◽  
Staircase Artifacts

Faults in the subsurface can be an avenue of, or a barrier to, hydrocarbon flow and pressure communication. Manual interpretation of discontinuities on 3D seismic amplitude volume is the most common way to define faults within a reservoir. Unfortunately, 3D seismic fault interpretation can be a time-consuming and tedious task. Seismic attributes such as coherence help define faults, but suffer from “staircase” artifacts and nonfault-related stratigraphic discontinuities. We assume that each sample of the seismic data is located at a potential fault plane. The hypothesized fault divides the seismic data centered at the analysis sample into two subwindows. We then compute the coherence for the two subwindows and full analysis window. We repeat the process by rotating the hypothesized fault plane along a set of user-defined discrete fault dip and azimuth. We obtain almost the same coherence values for the subwindows and the full window if the analysis point is not located at a fault plane. The “best” fault plane results in maximum coherence for the subwindows and minimum coherence for the full window if the analysis point is located at a fault plane. To improve the continuity of the fault attributes, we finally smooth the fault probability attribute along the estimated fault plane. We illustrate the effectiveness of our workflow by applying it to a synthetic and two real seismic data. The results indicate that our workflow successfully produces a continuous fault attribute without staircase artifacts and stratigraphic discontinuities.

On shear heating as an explanation for lithosphere–mantle decoupling

1978 ◽  
Vol 15 (8) ◽  
pp. 1284-1291
Author(s):  
T. J. T. Spanos ◽  
E. Nyland
Keyword(s):  
Material Properties ◽  
Shear Velocity ◽  
Final Solution ◽  
Low Velocity ◽  
Low Viscosity ◽  
Plate Velocity ◽  
First Approximation ◽  
Shear Heating ◽  
Rate Relation ◽  
Velocity Zone

Exact solutions can be found for steady fluid flow under constant shear, even if the stress–strain rate relation is nonlinear and shear heating connects the material properties to thermal behaviour. We present such solutions for a Newtonian material in which viscosity decreases exponentially with temperature, and for two empirical equations valid for high temperature creep. The onset of melting limits the range in which these solutions are applicable. If we assume that the region of the low velocity zone for shear waves is close to melting and that drag on this region by plates appears to a first approximation as a constant stress, we can predict surprisingly reasonable values for the plate velocity with respect to the mantle. The low viscosity of the zone becomes a consequence of melt induced by shear heating. Such melt would also explain a low Q and a reduction in shear velocity. A final solution is then given for an inhomogeneous material whose viscosity increases with depth. This can be interpreted as a material whose melting point increases with depth at a faster rate than the temperature of the material.

scholarly journals Seismic fault weakening via CO2 pressurization enhanced by mechanical deformation of dolomite fault gouges

Geology ◽  
2021 ◽  
Author(s):  
Hyun Na Kim ◽  
Byung-Dal So ◽  
Min Sik Kim ◽  
Kee Sung Han ◽  
Sol Bi Oh
Keyword(s):  
Carbon Dioxide Emissions ◽  
Fault Plane ◽  
High Energy ◽  
X Ray Diffraction ◽  
Effective Normal Stress ◽  
Seismic Fault ◽  
High Energy Ball Mill ◽  
Crystalline Dolomite ◽  
Fault Gouges ◽  
Low Crystalline

Carbon dioxide emissions from dolomite decarbonation play an essential role in the weakening of carbonate faults by lowering the effective normal stress, which is thermally activated at temperatures above 600–700 °C. However, the mechanochemical effect of low-crystalline ultrafine fault gouge on the decarbonation and slip behavior of dolomite-bearing faults remains unclear. In this study, we obtained a series of artificial dolomite fault gouges with systematically varying particle sizes and dolomite crystallinities using a high-energy ball mill. The laboratory-scale pulverization of dolomite yielded MgO at temperatures below 50 °C, indicating that mechanical decarbonation without significant heating occurred due to the collapse of the crystalline structure, as revealed by X-ray diffraction and solid-state nuclear magnetic resonance results. Furthermore, the onset temperature of thermal decarbonation decreased to ~400 °C. Numerical modeling reproduced this two-stage decarbonation, where the pore pressure increased due to low-temperature thermal decarbonation, leading to slip weakening on the fault plane even at 400–500 °C; i.e., 200–300 °C lower than previously reported temperatures. Thus, the presence of small amounts of low-crystalline dolomite in a fault plane may lead to a severely reduced shear strength due to thermal decomposition at ~400 °C with a small slip weakening distance.

scholarly journals Experimental evidence for crustal control over seismic fault segmentation

Geology ◽  
2020 ◽  
Vol 48 (8) ◽  
pp. 844-848
Author(s):  
M. Lefevre ◽  
P. Souloumiac ◽  
N. Cubas ◽  
Y. Klinger
Keyword(s):  
Brittle Material ◽  
Strike Slip ◽  
Segment Length ◽  
Physical Parameters ◽  
Structural Development ◽  
Seismic Fault ◽  
Geometrical Complexity ◽  
Scaling Relationship ◽  
Earthquake Ruptures ◽  
Analogue Models

Abstract Strike-slip faults are generally described as continuous structures, while they are actually formed of successive segments separated by geometrical complexities. Although this along-strike segmentation is known to affect the overall dynamics of earthquakes, the physical processes governing the scale of this segmentation remain unclear. Here, we use analogue models to investigate the structural development of strike-slip faults and the physical parameters controlling segmentation. We show that the length of fault segments is regular along strike and scales linearly with the thickness of the brittle material. Variations of the rheological properties only have minor effects on the scaling relationship. Ratios between the segment length and the brittle material thickness are similar for coseismic ruptures and sandbox experiments. This supports a model where crustal seismogenic thickness controls fault geometry. Finally, we show that the geometrical complexity acquired during strike-slip fault formation withstands cumulative displacement. Thus, the inherited complexity impedes the formation of an ever-straighter fault, and might control the length of earthquake ruptures.

scholarly journals Models of ice-atmosphere interactions for the Greenland ice sheet

1996 ◽  
Vol 23 ◽  
pp. 149-153 ◽  
Author(s):  
Roger J. Braithwaite
Keyword(s):  
Energy Balance ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Physical Models ◽  
Balance Model ◽  
Ice Dynamics ◽  
Degree Day ◽  
A Value ◽  
First Approximation ◽  
Dynamics Models

Simple models to calculate melt and refreezing are reviewed. Both degree-day and energy-balance models can give distributed melt inputs to ice-dynamics models but have only been tested extensively in West Greenland, and more data are needed from the remoter parts of Greenland. The energy-balance model is more realistic but needs input data that are not generally available over the whole ice sheet. On the other hand, degree-day factors vary from situation to situation although a value of about 8 kg m−2 d−1 deg−1 for ice ablation is a reasonable first approximation as assumed in recent ice-dynamics models. Meltwater refreezing in the accumulation area can be modelled very simply but more detailed physical models are needed to describe the shifts in accumulation zones under different climates.

scholarly journals Models of ice-atmosphere interactions for the Greenland ice sheet

1996 ◽  
Vol 23 ◽  
pp. 149-153 ◽  
Author(s):  
Roger J. Braithwaite
Keyword(s):  
Energy Balance ◽  
Ice Sheet ◽  
Greenland Ice Sheet ◽  
Physical Models ◽  
Balance Model ◽  
Ice Dynamics ◽  
Degree Day ◽  
A Value ◽  
First Approximation ◽  
Dynamics Models

Simple models to calculate melt and refreezing are reviewed. Both degree-day and energy-balance models can give distributed melt inputs to ice-dynamics models but have only been tested extensively in West Greenland, and more data are needed from the remoter parts of Greenland. The energy-balance model is more realistic but needs input data that are not generally available over the whole ice sheet. On the other hand, degree-day factors vary from situation to situation although a value of about 8 kg m−2d−1deg−1for ice ablation is a reasonable first approximation as assumed in recent ice-dynamics models. Meltwater refreezing in the accumulation area can be modelled very simply but more detailed physical models are needed to describe the shifts in accumulation zones under different climates.

Sign in / Sign up

Export Citation Format

Share Document