Dilatancy And The Seismic Focal Mechanism

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Ductile Precambrian fabric control of seismic anisotropy in

extensive dilatancy anisotropy (EDA) [Crampin, 1987; crust and may be a more significant mechanism for producing seismic anisotropy than vertical fluid-filled posite focal mechanism in the


the focal region. The time scales of the above processes would presumably be quite different. In alternatives 1 and 2 one must postulate that crack closure or redistribution is part of the natural sequence of events that follow onset of dilatancy and precede failure.

Index [assets.cambridge.org]

fault-plane solution see focal mechanism faults and tectonic regions, by location Africa Rift system, 323 4 Witwatersrand, section 6.5.3 Alaska Aleutian Arc, 284 5 California Calaveras, 334 6 Camp Rock/Emerson, 212 14 Cleghorn, 162 Coyote Creek, 175 Eastern California shear zone, 212, 250 Elmore Ranch, 242 Hayward, 237, 334 6

Yun Liu,132 Stuart Crampin' and Rachael E. Abercrombie3'*

tation inferred from focal mechanism studies (Jones 1988) in the area is in a N17 W direction, consistent with the right- lateral strike-slip motion on the major fault and with the principal horizontal strain measurements in the area (Savage, Prescott & Gu 1986). However, this cannot explain the exist-

Magnetic transfer function entropy and the 2009 w 6.3 L

seismic velocities, electrical conductivity and crustal defor-mations may occur (Wyss, 1997). In order to explain such observed phenomena, many models have been proposed and among those most often referred to, there is the dilatancy model which represents essentially an increase in porosity (Brace et al., 1966; Brace, 1975).

Tectonics, magmatism and paleo-fluid distribution in a strike

seismic activity (Haberland et al., 2006; Lange et al., 2008) is present throughout the LOFS. At the southern termination of LOFS (Aysén Fjord) a seismic swarm occurred in April 2007 together with a Mw 6.2 earthquake at 12 km of depth, with a right-lateral focal mechanism at a NS-striking fault plane (Fig. 1a) (Legrand et al., 2011). Similarly, at

Publications of Yehuda Ben-Zion Books / Special Volumes

temporal changes of shallow seismic velocities at the Garner Valley near Anza, California, in relation to the M7.2 2010 El Mayor-Cucapah earthquake, J Geophys.

Index [assets.cambridge.org]

earthquake focal mechanism 7, 15, 17, 145, 158 auxiliary plane 18 B axis 18 beach balls 158 compressional quadrant 159 dilatational quadrant 159 fault plane 18 inversion of multiple mechanisms 162 low friction fault planes 161 nodal planes 159 normal faulting focal mechanism 160 P axis 18, 161 relation to principal stresses 161, 187, 189


mechanism which generates electrical potential, caused, by diffusion of fluid into a dilatant, focal region. The details of this mechanism are demonstrated in the following figure (3.1.1). Fig. 3.1.1. Schematic diagram of electric double layer and velocity profile utilized, in a capillary (after Mizutani et al. 1976).

Slow Slip Predictions Based on Granit and Gabbro Friction

uous GPS observations. Section 5 discusses fault dilatancy as a mechanism for generating slow slip events over a much larger range of velocity-weakening fault and its implication for the downdip limit of a megathrust earthquake rupture, potential 3-D effects and differences in using the ageing and slip state evolution laws. 2. Model Setup 2.1.

International Journal of Rock Mechanics and Mining Sciences

Focal mechanism Asperity Acoustic emission Implosion Compaction ABSTRACT Fault heterogeneities such as bumps, bends, and stepovers are commonly observed on natural faults, but are challenging to recreate under controlled laboratory conditions. We study deformation and microseismicity of a


deployed in the New Madrid seismic zone, central USA, since October, 1989. Three major earthquakes(nr > 7) occurred in the zone in 18 I 1- 12 and the area is subject to constant microearthquake activity at focal depths of 3 to 1.5 km. The station density and signal frequencies of 8 to IO Hz, recorded at 100 Hz, provide an opportu-

Constraints on Friction, Dilatancy, Diffusivity, and

is aseismic rather than seismic. Similar to Hawthorne and Rubin (2010) our application of triggering models will be to slow slip. The other class of models (Perfettini & Schmittbuhl, 2001) is specific to earthquake occurrence in regions where the predominant strain release mechanism is aseismic slip and the seismic moment is a small fraction


with that predicted from dilatancy model. The various stages of the earth-quake cycle are shown in Fig. 2A. In addition, the dilatancy model predicts that, as pore pressure decreases and effective stress increases during stage II and part of stage III (Fig. 1), dila-tancy hardening should occur and the seismic activity should decrease. Figure

Rheology and stress in subduction zones around the aseismic

mechanism for slow events. This may involve a component of hydraulic fracture, as suggested by the fact that they occur in a zone characterized by high Vp/Vs ratios (e.g., Beroza and Ide 2010), indicating high water content. Tremor and slow slip events have also been attributed to Fig. 1 The seismic-aseismic transition in a subduction zone.

Best Available - DTIC

SEISMIC WAVES FOR THE IDENTIFICATION OP SEISMIC SOURCES. OCSCRIPTIVE NOTES (Typt ol report and Inclutlve dale ) Scientific Interim 5 UTHORISI (FitH name, middle inlllal, latl name) Keith ;4cCamy REPORT DATE T October 1973 CONTRACT OR GRANT NO AI^PA Order No. 1795 Fi962ö-71-C-02il5 6. PROJECT NO 1795-00-01

Hydrogeological responses to the 2016 Gyeongju earthquakes, 2

62 earthquake in Korea since instrumental seismic monitoring started in Korea in 1978. The 63 source mechanism of the Gyeongju earthquakes displayed strike-slip movement of a branch 64 of the Yangsan Fault (YSF) passing through the Gyeongju area (Kim et al., 2017b;Kim et al., 65 2016). Slip analysis and earthquake focal mechanism solutions have

Quantitative Geophysics and Geology

12.9 Focal mechanism and real fracture mechanism 249 12.10 Stick-slip motion and earthquake recurrence 252 12.11 Aseismic slip and silent earthquakes 253 12.12 Intermediate and deep earthquakes 256 12.13 Seismic hazard estimation from historical earthquakes 256 12.14 Palaeoseismicity 259 12.15 Long- and medium-term seismic prediction 260


seismic activity and source mechanism. ICHIKAWA (1971) has described some features of the focal mechanism of a number of subcrustal earthquakes during the period from 1926 to 1968, which include the present earthquake and some of its aftershocks. His results show that normal faulting earthquakes pre-Fig. 1.


earthquake, on December 14, 1975, indicate a focal mechanism similar to that of the Galway Lake earthquake, but rotated slightly counterclockwise; vertical planes strike N30°W and N60°E. Epicenters for aftershocks are too tightly clustered to indicate a fault plane. Depths range from 2 to 10 kin.

Near-field ground motion during earthquake preparation process

terms of the changes in dilatancy around the focal zone and saturation of dilatancy-formed cracks. The wave velocities for the cracked elastic solids have been approximated by Garvin and Knopoff (1973, 1975a,b). O'Connell and Budiansky (1974) and Budiansky and O'Connell (1976) calculated


and precursor time interval based on the dilatancy model. The size of the anomalous region, in this case, was estimated to be about two times as large as the aftershock area. The temporal variations of the b value in the earthquake frequency- magnitude relation and the seismic activity near the focal region were also investigated.

1965-24 9th Workshop on Three-Dimensional Modelling of

Information from double couple focal mechanisms Data produced by fault plane solutions Focal mechanisms of pure shear faults (no significant dilatancy), yield for both nodal planes the dip and azimuth of the plane (d and a) as well as the slip direction in the plane (rake angle r of slip vector s) when it corresponds to the fault plane

Foreshock Characteristics in Taiwan: Potential Earthquake Warning

Foreshock Characteristics in Taiwan: Potential Earthquake Warning Cheng-Horng Lin Institute of Earth Sciences, Academia Sinica. 2010/9/14

Publishing - IOPscience

semi-automatically from the seismic waveforms, and expressed mathematically in the formof the seismicmoment tensor.Visual representation of thefocal mechanism uses the so-called beachball diagram. Different areas of our globe have typical focal mechanisms to that demonstrated in figure 1.1 (Kagan and Jackson 2014).

Seismic precursors linked to super-critical fluids at oceanic

Seismic precursors linked to super-critical fluids at oceanic transform focal mechanism and earth dilatancy via the fluid compressibility and a possible link

Magnetotellurics and Seismotectonics in the Analysis of

formation, crack-tofault processes and volume dilatancy by microfi-acturing, the reader is referred to Scholz (1990) and Teisseyre (1995). Healing processes are expected to close the cracks and reduce conductivity, unless they are kept open by continuous accu- mulation of deformation, either seismic or aseismic. Thus, the

Dilatant Strengthening as a Mechanism for Slow Slip Events

defines dilatancy-efficiency, where h is shear-zone thickness. SSE are favored by large ǫh and low effective stress. The ratio E p to thermal-pressurization efficiency scales with 1/(σ− p∞), implying high p∞ favors SSE, consistent with seismic observations. For E p ∼ 10−3

Shear-wave splitting in the crust: Regional compressive

et al., 2000). Seismic anisotropy in the crust typical-ly originates from stress-aligned fluid-saturated grain-boundary cracks and pore throats, which have been called extensive-dilatancy anisotropy (EDA) cracks ∗Received 7 October 2011; accepted in revised form 12 December 2011; published 10 February 2012.

Hattori: ULF Geomagnetic Changes & Earthquakes

ance of a conductive area in the focal region preceding an earthquake. An increase of electric conductivity at the focal area is likely due to the dilatancy-diffusion (Scholz et al. 1973). That is, the flow of underground water into the focal region plays an important role. A conventional

Structural permeability of fluid-driven fault-fracture meshes

composite strike-slip focal mechanism (after Hagiwara & Iwata 1968, Ichikawa 1969, Tsuneishi & Nakamura 1970). Structural permeability of fault-fracture meshes 1033 slip fault-fracture mesh

Modeling crustal deformation and rupture processes related to

The swarm was accompanied by seismic focal area expan- inducing dilatancy in the fault-crust system identified recently as a driving mechanism for an earthquake

Earthquake Prediction: A Physical Basis

Aug 01, 2017 with that predicted from the dilatancy model. The various stages of the earth-quake cycle are shown in Fig. 2A. In addition, the dilatancy model predicts that, as pore pressure decreases and effective stress increases during stage II and part of stage III (Fig. 1), dila-tancy hardening should occur and the seismic activity should decrease. Figure

Multidisciplinary Approach Earthquake

Preliminary StudiesofSeismic RiskinTurkey, and the Occurrence ofUpperBounded and OtherLarge Earthquake Magnitudes 143 M. Tokay Faults andRecentlyActive BreaksAlongthe NorthAnatolian FaultZoneBetweenGeredeand Ilgaz 173 T. Ah]os, H. Korhonen,J. Saari SomeAspectsofthe SeismicityintheNorth Anatolian Fault Zone 185 B. Sikosek

GEOLOGY Copyright © 2018 Do slow slip events trigger large

fluids could weaken this region through dilatancy hardening (2) or other mechanism. Further updip, conditions once again favor slow slip and do so persistently (6, 20). If the seismogenic zone is close to failure, as was the case for 2012 earthquake when the Nicoya seg-ment was more than 20% past its average 50-year characteristic

Foreshocks and short-term hazard assessment of large

April 2009. The focal mechanism of the L Aquila mainshock (star) was calculated by INGV. Note the dense concentration of foreshock epicenters close to the mainshock epicenter in the last 10 days pre-ceding the mainshock occurrence, which indicates that foreshocks moved towards the mainshock nucleation area.

Proceedings of the 7th International Conference Problems of

Kiyoo Mogi [8] has paid attention to the fact that in focal areas of strongest earthquakes the seismic activity decreases in the same way, and at the same time seismic activity increases in neighboring regions (so-called ring-type form of seismicity). But just such form of seismicity is characteristic for reservoir-induced earthquakes.

A multiscale study of the mechanisms controlling shear

A multiscale study of the mechanisms controlling shear velocity anisotropy in the San Andreas Fault Observatory at Depth Naomi L. Boness1 and Mark D. Zoback2 ABSTRACT

Seismological Studies for Tensile Faults

sumed that volume dilatancy occurs within a fault zone as slip occurs during nucleation prior to a macroscopic shear crack. The fault zone dilatancy mechanism may be either joint dilatancy, in which the fault walls must move apart to accommodate slip, or dilatancy due to shear of granular materials, such as gouge or breccia, within a fault zone. If