Earthquake Prediction: A Physical Basis

Scholz, Christopher H.; Sykes, Lynn R.; Aggarwal, Yash

doi:10.1126/science.181.4102.803

Cited by 1,023 publications

(422 citation statements)

References 17 publications

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“…Knowledge of the amount, size, and geometry of these cracks and how they effect the mechanical behavior of rock (peak strength, stiffness, and permeability) is extremely important in engineering endeavors and in the understanding of geological processes. In particular, the way in which fractures form and coalesce may have importance in earthquake understanding and prediction [Locknet, 1995;Scholz et al, 1973]. It has long been known that the strength of brittle rocks under compression depends on the growth of flaws and cracks and how these cracks propagate and coalesce into larger shear faults.…”

Section: Introductionmentioning

confidence: 99%

Micromechanical modeling of cracking and failure in brittle rocks

Hazzard¹,

Young²,

Maxwell³

2000

J. Geophys. Res.

240

108

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Abstract. Dynamic micromechanical models are used to analyze crack nucleation and propagation in brittle rock. Models of rock are created by bonding together thousands of individual particles at points of contact. The feasibility of using these bonded particle models to reproduce rock mechanical behavior is explored by comparing model behavior to results from actual laboratory tests on different rock types. The behavior of two granite models are examined in detail to study cracking and failure patterns that occur during compressional loading. Because discontinuum models are being used, the rock models are free to crack and break apart under stress, such that the micromechanics of cracking can be examined. Stress waves are allowed to propagate outward from each crack, and it is shown that these dynamic waves significantly affect the rock behavior. As the peak stress in the modeled rock is approached and many of the bonds are close to breaking, a passing wave from a nearby crack is sufficient to break more bonds. This causes clusters of cracks to be created, and then eventual macroscopic shear failure occurs as these clusters connect to bisect the sample. The failure patterns observed in the granite models are similar to those observed in actual laboratory tests. . These studies show that in sandstones, shear localization usually does not develop until after the peak stress has been reached. Most of the cracking occurring before the peak stress appears to be intergranular (between grains). This is a departure from low-porosity crystalline rocks (granite) in which many of the cracks are intragranular [Tapponnier and Brace, 1976]. In sandstones it appears that most cracking occurs along grain boundaries, either by widening of preexisting microcracks or by shear rupturing of the cement at the grain contacts caused by rotation and slip of the grains. The high level of acoustic emissions (AE) recorded during dilation gives evidence that this second process is occurring. 16,683

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Section: Introductionmentioning

confidence: 99%

Micromechanical modeling of cracking and failure in brittle rocks

Hazzard¹,

Young²,

Maxwell³

2000

J. Geophys. Res.

240

108

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“…When it is viewed in this light, Scholz et al [1973] describe the phenomenon of positive dilatancy in rocks as a physical basis for such possible earthquake precursors as change in seismic velocity ratio, electrical resistivity, radon emission, and geodetic measurements, Beaumont and Berger [1974] computed the effect of dilatancy on the tidal response of the crust, and Whitcomb [1975] examined 3495 ltu AND LIVANOS: BULGING IN UNIAXIAl.LY COMPRESSED GRANITE quantitatively the dependence of vertical geodetic (including leveling, tilt, and geometric measurement relative to a celestial frame of reference), and gravity measurements in relation to dilatancy density change. A volume of crust undergoing positive dilatancy is assumed in these calculations, and the consequences are then computed.…”

Section: Introductionmentioning

confidence: 99%

Dilatancy and precursory bulging along incipient fracture zones in uniaxially compressed westerly granite

Liu¹,

Livanos²

1976

J. Geophys. Res.

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The existence of precursory bulge along an incipient fracture zone in a uniaxially compressed Westerly granite sample has been investigated by two optical methods. The first method is the method of slit diffraction. The cross section of a cylindrical rock sample is monitored by bringing two straightedges next to the rock sample to form two slits (each slit being formed between one straightedge and one side of the rock sample) and by illuminating alternately the two slits with a collimated laser beam. The FraunhoFer diffraction pattern is recorded on film in the direction perpendicular to the straightedge and can be interpreted as the absolute value squared of the one-dimensional spatial Fourier transform of the slit under certain conditions, thereby providing a simple method of magnification of the rock surface geometry. The conditions under which the Fraunhofer diffraction pattern can be interpreted as the absolute value squared of a one-dimensional Fourier transform are related to the radius of the rock sample, width of the slit, position of the recording film plane, and nature of deformation of the rock surface and are presented in this paper. The films are digitized by a microdensitometer. The data are analyzed by digital filtering and interpolation techniques to give a strain resolution of 10-•. During a test with the slit diffraction method, strain inhomogeneities in terms of local bulges indicative of incipient failure zones were found to develop at -92% of the uniaxial compressive strength, and their propagation is traced at 2.66-s intervals until failure. Local strains in the incipient failure zones are of the order of 10-• before failure takes place. Because of the large amplitude of the strain inhomogeneity prior to failure recorded by the slit diffraction method, we then tried the faster method of recording without magnification by a motion picture camera. In the second test a precursory bulge in the middle of the sample first appeared at -3.75 s prior to failure at a load of >99.7% of the uniaxial compressive strength. The bulge developed rapidly in successive frames until eventually a failure plane passed through this sharp bulge. The results from both tests demonstrate the formation of a concentrated weak zone as a result of the interaction and coalescence among the microcracks in the final stage of the test, which then develop into fracture zones. The bulging is the result of accentuated deformation in the weak zone because of its reduced deformation moduli. It is considered that the local bulge and orientation of the fracture zones in the first test were controlled by the stress concentration at the sample-load block interface, whereas those in the second test were controlled mainly by the inhomogeneity in the material properties within the sample. The precursor times of both tests do not fit into the empirical relationship between precursor time and fault dimension as derived from earthquakes and mine rock bursts. The precursor times of these tests are too long by 3 orders of magnitude in compa...

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“…5M+2.6 (TSUBOI, 1967), is penetrated by one of the travel-paths of our experiment to a certain extent, and (b) whether or not 1.15 (SCHOLZ et al, 1973), includes at leas tone event (shot time) of our experiment. Since no such adequate earthquake was found, we have not yet had an opportunity to verify whether the precursory P-wave delay had been generated or not in our research region.…”

Section: Relation To Earthquakes Of Moderate Magnitudementioning

confidence: 99%