Results 1  10
of
12
Seismological studies at Parkfield VI: Moment release rates and estimates of source parameters for small repeating earthquakes
 Bull. Seismol. Soc. Am
, 1998
"... Abstract Waveform data from a borehole network of broadband seismographic stations have been used to study microearthquakes along the Parkfield segment of the San Andreas fault (SAF). Analysis of almost 10 years of such data demonstrates that much of the seismicity in this region consists of repeati ..."
Abstract

Cited by 45 (4 self)
 Add to MetaCart
Abstract Waveform data from a borehole network of broadband seismographic stations have been used to study microearthquakes along the Parkfield segment of the San Andreas fault (SAF). Analysis of almost 10 years of such data demonstrates that much of the seismicity in this region consists of repeating sequences, quasiperiodic sequences of earthquakes that are essentially identical in terms of waveform, size, and location. Scalar seismic moments have been estimated for 53 of these repeating sequences and combined with equivalent estimates from 8 similar but larger event sequences from the Stone Canyon section of the fault and the main Parkfield sequence. These estimates show that seismic moment is being released as a function of time in a very regular manner. Measurements of the moment release rate, combined with an assumed tectonic loading rate, lead to estimates of the seismic parameters source area, slip, and recurrence interval. Such parameters exhibit a systematic dependence upon source size over a range of 101 ° in seismic moment that can be described by three simple scaling relationships. Several implications of these scaling relationships are explored, including the repeat time of earthquakes, average stress drop, strength of the fault, and heat generated by earthquakes. What emerges from this analysis of moment release rates is a quantitative description of an earthquake process that is controlled by small strong asperities that occupy less than 1 % of the fault area. This means that the fault is highly heterogeneous with respect to stress, strength, and heat generation. Such heterogeneity helps to explain many of the apparent contradictions that are encountered in the study of earthquakes, such as why faults appear weak, why significant heat flow is not observed, how significant high frequencies can be generated by large earthquakes, and how various geologic features such as pseudotachylytes might form.
Fracture theory and its seismological applications
 In Continuum theories in solid Earth physics (ed. R. Teisseyre). Physics and Evolution of the Earth’s Interior
, 1986
"... Fracture phenomena pose significant geophysical problems over a vast range of size scales. These encompass the atomistic and microstructural scales of interest for an understanding of cataclastic rock deformation and friction in the manner of materials science, the laboratory scale at ..."
Abstract

Cited by 14 (2 self)
 Add to MetaCart
Fracture phenomena pose significant geophysical problems over a vast range of size scales. These encompass the atomistic and microstructural scales of interest for an understanding of cataclastic rock deformation and friction in the manner of materials science, the laboratory scale at
Novikova, `Duration of earthquake fault motion in California', Earthquake eng. struct. dyn
, 1995
"... Duration of high frequency (525 Hz) radiation of energy from earthquake sources in California is consistent with the estimates of fault length and with dislocation velocity estimates of 23 km/sec. This duration can be described by an exponential function of magnitude for 2.5 < M < 7.5. It is ..."
Abstract

Cited by 3 (2 self)
 Add to MetaCart
Duration of high frequency (525 Hz) radiation of energy from earthquake sources in California is consistent with the estimates of fault length and with dislocation velocity estimates of 23 km/sec. This duration can be described by an exponential function of magnitude for 2.5 < M < 7.5. It is related to the times it takes the dislocation to spread over the fault width (1/f2), and the fault length ( 1 / f,), and to reach its ultimate amplitude (To). The results in this paper can be used to estimate the range of amplitudes and the duration of long period pulses of strong ground motion near faults, as these long period pulses can be related to the properties of highfrequency radiation from the source. Such pulses must be considered in the analyses of yielding structures, when the average peak acceleration of the pulse exceeds the yield resistance seismic coefficient of the structure.
Scattering, and Attenuation of the Seismic Waves
"... NOT ICE OF T,,:<: r UL 70 DTI C This te h~~i i ~ it! te re io " d in appr'oved f'or pui.0 Ii ~ ~)12.Distribution Is unlimited. ..."
Abstract
 Add to MetaCart
NOT ICE OF T,,:<: r UL 70 DTI C This te h~~i i ~ it! te re io " d in appr'oved f'or pui.0 Ii ~ ~)12.Distribution Is unlimited.
INVESTIGATING THE MECHANICS OF EARTHQUAKES USING MACROSCOPIC SEISMIC PARAMETERS
, 2002
"... Investigating the mechanics of earthquakes using macroscopic seismic parameters ..."
Abstract
 Add to MetaCart
Investigating the mechanics of earthquakes using macroscopic seismic parameters
A model of interseismic fault slip in the presence of asperities
"... A 2D model which represents a slipping fault with nonuniform Coulomb friction is studied. The fault plane is subject to a uniform ambient shear stress, slowly increasing with time. Aseismic fault creep is assumed to start in a weak zone, when the ambient stress reaches a strength threshold. The so ..."
Abstract
 Add to MetaCart
(Show Context)
A 2D model which represents a slipping fault with nonuniform Coulomb friction is studied. The fault plane is subject to a uniform ambient shear stress, slowly increasing with time. Aseismic fault creep is assumed to start in a weak zone, when the ambient stress reaches a strength threshold. The solution for the resulting dislocation is worked out analytically using a technique based on Chebyshev polynomials. It is found that the dislocation partially propagates into the adjacent asperities, concentrating stress onto them and preparing the conditions which will produce the asperity failure and the accompanying earthquake. Propagation is not selfsimilar and occurs at increasing velocity. A nonlinear slip hardening effect is reproduced. The nearness to earthquake instability is measured by a dimensionless parameter which depends on Coulomb friction and ambient shear stress and decreases to zero with time. An upper boundary to the critical value of this parameter, at which instability may occur, is estimated and is found to depend on the ratio between the sizes of the asperity and the weak zone. Key words: aseismic fault slip, asperity model, sliding instability.
Comparison of the radiated fields generated by the fracture of a circular crack and a circular asperity
"... Summary. The ‘farfield ’ velocity and acceleration pulses radiated by the fracturing of a circular crack and a circular asperity are compared to determine the differences in the fields radiated by them. The cases of constant velocity fracture propagation as well as spontaneous fracture propagation ..."
Abstract
 Add to MetaCart
(Show Context)
Summary. The ‘farfield ’ velocity and acceleration pulses radiated by the fracturing of a circular crack and a circular asperity are compared to determine the differences in the fields radiated by them. The cases of constant velocity fracture propagation as well as spontaneous fracture propagation are studied. The circular crack and asperity studied are of the same size and have the same average stress drop, although the distribution of the stress drop on the circular areas is different due to the inherent differences between the two problems. Since the results presented are dimensionless, they can also be used to compare the radiated field due to a crack having a given average stress drop with the radiated field due to an asperity having, say, twice this average stress drop, simply by multiplying the asperity pulses by two, and so on for the other nondimensionalizing parameters. For the spontaneous problem, a complex fracture process is found for both problems. Due to the differences in initial conditions, it is shown that an asperity must be relatively stronger than a crack to have the same average fracture speed. It is found that no simple relation exists between the slope of the velocity pulse due to asperity failure and the average stress drop as it does for the constant velocity crack problem. Comparison of velocity, acceleration and energyflux pulse shapes show that there are clear differences in the details of the radiated fields of the crack and the asperity models, which could be used to distinguish between them. In particular, it is found that a spontaneous crack may radiate a higher peak ground velocity and acceleration than the corresponding asperity, in some directions from the source while in other directions it is the asperity that radiates higher peak velocity and acceleration. These directions depend on the details of the fracture process for each problem. Key words: crack, asperity, fracture, strong ground motion 1
to Complex Subduction Zone Earthquakes' A Discrete Interaction Matrix Approach
"... In recent years it has been recognized that the level of shear and normal stress along a fault can vary; thus the stress is spatially and temporally inhomogeneous. Moreover, it has also been suspected that faults might interact in some way, with the result that a variety of earthquake magnitudes mig ..."
Abstract
 Add to MetaCart
(Show Context)
In recent years it has been recognized that the level of shear and normal stress along a fault can vary; thus the stress is spatially and temporally inhomogeneous. Moreover, it has also been suspected that faults might interact in some way, with the result that a variety of earthquake magnitudes might be produced along a given length of fault at varying times. In order to explore these ideas we have developed a quantitative formalism, which we call the interaction matrix method, to express the influence of one fault upon another. This matrix is calculated by use of the energy change for a system of interacting cracks or faults and therefore gives energyconsistent results. Specifically, the interaction matrix relates the areaaveraged stress on the fault segment to the areaaveraged slip state on all the other fault segments in the system. Since any fault can be subdivided into an arbitrary number of fault segments, the interaction matrix can have arbitrary dimension; in fact, the continuum limit is recovered as the dimension of the matrix approaches infinity. We combine this matrix method with a segmentation, or "patch, " model for earthquakes, in which each discrete segment of a fault has the same coseismic stress change (defined as the difference between the driving stress at which healing occurs minus the driving stress at which sliding starts) each time it slips. We show that slip on a patch during an earthquake can vary substantially, depending on how it interacts with other nearby patches. In this model it is quite