Nonuniform friction as a physical basis for earthquake mechanics

Nur, Amos

doi:10.1007/bf00876550

Cited by 68 publications

(42 citation statements)

References 21 publications

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“…Byedee [1970] and Nur [1978] have proposed that fault instability is related to variation of sliding friction with displacement as well as with position. One might imagine a fault as two rough surfaces pressed together.…”

Section: Introductionmentioning

confidence: 80%

“…Heterogeneity is certainly important to the generation of damaging high-frequency ground motion, and it may be essential in determining the occurrence and size of earthquakes. Such concepts and relevant observations have been reviewed by Aki [1979] and Nur [1978]. Bakun et al [1980] find correlations of seismicity with discontinuities of fault geometry.…”

Section: Introductionmentioning

confidence: 99%

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A stochastic fault model: 1. Static case

Andrews¹

1980

J. Geophys. Res.

283

195

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The number‐size distribution of earthquakes requires that irregularities exist on a fault at all length scales. The assumption of self‐similar irregularity is used to formulate a stochastic description of the faulting process. A random irregularity is termed self similar if it remains statistically similar upon a change of length scale. Self‐similar geometric irregularity of a fault surface is represented in this model by stress and friction functions that fluctuate self similarly on a plane. If the set of rupture areas of all earthquakes on the brittle portion of a fault plane is assumed to be self similar, then the number of ruptures with area greater than A is proportional to 1/A. If stress drop is independent of earthquake size, then the number of earthquakes with moment greater than M0 is proportional to M0−⅔. The size of an earthquake is determined by spatial fluctuation of the initial stress and sliding friction functions. The spectrum of the stress function is related to both the average stress drop as a function of earthquake size and the number‐moment distribution. A model of the slip and stress change functions of an earthquake is constructed in the Fourier transform domain. While the stress function becomes smoother in an earthquake at the length scale of the rupture, it becomes rougher at shorter length scales to prepare the fault for future smaller earthquakes. Seismicity is a cascade of stored elastic energy from longer to shorter wavelengths.

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Section: Introductionmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

A stochastic fault model: 1. Static case

Andrews¹

1980

J. Geophys. Res.

283

195

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“…Non-uniform friction has been modelled t o various degrees of complexity (see, e.g. Weertman 1964;Walsh 1968;Burridge & Halliday 1971;Nur 1978). Elaborate numerical models have been developed by Mikumo & Miyatake (1978, Miyatake (1980) and Mikumo (1981).…”

Section: Introductionmentioning

confidence: 99%

Fault slip beyond a barrier on a transform plate boundary

Bonafede

Boschi

Dragoni

1983

Geophysical Journal International

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A strike-slip plate boundary is considered with non-uniform strength. Depth-dependent slip on the fault surface is assumed to occur aseismically in the lower fault section, in response to a basal shear stress, and seismically in the brittle upper section. The upper fault section acts as a barrier, preventing aseismic slip from reaching shallower depths. If, however, friction decreases in the proximity of the Earth's surface, brittle fracture may occur beyond the barrier. It is found that, when friction in the uppermost fault section exceeds the applied shear stress, fault slip occurs there with a smaller amplitude than at larger depth. This may explain the discrepancies, which have been sometimes reported, between fault offsets observed at the Earth's surface and fault offsets inferred from seismograms by using simpler dislocation models.

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“…It has long been recognized that the earthquake frequencymagnitude relation, observed essentially wherever seismicity occurs, implies strong crustal heterogeneity in tectonic stress, fault strength, frictional properties [e.g., Mogi, 1963;$cholz, 1968;Hanks, 1977;Dieterich, 1977;Nur, 1978], or other factors involved in seismic faulting. Without such heterogeneity it is difficult to explain how earthquakes of all magnitudes can occur on the same fault segment, without significant mutual interaction.…”

Section: Introductionmentioning

confidence: 99%

A complete solution of a one‐dimensional propagating fault with nonuniform stress and strength

Israel¹,

Nur²

1979

J. Geophys. Res.

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We have investigated details of the dynamics of faults with strongly variable stress and frictional strength. These factors are in all likelihood responsible for nonuniform fault slip, multiple events, random ground acceleration, and the earthquake frequency‐magnitude relation. In order to obtain a full dynamic solution to greatly heterogeneous faulting we used a one‐dimensional continuum model in which stress and strength varied along the fault. The results show that the process of rupture in a heterogeneous system is closely linked to the stopping phase of the motion, or the healing process of faults. The process, which may involve strong nonlinear effects such as discontinuous motion, cannot be seen in static models and requires a dynamic approach with a numerical scheme which remains stable at high frequencies. We have used the method of characteristics to obtain the results in this paper. We found that heterogeneous rupture can be due to either initially nonuniform stress or spatially nonuniform frictional strength. However, nonuniform stress drop—the difference between tectonic stress and frictional stress—tends to become smoother with increasing slip. After some initial heterogeneous sliding, fault slip in the model becomes uniform and repetitious, a condition which is clearly not observed in nature. Spatially variable strength, however, can produce and maintain a heterogeneous stress drop. We found that when the strength was sufficiently variable from place to place, the final stress was statistically at least as variable as the initial stress. This means that the character of fault activity can remain heterogeneous with time; this would conform to the behavior observed in situ. We conclude therefore that spatially variable fracture energy may in fact be responsible for the heterogeneous nature of earthquake faulting. Nonuniform stress by itself cannot maintain with time the heterogeneous nature of faults. The model is applied to the irregular slip distribution of the Borrego Mountain (Coyote Creek), California, earthquake of April 1968 and reveals links among irregular rupture propagation, multiple events, fault slip, and stress drop.

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Nonuniform friction as a physical basis for earthquake mechanics

Cited by 68 publications

References 21 publications

A stochastic fault model: 1. Static case

A stochastic fault model: 1. Static case

Fault slip beyond a barrier on a transform plate boundary

A complete solution of a one‐dimensional propagating fault with nonuniform stress and strength

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