摘要:

The power spectra of many geophysical phenomena are well approximated by a power‐law dependence on frequency or wavenumber. I derive a simple expression for the root‐mean square variability of a process with such a spectrum over an interval of time or space. The resulting expression yields the power‐law time dependence characteristic of fractal processes, but can be generalized to give the temporal variability for more general spectral behaviors. The method is applied to spectra of crustal strain (to show what size of strain events can be detected over periods of months to seconds) and of sea level (to show the difficulty of extracting long‐term rates from short r

ISSN:0094-8276    

DOI:10.1029/91GL02832

年代:1992

数据来源: WILEY

摘要:

Temperature‐dependent viscosity places constraints on the spherical harmonic spectrum of thermal convection in the earth's mantle. Viscosity, being a strong function of temperature, gives rise to quantized feed‐back loops among low‐order modes in the governing equations. This nonlinear resonance is proposed as the cause of the dominance of a low‐order convective pattern in the earth's

ISSN:0094-8276    

DOI:10.1029/92GL00163

年代:1992

数据来源: WILEY

摘要:

Love waves from the 1990 Philippine Islands earthquake show large amplitude anomalies at broadband seismograph stations in Japan, while Rayleigh waves do not. We calculate synthetic seismograms using the fully coupled eigensolutions obtained by a variational method to see if this anomalous behavior of surface waves is explained by the laterally heterogeneous earth model M84A of Woodhouse and Dziewonski. We show that the anomalous long‐period surface wave amplitude behavior can be reproduced relatively well by M84

ISSN:0094-8276    

DOI:10.1029/91GL03005

年代:1992

数据来源: WILEY

摘要:

The moment release rate in the Kodiak Island (KI) segment increased prior to the great 1964 Prince William Sound earthquake (MW= 9.2). Starting in 1983 the moment release rate in the Shumagin Island (SI) segment shows a similar increase. In July 1990, an outer‐rise reverse earthquake showed arc‐normal compression at a depth of 42 km seaward of the Alaska Peninsula (AP) segment. Because accelerating moment release and arc‐normal compression have both been proposed as precursors to large and great earthquakes, we suggest this is evidence that the SI‐AP region is nearing the end of the seismic cycle between large thrust eart

ISSN:0094-8276    

DOI:10.1029/92GL00260

年代:1992

数据来源: WILEY

摘要:

In this paper, a simple approximate method that converts the distribution of kinematic rupture parameters on a fault into that of physical or dynamic parameters, is proposed. The method in which the static stress drop assumed to be equal to the dynamic stress drop, is applied to investigate rupture dynamics of the 1979 Imperial Valley, California, earthquake (M=6.5). The dynamic rupture process is reconstructed by using a propagating crack, which is a process of expanding area of stress release. If we know the amount of stress drop and rupture time at each point on the fault, dynamic rupture process can be simulated. We use the kinematic parameters previously obtained by using waveform inversion techniques. With constraints of the kinematic parameters, the dynamic rupture process of the event can be reconstructed and several dynamic parameters, stress drop and strength excess (the difference between strength and applied initial stress), can be estimated at each point on the fault. By applying this method to the 1979 Imperial Valley earthquake, we found that the rupture initiated at the low strength excess part first, and then expanded toward the north, and ruptured a large‐size high stress drop region located in the north part of the fault, and finally decelerated and stopped at the north edge where the strength is high and stress drop is low. These features are well explained by barrier model [Das and Aki, 1977] and are quite similar to those obtained by Quin in 1990 who investigated the dynamic rupture process by the Monte Carlo technique with a large number of trials. Since repeated calculation is unnecessary, our method is very effective and practical compared with his metho

ISSN:0094-8276    

DOI:10.1029/92GL00082

年代:1992

数据来源: WILEY

摘要:

The Kapuskasing uplift, located in the central Canadian shield, represents an oblique exposure of the Archean middle to lower crust. The Ivanhoe Lake fault zone, believed to be the basal thrust carrying the high‐grade rocks of the Kapuskasing zone over the low‐grade Abitibi greenstone belt, holds the key to understanding the nature and evolution of the Kapuskasing uplift. Despite numerous geological and geophysical studies, including LITHOPROBE deep seismic reflection profiles, and because of very limited bedrock exposure in the area, the shallow structure of the Ivanhoe Lake fault zone remains obscure. Here we present results obtained by reprocessing data from a LITHOPROBE seismic reflection profile across the fault zone. For the first time, the Ivanhoe Lake fault zone is clearly imaged on the seismic section as a series of west‐dipping reflectors with an average dip of 20°, which can be traced to the surface. The results support the conclusion that fault zones form good refl

ISSN:0094-8276    

DOI:10.1029/91GL03180

年代:1992

数据来源: WILEY

摘要:

Complexity of fault systems in Japan and the Philippines is quantitatively measured using fractal dimension. The areas studied are the Median Tectonic Line, Izu, Unzen on the Japanese Islands, and the fault system yielded by the Philippine earthquake which occurred on July 16, 1990. Results are summarized as follows: Fractal dimensions along the Median Tectonic Line vary between 1 and 1.3. The Unzen area gives the highest fractal dimension (1.4) of all the areas studied, which implies that the fault system there is the most complex. Fractal dimension of the fault system associated with the Philippine earthquake is smaller than 1. It can be interpreted that this fault system is almost one‐dimensional, with truncated by numerous gaps of various size

ISSN:0094-8276    

DOI:10.1029/92GL00202

年代:1992

数据来源: WILEY

摘要:

A series of experiments scaled for gravity on the formation of faults in a laboratory model of the earth's lithosphere have shown that the obtained fault patterns are self‐similar and can be characterized by various fractal dimensions. By analyzing a large set of experimental results, we discover a remarquable scaling law relating the generalized fractal dimensions Dqthe fault barycenter fractal dimension ‘b’ and the exponent ‘a’ of the fault length distribution. : D0≈b is independent of ‘a’ whereas Dq≥1=b+2−a, for 2≤a≤3 as f

ISSN:0094-8276    

DOI:10.1029/91GL02711

年代:1992

数据来源: WILEY

摘要:

A simple model is presented in which a fault is represented by a one‐dimensional array of elements to which a remote stress is applied. The fracture toughnesses of the fault elements are initially generated by a random walk function, but the fracture system quickly becomes organized into a fractal set characterised by a (box‐counting) fractal dimension. The slope, b, of the frequency‐magnitude distribution and the fractal dimension of the crack population are measured at each step, and found to vary in a similar manner to the seismic b‐value and fractal dimension of earthquake epicentres. The model also predicts the observed variation of b‐value of acoustic emissions in laboratory ex

ISSN:0094-8276    

DOI:10.1029/92GL00274

年代:1992

数据来源: WILEY

摘要:

We have measured cosmic ray produced10Be (t½= 1.5 My) and26Al (t½= 0.72 My) as functions of depth in a core of quartz sandstone bedrock collected in South Victoria Land, Antarctica. These data were used to place limits on the exposure age and erosion rate of the exposed surface, and to calculate the effective attenuation lengths of cosmic rays producing these nuclides. These latter results indicate that the production attenuation length for26Al is comparable to that for10Be . This suggests that the production ratio26Al:10Be does not vary substantially with depth in a rock, and that its value at the surface of exposed rock is not strongly affected by erosional losses, allowing wider use of the ratio in determining exposure age

ISSN:0094-8276    

DOI:10.1029/92GL00266

年代:1992

数据来源: WILEY