A Source Theory for Complex Earthquakes

Blandford, R. R.

doi:10.21236/ada001061

Cited by 14 publications

(19 citation statements)

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“…A shallow (1-2 km), small 45° dip-slip earthquake would send out identical P-waves up and down, resulting in P-pP cancellation. These are the same events which can show compvessional first motions at all teleseismic distances; and which are difficult to discriminate by Mjtrn^, Douglas et al (1973), Blandford (1974). Another possibility is that we may find ourselves on a node of the P radiation pattern, and that this pattern will be less smoothed out by inhomogeneities at long periods than at short periods.…”

Section: -mentioning

confidence: 93%

“…Figure 5 shows complexity plotted against the integrated low frequency spectrum and we note that with a graphically determined cutoff at .25 we detect 22 of 26 explosions and 36 out of 40 earthquakes. The combining of complexity and integrated low frequency spectral measurements tends to improve the A negatively sloped line has been obtained by Anglin, 1971. Blandford, 1974, has also discussed the simultaneous increase in complexity and decrease in low frequency power for earthquakes from a theoretical point of view.…”

Section: Splctral Ratios and Complexitymentioning

confidence: 93%

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An Examination of Some New and Classical Short Period Discriminants

Shumway¹,

Blandford²

1974

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Section: -mentioning

confidence: 93%

Section: Splctral Ratios and Complexitymentioning

confidence: 93%

An Examination of Some New and Classical Short Period Discriminants

Shumway¹,

Blandford²

1974

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“…ANDREWS (1978) proposed such a hierarchical relationship for seismicity; here it is assumed for a single event. Note that there is no need to relate each scale to a population of individual subevents of a specific size and/or duration, as was hypothesized by BLANDFORD (1975) or HANKS (1979. The discussed concept of multiplicity of scales in an earthquake rupture has not much in common with the traditional view of brittle crack with only two widely separated scales, as mentioned above.…”

Section: Discussionmentioning

confidence: 99%

Approximate Stochastic Self-Similarity of Envelopes of High-Frequency Teleseismic P-Waves from Large Earthquakes

Gusev

2010

Pure Appl. Geophys.

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A wavetrain of high-frequency (HF) P waves from a large earthquake, when recorded at a distant station, looks like a segment of modulated noise, with its duration close to the duration of rupture. These wavetrains, with their bursts and fadings, look much more intermittent than a segment of common stationary random noise. We try to describe quantitatively this bursty behavior. To this end, variogram and spectral analyses are applied to time histories of P-wave envelopes (squared-amplitude or instant-power signals) in six HF bands of 1-Hz width. Nine M w = 7.6-9.2 earthquakes were examined, using, in total, 232 records and 992 single-band traces. Variograms of integrated instant power are approximately linear on a log-log scale, indicating that the correlation structure of the instant-power signal is approximately self-similar. Also, estimates of the power spectrum of the instant-power signal look approximately linear on a log-log scale. Log-log slopes of the variograms and spectra deliver estimates of the Hurst exponent H that are mostly in the range 0.6-0.9, markedly above the value H = 0.5 of uncorrelated (white-noise) signals. The preferred estimate over the entire data set is H = 0.83, still, this estimate may include some bias, and must be treated as preliminary. The inter-event scatter of H estimates is about 0.04, reflecting individual event-to-event variations of H. Many of the average log-log spectral plots show slight concavity that perturbs the approximately linear slope; this is a secondary effect that seems to be mostly related to the limited bandwidth of the data. Evidence is given in support of the idea that the observed approximately selfsimilar correlation structure of the P-wave envelope originates in a similar structure of the body wave instant-power signal radiated by the source, so that the propagation-related distortions can be regarded as limited. The facts presented suggest that the spacetime organization of the earthquake rupture process is multiscaled and bears significant fractal features; it deviates from the brittlecrack model with its two well-separated characteristic scales. Phenomenologically, the high-frequency body-wave radiation from an earthquake source can be thought of as a product of stationary noise and the square root of a positive random envelope function with a power-law spectrum. From the viewpoint of applications, the self-similarity of body wave envelopes provides a useful constraint for earthquake source models used to simulate strong ground motions.

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“…In simple incoherent source models (BLANDFORD, 1975;HANKS, 1979;etc. ) all HF subsources are assumed statistically independent, their time histories uncorrelated, and their energy contributions additive.…”

Section: Creating Random Subsource Time Functions With Appropriate Spmentioning

confidence: 99%

“…Since then, aggregates of dislocations/subearthquakes with broad spectrum of sizes, often with power-law (''Gutenberg-Richter-like'') size distribution, were used as a model of a broadband source. BLANDFORD (1975) and HANKS (1979) tried to explain in this way the power-law HF tail of the , or more generally x -c ) source spectrum; space-time structure of a source was not defined in these models. Following this line, ZENG et al (1994) cover fault surface by several populations of circular cracks with hierarchy of sizes.…”

Section: Introductionmentioning

confidence: 99%

Broadband Kinematic Stochastic Simulation of an Earthquake Source: a Refined Procedure for Application in Seismic Hazard Studies

Gusev

2010

Pure Appl. Geophys.

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To carry out a realistic simulation of earthquake strong ground motion for applied studies, one needs an earthquake fault/source simulator that can integrate most relevant features of observed earthquake ruptures. A procedure of this kind is proposed that creates a broadband kinematic source model. At lower frequencies, the source is described as propagating slip pulse with locally variable velocity. The final slip is assumed to be a twodimensional (2D) random function. At higher frequencies, radiation from the same running strip is assumed to be random and incoherent in space. The model is discretized in space as a grid of point subsources with certain time histories. At lower frequencies, a realistic shape of source spectrum is generated implicitly by simulated kinematics of slip pulse propagation. At higher frequencies, the original approach is used to generate signals with spectra that plausibly approximate the prescribed smooth far-field source spectrum. This spectrum is set on the basis of the assumedly known regional empirical spectral scaling law, and subsource moment rate time histories are conditioned so as to fit this expected spectrum. For the random function that describes final slip over the fault area, lognormal probability distribution of amplitudes is assumed, on the basis of exploratory analysis of inverted slip distributions. Similarly, random functions that describe local slip rate time histories are assumed to have lognormal distribution of envelope amplitudes. In this way one can effectively emulate expressed ''asperities'' of final slip and occasional occurrence of large spikes on near-source accelerograms. A special procedure is proposed to simulate the spatial coherence of high-frequency fault motion. This approach permits the simulation of fault motion plausibly at high spatial resolution, fulfilling the prerequisite for simulation of strong motion in the vicinity of a fault. A particular realization (sample) of a source created in a simulation run depends on several random seeds, and also on a considerable number of parameters. Their values can be selected so as to take into account expected source features; they can also be perturbed to examine the source-related component of uncertainty of strong motion. The proposed approach to earthquake source specification is well adapted to the study of deterministic seismic hazard: it may be used for simulation of individual scenario events, or suites of such events, as well as for analysis of uncertainty for expected ground motion parameters from a particular class of events. Examples are given of application of the proposed approach to strong motion simulations and related uncertainty estimation.

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A Source Theory for Complex Earthquakes

Cited by 14 publications

References 0 publications

An Examination of Some New and Classical Short Period Discriminants

An Examination of Some New and Classical Short Period Discriminants

Approximate Stochastic Self-Similarity of Envelopes of High-Frequency Teleseismic P-Waves from Large Earthquakes

Broadband Kinematic Stochastic Simulation of an Earthquake Source: a Refined Procedure for Application in Seismic Hazard Studies

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