Inversion of arrival-times in a region of dilatancy anisotropy

Doyle, Mark; Crampin, Stuart; McGonigle, Robert; Evans, Russ

doi:10.1007/bf00880737

Cited by 4 publications

(3 citation statements)

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“…(4) The orientation of the anisotropy derived from analyses of the polarization of shear-waves was consistent with that derived from independent inversion of P-and S-wave arrival times (Doyle et al 1985).…”

Section: Introductionmentioning

confidence: 60%

The Turkish Dilatancy Project (TDP3): multidisciplinary studies of a potential earthquake source region

Evans

Beamish

Crampin

et al. 1987

Geophysical Journal International

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The section of the North Anatolian Fault lying near the city of Izmit, at the east of the Marmara Sea, has been identified as a seismic gap and the possible site of a future major earthquake. Previously published studies of records from an earthquake swarm within the gap (TDP1 and TDPZ) provided the first evidence that shear-wave splitting occurs in earthquake source regions, a conclusion since verified by many studies at other locations. A third field study (TDP3) was mounted in the Izmit region during the summer of 1984.Observations were made over an eight-month period and included geomagnetic and geoelectric measurements in addition to a series of observations utilising dense arrays of three-component seismometers. Earthquake activity in the principal study area was monitored over a period of eight months.Records showed features similar to those observed in the earlier studies. In particular:(1) almost all shear waves emerging within the shear-wave window displayed shear-wave splitting; and (2) the polarizations of the first arriving (faster) split shearwaves showed sub-parallel alignments, characteristic of propagation through a distribution of parallel vertical cracks striking perpendicular to the minimum compressional stress.These and other observations support the conclusion of earlier studies -that the upper crust is pervaded by distributions of microcracks aligned by stress, known as extensive-dilatancy anisotropy.A search for time dependence in shear-wave phenomena has revealed temporal variations in the delays between the split shear-waves throughout the course of the TDP3 study, but as yet this has not been correlated with specific earthquake activity. 266 R . Evans et al.

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Section: Introductionmentioning

confidence: 60%

The Turkish Dilatancy Project (TDP3): multidisciplinary studies of a potential earthquake source region

Evans

Beamish

Crampin

et al. 1987

Geophysical Journal International

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“…Anisotropic parameters are almost always expensive to compute directly. This makes procedures which use database, look-up table, techniques particularly attractive (Doyle et al 1985), particularly as more sophisticated versions allow comprehensive statistics to be computed (MacBeth, 1991a, b). There are two parameters of shear-wave splitting that offer possibilities for inversion, the polarizations of the leading split shear wave, and the time delay between the two split shear waves.…”

Section: Inversionmentioning

confidence: 99%

A decade of shear-wave splitting in the Earth's crust: what does it mean? what use can we make of it? and what should we do next?

Crampin

Lovell

1991

Geophysical Journal International

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225

169

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S U M M A R Y It is 10 years since shear-wave splitting, thought to be diagnostic of some form of seismic anisotropy, was first positively identified in the Earth's crust. From the beginning it was argued that the splitting was probably associated with the presence of stress-aligned cracks (inclusions) in the crust, and that this would provide the opportunity for monitoring the in situ geometry of cracks and stress in a variety of different circumstances and in a variety of different applications. The early promise was not immediately realized, and the first 10 years were spent mainly in observing the phenomena in a variety of different situations. However, 1990 appeared to mark a turning point for anisotropy. Papers at the Fourth International Workshop on Seismic Anisotropy and elsewhere have announced major progress in understanding, interpreting, and particularly processing shear-wave splitting, with direct applications to hydrocarbon production, and a possible (but disputed) application to monitoring stress changes before earthquakes. However, there is still much that we do not understand about the phenomenon, and we are clearly only just beginning to appreciate the enormous information content of the shear wavetrain and its potential applications to science and engineering in the Earth's crust.This paper briefly reviews the past 10 years, and speculates on how best we can exploit this new window of opportunity for exploring the internal structure of the crust. In particular, what causes the shear-wave splitting? what use can we make of the phenomenon? and what should we do next?

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“…Various earthquake parameters necessary for investigating shear-wave splitting have been determined for the TDP swarm, including hypocentre locations in effectively anisotropic structures(Doyle, McGonigle & Crampin 1982;Doyle, Crampin, McGonigle & Evans 1984), and fault~plane mechanisms(Evans, Asudeh, Crampin & tt9er 1984).…”

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confidence: 99%