Analysis of records of local earthquakes: the Turkish Dilatancy Projects (TDP1 and TDP2)

Autor: Russ Evans, Stuart Crampin, S. Balamir Üçer
Rok vydání: 1985
Předmět:
Zdroj: Geophysical Journal International. 83:1-16
ISSN: 1365-246X
0956-540X
DOI: 10.1111/j.1365-246x.1985.tb05152.x
Popis: Summary. This is the introduction to a series of papers analysing records from three-component seismometers immediately above a swarm of small earthquakes near the North Anatolian Fault in Turkey. The networks were set up to investigate the possibility of estimating dilatancy-induced adisotropy by monitoring shear-wave splitting in shear waves from local earthquakes as suggested by the hypothesis of extensive-dilatancy anisotropy (EDA). These networks were among the first closely-spaced digital three-component .seismometers to be deployed in the shear-wave window immediately over a seismic source zone, where the polarizations of incident shear waves can be recognized from surface recordings. Consequently, the seismograms display several new phenomena that have not been previously observed: (1) the polarizations of almost all shear waves arriving within the shear-wave window showed abrupt changes in direction characteristic of shear-wave splitting in synthetic seismograms modelling wave propagation through anisotropic rocks; (2) the polarizations of the faster split shear waves are in patterns characteristic of propagation through distributions of cracks aligned by the principal axes of stress, but not characteristic sf shear waves propagating through isotropic rock from a double-couple source oriented by the same stress axes; (3) many characteristics of the observed polarization patterns are similar to synthetic polarization diagrams for wave propagation through vertical parallel cracks; (4) the orientation of the anisotropy derived from the shear-wave polarizations is consistent with the common axes of stress of the fault-plane mechanisms; (5) the orientation of the shear-wave anisotropy is also similar to the orientation of the anisotropy derived independently from inverting P- and S-wave arrival times; and (6) there is some indication of a temporal change in polarization in one locality, such as might be expected if a change in a local stress anomaly altered the crack geometry.
Databáze: OpenAIRE
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