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

Evans, Russ; Beamish, David; Crampin, Stuart; Ucer, S. Balamir. 1987 The Turkish Dilatancy Project (TDP3): multidisciplinary studies of a potential earthquake source region. Geophysical Journal of the Royal Astronomical Society, 91 (2). 265-286.

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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 (TDPl and TDP2) 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; (2)the polarizations of the first arriving (faster) split shear-waves 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 micro­ cracks 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 wi th specific earthquake activity.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: BGS Programmes > Seismology and Geomagnetism
NORA Subject Terms: Earth Sciences
Date made live: 18 Apr 2016 11:48 +0 (UTC)

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