Origin of crustal anisotropy: Shear wave splitting studies in Japan

Conference · Tue Jul 10 04:00:00 EDT 1990 · Journal of Geophysical Research; (United States)

OSTI ID:5446740

Kaneshima, Satoshi ^[1]

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1. Univ. of Tokyo (Japan)

Shear wave splitting manifested as leading shear wave polarization, that is, parallel alignment of leading shear wave particle motions from a variety of sources, has been observed at a number of seismograph stations in Japan. Detected on shear wave seismograms from crustal earthquakes over a wide range of source zones and source-receiver azimuths, the shear wave splitting can be attributed to crustal anisotropy. This paper discusses the relation between leading shear wave polarization directions and tectonic features of Japan. To explain the observed shear wave splitting, the author proposes that at least three phenomena should be taken into account: stress-induced microcracks primarily aligned in vertical or subvertical planes; cracks or fractures in the vicinity of active faults having their orientation parallel to the fault planes; and intrinsic rock anisotropy resulting from preferred orientation of minerals. Travel time differences between leading and slower split shear waves from crustal and upper mantle earthquakes analyzed for about one third of the stations suggest that the crustal anisotropy which causes the observed shear wave splitting may be limited to the upper 15-25 km. This implies that the density of nonhorizontally aligned cracks or fractures below 15-25 km and into the upper mantle is much smaller than that in the crust above 15-25 km.

• OSTI ID: 5446740
• Report Number(s): CONF-880531--
• Conference Information: Journal Name: Journal of Geophysical Research; (United States) Journal Volume: 95:B7
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ANISOTROPY
ASIA
BIREFRINGENCE
CONTINENTAL CRUST
DEPTH
DETECTION
DEVELOPED COUNTRIES
DIAGNOSTIC TECHNIQUES
DIMENSIONS
DISTRIBUTION
EARTH CRUST
EARTH MANTLE
EARTHQUAKES
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOPHYSICAL SURVEYS
JAPAN
MECHANICS
MINERALS
ORIENTATION
POLARIZATION
REFRACTION
ROCK MECHANICS
SEISMIC DETECTION
SEISMIC EVENTS
SEISMIC S WAVES
SEISMIC SURVEYS
SEISMIC WAVES
SURVEYS
TECTONICS
TIME DEPENDENCE
TOMOGRAPHY
WAVE PROPAGATION