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Seismic Anisotropy in the Crust from Regional Telemetry Seismic Network in Yunnan of China

Author: ShiYuTao
Tutor: GaoYuan
School: China Seismological Bureau, Institute of Earthquake Prediction
Course: Solid Geophysics
Keywords: anisotropy shear-wave splitting polarization of fast shear-wave principal compressive stress SAM technique time-delay
CLC: P313.2
Type: Master's thesis
Year: 2006
Downloads: 47
Quote: 2
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Abstract


Parallel vertical cracks widely exist in the lithosphere (EDA cracks) and result in shear wave splitting in the earth’s curst, at least in the upper lithosphere. Splitting will occur while shear wave transmits in anisotropy media. The polarization of fast shear-wave is consistent with the crack’s direction, which means that the polarization of fast shear-wave reflects the direction of the principal compressive stress. The time delay of slow shear wave reflects the extent of anisotropic media. To the structure with EDA cracks and liquid, APE theory can be used to explain its dynamic change.Yunnan region is located at eastern edge of Tibetan plateau. There are many big intersected rupture zones with strong seismic activities. The geological structures in the area are very complex, which mainly distribute along NE、NW and NS direction. The direction of compressive stress axis is NNW, caused by rock curst in eastern part crushed to the south-eastern. Since 2000, many earthquakes with Ms≥5.0 occurred for several times, thus there are many data which can be used for analysis of shear wave splitting. This paper shows the research of shear wave splitting by applying near field data from regional telemetry seismic network in Yunnan region. There are several hundred efficient records within shear wave window, and SAM method is selected as the main tool to analyze crustal anisotropy in Yunnan region. Because of the fact that the geological structure is complicated in Yunnan region, the polarizations are complicated.Generally, polarizations of fast shear-wave are mainly in NW, NNW and NW direction, which are almost consistent with regional principal compressive stress. Results show that the range of time-delay is from 1.0 to 7.3 ms/km, average value is 2.78 ms/km. Fast shear-wave polarizations of the stations which locate in active ruptures are

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CLC: > Astronomy,Earth Sciences > Geophysics > Earth ( rock circles ) physics ( geophysics ) > Tectonic physics, rock group learning (structure of petrology ) > Tectonic
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