عنوان

Seismic velocity structure and attenuation of the Arabian plate

TLpq304019822

انگلیسی

Seismic velocity structure and attenuation of the Arabian plate

[Thesis]

H. A. A. Ghalib

R. B. Herrmann

Saint Louis University

1992

338

Ph.D.

Saint Louis University

1992

This study consists of two distinct parts. Each describes an effort to advance our current understanding of the Arabian plate seismotectonic environment. In the first part, the dispersive properties of long-period Rayleigh waves are used to investigate the plate's seismic velocity structure variation. The mixed-path fundamental- and higher-mode group velocity dispersion curves are calculated using a single-station method. To facilitate interpreting the variation, two approaches are followed in the analysis of data. First, the dispersion curves for each station are averaged according to their similarity and mixed-path orientation. Second, pure-path dispersion curves are estimated using the grid-dispersion inversion method. An iterative nonlinear differential inversion technique and a single layer over half-space starting model are used to invert all the dispersion curves. The mixed-path models show significant variation in the plate's structure. Beneath a thick sedimentary layer, two discontinuities at 15-20 and 35-55 km depth are observed in the region. According to the three-dimensional model, the most dominant features are the Arabian shield and Mesopotamian foredeep. Within the crust the velocity is highest under the shield, but below 40 km depth it is lower than the rest of the plate. In the second part, the attenuation of high-frequency seismic wave is investigated, and the developed "extended coda-Q" technique is applied to short period Lg coda waves. This technique is based on least squares principles, and provides a deterministic procedure for estimating the quality factor and its frequency dependence simultaneously. At 1 Hz an average of Qo = 214, usd\zetausd = 0.6, and usd\gammausd = 0.0045 km are found for the Arabian plate. The lowest Qo values are found along the Zagros. In comparison, the Arabian shield shows surprisingly low Qo values that may be attributed to its young age, intensive metamorphism and deformation.

coda waves

Earth sciences

Geology

Geophysics

Geophysics

H. A. A. Ghalib

R. B. Herrmann

p

[Thesis]

276903

a

Y