Abstract

The shear velocity and Q (sub beta ) structure for the upper 1 km in different tectonic regions of the Arabian shield have been investigated using high-frequency vertical component records of Rayleigh waves (1-20 Hz), which were recorded at source-to-receiver separations 55-80 km during a deep seismic refraction survey. Group and phase velocities of the fundamental and first higher modes were inverted for the shear-wave velocity structure; Rayleigh-wave attenuation coefficients were determined from the decay of the amplitude spectrum of the fundamental mode and used to invert for the Q (sub beta ) structure. Models derived from the data were tested by calculating synthetic seismograms for the fundamental and the first higher modes from surface-wave theory with a center of compression used to represent the source; both band-pass filtered step and Dirac delta source time functions were tested. Modeling indicates that the shear-wave velocity of the shield increases from 2.6 km/s to 3.4 km/s in the upper 400 m of the crust. Q (sub beta ) increases from 30 in the upper 50 m to 150 at 500 m depth. The underlying material has a Q (sub beta ) of 400-500 for the outcropping igneous rocks such as granite and may reach values higher than 700 for the metamorphic green schist rock. A band-pass filtered Dirac delta source time function produces the synthetic that is the best fit with observations.

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