The crustal and upper-mantle structure of the interior Arabian platform

The crustal and upper-mantle Velocity structure of the interior Arabian platform is derived using the spectral analysis of long-period P-wave amplitude ratios. The ratio of the vertical to the horizontal component is utilized to obtain crustal transfer functions using the Thomson-Haskell matrix formulation for horizontally layered crustal models. 20 earthquakes recorded at the long-period station RYD between azimuths N20 degrees W and N150 degrees E were selected for the analysis based on the following criteria: focal depths in the range 5 to 215 km, body-wave magnitudes greater than 5.0, and epicentral distances in the range 7 degrees to 97 degrees. A careful quality check of the data left us with six events, out of 29, that had short epicentral distances (< 20 degrees) to be analysed. The selection criterion for the final model in the forward modelling process was based on the correlation coefficient between observed and theoretical transfer function. The model suggested that the crust consists of five distinct layers. The upper crustal layer has a P-wave velocity of about 5.6 km s(-1) and is about 3 km thick. The second layer has a velocity of about 6.3 km s(-1) and is 10 km thick. The third layer has a velocity of 6.6 km s(-1) and is 8 km thick. The fourth layer has a velocity of 6.9 km s(-1) and is 15 km thick. The lower layer has a velocity of about 7.6 km s(-1) and is 10 km thick. For the Mohorovicic discontinuity, a velocity of 8.3 km s(-1) for the upper mantle and 46 km depth are indicated.