RECEIVER FUNCTION ANALYSIS FOR CRUSTAL STRUCTURE BENEATH PAKISTAN

We performed a receiver function analysis to study crust and uppermost upper mantle structure beneath Pakistan. We used data recorded between June 2008 and June 2009 by a newly installed broadband network of Micro Seismic Studies Programme. We selected events whose magnitudes are greater than 5 in the epicentral distance range from 30 to 90 degrees. We found that amplitudes of tangential components are comparable to those of radial components for some stations. We investigated the orientations of horizontal components by varying rotation angles. The results suggest that the deviation of the orientations of the horizontal components from the North-South and East-West directions is minor, and that the large observed tangential components are likely to be caused by structural effects such as dipping of interfaces.

We calculated radial receiver functions using extended time multitaper frequency domain cross-correlation receiver function estimation method. We selected stations for which receiver functions with high signal-to-noise ratios are obtained among the 17 stations. The obtained receiver functions show a significant azimuthal dependence, which suggests the complexity of the structures beneath these stations. This is consistent with the large tangential components mentioned above. We performed inversion of the obtained receiver functions to determine velocity structures of crust and upper mantle using a genetic algorithm inversion technique. The results suggest that the Moho beneath the stations in the Potwar region is thick (around a depth of 50 km), while it becomes thinner in the center of Pakistan. This is qualitatively consistent with previous studies.