Regional waveform propagation in the Arabian Peninsula

Regional waveform propagation is characterized in the Arabian Peninsula usi ng data from a temporary network of broadband seismometers. Between Novembe r 1995 and March 1997, 332 regional (delta < 15 degrees) events were record ed from nine stations deployed across the Arabian Shield. Regional phase pr opagation was analyzed in two ways: by individual inspection of the wavefor ms and by stacking of waveforms. Inspection of the waveforms revealed consi stent variations in individual seismograms according to the region of origi n. Waveforms from events in the Gulf of Aqaba, northwest of the network, po ssess weak Pn, Pg, and Sn but show a prominent L-g phase. In contrast, clea r Pn, Sn, and Lg are observed for events located in the Zagros, a region no rtheast of the network. Events near the Straits of Hormuz also display Pn a nd Sn but lack a strong high-frequency Lg. Southern Red Sea and African ear thquakes have moderate-amplitude body phases with some Lg. For the stacks t he data were high-pass filtered at 1 Hz, rectified, binned, and then stacke d by time/distance or by time/slowness. The time/distance stacks show clear differences between regions that correspond to the variations observed in individual seismograms. The time/slowness stacks allow comparison of relati ve phase velocities and amplitudes. Pn velocity under the network was estim ated to be 8.0 +/- 0.2 km/s, consistent with data from prior refraction pro files. The area of inefficient Pn and Sn propagation coincides with an area of Holocene volcanism and suggests that anomalous upper mantle underlies m uch of the Arabian Shield.