A Study of Seismic Wave Propagation at Regional Distances in Five Areas of the World

摘要

Propagation and excitation of regional phases in southern Africa, the southwestern United States, the Pakistan-India region, South America, and the Kamchatka-Kuriles region were studied. Comparison of the shield areas of South America, Pakistan and southern Africa reveals no appreciable differences in the excitation and attenuation of regional phases in these areas. On the other hand, excitation and attenuation rates for all regional phases are markedly different in the southwestern United States. The mountainous areas of South America are characterized by highly variable propagation characteristics, with Sn and Lg being absent from many seismograms studied. Attenuation of Sn and Lg is especially severe along the southern Andes mountains in Chile and Argentina. For these areas, the value of regional phases for detection and discrimination is highly questionable. The Andes region is also characterized by highly unusual seismograms with scattered, emergent phases resembling lunar seismograms. These problems are present, though to a much lesser degree, in the mountainous areas surrounding India and Pakistan. These areas are also characterized by highly variable propagation efficiency and by spatial attenuation that is higher than that of the shield.