CRUSTAL STRUCTURE AND SURFACE-WAVE DISPERSION

Abstract

Properties of the suboceanic crust are deduced from dispersion of earthquake surface waves. Love waves and Rayleigh waves on seismograms of the Honolulu station from shocks occurring in the circum-Pacific earthquake belt show typical oceanic crust throughout the Pacific Ocean. They do not reveal anomalous areas of continental proportions which may once have stood above sea level. Similar results are obtained for parts of the North Atlantic. The method, however, is insensitive to relatively small or thin structures. The Easter Island Rise is somewhat anomalous and possibly represents a deviation toward the continental type of crust. Some earthquakes cause a short-period train of surface waves to predominate over the more common long-period surface waves for purely oceanic paths. The beginning of the train is identified definitely as Love-wave motion. The later part of the train, which is apparently a noncoherent mixture of Love and Rayleigh waves, with periods of 6 to 9 seconds, is similar in character to long-period microseisms. These waves are sharply attenuated at continental margins but propagate easily through either continents alone or oceans alone. From the coast of North America to the Easter Island Rise shocks generally produce short-period surface waves at Honolulu, and other Pacific shocks produce long-period waves. Hawaiian shocks produce short periods on the North American coast.