Crustal structure of the Philippine Sea

Abstract

The results of twenty‐eight seismic refraction profiles recorded in the various physiographic provinces of the Philippine Sea as part of the United States and Japan Science Cooperation Program are presented in four schematic structure sections. The basins of the Philippine Sea have fairly normal oceanic crust that includes, between the sea floor and layer 2, a layer of about 3.5‐km/sec velocity controlling the characteristic rough topography. Crustal thickening beneath the Nansei Shoto, Oki‐Daito, Kyushu‐Palau, and the Honshu‐Mariana ridges is associated mainly with an increase in thickness of the 3.5‐km/sec layer and a thick underlying section of material with a velocity between 5.5 and 6.0 km/sec. Beneath the Nansei Shoto trench and the Honshu‐Mariana trench, there is a tendency for layer 2 to increase and layer 3 to decrease in thickness as the trench is approached from the adjacent oceanic sector.

Lateral Variations of Rayleigh-Wave Dispersions in the Philippine Sea Region

“…For group-velocity with periods of less than 36 sec, the Parece Vela basin shows a higher group-velocity than the whole West Philippine plate, which might indicate a thinner crust and relatively higher velocity in the upper-mantle lid than in the rest of the regions. Murauchi et al (1968) suggested a high P n velocity of about 8.4 km sec -1 beneath the Parece Vela basin, larger than that of the Western Philippine Sea Basin, which has a P n velocity of about 8.0 km sec -1…”

“…Rayleigh-wave phase velocities obtained from the broadband OBS array in the Philippine Sea region also give systematically lower values than those obtained in the Pacific for comparable geological ages (Isse et al 2004). In addition, crustal thickness inferred from seismic refraction profiles reveals that the crust of the Philippine Sea Basin is 12 km thick and that the crust of the Oki-Daito ridge is thicker (Murauchi et al 1968).…”

Hydrothermal Activity in the Okinawa Trough Back-Arc Basin: Geological Background and Hydrothermal Mineralization

“…27.1). Previous surveys on the crustal thickness in the area documented the thinned nature of the continental crust, which is less than 20 km thick (Lee et al 1980;Hirata et al 1991;Klingelhoefer et al 2009), whereas thicker crust occurs in the middle (Murauchi et al 1968;Nagumo et al 1986) and northern parts (Iwasaki et al 1990) of the trough. Such geophysical evidence suggests that backarc basin formation is most pronounced in the southernmost part of the Okinawa Trough.…”

Backarc basin oceanic crust and uppermost mantle seismic velocity structure of the Shikoku Basin, south of Japan

“…In the 1960s, P-wave velocity (V p ) models of these marginal basins in the Philippine Sea were obtained by two-ship refraction experiments (e.g., P3 and P9, shown in Fig. 1) by Murauchi et al (1968). These researchers analyzed the observed travel time data using a slope-intercept method and obtained the layered V p models.…”