Lateral variations in the structure of the Philippine Sea Plate

Abstract

Multiple‐filter analysis is applied to surface waves with their paths almost entirely inside the Philippine Sea plate. The resulting dispersion data are used to study the crustal and upper mantle structures of the plate. Effort is made to examine the intraplate structural variations. Part of the Philippine Sea plate appears to have a thin plate thickness of about 30 km and is overlying a very low velocity mantle. Lateral structural variations in the plate are indicated by the dispersion data. The plate can be divided into several elongated regions, all of which are parallel to the eastern plate boundary and each having a rather distinct crustal and upper mantle structure. The active marginal basin region, located immediately to the west of the Mariana trench, probably represents an area of lithospheric generation. This is supported by the very low shear wave velocity, high heat flow, and magmatism. The Kyushu‐Palau ridge along the central portion of the plate seems to have a thicker lithosphere, in contrast to its two flank regions, the Philippine basin and the Parece Vela basin.

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

“…We deduce that there is no obvious velocity change between lithosphere and asthenosphere to about a depth of 100 km in this region. This seems to be somewhat different from previous studies (e.g., Seekins and Teng 1977;Yu and Chang 1991;Oda and Senna 1994). From phase-velocity with periods greater than 50 sec, high velocity entering the Eastern Volcano Belt and Active Marginal Basin should be related to the subduction of the Pacific plate.…”

“…The periods of the peak group-velocity observed in tectonically active regions are not obvious, and the groupand phase-velocities in these regions are mostly lower than the rest of the regions. Perhaps the lithosphere is thin and shear velocity is low in the uppermost mantle in these tectonically active regions (Seekins and Teng 1977;Yu and Chang 1991;Oda and Senna 1994), which are also characterized by high heat flow (Watanabe et al 1970). Indeed, a further velocity structure inversion is necessary for inferring the lithospheric thickness and uppermost-mantle shear velocity beneath these tectonically active regions.…”

“…Past studies of surface waves across the Philippine Sea and the surrounding areas have provided some important information about lateral variations in plate thickness and upper mantle shear velocities (e.g., Seekins and Teng 1977;Yu and Chang 1991;Oda and Senna 1994;Lebedev et al 1997;Nakamura and Shibutani 1998). Although there are some differences between the results, especially for plate thickness in relation to geological and topographic features, the fact that there is lateral variation in structure beneath the Philippine Sea is revealed.…”

Seismic and aseismic slip along subduction zones and their tectonic implications

“…This counter flow may take place in the form of episodic interarc spreading, with upwelling material eventually forming a thin lithosphere between the continental lithosphere and the retreating subduction zone ( Figure Se). Such a thin lithosphere has been found for the Philippine Sea by surface-wave studies [Kanamori and Abe, 196S;Seekins and Teng, 1976]. As this newly created lithosphere cools and becomes rigid, a new episode of subduction may commence at the boundary between this new lithosphere and the continental lithosphere ( Figure Sf).…”

The Earth's Gravity Field and Density Models of the Crust and Lithosphere in the Marginal Basins of Eastern Asia

“…1 and 2). The results of detailed analysis of the Rayleigh and Love waves were used for the density modeling in the Philippine Sea (SEEKINS and TENG, 1977). Combined interpretation of gravimetric and seismic data has made it possible for us to compile a schematic map of the lithosphere (Fig.…”