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A stagnant slab is a subducted slab of oceanic lithosphere subhorizontally deflected above, across, or below the 660 km discontinuity. This phenomenon has now been widely recognized beneath subduction zones around the circum-Pacific and in the Mediterranean. Collaboration of seismic and electromagnetic observations, mineral physics measurements, and geodynamic modeling has begun to provide a consistent picture of stagnant slab.

type:text, A stagnant slab is a subducted slab of oceanic lithosphere subhorizontally deflected above, across, or below the 660 km discontinuity. This phenomenon has now been widely recognized beneath subduction zones around the circum-Pacific and in the Mediterranean. Collaboration of seismic and electromagnetic observations, mineral physics measurements, and geodynamic modeling has begun to provide a consistent picture of stagnant slab.

A stagnant slab is a subducted slab of oceanic lithosphere subhorizontally deflected above, across, or below the 660 km discontinuity. This phenomenon has now been widely recognized beneath subduction zones around the circum-Pacific and in the Mediterranean. Collaboration of seismic and electromagnetic observations, mineral physics measurements, and geodynamic modeling has begun to provide a consistent picture of stagnant slab.

A stagnant slab is a subducted slab of oceanic lithosphere subhorizontally deflected above, across, or below the 660 km discontinuity. This phenomenon has now been widely recognized beneath subduction zones around the circum-Pacific and in the Mediterranean. Collaboration of seismic and electromagnetic observations, mineral physics measurements, and geodynamic modeling has begun to provide a consistent picture of stagnant slab.

[1] We determined three-dimensional shear wave speed structure beneath the South Pacific superswell down to a depth of 200 km by analyzing Rayleigh wave records from broadband ocean bottom seismograph stations and island stations in the Pacific Ocean. The ocean bottom stations were deployed from 2003 to 2005 on the seafloor in the French Polynesian region, which enabled us to study the upper mantle structure beneath the Superswell with unprecedentedly high resolution. We measured the dispersions of fundamental mode Rayleigh waves at periods between 40 and 140 seconds by the two-station method. We found pronounced slow anomalies near the hot spots and in the Lau Basin. The slow anomalies beneath the hot spots have deeper-rooted than those associated with the Lau basin. The slow anomalies near the Society, Macdonald, Marquesas, and Pitcairn hot spots continue down to at least 200 km depth.

[1] We obtained three-dimensional (3-D) shear wave speed structure beneath the Philippine Sea and the surrounding region from seismograms recorded by land-based and long-term broadband ocean bottom seismographic stations. The ocean bottom data gave us a better station coverage to obtain a higher spatial resolution (about 300–400 km) in the Philippine Sea than in previous studies. We employed a new technique of surface wave tomography, in which multimode phase speeds are measured and inverted for a 3-D shear wave speed structure by incorporating the effects of finite frequency and ray bending. There is a sharp speed contrast along the Izu-Bonin-Mariana trench, across which the Philippine Sea side has a significantly slower upper mantle than the Pacific Ocean side. In the upper 120 km, the shear wave speed structure is well correlated with the age of the provinces. At depths greater than 160 km, the pattern is dominated by fast anomalies of the subducted slabs of the Pacific plate and two slow anomalies to the south of the Daito ridge and in the southernmost part of the Philippine Sea.

[1] We determined three-dimensional shear wave speed structure beneath the South Pacific superswell down to a depth of 200 km by analyzing Rayleigh wave records from broadband ocean bottom seismograph stations and island stations in the Pacific Ocean. The ocean bottom stations were deployed from 2003 to 2005 on the seafloor in the French Polynesian region, which enabled us to study the upper mantle structure beneath the Superswell with unprecedentedly high resolution. We measured the dispersions of fundamental mode Rayleigh waves at periods between 40 and 140 seconds by the two-station method. We found pronounced slow anomalies near the hot spots and in the Lau Basin. The slow anomalies beneath the hot spots have deeper-rooted than those associated with the Lau basin. The slow anomalies near the Society, Macdonald, Marquesas, and Pitcairn hot spots continue down to at least 200 km depth.

[1] We obtained three-dimensional (3-D) shear wave speed structure beneath the Philippine Sea and the surrounding region from seismograms recorded by land-based and long-term broadband ocean bottom seismographic stations. The ocean bottom data gave us a better station coverage to obtain a higher spatial resolution (about 300–400 km) in the Philippine Sea than in previous studies. We employed a new technique of surface wave tomography, in which multimode phase speeds are measured and inverted for a 3-D shear wave speed structure by incorporating the effects of finite frequency and ray bending. There is a sharp speed contrast along the Izu-Bonin-Mariana trench, across which the Philippine Sea side has a significantly slower upper mantle than the Pacific Ocean side. In the upper 120 km, the shear wave speed structure is well correlated with the age of the provinces. At depths greater than 160 km, the pattern is dominated by fast anomalies of the subducted slabs of the Pacific plate and two slow anomalies to the south of the Daito ridge and in the southernmost part of the Philippine Sea.