Origin of the southern Okinawa Trough volcanism from detailed seismic tomography

Abstract

[1] Magmatism associated with subducting plate edges or slab tears has been suggested in the southern Okinawa Trough. The cross back-arc volcanic trail, which consists of a cluster of about 70 seamounts, is located above a Ryukyu slab tear lying along the 123.3°E meridian. In November 2003, more than 3300 earthquakes recorded in this area by 15 ocean bottom seismometers and surrounding land stations during a period of 12 days were used to determine the three-dimensional Vp and Vs velocity structures and Vp/Vs ratios. A mantle inflow characterized by low Vp and Vs and high Vp/Vs passing through the slab tear is imaged. The fluid and/or melt component is rising obliquely from the slab tear in the directions of the cross back-arc volcanic trail, the northern slope of the southern Okinawa Trough and to north of Iriomote Island. The asthenospheric intake is also imaged by an inclined chip-like high Vp/Vs and low Vp and Vs body dipping northerly, which might be linked to the slab retreat. West of the slab tear, most of the earthquakes are located around low Vp and Vs and high Vp/Vs bodies, which suggests that the seismicity is related to magmatic and/or fluid activities. East of it, earthquakes are concentrated in an area characterized by high Vp and Vs velocities and low Vp/Vs, suggesting that the magma chamber is absent beneath the axial part of the trough and that normal faulting is the main factor controlling the seismicity.

Mantle flow through a tear in the Nazca slab inferred from shear wave splitting

“…Studies of the slab-mantle relationship are often broad in scope, utilizing coarse global tomography models to discuss mantle-scale processes [e.g., Zhao, 2004;Li et al, 2008;Faccenna et al, 2014]. Relatively little work has been done connecting slab tears [e.g., MacDougall et al, 2014], a prominent feature in seismic imaging of subduction zones worldwide [e.g., Lin et al, 2007;Miller et al, 2009;Jolivet et al, 2015], to mantle dynamics. Relatively little work has been done connecting slab tears [e.g., MacDougall et al, 2014], a prominent feature in seismic imaging of subduction zones worldwide [e.g., Lin et al, 2007;Miller et al, 2009;Jolivet et al, 2015], to mantle dynamics.…”

Tomography of the westernmost Ryukyu subduction zone and the serpentinization of the fore‐arc mantle

“…Recently, Lin et al [2004] provided a new model for NE Taiwan using CWB data, while we show in this paper that a joint network approach, despite its uneven aperture toward the east, is helpful to better constrain the structure beneath the margin of the Taiwan network. In a follow‐up effort, Lin et al [2007] extended their model to offshore 124°E by incorporating JMA and 12‐day OBS data. In addition to the difference in data set, this study differs from Lin et al [2004, 2007] in the inversion strategy and interpretations.…”

New Attenuation Relationship for Peak Ground and Pseudo-Spectral Acceleration of Normal-Faulting Earthquakes in Offshore Northeast Taiwan

“…As evaluated by McGarr (1984), the crustal strength in an extensional region is approximately one third of that in a compressional region. The Ryukyu Arc and Okinawa Trough, where the analyzed normal-faulting earthquakes occurred, are considered typical extensional tectonic environments (Shinjo 1999;Lin et al 2004Lin et al , 2007. By contrast, the source region where the normal-faulting Fukushima earthquake and its related normal-faulting sequence occurred was considered a typical E-W compressional environment (Kubo et al 2002;Townend and Zoback 2006) before the 2011 Tohoku earthquake (M w 9.0).…”