Abstract
Abstract We have investigated regional shear-wave splitting beneath the Ryukyu arc in order to clarify the mantle flow beneath the Ryukyu arc and compare it with the extension of the Okinawa Trough. The splitting of regional shear waves (direct S) in the central and southern Ryukyu arc regions was analyzed in terms of fast-polarization direction and delay time using data from 11 short-period stations and two broadband seismic stations. The events occurred at depths ranging between 45 and 217 km, and the magnitude of the events ranged from 2.8 to 5.2. In general, the orientations of fast polarization were found to parallel to the strike of the Ryukyu Trench, with average delay times of 0.25–0.56 s. Specifically, the orientation of fast polarization was parallel to the direction of the extension in the south Ryukyu arc, suggesting that the direction of mantle flow is parallel to the extension in the south Okinawa Trough. However, the orientation of fast polarization was oblique to the direction of extension in the central Ryukyu arc, indicating that the mantle flow beneath the central Ryukyu arc is not parallel to the extension of the central Okinawa Trough. Based on these results, we suggest that the difference between the direction of the mantle flow and that of the lithosphere extension induces extensional strain with a simple shear component, which in turn causes oblique rifting in the central Okinawa Trough.
Highlights
The Okinawa Trough, which is in the rifting stage (Letouzey and Kimura, 1985; Sibuet et al, 1995, 1998), is a good test field for studying the deformation of arcs migrating away from the continent
The observed S-wave splitting in the mantle wedge is induced by aligned olivine, and the polarization of fast S-waves is oriented in the direction of mantle flow (Zhang and Karato, 1995)
The earthquakes at depths shallower than 70 km resulted in fast polarizations that varied among the stations
Summary
The Okinawa Trough, which is in the rifting stage (Letouzey and Kimura, 1985; Sibuet et al, 1995, 1998), is a good test field for studying the deformation of arcs migrating away from the continent. The extensional axes of the focal mechanism solutions in the central and southern Okinawa Trough are oriented NNW-SSE and N-S, respectively (Fournier et al, 2001; Kubo and Fukuyama, 2003). Investigation of the mantle flow beneath the Okinawa Trough would shed light on the mechanism of extension of the trough. The observed S-wave splitting in the mantle wedge is induced by aligned olivine, and the polarization of fast S-waves is oriented in the direction of mantle flow (Zhang and Karato, 1995).
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
