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Overview of seismic activity and historical earthquake disasters in Okinawa region
Published in Ömer Aydan, Takashi Ito, Takafumi Seiki, Katsumi Kamemura, Naoki Iwata, 2019 Rock Dynamics Summit, 2019
Y. Kamada, A. Kamiya, S. Arakaki, T. Isikawa, Y. kawajo
The tectonics of the Ryukyu subduction zone is characterized by mainly two factors, firstly sub-ducting the oceanic plate beneath the continental plate, secondly the existence of the active back arc basin called “Okinawa Trough”. The Ryukyu Arc extends over 1,400 km from Kyusyu, Japan to Taiwan, which runs along the Ryukyu trench (Fig.3). The Philippine Sea plate subducts beneath the Eurasian plate northwestward. The Okinawa Trough located northwestward of the Ryukyu Arc is typical back-arc basin in continental margin which the seafloor depth exceeds 2000m, is now active opening (Sibuet et al. 1998, Arai et al. 2016). Associated with the continental rifting, it caused active seismic activity, especially southern part of the Okinawa Trough. Also southwest part of the Ryukyu subduction zone is characterized by extreme fast velocity of the plate convergence rate. Some studies that utilize a Global Positioning System (GPS) show the rate of subducting plate motion is about 7cm/yr, which the rate increase as going to southwestward (Nishimura et al. 2004). In addition, the southern Okinawa Trough is active opening to southward, eventually total relative plate convergence rate result in approximately 12cm/yr (Ando et al. 2009). There is no such subduction zone in the world (Heki et al. 2008). On account of the reason that such the extreme plate convergence rate and no interplate great earthquakes (M>8) have been observed in the last few hundred years, the plate coupling rate in the Ryukyu subduction zone is assumed to be weak (Peterson et al. 1984). On the other hand, recent studies revealed the noteworthy events have discovered in the Ryukyu subduction zone, for example, “Slow-Slip Events” (Heki et al. 2008), “Low-Frequency Earthquakes” (Arai et al. 2016), “Very Low Frequency Earthquakes” (Nakamura et al. 2015). Such of the advanced research could elucidate the complex structure of this area.
Two-stage influences of hydrothermal fluids on pumice near the Iheya North hydrothermal field, Okinawa Trough
Published in Marine Georesources & Geotechnology, 2018
Yuxiang Zhang, Zhigang Zeng, Haiyan Qi, Xuebo Yin, He Li, Xiaoyuan Wang, Shuai Chen
The Okinawa Trough (OT) is a nascent back arc basin developed on the eastern edge of Eurasian continental lithosphere and is located west of the Ryukyu Arc and the Ryukyu Trench, extending from the north of Taiwan Island to the southwest of Kyushu Island (Figure 1). The OT is divided into northern part (NOT), middle part (MOT), and southern part (SOT) by the Tokara fault and the Kerama fault, respectively (Yan and Shi 2014). The OT has extremely high heat flow value (up to 400–600 mW/m2, Yamano et al. 1989) and has active volcanism and hydrothermal activities. Many volcanic belts/zones (e.g., volcanic arc-rift migration phenomenon zone) and isolated submarine volcanoes have been recognized in the OT (Sibuet et al. 1998). Some high-temperature hydrothermal fields have been discovered in the MOT and the SOT (e.g., Halbach, Pracejus, and Maerten 1993; Ishibashi and Urabe 1995; Glasby and Notsu 2003; Suzuki et al. 2008; Kawagucci et al. 2011).