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末永 伸明都市安全研究センター研究員
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■ 論文- 2026年04月, Journal of Geophysical Research: Solid Earth研究論文（学術雑誌）
- Elsevier BV, 2026年02月, Earth and Planetary Science Letters, 676, 119806 - 119806研究論文（学術雑誌）
- Earth and Planetary Physics, 2026年, Earth and Planetary Physics, 10(1) (1), 13 - 21研究論文（学術雑誌）
- Earth and Planetary Physics, 2026年, Earth and Planetary Physics, 10(1) (1), 13 - 21研究論文（学術雑誌）
- Tectonic plates bend and deform when approaching a subduction zone, creating intense faulting and highly variable stress and strain fields across short distances inside the slab. In September 2017, a large Mw8.2 intraplate normal fault occurred in southern Mexico, with an epicentral area located within a seismic gap where no megathrust had struck in more than a century. Despite the relatively young and hot Cocos plate, this seismic episode ruptured almost the entire slab below the brittle–ductile transition zone that normally limits the depth extent of such events. Here, we present a high-resolution thermomechanical model of spontaneous subduction for this area, where bending-induced brittle and ductile deformation and grain plate damage are considered. Modeling results show that the 2017 Mw8.2 Tehuantepec normal fault earthquake occurred due to the reactivation of one of the outer-rise-formed abyssal faults. In addition, the hypocenter was located in a stable, hydrated region of the lithospheric mantle at the transition limit between the elastic and ductile regimes. We found that earthquake rupture orientation is consistent with a region where a clear localized shear band of reduced effective viscosity is predicted. We propose that the rupture of this large intraslab event propagated in the ductile portion of the slab initially by a transformational faulting process, followed by a thermal runaway mechanism at greater depths and higher temperature.Frontiers Media SA, 2025年07月, Frontiers in Earth Science, 13研究論文（学術雑誌）
- Three-dimensional thermomechanical modelling beneath Guerrero, Mexico, and its relation to the occurrence of interplate seismic phenomenaIn this study, we investigated the relationships among the occurrence regions of megathrust earthquakes and slow earthquakes, estimated interplate temperatures, and dehydration processes at the plate interface in the subduction zone of the Cocos plate in Mexico, with a focus on the Guerrero seismic gap. For this purpose, we performed a series of 3-D thermomechanical numerical simulations of subduction based on a combination of multiple unknown model parameters. Comparing the temperature field for the optimal model with the occurrence region of the interplate seismic phenomena, the temperature along the slab surface where megathrust earthquakes tend to occur is estimated to range from 200 to 400 °C. In addition, the occurrence areas of recent long-term slow slip events (hereafter referred to as L-SSEs) with a recurrence interval of ~ 4 years in the range where the amount of slip is 10 cm or more correspond to a temperature range of 350 to 550 °C outside the Guerrero seismic gap region. On the other hand, in the Guerrero seismic gap region, L-SSE slip is observed up to shallower areas, but the updip limit temperature in the region with the largest slip amount (~ 14 cm) is also estimated to be approximately 350 °C. Furthermore, for regions affected by tectonic tremors (hereafter referred to as TTs) within seaside swarms and inland swarms, our temperature estimates range from 500 to 570 °C and from 600 to 700 °C, respectively. Finally, we compared the estimated dehydration processes on the plate interface for the optimal model with interseismic events. These findings suggest that considerable dehydration from MORB within the oceanic crust and ultramafic rock within the slab mantle occurred near long-term slow slip events and tectonic tremor regions.2025年03月, Scientific Reports, 15(1) (1), 7513, 英語研究論文（学術雑誌）
- 2025年, Pure and Applied Geophysics, 182(4) (4)研究論文（学術雑誌）
- 2025年, Progress in Earth and Planetary Science, 12(1) (1)研究論文（学術雑誌）
- Elsevier BV, 2024年08月, Environmental Modelling & Software, 179, 106129 - 106129研究論文（学術雑誌）
- Abstract In southern Chile, the Nazca plate is subducting beneath the South American plate. This region was struck by megathrust earthquakes in 1960 and 2010 and is characterized by the existence of a volcanic chain. In this region, we modeled a three-dimensional thermal structure associated with the subduction of the Nazca plate by using numerical simulations. Based on the obtained temperature distribution, we determined the updip and downdip limit temperatures for the region ruptured by these two megathrust earthquakes. In addition, the distributions of water content and dehydration gradient were calculated by using appropriate phase diagrams and compared with the location of the volcanic chain. As a result, we infer that the coseismic slip of the 2010 Mw8.8 Maule earthquake occurred only at temperatures lower than and around the 350 °C isotherm that resembles the beginning of the brittle‒ductile transition. We also deduce that the rupture of the 1960 Mw9.5 Valdivia earthquake propagated up to the 450 °C isotherm because the magnitude was considerably large and the young hot plate subducted near the Chile Ridge. In addition, the hydrous minerals in the turbidites, MORB and ultramafic rocks released fluids via dehydration reactions, and dehydrated water migrated upward almost vertically, decreasing the melting point of the mantle wedge and contributing to the formation of the volcanic chain.Springer Science and Business Media LLC, 2024年01月, Geoscience Letters, 11(1) (1)研究論文（学術雑誌）
- Abstract Compared to normal arc-related volcanic eruptions, the formation of a volcanic caldera is a relatively atypical event. During caldera formation a series of large volumes of magma are erupted, reducing the structural support for the rock above the magma chamber and creating a large depression at the surface called caldera. Los Humeros volcanic field (LHVF) represents one of the largest volcanic calderas in Mexico. It is located some 400 km from the trench at the eastern edge of the Trans Mexican Volcanic Belt where the depth to the Cocos slab is more than 300 km. In this study we employ high-resolution two-dimensional thermomechanical numerical simulations of magma intrusions and a horizontal tectonic strain rate to better understand the influence of crustal deformation for the formation of Los Humeros caldera. A minimum number of three thermal anomaly pulses of hydrated mantle material (with diameter of 15 km or more) and a regional strain rate of 7.927 × 10–16 s−1 are required for magma to reach the surface. Modeling results show that regional extension coupled with deep thermal anomalies (with a temperature excess of ΔT ≥ 100 °C) that come in a specific chain-type sequence produce surface deformation patterns similar to LHVF. We propose an asthenospheric sub-slab deep source (> 300 km depth) for the thermal anomalies where previous studies showed the existence of a gap or tear in the Cocos slab.Springer Science and Business Media LLC, 2023年12月, Scientific Reports, 13(1) (1)研究論文（学術雑誌）
- Abstract The subduction of the Philippine Sea (PHS) plate along the Nankai Trough in in southwest Japan is a relatively recent process compared with subduction along the Japan Trench in northeast Japan. However, the tectonic evolution of the PHS plate along the Nankai Trough is still controversial and not fully understood. There are several competing hypotheses based on different estimates for the time variations of convergence rate and plate age. Our study employs numerical modelling of subduction in order to evaluate the slab evolution for the last 15 Myr and aims to evaluate each tectonic scenario against the present-day slab geometry along a profile passing through the Shikoku and Chugoku regions. The modelling strategy involves a parameter study where subduction initiation and various subduction parameters are analyzed in terms of subduction geometry evolution. Two-dimensional visco-elasto-plastic numerical simulations of spontaneous bending subduction predict that convergence rate and plate age variations play an important role in the evolution of subduction geometry. Modeling results after 15 Myr of evolution reveal that the tectonic model based on a high convergence rate between ~ 15 Ma and ~ 3 Ma produces a slab geometry that agrees well with the observed present-day slab shape specific for the Shikoku and Chugoku regions.Springer Science and Business Media LLC, 2023年10月, Scientific Reports, 13(1) (1)研究論文（学術雑誌）
- Abstract The southern Chile subduction zone is a complex tectonic environment, where the Chile Ridge, the Nazca (NZ) and Antarctic (AN) plates subduct underneath the South American (SA) plate. The intersection between the NZ, AN and SA plates is referred to as the Chile Triple Junction (CTJ). In this region, a gap, often referred to as a slab window, has been formed between the NZ and AN slabs due to the divergence in their plate motion velocities, with volcanoes existing mainly above the subducted NZ and AN plates. In this study, we constructed a three-dimensional thermomechanical model associated with simultaneous subduction of the NZ and AN plates near the CTJ. The results show that the current temperature distributions on the upper surface of the slabs are higher closer to the Chile Ridge, and the AN plate has a distribution of elevated temperatures relative to the NZ plate at the same depth due to the northward migration of the CTJ and the slower convergence rate of the AN plate. Moreover, we calculated the water content and dehydration gradient from the temperature distribution near the upper surface of the slab and discussed their relationship to the distribution of volcanoes. In the northern part of the model domain, high dehydration gradients were obtained below the volcanic chain. Therefore, we suggest that the water released from the slab and the mantle wedge decreased the melting point of the mantle wedge just above the slab and produced melts, which may have contributed to form the overlying volcanoes.Springer Science and Business Media LLC, 2023年07月, Geoscience Letters, 10(1) (1)研究論文（学術雑誌）
- Abstract The geometry of the Philippine Sea slab (PHS) subducting beneath the Japanese islands has been imaged to 400 km depth beneath the Kyushu and Chugoku regions, whereas the PHS slab geometry beneath the Hokuriku region has only been determined to ~ 140 km depth, thereby indicating a large east–west asymmetry in the slab subduction. However, geologic evidence suggests that there was symmetrical east–west seafloor spreading along the axis of the Kinan seamount chain when the Shikoku basin was an active spreading center in the PHS plate. This inconsistency suggests that the PHS slab should be present beneath the Hokuriku region. Here we perform P-wave travel-time tomography across central Japan and conduct a two-dimensional plate subduction numerical simulation that reproduces the dual subduction of the PHS and Pacific (PAC) plates to elucidate the PHS slab geometry beneath central Japan. The tomography results reveal a high-velocity anomaly at ~ 150–250 km depth that extends from Wakasa bay to Noto peninsula and a slab window beneath the Hokuriku region. The numerical simulation results suggest that the PHS slab may have torn when it collided with the PAC slab, with the once leading edge of the PHS slab now present along the upper surface of the PAC slab beneath Noto peninsula. These results indicate that the PHS slab exists at ~ 250 km depth beneath the Hokuriku region, although it has been torn owing to its collision with the PAC slab, with this tear propagating westward to form a triangular slab window beneath the Hokuriku region. Graphical AbstractSpringer Science and Business Media LLC, 2023年05月, Earth, Planets and Space, 75(1) (1)研究論文（学術雑誌）
- 2023年, Physics of the Earth and Planetary Interiors, 334研究論文（学術雑誌）
- Abstract The Alaska subduction zone is characterized by a subducting oceanic plateau, which is referred to as the Yakutat terrane. Tectonic tremors occur in this zone, and there are few volcanoes above the subducted Yakutat terrane. In this study, we performed a 3-D numerical simulation of a thermal structure associated with the simultaneous subduction of the Yakutat terrane and Pacific plate to elucidate the mechanism of tectonic tremors, which typically involve the presence of water. We calculated the water content distribution near the slab surface by using the thermal structure obtained from our simulation and phase diagrams of the hydrous minerals included in the slab. As a result, dehydration from the marine sedimentary layer and oceanic crust was observed near the area where tectonic tremors occurred. Tectonic tremors occur only in the Yakutat terrane because the marine sedimentary layer and oceanic crust are thicker there, and the total amount of water content in these layers is higher; therefore, the amount of dehydration is also higher there than in the Pacific plate. Additionally, there are few volcanoes above the subducted Yakutat terrane because little water remains within the slab beneath the volcanic chain where magma is produced.Springer Science and Business Media LLC, 2022年12月, Scientific Reports, 12(1) (1)研究論文（学術雑誌）
- 2022年, Tectonophysics, 843研究論文（学術雑誌）
- Tokyo Geographical Society, 2021年08月, Journal of Geography (Chigaku Zasshi), 130(4) (4), 585 - 597研究論文（学術雑誌）
- Several interplate seismic events, such as short-term slow slip events (S-SSEs) and low-frequency earthquakes (LFEs), have been identified in the Ryukyu Trench, southwestern Japan. As one of the specific characteristics of this seismicity, the depths at which S-SSEs occur at the plate interface beneath Okinawa Island are approximately 5-10 km shallower than those beneath the Yaeyama Islands. To elucidate the cause of this difference in depth, we constructed a three-dimensional, Cartesian thermomechanical subduction model and applied the subduction history of the Philippine Sea (PHS) plate in the model region. As a result, the interplate temperatures at which S-SSEs take place were estimated to range from 350 to 450 °C beneath Okinawa Island and from 500 to 600 °C beneath the Yaeyama Islands. The former temperature range is consistent with previous thermal modelling studies for the occurrence of slow earthquakes, but the latter temperature range is by approximately 150 °C higher than the former. Therefore, explaining how the depth difference in S-SSEs could be caused from the aspect of only the thermal regime is difficult. Using phase diagrams for hydrous minerals in the oceanic crust and mantle wedge, we also estimated the water content distribution on and above the plate interface of the PHS plate. Near the S-SSE fault planes, almost the same amount of dehydration associated with phase transformations of hydrous minerals from blueschist to amphibolite and from amphibolite to amphibole eclogite within the oceanic crust were inferred along Okinawa Island and the Yaeyama Islands, respectively. On the other hand, the phase transformations within the mantle wedge were inferred only beneath the Yaeyama Islands, whereas no specific phase transformation was inferred beneath Okinawa Island around the S-SSE occurrence region. Therefore, we conclude that dehydrated fluid derived from the oceanic crust at the plate interface would play a key role in the occurrence of S-SSEs.2021年05月, Scientific reports, 11(1) (1), 11251 - 11251, 英語, 国際誌研究論文（学術雑誌）
- The SW Japan arc built by subduction of the Philippine Sea (PHS) plate exhibits uneven distribution of volcanoes: thirteen Quaternary composite volcanoes form in the western half of this arc, Kyushu Island, while only two in the eastern half, Chugoku district. Reconstruction of the PHS plate back to 14 Ma, together with examinations based on thermal structure models constrained by high-density heat flow data and a petrological model for dehydration reactions suggest that fluids are discharged actively at depths of 90-100 km in the hydrous layer at the top of the old (> 50 Ma), hence, cold lithosphere sinking beneath Kyushu Island. In contrast, the young (15-25 Ma) oceanic crust downgoing beneath Chugoku district releases fluids largely at shallower depths, i.e. beneath the non-volcanic forearc, to cause characteristic tectonic tremors and low-frequency earthquakes (LFEs) and be the source of specific brine springs. Much larger amounts of fluids supplied to the magma source region in the western SW Japan arc could build more densely-distributed volcanoes.2020年09月, Scientific reports, 10(1) (1), 15005 - 15005, 英語, 国際誌研究論文（学術雑誌）
- 2019年09月, Journal of Geodynamics, 129, 299 - 312, 英語[査読有り]研究論文（学術雑誌）
- 2019年06月, Journal of Geophysical Research: Solid Earth, 124(7) (7), 6848 - 6865, 英語[査読有り]研究論文（学術雑誌）
- 2018年03月, Journal of Geophysical Research Solid Earth, 123(4) (4), 3080 - 3097, 英語[査読有り]研究論文（学術雑誌）
- 2018年01月, Tectonophysics, 723, 288 - 296, 英語[査読有り]研究論文（学術雑誌）
- 2016年11月, PHYSICS OF THE EARTH AND PLANETARY INTERIORS, 260, 44 - 52, 英語[査読有り]研究論文（学術雑誌）