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Numerical Modeling of Mantle Dynamics by Takao Eguchi
Annual Report of the Earth Simulator Center April, Mar 1, 2004
A numerical simulation of mantle convection is the most powerful tool for the understanding of th... more A numerical simulation of mantle convection is the most powerful tool for the understanding of the dynamics and evolution of the Earth's mantle. To this goal, we optimized or newly developed the simulation codes which can handle various complexities relevant for the realistic mantle convection. These codes are utilized to study the effects of solid-state phase transitions and strongly variable viscosity on the convective planforms in the mantle, and to predict the motion of the surface plates on the Earth. Keywords: mantle convection, plate ...
Papers by Takao Eguchi
Journal of Geography (Chigaku Zasshi), 2007
Journal of Geography (Chigaku Zasshi), 2007
Nature, Feb 15, 1990
Observations of crustal deformation associated with seismic swarm and sea-floor volcanic activity... more Observations of crustal deformation associated with seismic swarm and sea-floor volcanic activity off the east coast of the Izu Peninsula, Japan, in July 1989, using a fixed-point GPS network are reported. These measurements are used to capture some rarely observed features of seismic and volcanic activity. GPS fixed-point measurements are used for the first time to follow the evolution with time of the crustal movements; such measurements provide a continuous uninterrupted record of deformation. The observations are supported by independent data from other sources, thus providing further evidence of the utility of the GPS.
Physics of the Earth and Planetary Interiors, Dec 31, 1983
The overall pattern of the recent tectonic stress field in the eastern part of the Eurasian plate... more The overall pattern of the recent tectonic stress field in the eastern part of the Eurasian plate is inferred from the geological features of large transcurrent and reverse faults, graben structures and from focal mechanism solutions of shallow earthquakes. NE-SW striking trajectory lines, of maximum horizontal tectonic stress axis (σ Hmax), are estimated at the north of Tibet and mainland China, but its strike turns to easterly near the eastern margin of the Eurasian plate. This suggests that the main origin of the σ Hmax in East Eurasia is due to a compressive stress regime along, the Himalayan belt, Tibet and the Japan Trench (and also the Sakhalin and Nankai Trough). This tectonic stress field seems to provide some influence on the extensional tectonics in the Shansi region, Baikal, and also in the Okinawa Trough where the N-S opening has been confirmed. The systematic view of the tectonic stress field in East Eurasia, makes it possible to appreciate the fundamental background of a number of complicated intra-plate tectonics.
We present a new view of three-dimensional geometry of slab(s) subducted just beneath the Tokyo m... more We present a new view of three-dimensional geometry of slab(s) subducted just beneath the Tokyo metropolitan area, central Japan. Previously, several different models of the surface geometry of the subducted Philippine sea plate slab (PH slab) have been published using seismological data. First, we discriminate previously unknown seismic slab (called slab SG, or seismic slab SG) above the downgoing Pacific plate slab (PC slab), second propose possible models of the slab SG internal structure, and third discuss and demonstrate the tectonic background of slab SG. It is clear that the recent surface models of PH slab corresponds to the shallowest part of slab SG. Most of previous studies paid little attention to the tectonic characteristics of the vertical extent and/or the bottom geometry of slab SG with variable thickness. The bottom extent of slab SG beneath the Metropolitan area reaches 36.5N at least. The horizontal extent of seismic slab SG covers most of the Kanto Plain Lowland. The bottom depth of slab SG is approximately 120km near 36.5N and 139.0E, being the same as of the surface depth of PC slab there. Below the Sagami trough axis near 34.5N and 140.0E, slab SG locates at a depth of 80 to 90km. We confirmed that southernmost part of slab SG extends to areas around 34.3N and 140.3E at least, where seismic observation network density is not sufficient to locate correctly seismic events. The deepest portion of slab SG generally strikes the NNW-SSE direction, being approximately parallel to the volcanic front. The thickness of slab SG decreases gradually at areas west of the NNW-SSE striking deepest corner. We propose four basic internal models of slab SG as follows. (1) Slab SG consists of both PH slab at shallower depth and a deeper underlain slab (slab SL). (2) Bookshelf-like configuration of northwardly inclined multi-slabs on PC slab due to the intermittent southward shift of accumulation sites of short slab tips with episodic subduction at just south of the previously active paleo-Sagami trough(s). The evolutional bookshelf model is partly similar to accretion process near the deep trench system, but dynamic situation is not the same. (3) A structure combining models (1) and (2). (4) Slab SG is merely the eastern part, having been cooled by the downgoing PC slab, of 65 to 70km thick lithosphere of IOB (Izu Outer Block). IOB is the northeastern margin of the Philippine sea plate, ranging from the volcanic front along the Izu-Bonin Island arc to the Izu-Bonin trench.
International Association of Geodesy Symposia, 1990
Tectonophysics, 1984
Eguchi, T., 1984. Seismotectonics of the FiJi Plateau and Lau Basin. In: R.L. Carlson and K. Koba... more Eguchi, T., 1984. Seismotectonics of the FiJi Plateau and Lau Basin. In: R.L. Carlson and K. Kobayashi (Editors), Geodynamics of Back-arc Regions. Tectonophysics, 102: 17-32. Focal mechanism solutions of shallow earthquakes in the Fiji Plateau and Lau Basin provide significant contributions to the understanding of the recent tectonic movements beneath these marginal seas. Left-lateral shear zones are identified on the linear shallow seismic zone extending from north of the Fiji Islands to the northern end of the Lau Basin. In the central area of the Fiji Plateau and in the northern part of the Lau Basin nearly NW-SE trending opening tectonics is suggested. Nearly E-W striking compressional tectonics is inferred near the western edge of the Hazel Holme Fracture Zone.
Journal of Geography (Chigaku Zasshi), 2007
To unveil dynamic process associated with three-dimensional unsteady mantle convection, we carrie... more To unveil dynamic process associated with three-dimensional unsteady mantle convection, we carried out numerical simulation on passively exerted flows by simplified local hot sources just above the CMB and/or large-scale cool masses beneath smoothed subduction zones. 2. Simulation Method During the study, we used our individual code developed with the finite difference method. The basic three equations are for the
Earth and Planetary Science Letters, 1999
According to the theory of plate tectonics proposed in the late 1960's, the Earth's surfa... more According to the theory of plate tectonics proposed in the late 1960's, the Earth's surface is covered by about ten rigid plates, which are generated at mid-oceanic ridges, move to oceanic trenches, and there subduct into the mantle. A theory of plate tectonics explains most geologic phenomena such as seismicity, volcanism, and magnetic striping of the ocean-floor. However, the theory
Earth, Planets and Space, 1999
We designed a new pop-up type Ocean Bottom Seismometer (OBS) in order to study micro-earthquakes ... more We designed a new pop-up type Ocean Bottom Seismometer (OBS) in order to study micro-earthquakes in off-shore areas. With a 57 cm O.D. sphere of high tension aluminium alloy, the OBS system, including one vertical and one horizontal geophone, can safely operate on ocean floors of up to 6000 m depth for seismic observations. The amplified seismic data and the time code are directly recorded on the four-channel cassette deck for periods of up to one month. The frequency response curve throughout the recording and play-back system is flat for the range, 1-15 Hz (-3 dB). The anchor release and the geophone clamp are operated by an acoustic command signal.
Annual Report of the Earth Simulator Center April, Mar 1, 2004
A numerical simulation of mantle convection is the most powerful tool for the understanding of th... more A numerical simulation of mantle convection is the most powerful tool for the understanding of the dynamics and evolution of the Earth's mantle. To this goal, we optimized or newly developed the simulation codes which can handle various complexities relevant for the realistic mantle convection. These codes are utilized to study the effects of solid-state phase transitions and strongly variable viscosity on the convective planforms in the mantle, and to predict the motion of the surface plates on the Earth. Keywords: mantle convection, plate ...
Journal of Geography (Chigaku Zasshi), 2007
Journal of Geography (Chigaku Zasshi), 2007
Nature, Feb 15, 1990
Observations of crustal deformation associated with seismic swarm and sea-floor volcanic activity... more Observations of crustal deformation associated with seismic swarm and sea-floor volcanic activity off the east coast of the Izu Peninsula, Japan, in July 1989, using a fixed-point GPS network are reported. These measurements are used to capture some rarely observed features of seismic and volcanic activity. GPS fixed-point measurements are used for the first time to follow the evolution with time of the crustal movements; such measurements provide a continuous uninterrupted record of deformation. The observations are supported by independent data from other sources, thus providing further evidence of the utility of the GPS.
Physics of the Earth and Planetary Interiors, Dec 31, 1983
The overall pattern of the recent tectonic stress field in the eastern part of the Eurasian plate... more The overall pattern of the recent tectonic stress field in the eastern part of the Eurasian plate is inferred from the geological features of large transcurrent and reverse faults, graben structures and from focal mechanism solutions of shallow earthquakes. NE-SW striking trajectory lines, of maximum horizontal tectonic stress axis (σ Hmax), are estimated at the north of Tibet and mainland China, but its strike turns to easterly near the eastern margin of the Eurasian plate. This suggests that the main origin of the σ Hmax in East Eurasia is due to a compressive stress regime along, the Himalayan belt, Tibet and the Japan Trench (and also the Sakhalin and Nankai Trough). This tectonic stress field seems to provide some influence on the extensional tectonics in the Shansi region, Baikal, and also in the Okinawa Trough where the N-S opening has been confirmed. The systematic view of the tectonic stress field in East Eurasia, makes it possible to appreciate the fundamental background of a number of complicated intra-plate tectonics.
We present a new view of three-dimensional geometry of slab(s) subducted just beneath the Tokyo m... more We present a new view of three-dimensional geometry of slab(s) subducted just beneath the Tokyo metropolitan area, central Japan. Previously, several different models of the surface geometry of the subducted Philippine sea plate slab (PH slab) have been published using seismological data. First, we discriminate previously unknown seismic slab (called slab SG, or seismic slab SG) above the downgoing Pacific plate slab (PC slab), second propose possible models of the slab SG internal structure, and third discuss and demonstrate the tectonic background of slab SG. It is clear that the recent surface models of PH slab corresponds to the shallowest part of slab SG. Most of previous studies paid little attention to the tectonic characteristics of the vertical extent and/or the bottom geometry of slab SG with variable thickness. The bottom extent of slab SG beneath the Metropolitan area reaches 36.5N at least. The horizontal extent of seismic slab SG covers most of the Kanto Plain Lowland. The bottom depth of slab SG is approximately 120km near 36.5N and 139.0E, being the same as of the surface depth of PC slab there. Below the Sagami trough axis near 34.5N and 140.0E, slab SG locates at a depth of 80 to 90km. We confirmed that southernmost part of slab SG extends to areas around 34.3N and 140.3E at least, where seismic observation network density is not sufficient to locate correctly seismic events. The deepest portion of slab SG generally strikes the NNW-SSE direction, being approximately parallel to the volcanic front. The thickness of slab SG decreases gradually at areas west of the NNW-SSE striking deepest corner. We propose four basic internal models of slab SG as follows. (1) Slab SG consists of both PH slab at shallower depth and a deeper underlain slab (slab SL). (2) Bookshelf-like configuration of northwardly inclined multi-slabs on PC slab due to the intermittent southward shift of accumulation sites of short slab tips with episodic subduction at just south of the previously active paleo-Sagami trough(s). The evolutional bookshelf model is partly similar to accretion process near the deep trench system, but dynamic situation is not the same. (3) A structure combining models (1) and (2). (4) Slab SG is merely the eastern part, having been cooled by the downgoing PC slab, of 65 to 70km thick lithosphere of IOB (Izu Outer Block). IOB is the northeastern margin of the Philippine sea plate, ranging from the volcanic front along the Izu-Bonin Island arc to the Izu-Bonin trench.
International Association of Geodesy Symposia, 1990
Tectonophysics, 1984
Eguchi, T., 1984. Seismotectonics of the FiJi Plateau and Lau Basin. In: R.L. Carlson and K. Koba... more Eguchi, T., 1984. Seismotectonics of the FiJi Plateau and Lau Basin. In: R.L. Carlson and K. Kobayashi (Editors), Geodynamics of Back-arc Regions. Tectonophysics, 102: 17-32. Focal mechanism solutions of shallow earthquakes in the Fiji Plateau and Lau Basin provide significant contributions to the understanding of the recent tectonic movements beneath these marginal seas. Left-lateral shear zones are identified on the linear shallow seismic zone extending from north of the Fiji Islands to the northern end of the Lau Basin. In the central area of the Fiji Plateau and in the northern part of the Lau Basin nearly NW-SE trending opening tectonics is suggested. Nearly E-W striking compressional tectonics is inferred near the western edge of the Hazel Holme Fracture Zone.
Journal of Geography (Chigaku Zasshi), 2007
To unveil dynamic process associated with three-dimensional unsteady mantle convection, we carrie... more To unveil dynamic process associated with three-dimensional unsteady mantle convection, we carried out numerical simulation on passively exerted flows by simplified local hot sources just above the CMB and/or large-scale cool masses beneath smoothed subduction zones. 2. Simulation Method During the study, we used our individual code developed with the finite difference method. The basic three equations are for the
Earth and Planetary Science Letters, 1999
According to the theory of plate tectonics proposed in the late 1960's, the Earth's surfa... more According to the theory of plate tectonics proposed in the late 1960's, the Earth's surface is covered by about ten rigid plates, which are generated at mid-oceanic ridges, move to oceanic trenches, and there subduct into the mantle. A theory of plate tectonics explains most geologic phenomena such as seismicity, volcanism, and magnetic striping of the ocean-floor. However, the theory
Earth, Planets and Space, 1999
We designed a new pop-up type Ocean Bottom Seismometer (OBS) in order to study micro-earthquakes ... more We designed a new pop-up type Ocean Bottom Seismometer (OBS) in order to study micro-earthquakes in off-shore areas. With a 57 cm O.D. sphere of high tension aluminium alloy, the OBS system, including one vertical and one horizontal geophone, can safely operate on ocean floors of up to 6000 m depth for seismic observations. The amplified seismic data and the time code are directly recorded on the four-channel cassette deck for periods of up to one month. The frequency response curve throughout the recording and play-back system is flat for the range, 1-15 Hz (-3 dB). The anchor release and the geophone clamp are operated by an acoustic command signal.
Tectonophysics, 1984
Eguchi, T., 1984. Seismotectonics around the Mariana Trough. In: R.L. Carlson and K. Kobayashi (E... more Eguchi, T., 1984. Seismotectonics around the Mariana Trough. In: R.L. Carlson and K. Kobayashi (Editors), Geodynamics of Back-arc Regions. Tectonophysics, 102: 33-52. Strike-slip type mechanism solutions, with approximately east-west striking tension axes, were obtained for large shallow earthquakes under the central topographic high of the northern Mariana Trough. These solutions are consistent with the model that spreading is in progress in the direction perpendicular to the structural lineations trending N-S in most of the trough and NNW-SSE in the northern part. Weak coupling at the subduction zone between the Pacific plate and the landward plate (Mariana platelet) is suggested by the occurrence of few thrust type and many normal fault type earthquakes near the Mariana Trench. Spreading striking nearly E-W with an approximate total rate of 6 cm/yr in the widest section of the trough is speculatively inferred from the plate motion model of the Philippine Sea plate with respect to the surrounding plates and from the anchored slab model and the collision effect of the Caroline Ridge with the Philippine Sea plate.