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Jiří Vaněk - One of the best experts on this subject based on the ideXlab platform.
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Internal tectonic structure of the Central American Wadati-Benioff Zone based on analysis of aftershock sequences
Journal of Geophysical Research, 2007Co-Authors: Aleš Špičák, Václav Hanuš, Jiří Vaněk, Marie BěhounkováAbstract:[1] Relocated Engdahl et al. (1998) global seismological data for 10 aftershock sequences were used to analyze the internal tectonic structure of the Central American subduction Zone; the main shocks of several of these were the most destructive and often referenced earthquakes in the region (e.g., the 1970 Chiapas, 1983 Osa, 1992 Nicaragua, 1999 Quepos, 2001 El Salvador earthquakes). The spatial analysis of aftershock foci distribution was performed in a rotated Cartesian coordinate system (x, y, z) related to the Wadati-Benioff Zone, and not in a standard coordinate system (ϕ, λ, h are latitude, longitude, focal depth, respectively). Available fault plane solutions were also transformed into the plane approximating the Wadati-Benioff Zone. The spatial distribution of earthquakes in each aftershock sequence was modeled as either a plane fit using a least squares approximation or a volume fit with a minimum thickness rectangular box. The analysis points to a quasi-planar distribution of earthquake foci in all aftershock sequences, manifesting the appurtenance of aftershocks to fracture Zones. Geometrical parameters of fracture Zones (strike, dip, and dimensions) hosting individual sequences were calculated and compared with the seafloor morphology of the Cocos Plate. The smooth character of the seafloor correlates with the aftershock fracture Zones oriented parallel to the trench and commonly subparallel to the subducting slab, whereas subduction of the Cocos Ridge and seamounts around the Quepos Plateau coincides with steeply dipping fracture Zones. Transformed focal mechanisms are almost exclusively (>90%) of normal character.
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Earthquake occurrence along the Java trench in front of the onset of the Wadati‐Benioff Zone: Beginning of a new subduction cycle?
Tectonics, 2007Co-Authors: Aleš Špičák, Václav Hanuš, Jiří VaněkAbstract:[1] Spatial distribution of earthquake foci in the central part of the Sunda Arc was analyzed using global seismological data. The analysis revealed the existence of a distinct strip of earthquakes distributed along the Java trench, separated by a trench-parallel, 50–150 km wide aseismic link from seismicity belonging to the Wadati-Benioff Zone of the recently subducting slab. The seismicity pattern at the plate margin corresponds well with the morphology of the seafloor: The along-trench seismicity correlates with the position of the Java trench and the onset of the Wadati-Benioff Zone correlates with the Java trough. The GPS measurements performed in three analogous structural units of the neighboring Sumatran convergent margin point to substantial differences in velocities of movement of the respective units and correlate with the spatial distribution of earthquake foci. We interpret the distinct along-trench seismicity as a consequence of the onset of a new subduction cycle due to the rapid convergent movement of the Indo-Australian plate relative to the aseismic lithospheric link.
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earthquake occurrence along the java trench in front of the onset of the wadati Benioff Zone beginning of a new subduction cycle
Tectonics, 2007Co-Authors: Aleš Špičák, Václav Hanuš, Jiří VaněkAbstract:[1] Spatial distribution of earthquake foci in the central part of the Sunda Arc was analyzed using global seismological data. The analysis revealed the existence of a distinct strip of earthquakes distributed along the Java trench, separated by a trench-parallel, 50–150 km wide aseismic link from seismicity belonging to the Wadati-Benioff Zone of the recently subducting slab. The seismicity pattern at the plate margin corresponds well with the morphology of the seafloor: The along-trench seismicity correlates with the position of the Java trench and the onset of the Wadati-Benioff Zone correlates with the Java trough. The GPS measurements performed in three analogous structural units of the neighboring Sumatran convergent margin point to substantial differences in velocities of movement of the respective units and correlate with the spatial distribution of earthquake foci. We interpret the distinct along-trench seismicity as a consequence of the onset of a new subduction cycle due to the rapid convergent movement of the Indo-Australian plate relative to the aseismic lithospheric link.
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how the state of stress varies in the wadati Benioff Zone indications from focal mechanisms in the wadati Benioff Zone beneath sumatra and java
Geophysical Journal International, 2000Co-Authors: Alice Slancová, Václav Hanuš, Aleš Špičák, Jiří VaněkAbstract:Summary This study concentrates on the detailed determination of the state of stress in the Wadati–Benioff Zone in the lithosphere subducting under Sumatra and Java. The orientations of P- and T-axes of earthquake focal mechanisms (HCMT) are used to define a system of domains in which a uniform state of stress is assumed. The method of Gephart & Forsyth is then used to determine the state of stress in each domain. We succeeded in delimiting eight domains: three (SI–SIII) in the Sumatra region and five (JI–JV) in the Java region. Domains with similar states of stress occur in both regions in similar positions. The maximum compression σ1 is perpendicular to the trench in domains SI, SII and JII, that is, within the depth range 0–165 km. The orientation of σ1 is almost parallel to the trench in domains SIII and JIII (depth range 25–225 km). The boundary between domains SII and SIII, and JII and JIII is not distinct (covering the depth range 40–165 km). It seems that the focal mechanisms belonging to domains SII and SIII, and similarly to domains JII and JIII, occur in different stress layers and that we observe an overlap of earthquakes with different focal mechanisms from two different stress-state layers, parallel to the Wadati–Benioff Zone. In domains JIV and JV, the states of stress correspond to the stress pattern observed in other subduction Zones: slab-dip-parallel extension is observed in domain JIV (depth range 225–315 km) and slab-dip-parallel compression is observed in domain JV (deeper than 400 km).
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How the state of stress varies in the Wadati–Benioff Zone: indications from focal mechanisms in the Wadati–Benioff Zone beneath Sumatra and Java
Geophysical Journal International, 2000Co-Authors: Alice Slancová, Václav Hanuš, Aleš Špičák, Jiří VaněkAbstract:Summary This study concentrates on the detailed determination of the state of stress in the Wadati–Benioff Zone in the lithosphere subducting under Sumatra and Java. The orientations of P- and T-axes of earthquake focal mechanisms (HCMT) are used to define a system of domains in which a uniform state of stress is assumed. The method of Gephart & Forsyth is then used to determine the state of stress in each domain. We succeeded in delimiting eight domains: three (SI–SIII) in the Sumatra region and five (JI–JV) in the Java region. Domains with similar states of stress occur in both regions in similar positions. The maximum compression σ1 is perpendicular to the trench in domains SI, SII and JII, that is, within the depth range 0–165 km. The orientation of σ1 is almost parallel to the trench in domains SIII and JIII (depth range 25–225 km). The boundary between domains SII and SIII, and JII and JIII is not distinct (covering the depth range 40–165 km). It seems that the focal mechanisms belonging to domains SII and SIII, and similarly to domains JII and JIII, occur in different stress layers and that we observe an overlap of earthquakes with different focal mechanisms from two different stress-state layers, parallel to the Wadati–Benioff Zone. In domains JIV and JV, the states of stress correspond to the stress pattern observed in other subduction Zones: slab-dip-parallel extension is observed in domain JIV (depth range 225–315 km) and slab-dip-parallel compression is observed in domain JV (deeper than 400 km).
Aleš Špičák - One of the best experts on this subject based on the ideXlab platform.
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Internal tectonic structure of the Central American Wadati-Benioff Zone based on analysis of aftershock sequences
Journal of Geophysical Research, 2007Co-Authors: Aleš Špičák, Václav Hanuš, Jiří Vaněk, Marie BěhounkováAbstract:[1] Relocated Engdahl et al. (1998) global seismological data for 10 aftershock sequences were used to analyze the internal tectonic structure of the Central American subduction Zone; the main shocks of several of these were the most destructive and often referenced earthquakes in the region (e.g., the 1970 Chiapas, 1983 Osa, 1992 Nicaragua, 1999 Quepos, 2001 El Salvador earthquakes). The spatial analysis of aftershock foci distribution was performed in a rotated Cartesian coordinate system (x, y, z) related to the Wadati-Benioff Zone, and not in a standard coordinate system (ϕ, λ, h are latitude, longitude, focal depth, respectively). Available fault plane solutions were also transformed into the plane approximating the Wadati-Benioff Zone. The spatial distribution of earthquakes in each aftershock sequence was modeled as either a plane fit using a least squares approximation or a volume fit with a minimum thickness rectangular box. The analysis points to a quasi-planar distribution of earthquake foci in all aftershock sequences, manifesting the appurtenance of aftershocks to fracture Zones. Geometrical parameters of fracture Zones (strike, dip, and dimensions) hosting individual sequences were calculated and compared with the seafloor morphology of the Cocos Plate. The smooth character of the seafloor correlates with the aftershock fracture Zones oriented parallel to the trench and commonly subparallel to the subducting slab, whereas subduction of the Cocos Ridge and seamounts around the Quepos Plateau coincides with steeply dipping fracture Zones. Transformed focal mechanisms are almost exclusively (>90%) of normal character.
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Earthquake occurrence along the Java trench in front of the onset of the Wadati‐Benioff Zone: Beginning of a new subduction cycle?
Tectonics, 2007Co-Authors: Aleš Špičák, Václav Hanuš, Jiří VaněkAbstract:[1] Spatial distribution of earthquake foci in the central part of the Sunda Arc was analyzed using global seismological data. The analysis revealed the existence of a distinct strip of earthquakes distributed along the Java trench, separated by a trench-parallel, 50–150 km wide aseismic link from seismicity belonging to the Wadati-Benioff Zone of the recently subducting slab. The seismicity pattern at the plate margin corresponds well with the morphology of the seafloor: The along-trench seismicity correlates with the position of the Java trench and the onset of the Wadati-Benioff Zone correlates with the Java trough. The GPS measurements performed in three analogous structural units of the neighboring Sumatran convergent margin point to substantial differences in velocities of movement of the respective units and correlate with the spatial distribution of earthquake foci. We interpret the distinct along-trench seismicity as a consequence of the onset of a new subduction cycle due to the rapid convergent movement of the Indo-Australian plate relative to the aseismic lithospheric link.
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earthquake occurrence along the java trench in front of the onset of the wadati Benioff Zone beginning of a new subduction cycle
Tectonics, 2007Co-Authors: Aleš Špičák, Václav Hanuš, Jiří VaněkAbstract:[1] Spatial distribution of earthquake foci in the central part of the Sunda Arc was analyzed using global seismological data. The analysis revealed the existence of a distinct strip of earthquakes distributed along the Java trench, separated by a trench-parallel, 50–150 km wide aseismic link from seismicity belonging to the Wadati-Benioff Zone of the recently subducting slab. The seismicity pattern at the plate margin corresponds well with the morphology of the seafloor: The along-trench seismicity correlates with the position of the Java trench and the onset of the Wadati-Benioff Zone correlates with the Java trough. The GPS measurements performed in three analogous structural units of the neighboring Sumatran convergent margin point to substantial differences in velocities of movement of the respective units and correlate with the spatial distribution of earthquake foci. We interpret the distinct along-trench seismicity as a consequence of the onset of a new subduction cycle due to the rapid convergent movement of the Indo-Australian plate relative to the aseismic lithospheric link.
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how the state of stress varies in the wadati Benioff Zone indications from focal mechanisms in the wadati Benioff Zone beneath sumatra and java
Geophysical Journal International, 2000Co-Authors: Alice Slancová, Václav Hanuš, Aleš Špičák, Jiří VaněkAbstract:Summary This study concentrates on the detailed determination of the state of stress in the Wadati–Benioff Zone in the lithosphere subducting under Sumatra and Java. The orientations of P- and T-axes of earthquake focal mechanisms (HCMT) are used to define a system of domains in which a uniform state of stress is assumed. The method of Gephart & Forsyth is then used to determine the state of stress in each domain. We succeeded in delimiting eight domains: three (SI–SIII) in the Sumatra region and five (JI–JV) in the Java region. Domains with similar states of stress occur in both regions in similar positions. The maximum compression σ1 is perpendicular to the trench in domains SI, SII and JII, that is, within the depth range 0–165 km. The orientation of σ1 is almost parallel to the trench in domains SIII and JIII (depth range 25–225 km). The boundary between domains SII and SIII, and JII and JIII is not distinct (covering the depth range 40–165 km). It seems that the focal mechanisms belonging to domains SII and SIII, and similarly to domains JII and JIII, occur in different stress layers and that we observe an overlap of earthquakes with different focal mechanisms from two different stress-state layers, parallel to the Wadati–Benioff Zone. In domains JIV and JV, the states of stress correspond to the stress pattern observed in other subduction Zones: slab-dip-parallel extension is observed in domain JIV (depth range 225–315 km) and slab-dip-parallel compression is observed in domain JV (deeper than 400 km).
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How the state of stress varies in the Wadati–Benioff Zone: indications from focal mechanisms in the Wadati–Benioff Zone beneath Sumatra and Java
Geophysical Journal International, 2000Co-Authors: Alice Slancová, Václav Hanuš, Aleš Špičák, Jiří VaněkAbstract:Summary This study concentrates on the detailed determination of the state of stress in the Wadati–Benioff Zone in the lithosphere subducting under Sumatra and Java. The orientations of P- and T-axes of earthquake focal mechanisms (HCMT) are used to define a system of domains in which a uniform state of stress is assumed. The method of Gephart & Forsyth is then used to determine the state of stress in each domain. We succeeded in delimiting eight domains: three (SI–SIII) in the Sumatra region and five (JI–JV) in the Java region. Domains with similar states of stress occur in both regions in similar positions. The maximum compression σ1 is perpendicular to the trench in domains SI, SII and JII, that is, within the depth range 0–165 km. The orientation of σ1 is almost parallel to the trench in domains SIII and JIII (depth range 25–225 km). The boundary between domains SII and SIII, and JII and JIII is not distinct (covering the depth range 40–165 km). It seems that the focal mechanisms belonging to domains SII and SIII, and similarly to domains JII and JIII, occur in different stress layers and that we observe an overlap of earthquakes with different focal mechanisms from two different stress-state layers, parallel to the Wadati–Benioff Zone. In domains JIV and JV, the states of stress correspond to the stress pattern observed in other subduction Zones: slab-dip-parallel extension is observed in domain JIV (depth range 225–315 km) and slab-dip-parallel compression is observed in domain JV (deeper than 400 km).
Václav Hanuš - One of the best experts on this subject based on the ideXlab platform.
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Internal tectonic structure of the Central American Wadati-Benioff Zone based on analysis of aftershock sequences
Journal of Geophysical Research, 2007Co-Authors: Aleš Špičák, Václav Hanuš, Jiří Vaněk, Marie BěhounkováAbstract:[1] Relocated Engdahl et al. (1998) global seismological data for 10 aftershock sequences were used to analyze the internal tectonic structure of the Central American subduction Zone; the main shocks of several of these were the most destructive and often referenced earthquakes in the region (e.g., the 1970 Chiapas, 1983 Osa, 1992 Nicaragua, 1999 Quepos, 2001 El Salvador earthquakes). The spatial analysis of aftershock foci distribution was performed in a rotated Cartesian coordinate system (x, y, z) related to the Wadati-Benioff Zone, and not in a standard coordinate system (ϕ, λ, h are latitude, longitude, focal depth, respectively). Available fault plane solutions were also transformed into the plane approximating the Wadati-Benioff Zone. The spatial distribution of earthquakes in each aftershock sequence was modeled as either a plane fit using a least squares approximation or a volume fit with a minimum thickness rectangular box. The analysis points to a quasi-planar distribution of earthquake foci in all aftershock sequences, manifesting the appurtenance of aftershocks to fracture Zones. Geometrical parameters of fracture Zones (strike, dip, and dimensions) hosting individual sequences were calculated and compared with the seafloor morphology of the Cocos Plate. The smooth character of the seafloor correlates with the aftershock fracture Zones oriented parallel to the trench and commonly subparallel to the subducting slab, whereas subduction of the Cocos Ridge and seamounts around the Quepos Plateau coincides with steeply dipping fracture Zones. Transformed focal mechanisms are almost exclusively (>90%) of normal character.
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Earthquake occurrence along the Java trench in front of the onset of the Wadati‐Benioff Zone: Beginning of a new subduction cycle?
Tectonics, 2007Co-Authors: Aleš Špičák, Václav Hanuš, Jiří VaněkAbstract:[1] Spatial distribution of earthquake foci in the central part of the Sunda Arc was analyzed using global seismological data. The analysis revealed the existence of a distinct strip of earthquakes distributed along the Java trench, separated by a trench-parallel, 50–150 km wide aseismic link from seismicity belonging to the Wadati-Benioff Zone of the recently subducting slab. The seismicity pattern at the plate margin corresponds well with the morphology of the seafloor: The along-trench seismicity correlates with the position of the Java trench and the onset of the Wadati-Benioff Zone correlates with the Java trough. The GPS measurements performed in three analogous structural units of the neighboring Sumatran convergent margin point to substantial differences in velocities of movement of the respective units and correlate with the spatial distribution of earthquake foci. We interpret the distinct along-trench seismicity as a consequence of the onset of a new subduction cycle due to the rapid convergent movement of the Indo-Australian plate relative to the aseismic lithospheric link.
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earthquake occurrence along the java trench in front of the onset of the wadati Benioff Zone beginning of a new subduction cycle
Tectonics, 2007Co-Authors: Aleš Špičák, Václav Hanuš, Jiří VaněkAbstract:[1] Spatial distribution of earthquake foci in the central part of the Sunda Arc was analyzed using global seismological data. The analysis revealed the existence of a distinct strip of earthquakes distributed along the Java trench, separated by a trench-parallel, 50–150 km wide aseismic link from seismicity belonging to the Wadati-Benioff Zone of the recently subducting slab. The seismicity pattern at the plate margin corresponds well with the morphology of the seafloor: The along-trench seismicity correlates with the position of the Java trench and the onset of the Wadati-Benioff Zone correlates with the Java trough. The GPS measurements performed in three analogous structural units of the neighboring Sumatran convergent margin point to substantial differences in velocities of movement of the respective units and correlate with the spatial distribution of earthquake foci. We interpret the distinct along-trench seismicity as a consequence of the onset of a new subduction cycle due to the rapid convergent movement of the Indo-Australian plate relative to the aseismic lithospheric link.
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how the state of stress varies in the wadati Benioff Zone indications from focal mechanisms in the wadati Benioff Zone beneath sumatra and java
Geophysical Journal International, 2000Co-Authors: Alice Slancová, Václav Hanuš, Aleš Špičák, Jiří VaněkAbstract:Summary This study concentrates on the detailed determination of the state of stress in the Wadati–Benioff Zone in the lithosphere subducting under Sumatra and Java. The orientations of P- and T-axes of earthquake focal mechanisms (HCMT) are used to define a system of domains in which a uniform state of stress is assumed. The method of Gephart & Forsyth is then used to determine the state of stress in each domain. We succeeded in delimiting eight domains: three (SI–SIII) in the Sumatra region and five (JI–JV) in the Java region. Domains with similar states of stress occur in both regions in similar positions. The maximum compression σ1 is perpendicular to the trench in domains SI, SII and JII, that is, within the depth range 0–165 km. The orientation of σ1 is almost parallel to the trench in domains SIII and JIII (depth range 25–225 km). The boundary between domains SII and SIII, and JII and JIII is not distinct (covering the depth range 40–165 km). It seems that the focal mechanisms belonging to domains SII and SIII, and similarly to domains JII and JIII, occur in different stress layers and that we observe an overlap of earthquakes with different focal mechanisms from two different stress-state layers, parallel to the Wadati–Benioff Zone. In domains JIV and JV, the states of stress correspond to the stress pattern observed in other subduction Zones: slab-dip-parallel extension is observed in domain JIV (depth range 225–315 km) and slab-dip-parallel compression is observed in domain JV (deeper than 400 km).
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How the state of stress varies in the Wadati–Benioff Zone: indications from focal mechanisms in the Wadati–Benioff Zone beneath Sumatra and Java
Geophysical Journal International, 2000Co-Authors: Alice Slancová, Václav Hanuš, Aleš Špičák, Jiří VaněkAbstract:Summary This study concentrates on the detailed determination of the state of stress in the Wadati–Benioff Zone in the lithosphere subducting under Sumatra and Java. The orientations of P- and T-axes of earthquake focal mechanisms (HCMT) are used to define a system of domains in which a uniform state of stress is assumed. The method of Gephart & Forsyth is then used to determine the state of stress in each domain. We succeeded in delimiting eight domains: three (SI–SIII) in the Sumatra region and five (JI–JV) in the Java region. Domains with similar states of stress occur in both regions in similar positions. The maximum compression σ1 is perpendicular to the trench in domains SI, SII and JII, that is, within the depth range 0–165 km. The orientation of σ1 is almost parallel to the trench in domains SIII and JIII (depth range 25–225 km). The boundary between domains SII and SIII, and JII and JIII is not distinct (covering the depth range 40–165 km). It seems that the focal mechanisms belonging to domains SII and SIII, and similarly to domains JII and JIII, occur in different stress layers and that we observe an overlap of earthquakes with different focal mechanisms from two different stress-state layers, parallel to the Wadati–Benioff Zone. In domains JIV and JV, the states of stress correspond to the stress pattern observed in other subduction Zones: slab-dip-parallel extension is observed in domain JIV (depth range 225–315 km) and slab-dip-parallel compression is observed in domain JV (deeper than 400 km).
Cenka Christova - One of the best experts on this subject based on the ideXlab platform.
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stress field in the ryukyu kyushu wadati Benioff Zone by inversion of earthquake focal mechanisms
Tectonophysics, 2004Co-Authors: Cenka ChristovaAbstract:Abstract The study addresses the space distribution of the stress field in the Kyushu–Ryukyu Wadati–Benioff Zone based on homogeneous data of earthquake focal mechanisms and the inverse technique by Gephart and Forsyth [J. Geophys. Res. 89 (1984) 9305]. The used data set consists of 148 Harvard CMT solutions and 22 earthquake focal mechanisms listed in previous studies. The stress field parameters are determined for 0–40, 41–100 and h>100 km depth ranges. The top 100-km layer of the Wadati–Benioff Zone (WBZ) is characterized by strike normal maximum compression σ1 and steeper than the slab minimum compression σ3, the last indicating for unbalanced slab pull force. The Tokara channel ‘divides’ the subduction into two parts of different stress regime at depth greater than 100 km. To the south of the channel the slab is under slab parallel σ1 and slab normal σ3 while its northern part, beneath Kyushu, is under slab parallel extension and slab normal compression. The results of recent studies on the regional velocity structure and geochemistry of the volcanic lava indicate that the most plausible reason for the observed stress field difference below 100 km in the northern and rest part of the arc is the presence of hot low viscosity upper mantle west of Kyushu. The results of this study indicate that the forces involved in the contemporary subduction dynamics in the Ryukyu–Kyushu Wadati–Benioff Zone are related to the convergence between the Philippine Sea Plate and the Eurasian plate, the trench suction force, slab pull, the slab anchor force and, in the southern-central part of the arc, mantle resistance.
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Stress field in the Ryukyu–Kyushu Wadati–Benioff Zone by inversion of earthquake focal mechanisms
Tectonophysics, 2004Co-Authors: Cenka ChristovaAbstract:Abstract The study addresses the space distribution of the stress field in the Kyushu–Ryukyu Wadati–Benioff Zone based on homogeneous data of earthquake focal mechanisms and the inverse technique by Gephart and Forsyth [J. Geophys. Res. 89 (1984) 9305]. The used data set consists of 148 Harvard CMT solutions and 22 earthquake focal mechanisms listed in previous studies. The stress field parameters are determined for 0–40, 41–100 and h>100 km depth ranges. The top 100-km layer of the Wadati–Benioff Zone (WBZ) is characterized by strike normal maximum compression σ1 and steeper than the slab minimum compression σ3, the last indicating for unbalanced slab pull force. The Tokara channel ‘divides’ the subduction into two parts of different stress regime at depth greater than 100 km. To the south of the channel the slab is under slab parallel σ1 and slab normal σ3 while its northern part, beneath Kyushu, is under slab parallel extension and slab normal compression. The results of recent studies on the regional velocity structure and geochemistry of the volcanic lava indicate that the most plausible reason for the observed stress field difference below 100 km in the northern and rest part of the arc is the presence of hot low viscosity upper mantle west of Kyushu. The results of this study indicate that the forces involved in the contemporary subduction dynamics in the Ryukyu–Kyushu Wadati–Benioff Zone are related to the convergence between the Philippine Sea Plate and the Eurasian plate, the trench suction force, slab pull, the slab anchor force and, in the southern-central part of the arc, mantle resistance.
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stress field in the vanuatu new hebrides wadati Benioff Zone inferred by inversion of earthquake focal mechanisms evidence for systematic lateral and vertical variations of principal stresses
Journal of Geodynamics, 2004Co-Authors: Cenka Christova, Christopher H. Scholz, Honn KaoAbstract:Abstract We evaluate the stress tensor directions in several depth ranges along the Vanuatu Wadati–Benioff Zone by inversion of 550 earthquake Harvard CMT solutions. Our results show that although the strike of the Vanuatu slab varies by over 70 °C, the maximum compressive stress σ 1 is, nearly horizontal and slab normal all along the arc in the depth range 0–180 km. The minimum compressive stress σ 3 is down dip in the top 60 km and shows a clear tendency to vary systematically from down dip to strike aligned in the depth range 61–180 km. At depths below 180 km σ 1 rotates clockwise at about 30° in respect to the slab normal, while σ 3 is down dip. The variations of σ 3 direction below 60 km indicate that horizontal stretching of the slab modifies the slab pull force. The universal direction of σ 1 in the range 0–180 km implies that one of the dominant forces at Vanuatu is nearly horizontal and slab normal. In the top 60 km it is most likely related to the plate convergence. The only plausible force of this type at greater depth is the sea anchor force: the viscous resistance to the face-wise motion of the slab relative to the mantle. The change of σ 3 direction from strike aligned to down-dip tension at depth greater than 180 km suggests that the slab pull force may become more prominent with depth.
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Stress field in the Vanuatu (New Hebrides) Wadati–Benioff Zone inferred by inversion of earthquake focal mechanisms: evidence for systematic lateral and vertical variations of principal stresses
Journal of Geodynamics, 2004Co-Authors: Cenka Christova, Christopher H. Scholz, Honn KaoAbstract:Abstract We evaluate the stress tensor directions in several depth ranges along the Vanuatu Wadati–Benioff Zone by inversion of 550 earthquake Harvard CMT solutions. Our results show that although the strike of the Vanuatu slab varies by over 70 °C, the maximum compressive stress σ 1 is, nearly horizontal and slab normal all along the arc in the depth range 0–180 km. The minimum compressive stress σ 3 is down dip in the top 60 km and shows a clear tendency to vary systematically from down dip to strike aligned in the depth range 61–180 km. At depths below 180 km σ 1 rotates clockwise at about 30° in respect to the slab normal, while σ 3 is down dip. The variations of σ 3 direction below 60 km indicate that horizontal stretching of the slab modifies the slab pull force. The universal direction of σ 1 in the range 0–180 km implies that one of the dominant forces at Vanuatu is nearly horizontal and slab normal. In the top 60 km it is most likely related to the plate convergence. The only plausible force of this type at greater depth is the sea anchor force: the viscous resistance to the face-wise motion of the slab relative to the mantle. The change of σ 3 direction from strike aligned to down-dip tension at depth greater than 180 km suggests that the slab pull force may become more prominent with depth.
Oscar Jimenez - One of the best experts on this subject based on the ideXlab platform.
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Geometry and state of stress of the Wadati‐Benioff Zone in the Gulf of Tehuantepec, Mexico
Journal of Geophysical Research: Solid Earth, 2004Co-Authors: Hugo Bravo, Cecilio J Rebollar, Antonio Uribe, Oscar JimenezAbstract:[1] Data recorded in the Gulf of Tehuantepec and published moment tensor solutions were used to infer the geometry of the Wadati-Benioff Zone (W-B Zone) and the stress distribution of the subducted Cocos Plate. From northwest to southeast the subducted slab gently increases its dip, bends up at depths of the order of 100 km and about 240 km inland from the trench, then unbends and increases its dip toward the southeast below Chiapas. Contour lines of equal depth at 50 and 100 km show a significant contortion of the W-B Zone west of the Isthmus of Tehuantepec and coincide with significant changes in the topographic features of the crust. We calculated a Vp/Vs ratio of 1.75 for the whole area and a Moho depth in the Gulf of Tehuantepec of 28.5 ± 3.5 km. Near the trench, along the coupling Zone, T axes of interplate and intraplate earthquakes are oblique to the interface and parallel to the dip direction of the subducted plate, respectively. At depths greater than 50 km the T axes are roughly horizontal. Best fit stresses using the Gephart and Forsyth [1984] code resulted in the following variation of the minimum stresses (T axes) from northwest to southeast as (plunge, azimuth) σ3(40°, 37°) to σ3(28°, 72°), then to σ3(11°, 54°) and finally to σ3(27°, 35°). We also analyzed recordings from the 30 September 1999, Oaxaca earthquake Mw = 7.5 and its aftershocks. We inferred an approximate fault area of 80 by 30 km inside the subducted Cocos Plate.
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geometry and state of stress of the wadati Benioff Zone in the gulf of tehuantepec mexico
Journal of Geophysical Research, 2004Co-Authors: Hugo Bravo, Cecilio J Rebollar, Antonio Uribe, Oscar JimenezAbstract:[1] Data recorded in the Gulf of Tehuantepec and published moment tensor solutions were used to infer the geometry of the Wadati-Benioff Zone (W-B Zone) and the stress distribution of the subducted Cocos Plate. From northwest to southeast the subducted slab gently increases its dip, bends up at depths of the order of 100 km and about 240 km inland from the trench, then unbends and increases its dip toward the southeast below Chiapas. Contour lines of equal depth at 50 and 100 km show a significant contortion of the W-B Zone west of the Isthmus of Tehuantepec and coincide with significant changes in the topographic features of the crust. We calculated a Vp/Vs ratio of 1.75 for the whole area and a Moho depth in the Gulf of Tehuantepec of 28.5 ± 3.5 km. Near the trench, along the coupling Zone, T axes of interplate and intraplate earthquakes are oblique to the interface and parallel to the dip direction of the subducted plate, respectively. At depths greater than 50 km the T axes are roughly horizontal. Best fit stresses using the Gephart and Forsyth [1984] code resulted in the following variation of the minimum stresses (T axes) from northwest to southeast as (plunge, azimuth) σ3(40°, 37°) to σ3(28°, 72°), then to σ3(11°, 54°) and finally to σ3(27°, 35°). We also analyzed recordings from the 30 September 1999, Oaxaca earthquake Mw = 7.5 and its aftershocks. We inferred an approximate fault area of 80 by 30 km inside the subducted Cocos Plate.