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Gerardo Suárez - One of the best experts on this subject based on the ideXlab platform.
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stress distribution and geometry of the subducting Nazca Plate in northern chile using teleseismically recorded earthquakes
Geophysical Journal International, 1995Co-Authors: D. Comte, Gerardo SuárezAbstract:SUMMARY The stress distribution along the subducting Nazca Plate in northern Chile is analysed using focal mechanism solutions obtained from the inversion of long-period P, SV, and SH waveforms of 15 earthquakes (mb± 5.5), and from 212 events with reported focal mechanisms, which occurred between 1962 and 1993. A joint hypocentral determination was carried out to control the depth of 261 events (mb± 5.0) recorded at teleseismic distances. A change from tensional to compressional stress field along the upper part of the subducting slab is associated with the maximum depth extent of the coupled zone. This change occurs in northern Chile at ±200-250 km from the trench, at depths of ±60.10 km. This depth is larger than the maximum depth observed for the thrusting interPlate events (40 ± 10 km), probably meaning that, at depths of between 40 and 60 km, large low-dip angle thrust events do not nucleate. Seismic slip, however, probably extends down to 40 km in depth. The shallow dip angle (up to 60 km in depth) of the Wadati-Benioff zone does not show variations along the strike of the trench. However, a gradual southward flattening of the slab is observed at distances greater than 200–250 km from the trench. This change, observed from about 21°S, could be associated with a younger and probably more buoyant lithosphere than that observed to the north of this latitude. There are two gaps located between the three main clusters of seismicity; these gaps are clearly not related to detachments in the descending litosphere. The first cluster is located in and beneath the seismogenic interPlate contact, and is characterized by reverse and thrust faulting events over a scarce tensional activity. In the second cluster, the compressional seismicity is scarce for teleseismic events and is located beneath the normal faulting events. The third cluster corresponds to tensional events. Therefore, these gaps in seismicity could be associated with alternating changes from compressional to tensional stress field in the subducting slab.
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geometry and state of stress of the subducted Nazca Plate beneath central chile and argentina evidence from teleseismic data
Geophysical Journal International, 1994Co-Authors: Mario Araujo, Gerardo SuárezAbstract:SUMMARY Thirty new focal mechanisms of intermediate-depth earthquakes in the South American subduction zone were determined in the region between 21" and 33" S. The focal mechanisms and depths of earthquakes with magnitudes greater than 5.7 (mb) were constrained using a body-wave modelling method. The hypocentral depths of the other earthquakes, with 5.3 < mb < 5.7, were determined by identifying the arrival time of the depth phases pP and sP on seismograms from several teleseismic stations. These refined focal depths were used to draw detailed isodepth contours of the subducted Nazca Plate. In the northern part of the study area (21" to 24" S), the slab dips at an angle of approximately 30"seaching a maximum depth of about 300 km. Towards the south, the dip of the slab becomes horizontal from 27.5" to 30.5"s and remains horizontal to -33"s. This flat slab underPlates South America for a distance of 250 km. The transition from steep to horizontal subduction takes place rapidly over a flexure in the subducted slab. Quaternary volcanism stops abruptly at this transition. The geometry of the shallow part of the subduction zone was defined using modelled earthquakes published by several authors. The dip of the slab from the trench to a depth of about 80 km is the same along the whole subduction zone regardless of the geometry of the slab at greater depths. All of the intermediate-depth events studied show tensional focal mechanism except for one reverse-faulting earthquake. This compressional event occurred within the slab, about 40 km beneath the sheet of tensional earthquakes. This event suggests a complex stress regime in the downgoing Plate, where down-dip tensional events are on top and this compressional earthquake below. This polarity of the stresses is inverted relative to those found in double-planed seismic zones of the western Pacific, such as the Aleutians, Tonga and Honshu. The dip of the T axes of the intermediate-depth earthquakes shows a remarkable correlation with the gradient of the subducted slab. The mean difference between the dip of the T axes and that of the Plate is 1.4" with a 95 per cent interval of confidence of 8.8", as estimated by Fisher statistics. This observation suggests the state of stress within the slab is controlled primarily by the slab pull induced by the geometry and gradient of the subduction zone.
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Velocity structure in northern Chile: evidence of subducted oceanic crust in the Nazca Plate
Geophysical Journal International, 1994Co-Authors: D. Comte, Steven W. Roecker, Gerardo SuárezAbstract:SUMMARY 2-D P -wave velocity models were determined for the subduction zones near Iquique and Antofagasta in northern Chile, simultaneously inverting P - and S-wave arrival times from locally recorded earthquakes for velocity structure and hypocentral locations. A 2-D parametrization was used because of the paucity of data, but is justified by the lack of significant variations along the strike of the subduction zone observed from both refraction profiles and simple 3-D inversions. The crust and upper mantle are parameterized by constant velocity regions of irregular shape, with the size and boundaries of these regions governed by prior information about the structure and by the ability of the data to resolve P-wave velocities. Beneath the Antofagasta region there is evidencc of an approximately 10 km thick layer of oceanic crust attached to the top of the subducting Nazca Plate. This crust has a P-wave velocity of 7.3 f 0.1 km s-' and is observed down to a depth of 60 f 10 km. This depth also corresponds to the maximum depth of seismogenic coupling in the Chilean subduction zone. The subducted oceanic crust overlies an oceanic upper mantle with a P-wave velocity of 8.0 f 0.1 km s-'. Apparently, oceanic crust is being subducted beneath Iquique as well. However, this feature is less constrained by the data available from this region.
Silvina Nacif - One of the best experts on this subject based on the ideXlab platform.
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Seismic-gravimetric analysis of the subducted Nazca Plate 1 between 32°S and 36°S
Geodesy and Geodynamics, 2018Co-Authors: Lujan Eckerman, Silvana Spagnotto, Alejo Agüero, Patricia Martínez, Silvina NacifAbstract:The study region is seismically and tectonically characterized by the angle variations in the subduction of the Nazca Plate. The results obtained from earthquakes location between 32° and 36°S latitude and 67°–71°W longitude are presented in this work. The presence of a wedge of asthenospheric materials and the partial or total eclogitization of the subducted Nazca Plate and its relation with isostatic cortex models published was analyzed. In addition, a gravimetric profile obtained from gravity forward modeling is presented at 33.5°S, proposing a new configuration at depths for the main tectonic components: Nazca Plate, asthenospheric wedge and South American Plate. Also, a new density scheme using recently published velocity models was obtained.
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seismic gravimetric analysis of the subducted Nazca Plate 1 between 32 s and 36 s
Geodesy and Geodynamics, 2017Co-Authors: Lujan Eckerman, Silvana Spagnotto, Silvina Nacif, Alejo Agüero, Patricia MartínezAbstract:Abstract The study region is seismically and tectonically characterized by the angle variations in the subduction of the Nazca Plate. The results obtained from earthquakes location between 32° and 36°S latitude and 67°–71°W longitude are presented in this work. The presence of a wedge of asthenospheric materials and the partial or total eclogitization of the subducted Nazca Plate and its relation with isostatic cortex models published was analyzed. In addition, a gravimetric profile obtained from gravity forward modeling is presented at 33.5°S, proposing a new configuration at depths for the main tectonic components: Nazca Plate, asthenospheric wedge and South American Plate. Also, a new density scheme using recently published velocity models was obtained.
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s local wave seismic anisotropy in the forearc above the subducted Nazca Plate between 33 s and 34 5 s
Pure and Applied Geophysics, 2016Co-Authors: Silvina Nacif, Enrique G. TriepAbstract:S-wave splitting from local earthquakes within the Nazca Plate that are deeper than the interPlate seismogenic zone enabled the determination of the fast velocity direction, Φ, and the lag time, δt, in the forearc of the overriding Plate. Data were collected from 20 seismic stations, most of which were temporary, deployed between ~33.5°S and ~34.5°S and included part of the normal subduction section to the south and part of the transitional section to flat subduction to the north. The fast velocity direction has a complex pattern with three predominant directions northwest–southeast, north–south and northeast–southwest and relatively high δt. A quality evaluation of the highest measurements enabled us to identify possible cycle skipping in some of the measurements, which could be responsible for the large observed lag time. We consider that most of the anisotropy that was observed in the forearc is probably located in the mantle wedge, and a minor part is located in the crust. The complex pattern of splitting parameters when the anisotropy is associated at the mantle wedge could be the result of three-dimensional variations in the subducting Nazca Plate at these latitudes. Also, similarities between the splitting parameters and the principal compressional stress direction from Pliocene and Quaternary rocks suggest that the anisotropy in the crust could originate by tectonic local stress.
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S-Local-Wave Seismic Anisotropy in the Forearc Above the Subducted Nazca Plate Between 33°S and 34.5°S
Pure and Applied Geophysics, 2015Co-Authors: Silvina Nacif, Enrique G. TriepAbstract:S-wave splitting from local earthquakes within the Nazca Plate that are deeper than the interPlate seismogenic zone enabled the determination of the fast velocity direction, Φ, and the lag time, δt, in the forearc of the overriding Plate. Data were collected from 20 seismic stations, most of which were temporary, deployed between ~33.5°S and ~34.5°S and included part of the normal subduction section to the south and part of the transitional section to flat subduction to the north. The fast velocity direction has a complex pattern with three predominant directions northwest–southeast, north–south and northeast–southwest and relatively high δt. A quality evaluation of the highest measurements enabled us to identify possible cycle skipping in some of the measurements, which could be responsible for the large observed lag time. We consider that most of the anisotropy that was observed in the forearc is probably located in the mantle wedge, and a minor part is located in the crust. The complex pattern of splitting parameters when the anisotropy is associated at the mantle wedge could be the result of three-dimensional variations in the subducting Nazca Plate at these latitudes. Also, similarities between the splitting parameters and the principal compressional stress direction from Pliocene and Quaternary rocks suggest that the anisotropy in the crust could originate by tectonic local stress.
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new evidences of rupture of crust and mantle in the subducted Nazca Plate at intermediate depth
Journal of South American Earth Sciences, 2015Co-Authors: Silvana Spagnotto, Silvina Nacif, Orlando Álvarez, Enrique Triep, Laura GiambiagiAbstract:Abstract Between 33°–36°S, the Nazca Plate subducts below South American Plate with an angle of ∼30°, and it is seismically active until ∼200–280 km depth. At 33.5°S, the seismicity decreases drastically at 120 km depth, just below the volcanic arc. In this paper, we studied a pair of associated earthquakes located in the area where the frequency of seismicity changes. The hypocenters of the M w = 6.4, June 16th, 2000 and M w = 5.7 January 7th, 2003 earthquakes were found nearby, adjacent to the oceanic Moho, closely associated with each other. The slip on the plane of the 2000 event produced Coulomb stress changes on the fault plane of 2003, both westward dipping, with a variation from ∼1 bar near the hypocenter of the latter to ∼0.1 bars in the deepest part of the plane. The two earthquakes combined process describes a normal focal mechanism, which cuts through the crust and breaks the mantle, reaching depths of ∼40 km below the Moho. The composed fault plane of the 2000 and 2003 events corresponds to a west-dipping normal fault with strike and dip consistent with those of the outer ridge faults. Thus, these events could be related to a preexisting fault originated in that environment reactivated at depth. The slip on the composed fault plane is consistent with the bending produced by the slab pull. Dehydration could be associated to these events.
Susan L Beck - One of the best experts on this subject based on the ideXlab platform.
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Internal deformation of the subducted Nazca slab inferred from seismic anisotropy
Nature Geoscience, 2015Co-Authors: Caroline M. Eakin, Susan L Beck, George Zandt, Maureen D. Long, A. C. Scire, Lara S. Wagner, Hernando TaveraAbstract:Subducting oceanic Plates are often considered as cold, rigid slabs. Analysis of seismic anisotropy in the subducted Nazca Plate beneath Peru suggests that the Plate has deformed internally during subduction.
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geometry and brittle deformation of the subducting Nazca Plate central chile and argentina
Geophysical Journal International, 2007Co-Authors: M L Anderson, Patricia Alvarado, George Zandt, Susan L BeckAbstract:SUMMARY We use data from the Chile Argentina Geophysical Experiment (CHARGE) broad-band seismic deployment to refine past observations of the geometry and deformation within the subducting slab in the South American subduction zone between 30 ◦ S and 36 ◦ S. This region contains a zone of flat slab subduction where the subducting Nazca Plate flattens at a depth of ∼100 km and extends ∼300 km eastward before continuing its descent into the mantle. We use a grid-search multiple-event earthquake relocation technique to relocate 1098 events within the subducting slab and generate contours of the Wadati-Benioff zone. These contours reflect slab geometries from previous studies of intermediate-depth seismicity in this region with some small but important deviations. Our hypocentres indicate that the shallowest portion of the flat slab is a
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geometry and state of stress of the Nazca Plate beneath bolivia and its implication for the evolution of the bolivian orocline
Geology, 1996Co-Authors: Mark Andrew Tinker, Terry C Wallace, Susan L Beck, Stephen C Myers, Andrew PapanikolasAbstract:A series of deep earthquakes beneath Bolivia in 1994 provides valuable constraints on the geometry and state of stress of the subducting Nazca Plate. These earthquakes occurred northeast of the Bolivian orocline, which is bracketed between two regions of a “flattened” Wadati-Benioff zone. Furthermore, these events occurred in an area that experienced no seismicity in at least the past 30 years. North and south of this zone, the deep seismicity is abundant and indicates down-dip compression. Collectively, the seismicity defines the geometry of the deep Nazca slab, which is continuous and bent about a sharp arc. This bending is a function of the dynamic evolution of the South America–Nazca Plate system. Since the Tertiary, South America has incurred a maximum shortening along the Bolivian orocline. North and south of the orocline, the South American crust has shortened less; the differential shortening occurs in conjunction with the flattened and bent Wadati-Benioff zone. The upper Nazca slab has undergone a tremendous amount of horizontal deformation that is controlled by the convergence direction relative to the trend of the trench. In response, the lower slab has been slowly bent about an axis parallel to the dip orientation of the deep Nazca Plate.
Andreas Rietbrock - One of the best experts on this subject based on the ideXlab platform.
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Constraining the hydration of the subducting Nazca Plate beneath Northern Chile using subduction zone guided waves
Earth and Planetary Science Letters, 2017Co-Authors: Thomas Garth, Andreas RietbrockAbstract:Abstract Guided wave dispersion is observed from earthquakes at 180–280 km depth recorded at stations in the fore-arc of Northern Chile, where the 44 Ma Nazca Plate subducts beneath South America. Characteristic P-wave dispersion is observed at several stations in the Chilean fore-arc with high frequency energy (>5 Hz) arriving up to 3 s after low frequency (
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A narrowly spaced double‐seismic zone in the subducting Nazca Plate
Geophysical Research Letters, 2004Co-Authors: Andreas Rietbrock, Felix WaldhauserAbstract:[1] High-precision relocations of intermediate-depth earthquakes (80–130 km) below the Central Andes reveal a fine-scale double-layered Wadati-Benioff zone (WBZ). Upper and lower band of seismicity are separated by about 9 km and occur at the top of the oceanic crust and in the uppermost oceanic mantle, respectively. Analysis of focal mechanisms and waveform similarities indicate that fluid processes are causing the events. Earthquakes in the oceanic crust occur on pre-existing normal faults due to hydraulic embrittlement from metamorphic dehydration, and on subvertical faults that connect the two layers in a narrow depth range. Extensional faulting predominates in both layers, indicating that slab pull forces are the dominant stress source superseding possible unbending forces in this segment of the Nazca Plate.
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a narrowly spaced double seismic zone in the subducting Nazca Plate
Geophysical Research Letters, 2004Co-Authors: Andreas Rietbrock, Felix WaldhauserAbstract:[1] High-precision relocations of intermediate-depth earthquakes (80–130 km) below the Central Andes reveal a fine-scale double-layered Wadati-Benioff zone (WBZ). Upper and lower band of seismicity are separated by about 9 km and occur at the top of the oceanic crust and in the uppermost oceanic mantle, respectively. Analysis of focal mechanisms and waveform similarities indicate that fluid processes are causing the events. Earthquakes in the oceanic crust occur on pre-existing normal faults due to hydraulic embrittlement from metamorphic dehydration, and on subvertical faults that connect the two layers in a narrow depth range. Extensional faulting predominates in both layers, indicating that slab pull forces are the dominant stress source superseding possible unbending forces in this segment of the Nazca Plate.
Catherine Dorbath - One of the best experts on this subject based on the ideXlab platform.
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Double seismic zone of the Nazca Plate in northern Chile: High-resolution velocity structure, petrological implications, and thermomechanical modeling
Geochemistry Geophysics Geosystems, 2008Co-Authors: Catherine Dorbath, Muriel Gerbault, Gabriel Carlier, Michel GuiraudAbstract:This paper presents an interdisciplinary study of the northern Chile double seismic zone. First, a high-resolution velocity structure of the subducting Nazca Plate has been obtained by the tomoDD doubledifference tomography method. The double seismic zone (DSZ) is observed between 80 and 140 km depth, and the two seismic planes is 20 km apart. Then, the chemical and petrologic characteristics of the oceanic lithosphere associated with this DSZ are deduced by using current thermal-petrological-seismological models and are compared to pressure-temperature conditions provided by a numerical thermomechanical model. Our results agree with the common hypothesis that seismicity in both upper and lower planes is related to fluid releases associated with metamorphic dehydration reactions. In the seismic upper plane located within the upper crust, these reactions would affect material of basaltic (MORB) composition and document different metamorphic reactions occurring within high-P (>2.4 GPa) and low-T (130 km), lawsonite-amphibole eclogite conditions. The lower plane lying in the oceanic mantle can be associated with serpentinite dehydration reactions. The Vp and Vs characteristics of the region in between both planes are consistent with a partially (similar to 25-30 vol % antigorite, similar to 0-10% vol % brucite, and similar to 4-10 vol % chlorite) hydrated harzburgitic material. Discrepancies persist that we attribute to complexities inherent to heterogeneous structural compositions. While various geophysical indicators evidence particularly cold conditions in both the descending Nazca Plate and the continental fore arc, thermomechanical models indicate that both seismic planes delimit the inner slab compressional zone around the 400 degrees C (+/-50 degrees C) isotherm. Lower plane earthquakes are predicted to occur in the slab's flexural neutral plane, where fluids released from surrounding metamorphic reactions could accumulate and trigger seismicity. Fluids migrating upward from the tensile zone below could be blocked in their ascension by the compressive zone above this plane, thus producing a sheeted layer of free fluids, or a serpentinized layer. Therefore earthquakes may present either downdip compression and downdip tensile characteristics. Numerical tests indicate that the slab's thermal structure is not the only factor that controls the occurrence of inner slab compression. (1) A weak ductile subduction channel and (2) a cold mantle fore arc both favor inner slab compression by facilitating transmission of compressional stresses from the continental lithosphere into the slab. (3) Decreasing the radius of curvature of the slab broadens the depth of inner slab compression, whereas (4) decreasing upper Plate convergence diminishes its intensity. All these factors indicate that if DSZs indeed contour inner slab compression, they cannot be linked only to slab unbending, but also to the transmission of high compressional stresses from the upper Plate into the slab
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The Double Seismic Zone of the Nazca Plate in Northern Chile: High Resolution Velocity Structure, Petrological Implications and ThermoMechanical Modelling
Geochemistry Geophysics Geosystems, 2008Co-Authors: Catherine Dorbath, Muriel Gerbault, Gabriel Carlier, Michel GuiraudAbstract:This paper presents an interdisciplinary study of the Northern Chile Double Seismic Zone. First, a high resolution velocity structure of the subducting Nazca Plate has been obtained by a new double-difference tomography method. The double seismic zone (DSZ) is observed between 80 and 140 km depth and the two seismic planes are 20 km apart. Then, the chemical and petrologic characteristics of the oceanic lithosphere associated to this DSZ are deduced by using current thermal-petrological-seismological models, and are compared to pressure-temperature conditions provided by a numerical thermo-mechanical model. Our results agree with the common hypothesis that seismicity in both upper and lower planes are related to fluid releases associated to metamorphic dehydration reactions. In the seismic upper plane located within the upper crust, these reactions would affect material of basaltic (MORB) composition and document different metamorphic reactions occurring within high-P (> 2.4 GPa) and low-T (< 570°C) jadeite-lawsonite blueschists and, at greater depth (> 130 km), lawsonite-amphibole eclogite conditions. The lower plane lying in the oceanic mantle can be associated to serpentinite dehydration reactions. The Vp and Vs characteristics of the region in between both planes are consistent with a partially (~25-30 vol.% antigorite, ~0-10% vol. % brucite and ~4-10 vol. % chlorite) hydrated harzburgitic material. Discrepancies persist that we attribute to complexities inherent to heterogeneous structural compositions. While various geophysical indicators evidence particularly cold conditions in both the descending Nazca Plate and the continental fore-arc, thermo-mechanical models indicate that both seismic planes delimit the inner-slab compressional zone around the 400°C (±50°C) isotherm. Lower plane earthquakes are predicted to occur in the slabs flexural neutral plane, where fluids released from surrounding metamorphic reactions could accumulate and trigger seismicity. Fluids migrating upwards from the tensile zone below could be blocked in their ascension by the compressive zone above this plane, thus producing a sheeted layer of free fluids, or a serpentinized layer. Therefore earthquakes may present either down-dip compression and down-dip extension characteristics. Numerical tests indicate that inner-slab compression is not only favored by the slab's thermal structure such as Plate age. i) A weak ductile subduction channel, and ii) a cold mantle fore-arc both favor inner-slab compression by facilitating transmission of compressional stresses from the continental lithosphere into the slab. iii) Decreasing the radius of curvature of the slab broadens the depth of inner-slab compression, whereas iv) decreasing upper Plate convergence diminishes its intensity. All these factors indicate that if indeed DSZs contour inner-slab compression, they cannot only be linked to slab unbending, but also to the transmission of high compressional stresses from the upper Plate into the slab.
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Double seismic zone of the Nazca Plate in northern Chile: High-resolution velocity structure, petrological implications, and thermomechanical modeling
Geochemistry Geophysics Geosystems, 2008Co-Authors: Catherine Dorbath, Muriel Gerbault, Gabriel Carlier, Michel GuiraudAbstract:This paper presents an interdisciplinary study of the northern Chile double seismic zone. First, a high-resolution velocity structure of the subducting Nazca Plate has been obtained by the tomoDD double-difference tomography method. The double seismic zone (DSZ) is observed between 80 and 140 km depth, and the two seismic planes is 20 km apart. Then, the chemical and petrologic characteristics of the oceanic lithosphere associated with this DSZ are deduced by using current thermal-petrological-seismological models and are compared to pressure-temperature conditions provided by a numerical thermomechanical model. Our results agree with the common hypothesis that seismicity in both upper and lower planes is related to fluid releases associated with metamorphic dehydration reactions. In the seismic upper plane located within the upper crust, these reactions would affect material of basaltic (MORB) composition and document different metamorphic reactions occurring within high-P (>2.4 GPa) and low-T (130 km), lawsonite-amphibole eclogite conditions. The lower plane lying in the oceanic mantle can be associated with serpentinite dehydration reactions. The Vp and Vs characteristics of the region in between both planes are consistent with a partially (~25-30 vol % antigorite, ~0-10% vol % brucite, and ~4-10 vol % chlorite) hydrated harzburgitic material. Discrepancies persist that we attribute to complexities inherent to heterogeneous structural compositions. While various geophysical indicators evidence particularly cold conditions in both the descending Nazca Plate and the continental fore arc, thermomechanical models indicate that both seismic planes delimit the inner slab compressional zone around the 400°C (+/-50°C) isotherm. Lower plane earthquakes are predicted to occur in the slab's flexural neutral plane, where fluids released from surrounding metamorphic reactions could accumulate and trigger seismicity. Fluids migrating upward from the tensile zone below could be blocked in their ascension by the compressive zone above this plane, thus producing a sheeted layer of free fluids, or a serpentinized layer. Therefore earthquakes may present either downdip compression and downdip tensile characteristics. Numerical tests indicate that the slab's thermal structure is not the only factor that controls the occurrence of inner slab compression. (1) A weak ductile subduction channel and (2) a cold mantle fore arc both favor inner slab compression by facilitating transmission of compressional stresses from the continental lithosphere into the slab. (3) Decreasing the radius of curvature of the slab broadens the depth of inner slab compression, whereas (4) decreasing upper Plate convergence diminishes its intensity. All these factors indicate that if DSZs indeed contour inner slab compression, they cannot be linked only to slab unbending, but also to the transmission of high compressional stresses from the upper Plate into the slab.
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mapping the continuity of the Nazca Plate through its aseismic part in the arica elbow central andes
Physics of the Earth and Planetary Interiors, 1997Co-Authors: Catherine DorbathAbstract:Abstract Along the Peru-Chile trench, the subduction of the Nazca Plate under South America is well underlined by the Wadati Benioff zone. In the Central Andes, the seismicity defines a moderately deepening slab down to about 325 km. The occurrence of a scarce seismicity in the 550–650 km depth range, after a complete seismic quiescence, raises the question of the continuity of the slab. To answer this question we performed a 3-D teleseismic tomography of the mantle at 20°S. On the tomographic image, a higher velocity zone is associated with the subducted Plate where it is defined by the Wadati Benioff zone. At greater depth, this higher velocity body can be followed through the model down to the lower mantle. Our results provide clear evidence of the continuity of the slab throughout its seismically quiescent part. Moreover, they allow the imaging of the bending of the Nazca Plate in the Arica Elbow, where the general strike of the Andean chain changes and no deep seismicity has never been recorded. Finally, our results confirm the increase of the dip of the slab between 350 and 550 km in depth.
