Delimitation of domains with uniform stress in the subducted Nazca plate

Slancová, Alice; Špičák, Aleš; Hanuš, V.; Vaněk, Jiřı́

doi:10.1016/s0040-1951(99)00302-9

Cited by 6 publications

(4 citation statements)

References 29 publications

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“…Constrained events are shown with orange triangles, other symbols as in Fig. 2. mechanism solutions, especially closer to the trench and north of 31 • S. Overall, many solutions have a tensional axis that is subperpendicular to the trench, indicating that the likely mechanism for deformation is slab pull, similar to conclusions from previous studies of this subduction zone (Cahill & Isacks 1992;Araujo & Suarez 1994;Slancova et al 2000;Pardo et al 2002;Brudzinski & Chen 2005). However, pairing the focal mechanisms with the slab contours from our study reveals a consistent pattern…”

Section: G E O D Y N a M I C I N T E R P R E Tat I O Nsupporting

confidence: 87%

Geometry and brittle deformation of the subducting Nazca Plate, Central Chile and Argentina

Anderson

Alvarado

Zandt

et al. 2007

Geophysical Journal International

200

194

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S U M M A R YWe 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 associated with the inferred location of the subducting Juan Fernández Ridge at 31 • S and that the slab deepens both to the south and the north of this region. We have also determined first motion focal mechanisms for ∼180 of the slab earthquakes. The subhorizontal T-axis solutions for these events are almost entirely consistent with a slab pull interpretation, especially when compared to our newly inferred slab geometry. Deviations of T-axes from the direction of slab dip may be explained with a gap within the subducting slab below 150 km in the vicinity of the transition from flat to normal subducting geometry around 33 • S.

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Section: G E O D Y N a M I C I N T E R P R E Tat I O Nsupporting

confidence: 87%

Geometry and brittle deformation of the subducting Nazca Plate, Central Chile and Argentina

Anderson

Alvarado

Zandt

et al. 2007

Geophysical Journal International

200

194

View full text Add to dashboard Cite

show abstract

“…Intermediate depth subduction zone earthquakes are expected to exhibit downdip tension and normal faulting when the subducted slab is mechanically continuous to deeper depths, because the denser, deeper slab pulls on the buoyant, shallower slab. Regional studies of slab stress in the Chile‐Argentina subduction zone [ Chen et al ., ; Slancová et al ., ; Anderson et al ., ; Pardo et al ., ] support this concept. However, Anderson et al .…”

Section: Discussionmentioning

confidence: 98%

Electrical conductivity of the Pampean shallow subduction region of Argentina near 33 S: Evidence for a slab window

Burd

Booker

Mackie³

et al. 2013

Geochem Geophys Geosyst

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[1] We present a three-dimensional (3-D) interpretation of 117 long period (20-4096 s) magnetotelluric (MT) sites between 31 S and 35 S in western Argentina. They cover the most horizontal part of the Pampean shallow angle subduction of the Nazca Plate and extend south into the more steeply dipping region. Sixty-two 3-D inversions using various smoothing parameters and data misfit goals were done with a nonlinear conjugate gradient (NLCG) algorithm. A dominant feature of the mantle structure east of the horizontal slab is a conductive plume rising from near the top of the mantle transition zone at 410 km to the probable base of the lithosphere at 100 km depth. The subducted slab is known to descend to 190 km just west of the plume, but the Wadati-Benioff zone cannot be traced deeper. If the slab is extrapolated downdip it slices through the plume at 250 km depth. Removal of portions of the plume or blocking vertical current flow at 250 km depth significantly changes the predicted responses. This argues that the plume is not an artifact and that it is continuous. The simplest explanation is that there is a ''wedge''-shaped slab window that has torn laterally and opens down to the east with its apex at the plume location. Stress within the slab and seismic tomography support this shape. Its northern edge likely explains why there is no deep seismicity south of 29 S.

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“…The best-fitting model is searched for in a grid over the four model parameters, systematically adjusting one at a time through a wide range of possibilities (Gephart 1990). The measure of misfit is given by the smallest rotation about an axis of any orientation that brings one of the nodal planes and its slip direction into an orientation consistent with the stress model (Slancova et al 2000). Thus, for each stress model, the misfits between the orientation of the observed data and prediction are estimated and summed.…”

Section: R E G I O N a L S T R E S S T E N S O R A N A Ly S I Smentioning

confidence: 99%

Moment tensor inversion of recent small to moderate sized earthquakes: implications for seismic hazard and active tectonics beneath the Sea of Marmara

Pınar

Kuge²,

Honkura³

2003

Geophysical Journal International

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SUMMARY We retrieve the moment tensors of 64 small to moderate sized events that occurred mostly beneath the Sea of Marmara using near‐field data recorded at strong‐motion and broad‐band seismic stations. The near‐field displacement records are inverted to their sources utilizing Kuge's method where the best fit between the synthetic and observed seismograms is achieved through searching a centroid moment tensor (CMT) point in a grid scheme. We also analyse the stress fields acting in the eastern and western parts of the Sea of Marmara by inverting the P‐ and T‐axes of the focal mechanisms obtained. Significant biases in the stress tensors are obtained. The nearly horizontal maximum compressive axis σ1 in the western part is rotated 16° counter‐clockwise compared with σ1 in the eastern part. The σ2‐axis is close to vertical (shear tectonic regime) in the east and the plunge of σ2‐axis in the west is 36° (transpressive tectonic regime). Changes in the σ3‐axis are also observed, that is, it is close to horizontal in the east and dips 49° in the west. The spatial distribution of the focal mechanisms suggests that the stress field in the eastern part of the Sea of Marmara is homogenous compared with the western part, and we identify five distinct subsidiary faults. (1) a WNW–ESE‐striking, right‐lateral strike‐slip fault located a few kilometres SW of the Princes' Islands, (2) a WSW–ENE‐striking, right‐lateral strike‐slip fault named the Yalova–Hersek fault, (3) an E–W‐striking normal fault located onshore between Yalova and Çinarcik, (4) a NNW–SSE‐striking, left‐lateral strike‐slip fault located NE of the Princes' Islands and (5) minor thrust faults located in the Central High of the Sea of Marmara and in the vicinity of the Hersek Delta. The locations and the sense of motion of these five shear zones are explained by a very simple deformation model that requires a major E–W‐striking right‐lateral strike‐slip fault, namely the North Anatolian Fault (NAF), within a stress field with maximum compression, σ1, in the NW–SE direction and minimum compression, σ3, in the NE–SW direction, as was derived from the stress tensor analysis. The mechanisms of the events occurring in the western part of the Sea of Marmara reveal a heterogeneous stress field that may result from the change in the strike of NAF from nearly E–W to WSW. The western Marmara Sea events are consistent with a deformation model that requires a major right‐lateral strike‐slip fault striking ENE–WSW with a stress field with maximum principal stress axis, σ1, oriented ESE and minimum principal stress axis, σ3, oriented NNE.

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Delimitation of domains with uniform stress in the subducted Nazca plate

Cited by 6 publications

References 29 publications

Geometry and brittle deformation of the subducting Nazca Plate, Central Chile and Argentina

Geometry and brittle deformation of the subducting Nazca Plate, Central Chile and Argentina

Electrical conductivity of the Pampean shallow subduction region of Argentina near 33 S: Evidence for a slab window

Moment tensor inversion of recent small to moderate sized earthquakes: implications for seismic hazard and active tectonics beneath the Sea of Marmara

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