Structure of the subduction transition region from seismic array data in southern Peru

Phillips, K. E.; Clayton, Robert W.

doi:10.1093/gji/ggt504

Cited by 30 publications

(44 citation statements)

References 61 publications

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“…The relative abundance of lower crustal seismicity within the South American Plate overlying the flat slab region should also be noted for its potential indication of the level of interaction between the two plates. Here, the lower crust is defined as ∼40-70 km depth, based on receiver function results (Phillips & Clayton 2014). A cluster of seismicity between ∼55 and ∼85 km depth near the PG line, centred at ∼14…”

Section: Seismicitymentioning

confidence: 99%

“…In general, the ISC data form a scatter envelope around the EHB locations. Thus, the dip angle is estimated by visually selecting ISC hypocentre locations that are downdip of the trench and not within the overriding plate [as defined by teleseismic receiver functions (Phillips et al 2012;Phillips & Clayton 2014)], then performing a linear regression of the selected locations. Outliers in this selection process are events that are located significantly deeper than or off-trend from the main concentration (i.e.…”

Section: Slab Dipmentioning

confidence: 99%

“…Barazangi & Isacks 1976, 1979Yamaoka et al 1986) and continuous curvature (e.g. Hasegawa & Sacks 1981;Bevis & Isacks 1984;Boyd et al 1984;Grange et al 1984a;Cahill & Isacks 1992;Phillips & Clayton 2014) of the subducted Nazca Plate. The approximate spatial coincidence of the subducting Nazca Ridge with the transition in slab dip (Fig.…”

Section: Introductionmentioning

confidence: 99%

“…• S since it intersected the trench ∼11.2 Ma (Hampel 2002) make such tearing unlikely, as it is located too far from the transition in slab dip and there is no evidence of tearing to the north (Phillips & Clayton 2014). Lateral flexure, on the other hand, may be part of the geometrical response of subduction of the Nazca Plate beneath the inflected shape of the overriding South American Plate (Bevis & Isacks 1984).…”

Section: Introductionmentioning

confidence: 99%

“…Receiver functions along this array suggest a continuous slab with no clear breaks (Phillips & Clayton 2014). In order to test this conclusion and expand on investigations of this region with additional data and analyses, we use regional earthquakes recorded by the Peru Subduction Experiment (PeruSE; PeruSE 2013) and Central Andes Uplift and Geodynamics of High Topography (CAUGHT; Ward et al 2013) seismic arrays to study the fine-scale structure of the southern Peru subduction zone along the flat-to-normal transition (Fig.…”

Section: Introductionmentioning

confidence: 99%

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Seismic structure in southern Peru: evidence for a smooth contortion between flat and normal subduction of the Nazca Plate

Dougherty¹,

Clayton²

2014

Geophysical Journal International

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S U M M A R YRapid changes in slab geometry are typically associated with fragmentation of the subducted plate; however, continuous curvature of the slab is also possible. The transition from flat to normal subduction in southern Peru is one such geometrical change. The morphology of the subducted Nazca Plate along this transition is explored using intraslab earthquakes recorded by temporary regional seismic arrays. Observations of a gradual increase in slab dip coupled with a lack of any gaps or vertical offsets in the intraslab seismicity suggest warping of the slab. Concentrations of focal mechanisms at orientations which are indicative of slab bending are also observed along the change in slab geometry. The presence of a thin ultra-slow velocity layer (USL) atop the horizontal Nazca slab is identified and located. The lateral extent of this USL is coincident with the margin of the projected linear continuation of the subducting Nazca Ridge, implying a causal relationship wherein increased hydration of the ridge results in the formation of the USL downdip. Waveform modelling of the 2-D structure in southern Peru using a finite-difference algorithm provides constraints on the velocity and geometry of the slab's seismic structure and confirms the absence of any tears in the slab. The seismicity and structural evidence suggests smooth contortion of the Nazca Plate along the transition from flat to normal subduction. The slab is estimated to have experienced 10 per cent strain in the along-strike direction across this transition.

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Section: Seismicitymentioning

confidence: 99%

Section: Slab Dipmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Seismic structure in southern Peru: evidence for a smooth contortion between flat and normal subduction of the Nazca Plate

Dougherty¹,

Clayton²

2014

Geophysical Journal International

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Response of the mantle to flat slab evolution: Insights from local S splitting beneath Peru

Eakin

Long

Beck

et al. 2014

Geophysical Research Letters

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The dynamics of flat subduction, particularly the interaction between a flat slab and the overriding plate, are poorly understood. Here we study the (seismically) anisotropic properties and deformational regime of the mantle directly above the Peruvian flat slab. We analyze shear wave splitting from 370 local S events at 49 stations across southern Peru. We find that the mantle above the flat slab appears to be anisotropic, with modest average delay times (~0.28 s) that are consistent with~4% anisotropy in a~30 km thick mantle layer. The most likely mechanism is the lattice-preferred orientation of olivine, which suggests that the observed splitting pattern preserves information about the mantle deformation. We observe a pronounced change in anisotropy along strike, with predominately trench-parallel fast directions in the north and more variable orientations in the south, which we attribute to the ongoing migration of the Nazca Ridge through the flat slab system.

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Flat slab deformation caused by interplate suction force

Clayton

2015

Geophysical Research Letters

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We image the structure at the southern end of the Peruvian flat subduction zone, using receiver function and surface wave methods. The Nazca slab subducts to ~100 km depth and then remains flat for ~300 km distance before it resumes the dipping subduction. The flat slab closely follows the topography of the continental Moho above, indicating a strong suction force between the slab and the overriding plate. A high‐velocity mantle wedge exists above the initial half of the flat slab, and the velocity resumes to normal values before the slab steepens again, indicating the resumption of dehydration and ecologitization. Two prominent midcrust structures are revealed in the 70 km thick crust under the Central Andes: molten rocks beneath the Western Cordillera and the underthrusting Brazilian Shield beneath the Eastern Cordillera.

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Structure of the subduction transition region from seismic array data in southern Peru

Cited by 30 publications

References 61 publications

Seismic structure in southern Peru: evidence for a smooth contortion between flat and normal subduction of the Nazca Plate

Seismic structure in southern Peru: evidence for a smooth contortion between flat and normal subduction of the Nazca Plate

Response of the mantle to flat slab evolution: Insights from local S splitting beneath Peru

Flat slab deformation caused by interplate suction force

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