From Slab Coupling to Slab Pull: Stress Segmentation in the Subducting Nazca Plate

Bloch, Wasja; Schurr, Bernd; Kummerow, J.; Salazar, Pablo; Shapiro, Serge A.

doi:10.1029/2018gl078793

Cited by 25 publications

(30 citation statements)

References 50 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The apparent absence of deep DC earthquakes associated with upper plane unbending at the expected depth‐distance range in ePac slabs, may signal the slab stress deformation state transitions from flexurally dominated to a more prominent uniaxial component (Bloch et al., 2018). Alternatively, progressive warming of the upper part of the slab and/or processes related to dehydration may leave it essentially aseismic at these depths, with the consequence that the seismically active zone lies beneath the midplane.…”

Section: Discussionmentioning

confidence: 99%

“…uniform stretching due to slab pull (Bailey et al, 2009;Bloch et al, 2018;Isacks & Molnar, 1971;Rietbrock & Waldhauser, 2004), while DC regimes have been attributed to the propagation of compressional stress along the slab from interactions between the deep parts of the slab and the transition zone (Figures 1d and 1h Billen et al, 2003;Fujita & Kanamori, 1981;Gurnis et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

“…In ePac slabs such as Chile, intermediate depth focal mechanisms are strongly dominated by DT earthquakes, whereas wPac slabs such as Tonga tend to be dominated by DC events. DT regimes are often attributed to uniform stretching due to slab pull (Bailey et al., 2009; Bloch et al., 2018; Isacks & Molnar, 1971; Rietbrock & Waldhauser, 2004), while DC regimes have been attributed to the propagation of compressional stress along the slab from interactions between the deep parts of the slab and the transition zone (Figures 1d and 1h Billen et al., 2003; Fujita & Kanamori, 1981; Gurnis et al., 2000).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The Fingerprints of Flexure in Slab Seismicity

et al. 2020

View full text Add to dashboard Cite

Earthquake moment tensors in eastern Pacific (ePac) slabs typically show downdip tensional (DT) axes, whereas in the western Pacific (wPac), they typically show downdip compressional (DC) axes or have mixed orientations indicative of unbending. Prevailing conceptual models emphasize uniform stress/deformation modes, that is, bulk slab stretching or shortening, as the dominant control on intermediate depth seismic expression. In contrast, we propose that a diversity of seismic expression, including DT‐ and DC‐dominated regions, is consistent with expectations of flexural strain accumulation, based on systemic differences in slab geometry. Our analysis reveals two largely unrecognized features of ePac intraslab seismicity. First, earthquake clusters consistent with slab unbending are present in ePac slabs, albeit at much shallower depths than typical of wPac slabs. Second, intermediate depth ePac DT seismicity is strongly localized to the upper half of zones undergoing curvature increase, such as flat slab segments. Our study highlights how the seismic expression of slab flexure is impacted by the relative contribution of brittle and ductile deformation. The strongly asymmetric temperature structure that is preserved in sinking slabs means that seismicity disproportionately records the deformation regime in the colder part of the slab, above the neutral plane of bending. The expression of in‐plane stress may be discernible in terms of a systematic modifying effect on the seismic expression of flexure.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The Fingerprints of Flexure in Slab Seismicity

et al. 2020

View full text Add to dashboard Cite

show abstract

“…Some earthquakes sharply delineate the transitionally locked plate contact, which is defined by focal mechanisms that show shallow thrust on a ∼20 ∘ E dipping plane (Bloch et al, 2018), a sharp reflector between 40-and 50-km depth (Oncken et al, 2003;Yoon et al, 2009) and a negative amplitude of receiver functions (Figure 1, blue line, Yuan et al, 1992). Some earthquakes sharply delineate the transitionally locked plate contact, which is defined by focal mechanisms that show shallow thrust on a ∼20 ∘ E dipping plane (Bloch et al, 2018), a sharp reflector between 40-and 50-km depth (Oncken et al, 2003;Yoon et al, 2009) and a negative amplitude of receiver functions (Figure 1, blue line, Yuan et al, 1992).…”

Section: Introductionmentioning

confidence: 98%

Watching Dehydration: Seismic Indication for Transient Fluid Pathways in the Oceanic Mantle of the Subducting Nazca Slab

Bloch

John

Kummerow

et al. 2018

Geochem Geophys Geosyst

Self Cite

View full text Add to dashboard Cite

Intermediate depth seismicity in subduction zones often occurs in the form of two slab‐parallel bands. We estimated the seismic P to S wave velocity ratio within the shallowest part of the lower seismicity zone (LSZ) in the mantle of the subducting slab of the Central Andean subduction system at 50‐km depth, 30 km below the Moho, using local earthquake data. We find an exceptionally high VP/VS value larger than ∼2.0 that cannot be explained by a realistic solid lithology but requires the presence of fluid‐filled porosity. This implies that the incoming Nazca plate must be partially hydrated to this depth below the seafloor. We introduce a state‐of‐the‐art petrophysical model that takes into account the thermodynamic and poroelastic effects of dynamic metamorphic mineral dehydration at 1.8 GPa and consider anisotropic effects. The model shows that a high VP/VS value generally indicates that the medium is near the percolation threshold, that is, that porosity must be interconnected. This result is consistent with observations from outcrops of paleosubduction zones, laboratory experiments, and numerical simulations. It follows that the shallowest part of the LSZ of the Central Andes must reside at a temperature at which mineral dehydration reactions take place, here between 430 and 500 ° C. For the first time, we can confirm that the observations of transient dehydrating fluid‐filled vein structures with a pore volume in the order of only 10−3 are reasonable for the LSZ and enough to allow for effective drainage.

show abstract

“…In ePac slabs such as Chile, intermediate depth focal mechanisms are strongly dominated by DT earthquakes whereas wPac slabs such as Tonga tend to be dominated by DC events. DT regimes are often attributed to uniform stretching due to slab pull (Isacks & Molnar, 1971;Rietbrock & Waldhauser, 2004;Bloch et al, 2018;Bailey et al, 2009), while DC regimes have been attributed to the propagation of compressional stress along the slab from interactions between the deep parts of the slab and the transition zone (Figs 1d & 1h, Fujita & Kanamori, 1981;Gurnis et al, 2000;Billen et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

The fingerprints of flexure in slab seismicity

Sandiford¹,

Moresi²,

Sandiford³

et al. 2019

Preprint

View full text Add to dashboard Cite

Earthquake moment tensors in east Pacific (ePac) slabs typically show downdip tensional axes (DT), whereas in the west Pacific (wPac) they typically show downdip compressional axes (DC) or have mixed orientations indicative of unbending. Prevailing conceptual models emphasise uniform stress/deformation modes, i.e. bulk stretching or shortening, as the dominant control on intermediate depth seismic expression. In contrast we propose that much of the diversity in seismic expression is consistent with expectations of flexural strain accumulation due to systemic differences in slab geometry. Our analysis reveals two largely unrecognised features of ePac intraslab seismicity. Firstly, earth-quake clusters consistent with slab unbending are present in ePac slabs, albeit at much shallower depths than typical of wPac slabs. Secondly, intermediate depth ePac DT seismicity is strongly localised to the upper half of zones undergoing curvature increase, such as flat slab segments. Our study highlights how the seismic expression of slab flexure is impacted by the relative contribution of brittle and ductile deformation. The strongly asymmetric temperature structure that is preserved in sinking slabs means that seismicity disproportionately records the deformation regime in the colder part of the slab, above the neutral plane of bending. The expression of in-plane stress may be discernible in terms of a systematic modifying effect on the seismic expression of flexure.

show abstract

From Slab Coupling to Slab Pull: Stress Segmentation in the Subducting Nazca Plate

Cited by 25 publications

References 50 publications

The Fingerprints of Flexure in Slab Seismicity

The Fingerprints of Flexure in Slab Seismicity

Watching Dehydration: Seismic Indication for Transient Fluid Pathways in the Oceanic Mantle of the Subducting Nazca Slab

The fingerprints of flexure in slab seismicity

Contact Info

Product

Resources

About