Crustal Deformation Following Great Subduction Earthquakes Controlled by Earthquake Size and Mantle Rheology

SUMMARY Previous studies have shown that a low viscosity upper mantle can impact the wavelength of mantle flow and the balance of plate driving to resisting forces. Those studies assumed that mantle viscosity is independent of mantle flow. We explore the potential that mantle flow is not only influenced by viscosity but can also feedback and alter mantle viscosity structure owing to a non-Newtonian upper-mantle rheology. Our results indicate that the average viscosity of the upper mantle, and viscosity variations within it, are affected by the depth to which a non-Newtonian rheology holds. Changes in the wavelength of mantle flow, that occur when upper-mantle viscosity drops below a critical value, alter flow velocities which, in turn, alter mantle viscosity. Those changes also affect flow profiles in the mantle and the degree to which mantle flow drives the motion of a plate analogue above it. Enhanced upper-mantle flow, due to an increasing degree of non-Newtonian behaviour, decreases the ratio of upper- to lower-mantle viscosity. Whole layer mantle convection is maintained but upper- and lower-mantle flow take on different dynamic forms: fast and concentrated upper-mantle flow; slow and diffuse lower-mantle flow. Collectively, mantle viscosity, mantle flow wavelengths, upper- to lower-mantle velocities and the degree to which the mantle can drive plate motions become connected to one another through coupled feedback loops. Under this view of mantle dynamics, depth-variable mantle viscosity is an emergent flow feature that both affects and is affected by the configuration of mantle and plate flow.

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Spectral damping scaling factors for horizontal components of ground motions from subduction earthquakes using NGA-Subduction data

Earthquake Spectra ◽

10.1177/87552930211027903 ◽

2021 ◽

pp. 875529302110279

Author(s):

Sanaz Rezaeian ◽

Linda Al Atik ◽

Nicolas M Kuehn ◽

Norman Abrahamson ◽

Yousef Bozorgnia ◽

...

Keyword(s):

Ground Motions ◽

Damping Ratio ◽

Spectral Shape ◽

Parametric Models ◽

Scaling Factors ◽

Global Models ◽

Motion Models ◽

Subduction Earthquakes ◽

Crustal Earthquakes ◽

Subduction Zone Earthquakes

This article develops global models of damping scaling factors (DSFs) for subduction zone earthquakes that are functions of the damping ratio, spectral period, earthquake magnitude, and distance. The Next Generation Attenuation for subduction earthquakes (NGA-Sub) project has developed the largest uniformly processed database of recorded ground motions to date from seven subduction regions: Alaska, Cascadia, Central America and Mexico, South America, Japan, Taiwan, and New Zealand. NGA-Sub used this database to develop new ground motion models (GMMs) at a reference 5% damping ratio. We worked with the NGA-Sub project team to develop an extended database that includes pseudo-spectral accelerations (PSA) for 11 damping ratios between 0.5% and 30%. We use this database to develop parametric models of DSF for both interface and intraslab subduction earthquakes that can be used to adjust any subduction GMM from a reference 5% damping ratio to other damping ratios. The DSF is strongly influenced by the response spectral shape and the duration of motion; therefore, in addition to the damping ratio, the median DSF model uses spectral period, magnitude, and distance as surrogate predictor variables to capture the effects of the spectral shape and the duration of motion. We also develop parametric models for the standard deviation of DSF. The models presented in this article are for the RotD50 horizontal component of PSA and are compared with the models for shallow crustal earthquakes in active tectonic regions. Some noticeable differences arise from the considerably longer duration of interface records for very large magnitude events and the enriched high-frequency content of intraslab records, compared with shallow crustal earthquakes. Regional differences are discussed by comparing the proposed global models with the data from each subduction region along with recommendations on the applicability of the models.

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Geodetic analysis of the tectonic crustal deformation pattern in the North Aegean Sea, Greece

Mediterranean Geoscience Reviews ◽

10.1007/s42990-021-00049-6 ◽

2021 ◽

Author(s):

Ilias Lazos ◽

Sotirios Sboras ◽

Christos Pikridas ◽

Spyros Pavlides ◽

Alexandros Chatzipetros

Keyword(s):

Crustal Deformation ◽

Aegean Sea ◽

Deformation Pattern ◽

The North ◽

North Aegean ◽

North Aegean Sea

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Crustal deformation in Volcanic covered area as inferred from magnetotelluric studies: an example from India

Journal of Geodynamics ◽

10.1016/j.jog.2021.101840 ◽

2021 ◽

pp. 101840

Author(s):

K.S. Ajithabh ◽

Prasanta K. Patro

Keyword(s):

Crustal Deformation ◽

Covered Area

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The Hindu Kush slab break-off as revealed by deep structure and crustal deformation

Nature Communications ◽

10.1038/s41467-021-21760-w ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Sofia-Katerina Kufner ◽

Najibullah Kakar ◽

Maximiliano Bezada ◽

Wasja Bloch ◽

Sabrina Metzger ◽

...

Keyword(s):

Real Time ◽

Penetration Depth ◽

Continental Crust ◽

Crustal Deformation ◽

Deep Structure ◽

Continental Collision ◽

Variable Degree ◽

Finite Frequency ◽

Hindu Kush ◽

Short Times

AbstractBreak-off of part of the down-going plate during continental collision occurs due to tensile stresses built-up between the deep and shallow slab, for which buoyancy is increased because of continental-crust subduction. Break-off governs the subsequent orogenic evolution but real-time observations are rare as it happens over geologically short times. Here we present a finite-frequency tomography, based on jointly inverted local and remote earthquakes, for the Hindu Kush in Afghanistan, where slab break-off is ongoing. We interpret our results as crustal subduction on top of a northwards-subducting Indian lithospheric slab, whose penetration depth increases along-strike while thinning and steepening. This implies that break-off is propagating laterally and that the highest lithospheric stretching rates occur during the final pinching-off. In the Hindu Kush crust, earthquakes and geodetic data show a transition from focused to distributed deformation, which we relate to a variable degree of crust-mantle coupling presumably associated with break-off at depth.

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