Imperial College London

Saskia Goes

Faculty of EngineeringDepartment of Earth Science & Engineering

Professor of Geophysics
 
 
 
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Contact

 

+44 (0)20 7594 6434s.goes

 
 
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Location

 

4.47Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

128 results found

Chen YW, Wu J, Goes S, 2024, Lesser Antilles slab reconstruction reveals lateral slab transport under the Caribbean since 50 Ma, Earth and Planetary Science Letters, Vol: 627, ISSN: 0012-821X

The link between surface tectonic plates and mantle slabs is fundamental for paleo-tectonic reconstructions and for our understanding of mantle dynamics. Many seismic tomography-based studies have assumed vertical slab sinking and projected mantle features to the surface to reconstruct paleo-trench locations or explain tectonic features. Here, we used a slab-unfolding approach that does not require assumptions about sinking paths or rates to re-interpret the seismic structure of the Lesser Antilles slab underneath the Caribbean. A recent study invoked mainly vertical slab sinking and a highly folded and deformed slab to explain seismic Caribbean mantle structures. However, our results show that the upper-mantle Lesser Antilles slab structure can be better explained by limited intra-slab deformation and up to ∼900 km lateral slab transport towards the northwest after subduction. Our results indicate that such lateral slab transport can occur even with probable weaknesses in the slab that originate from a subducted fossil ridge-transform system. We ascribe the lateral slab transport in the mantle to a kinematic connection with the North American plate, which has migrated northwestward since the Eocene.

Journal article

Yu C, Goes S, Day EA, van der Hilst RDet al., 2023, Seismic evidence for global basalt accumulation in the mantle transition zone, SCIENCE ADVANCES, Vol: 9, ISSN: 2375-2548

Journal article

Davies R, Chen F, Goes S, Suchoy Let al., 2023, Controls on the Dynamics of Subducting Slabs in a 3-D Spherical Shell Domain

<jats:p>It has long been recognised that the shape of subduction zones is influenced by Earth&amp;#8217;s sphericity, but the effects of sphericity are regularly neglected in numerical and laboratory studies that examine the factors controlling subduction dynamics: most existing studies have been executed in a Cartesian domain, with the small number of simulations undertaken in a spherical shell incorporating plates with an oversimplified rheology, limiting their applicability. There are therefore many outstanding questions relating to the key controls on the dynamics of subduction. For example, do predictions from Cartesian subduction models hold true in a spherical geometry? When combined, how do subducting plate age and width influence the dynamics of subducting slabs, and associated trench shape? How do relic slabs in the mantle feedback on the dynamics of subduction? These questions are of great importance to understanding the evolution of Earth's subduction systems but remain under explored.In this presentation, we will target these questions through a systematic geodynamic modelling effort, by examining simulations of multi-material free-subduction of a visco-plastic slab in a 3-D spherical shell domain. We will first highlight the limitation(s) of Cartesian models, due to two irreconcilable differences with the spherical domain: (i) the presence of sidewall boundaries in Cartesian models, which modify the flow regime; and (ii) the reduction of space with depth in spherical shells, alongside the radial gravity direction, the impact of which cannot be captured in Cartesian domains, especially for subduction zones exceeding 2400 km in width. We will then demonstrate how slab age (approximated by co-varying thickness and density) and slab width affect the evolution of subducting slabs, using spherical subduction simulations, showing that: (i) as subducting plate age increases, slabs retreat more and subduct at a shallower dip angle, due to increased be

Other

Suchoy L, Goes S, Chen F, Davies DRet al., 2023, A 3-D numerical investigation of the impact of buoyant features on subduction dynamics and stress

<jats:p>The subduction of positively buoyant features has been suggested to cause flat or shallow dipping slabs, the formation of cusps in trench geometry and periods of reduction or full cessation of arc magmatism. Additionally, recent earthquake data indicates that the subduction of the Hikurangi plateau near New Zealand causes a rotation of intraplate stresses. In this study, we present a series of multi-material 3-D simulations of free subduction to investigate how subduction of buoyant elongated features, or ridges, impact downgoing plate velocities, trench motions, slab morphology and intraplate stress regime. We examine how these parameters are affected by the age of the subducting plate and the relative buoyancy and position of the buoyant ridge. We find that buoyant ridges change slab sinking and trench retreat rates and locally rotate intraplate stresses. These, in turn, modify the evolution of slab morphology at depth and trench shape at the surface, as trench retreat is reduced, or switches to trench advance, where the ridge subducts. These effects depend strongly on downgoing plate age: on young and weak plates, the change in trench shape is more localised than on old and strong plates. We observe slab shallowing around the ridge only in young plates, while the stronger pull by the more negatively buoyant old plates causes slab steepening near the buoyant ridge. Buoyant ridges on old plates which are located near stagnating or advancing regions, typical in wide slabs, modify trench behaviour more strongly than ridges in other regions of the trench. Bending-related intraplate earthquakes are more likely in older plates where higher stress is accumulated and the rotation due to the buoyant ridge is more widespread than for younger plates. The combined effects of buoyant feature location, subducting plate age and overriding plate properties can result in a range of responses: from mainly trench deformation, through local slab shallowing, to the forma

Other

Bastow I, Ogden C, Merry T, Kounoudis R, Bell R, Goes S, Zhou Pet al., 2023, Broadband seismological analyses in the Eastern Mediterranean: implications for late-stage subduction, plateau uplift and the development of the North Anatolian Fault

<jats:p>The eastern Mediterranean hosts extensional, strike-slip, and collision tectonics above a set of fragmenting subducting slabs. Widespread Miocene-Recent volcanism and ~2km uplift has been attributed to mantle processes such as delamination, dripping and/or slab tearing/break-off. We investigate this region using broadband seismology: mantle tomographic imaging (Kounoudis et al., 2020), SKS splitting analysis of seismic anisotropy (Merry et al., 2021), and receiver function study of crustal structure (Ogden &amp; Bastow, 2021). Anisotropy and crustal structure are more spatially variable than recognised previously, but variations correspond well with tomographically-imaged mantle structure. Moho depth correlates poorly with elevation, suggesting crustal thickness variations alone do not explain Anatolian topography: a mantle contribution, particularly in central and eastern Anatolia, is needed too. Lithospheric anisotropy beneath the North Anatolian Fault reveals a mantle shear zone deforming coherently with the surface, while backazimuthal variations in splitting parameters indicate fault-related lithospheric deformation. Anisotropic fast directions are either fault-parallel or intermediate between the principle extensional strain rate axis and fault strike, diagnostic of a relatively low-strained transcurrent mantle shear zone.</jats:p>

Other

Li L, Collier J, Henstock T, Goes Set al., 2023, Evidence for a higher porosity upper crust in the North Atlantic Ocean  

<jats:p>The most common way to estimate the porosity of the mature oceanic crust, and hence its contribution to geochemical exchange, is from the inversion of active source seismic data. Previous studies have suggested that hydrothermal activity effectively ceases in crust older than 10 Ma. This is based on observations that the seismic velocity of the uppermost crust increases rapidly within 10 Ma but changes little beyond that. The velocity increase is widely explained by reduced porosity and permeability due to hydrothermal mineral precipitation and fracture closure due to sediment blanketing. However, a potential problem with conventional wide-angle Ocean Bottom Seismometer (OBS) modelling over mature oceanic crust is the imaging geometry, where the water wave obscures the onset of the crustal refractions for tomographic inversion needed to resolve the velocity of the upper hundred meters of the igneous crust.&amp;#160;To investigate the issue of imaging geometry and accurately extract the physical properties of the upper crust, we applied downward continuation on conventional OBS records across 65 Ma Atlantic Ocean crust. The method eliminates the effect of the thick water column by locating shots on a datum close to the seabed. This enables refractions from the uppermost 100-200 m of igneous crust to be viewed as first arrivals, and hence significantly improves the accuracy of the velocity inversion of the upper layers. Using travel time picks from downward continued and original OBS records, we applied tomographic inversion with three starting models taken from the latest compilation of crustal velocity-depth (VZ) models. The three models have a velocity variation of &amp;#177;10% for the uppermost crust, representing a low, mean, and high bound for crustal VZ relations. By comparing the results, we show that with downward continued data the inverted velocity of the uppermost crust is less dependent on the starting model and converges to the sam

Other

Hicks S, Bie L, Rychert C, Harmon N, Goes S, Rietbrock A, Wei S, Collier J, Henstock T, Lynch L, Prytulak J, Macpherson C, Schlaphorst D, Wilkinson J, Blundy J, Cooper G, Davy R, Kendall J-Met al., 2023, Slab to back-arc to arc: fluid and melt pathways through the mantle wedge beneath the Lesser Antilles

<jats:p>Volatiles expelled from subducted plates promote melting of the overlying warm mantle, feeding arc volcanism. However, debates continue over the factors controlling melt generation and transport and how these determine the placement of volcanoes. To broaden our synoptic view of these fundamental mantle wedge processes, we image seismic attenuation beneath the Lesser Antilles arc, an end-member system that slowly subducts old, tectonised lithosphere. Punctuated anomalies with high ratios of bulk-to-shear attenuation (Q&amp;#954;-1/Q&amp;#181;-1 &gt; 0.6) and VP/VS (&gt;1.83) lie 40 km above the slab, representing expelled fluids that are retained in a cold boundary layer, transporting fluids towards the back-arc. The strongest attenuation (1000/QS~20), characterising melt in warm mantle, lies beneath the back-arc, revealing how back-arc mantle feeds arc volcanoes. Melt ponds under the upper plate and percolates toward the arc along structures from earlier back-arc spreading, demonstrating how slab dehydration, upper plate properties, past tectonics, and resulting melt pathways collectively condition volcanism.</jats:p>

Other

Hazzard JAN, Richards FD, Goes SDB, Roberts GGet al., 2023, Probabilistic Assessment of Antarctic Thermomechanical Structure: Impacts on Ice Sheet Stability, JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, Vol: 128, ISSN: 2169-9313

Journal article

Hazzard J, Richards F, Goes S, Roberts Get al., 2023, Probabilistic Assessment of Antarctic Thermomechanical Structure: Impacts on Ice Sheet Stability

<jats:p>Uncertainty in present-day glacial isostatic adjustment (GIA) rates represents at least 44% of the total gravity-based ice mass balance signal over Antarctica. Meanwhile, physical couplings between solid Earth, sea level and ice dynamics enhance the dependency of the spatiotemporally varying GIA signal on three-dimensional variations in mantle rheology. Improved knowledge of thermomechanical mantle structure is therefore required to refine estimates of current and projected ice mass balance. Here, we present a Bayesian inverse method for self-consistently mapping shear-wave velocities from high-resolution adjoint tomography into thermomechanical structure using calibrated parameterisations of anelasticity at seismic frequency. We constrain the model using regional geophysical data sets containing information on upper mantle temperature, attenuation and viscosity structure. Our treatment allows formal quantification of parameter covariances, and naturally permits propagation of material parameter uncertainties into thermomechanical structure estimates. We find that uncertainty in steady-state viscosity structure at 150 km depth can be reduced by 4-5 orders of magnitude compared with a forward-modelling approach neglecting covariance between viscoelastic parameters. By accounting for the dependence of viscosity on loading timescale, we find good agreement between our estimates of mantle viscosity beneath West Antarctica, and those derived from satellite GPS. Direct access to temperature structure allows us to estimate lateral variations in lithosphere-asthenosphere boundary (LAB) depth, geothermal heat flow (GHF), and associated uncertainties. We find evidence for shallow LAB depths (63 ± 13 km), and high GHF (76 ± 7 mW m^-2) beneath West Antarctica, suggesting a highly dynamic response to ice mass loss.</jats:p>

Journal article

Hicks S, Bie L, Rychert C, Harmon N, Goes S, Rietbrock A, Wei S, Collier J, Henstock T, Lynch L, Prytulak J, Macpherson C, Schlaphorst D, Wilkinson J, Blundy J, Cooper G, Kendall J-Met al., 2023, Slab to back-arc to arc: fluid and melt pathways through the mantle wedge beneath the Lesser Antilles

<jats:p>Volatiles expelled from subducted plates melt the overlying warm mantle, feeding arc volcanism. However, debates continue over the factors controlling melt generation and transport and how these determine the placement of volcanoes. To broaden our synoptic view of these fundamental mantle wedge processes, we image seismic attenuation beneath the Lesser Antilles arc, an end-member system that slowly subducts old, tectonised lithosphere. Punctuated anomalies with high ratios of bulk-to-shear attenuation (Qκ-1/Qµ-1 &gt; 0.6) and VP/VS (&gt;1.83) lie 40 km above the slab, representing expelled fluids that are retained in a cold boundary layer, transporting fluids towards the back-arc. The strongest attenuation (1000/QS~20), characterising melt in warm mantle, lies beneath the back-arc, revealing how back-arc mantle feeds arc volcanoes. Melt ponds under the upper plate and percolates toward the arc along structures from earlier back-arc spreading, demonstrating how slab dehydration, upper plate properties, past tectonics, and resulting melt pathways, collectively condition volcanism.</jats:p>

Journal article

Hicks S, Bie L, Rychert C, Harmon N, Goes S, Rietbrock A, Wei SS, Collier J, Henstock T, Lynch L, Prytulak J, Macpherson C, Schlaphorst D, Wilkinson J, Blundy J, Cooper G, Davy R, Kendall J-M, VoiLA Working Groupet al., 2023, Slab to back-arc to arc: fluid and melt pathways through the mantle wedge beneath the Lesser Antilles, Science Advances, Vol: 9, Pages: 1-14, ISSN: 2375-2548

Volatiles expelled from subducted plates promote melting of the overlying warm mantle, feeding arc volcanism. However, debates continue over the factors controlling melt generation and transport, and how these determine the placement of volcanoes. To broaden our synoptic view of these fundamental mantle wedge processes, we image seismic attenuation beneath the Lesser Antilles arc, an end-member system that slowly subducts old, tectonized lithosphere. Punctuated anomalies with high ratios of bulk-to-shear attenuation (Qκ−1/Qμ−1 > 0.6) and VP/VS (>1.83) lie 40 km above the slab, representing expelled fluids that are retained in a cold boundary layer, transporting fluids toward the back-arc. The strongest attenuation (1000/QS ~ 20), characterizing melt in warm mantle, lies beneath the back-arc, revealing how back-arc mantle feeds arc volcanoes. Melt ponds under the upper plate and percolates toward the arc along structures from earlier back-arc spreading, demonstrating how slab dehydration, upper-plate properties, past tectonics, and resulting melt pathways collectively condition volcanism.

Journal article

Chen F, Davies DR, Goes S, Suchoy L, Kramer SCet al., 2022, Comparing the Dynamics of Free Subduction in Cartesian and Spherical Domains, GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, Vol: 23

Journal article

Chen F, Davies DR, Goes S, Suchoy L, Kramer SCet al., 2022, How Slab Age and Width Combine to Dictate the Dynamics and Evolution of Subduction Systems: A 3-D Spherical Study, GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, Vol: 23

Journal article

Altoe I, Goes S, Assumpcao M, 2022, Thermo-Compositional Structure of the South American Platform Lithosphere: Evidence of Stability, Modification, and Erosion, GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, Vol: 23

Journal article

Chen F, Davies DR, Goes S, Suchoy L, Kramer SCet al., 2022, Comparing the Dynamics of Free Subduction in Cartesian and Spherical Domains

Journal article

Goes S, Yu C, ballmer M, Yan J, Van der Hilst Ret al., 2022, Compositional heterogeneity in the mantle transition zone, Nature Reviews Earth & Environment, Vol: 3, Pages: 533-550, ISSN: 2662-138X

Earth’s mantle transition zone (MTZ) is characterized by several sharp increases in seismic wave speed between ~300 km and ~850 km depth. These seismic discontinuities are generally attributed to solid-state phase transitions that lead to density and viscosity increases, which could cause a barrier to convection by segregating thermally and chemically heterogeneous material. This Review discusses insights into the role of MTZ compositional heterogeneity in mantle convection, derived from the joint constraints of MTZ discontinuity-reflected, discontinuity-refracted and discontinuity-transmitted seismic waves and thermodynamic and convection models. Growing seismic data sets and advances in analysis techniques show that the topography of these discontinuities mainly reflects variations in mantle temperature and, hence, present-day mantle flow. However, the discordant behaviour of the 410 km and 660 km discontinuities shows that the thermal structure is not vertically coherent across the MTZ in many areas, indicating that the MTZ delays the convective transport of cold material from above and hot material from below. Variable reflectivity of the MTZ discontinuity provides evidence of lateral and vertical heterogeneity in major element chemistry and volatile content. Seismic results are consistent with whole-mantle mechanical mixing of tectonic plates, with segregated material accumulating in the MTZ over multiple mantle convection cycles.

Journal article

Bie L, Hicks S, Rietbrock A, Goes S, Collier J, Rychert C, Harmon N, Maunder Bet al., 2022, Imaging slab-transported fluids and their deep dehydration from seismic velocity tomography in the Lesser Antilles subduction zone, Earth and Planetary Science Letters, Vol: 586, Pages: 117535-117535, ISSN: 0012-821X

Volatiles play a pivotal role in subduction zone evolution, yet their pathways remain poorly constrained. Studying the Lesser Antilles subduction zone can yield new constraints, where old oceanic lithosphere formed by slow-spreading subducts slowly. Here we use local earthquakes recorded by the temporary VoiLA (Volatile recycling in the Lesser Antilles) deployment of ocean-bottom seismometers in the fore- and back-arc to characterize the 3-D seismic structure of the north-central Lesser Antilles subduction zone. Along the slab top, mapped based on seismicity, we find low Vp extending to 130–150 km depth, deeper than expected for magmatic oceanic crust. The slab's most prominent, elevated Vp/Vs anomalies are beneath the fore- and back-arc offshore Guadeloupe and Dominica, where two subducted fracture zones lie with the obliquely subducting boundary between Proto-Caribbean and Equatorial Atlantic lithosphere. These structures, therefore, enhance hydration of the oceanic lithosphere as it forms and evolves and the subsequent dehydration of mantle serpentinite when subducted. Above the slab, we image the asthenosphere wedge as a high Vp/Vs and moderate Vp feature, indicating slab-dehydrated fluids rising through the overlying cold boundary layer that might induce melting further to the west. Our results provide new evidence for the impact of spatially-variable oceanic plate formation processes on slab dehydration and mantle wedge volatile transfer that ultimately impact volcanic processes at the surface, such as the relatively high magmatic output observed on the north-central islands in the Lesser Antilles.

Journal article

Suchoy L, Goes S, Chen F, Davies Ret al., 2022, How aseismic ridges modify the dynamics of free subduction: a 3-D numerical investigation, Frontiers in Earth Science, Vol: 10, ISSN: 2296-6463

The subduction of positively buoyant features has been implicated in the development of flat and shallow dipping slabs, the formation of cusps in trench geometry, and the cessation of associated arc magmatism. However, how such buoyant anomalies influence subduction dynamics to produce these different tectonic expressions remains debated. In this paper, using a series of multi-material 3-D simulations of free subduction, we investigate how linear buoyant ridges modify subduction dynamics, in particular downgoing plate velocities, trench motions and slab morphology. We examine the sensitivity of results to downgoing plate age (affecting buoyancy and strength), ridge buoyancy and ridge location along the trench, finding that buoyant ridges can locally change slab sinking and trench retreat rates, in turn modifying the evolution of slab morphology at depth and trench shape at the surface. In all cases examined, trench retreat is reduced, or switches to trench advance, where the ridge subducts. These effects depend strongly on downgoing plate age: on young, weak plates, the change in trench shape is more localised than on old, strong plates. Slab shallowing at the ridge only occurs for young plates, while the stronger and more negatively buoyant older plates pull down the ridge at a steeper angle than the rest of the slab. On old plates, ridges located near regions of trench stagnation or advance, which typically develop in wide slabs, have a stronger effect on trench and slab shape. The combined effects of buoyant feature location, subducting plate age and overriding plate properties can result in a range of responses: from mainly trench deformation, through local slab shallowing, to the formation of a flat slab, a variation in expressions also observed on Earth.

Journal article

Braszus B, Goes S, Allen R, Rietbrock A, Collier Jet al., 2022, Subduction history of the Caribbean from upper-mantle seismic imaging and plate reconstruction

<jats:p>&amp;lt;p&amp;gt;Even though the Caribbean region is constantly struck by the impact of geological hazards, the details of the Caribbean plate's evolution are still not completely understood. This interdisciplinary study combines and jointly interprets seismic tomography data with trench positions derived from plate reconstruction which constrains some of the most important events governing the evolution of the Caribbean plate.&amp;amp;#160;&amp;lt;br&amp;gt;Our new teleseismic P-wave tomography model of the upper mantle beneath the Caribbean includes manually processed and analysed data from 32 ocean-bottom seismometers installed for 16 months during the VoiLA experiment as well as recordings from 192 permanent and temporary land stations. Reconstruction tests show improved resolution compared to previous models and a sufficient recovery of a synthetic anomaly assimilating the Caribbean slab.&amp;amp;#160;&amp;lt;br&amp;gt;Based on reconstructed trench positions we attribute slab fragments residing in depths of 700-1200km to 90&amp;amp;#8211;115 Myr old westward subduction along the Great Arc of the Caribbean (GAC) prior to Caribbean Large Igneous Province volcanism, rather than to eastward dipping Farallon subduction.&amp;amp;#160;&amp;lt;br&amp;gt;In the mantle transition zone, the imaged slab coincides with predicted trench positions from 50-70 Ma with a slab window approximately at the location of the subducted Proto-Caribbean spreading ridge.&amp;lt;br&amp;gt;Along the otherwise continous slab in the shallow upper mantle from Hispanola to Grenada several tears are interpreted as ruptures along fault zones in the Proto-Caribbean crust as well as the subducted extinct Proto-Caribbean spreading ridge.&amp;amp;#160;&amp;lt;/p&amp;gt;</jats:p>

Journal article

Hazzard J, Richards F, Roberts G, Goes Set al., 2022, Reducing Uncertainty in Upper Mantle Rheology, Lithospheric Thickness and Geothermal Heat Flow Using a Bayesian Inverse Framework to Calibrate Experimental Parameterisations of Anelasticity

<jats:p>&amp;lt;p&amp;gt;Uncertainty in present-day glacial isostatic adjustment (GIA) rates represent at least 44% of the total gravity-based ice mass balance signal over Antarctica. Meanwhile, physical couplings between solid Earth, sea level and ice dynamics enhance the dependency of the spatiotemporally varying GIA signal on 3D rheology. For example, the presence of low-viscosity mantle beneath melting marine-based ice sheet sectors such as the Amundsen Sea Embayment may delay or even prevent unstable grounding line retreat. Improved knowledge of upper mantle thermomechanical structure is therefore required to refine estimates of current and projected ice mass balance.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Here, we present a Bayesian inverse method for mapping shear wave velocities from high-resolution adjoint tomography into thermomechanical structure using a calibrated parameterisation of anelasticity at seismic frequency. We constrain the model using regional geophysical data sets containing information on upper mantle temperature, attenuation and viscosity structure. The Globally Adaptive Scaling Within Adaptive Metropolis (GASWAM) modification of the Metropolis-Hastings algorithm is utilised to allow efficient exploration of the multi-dimensional parameter space. Our treatment allows formal quantification of parameter covariances, and naturally permits us to propagate uncertainties in material parameters into uncertainty in thermomechanical structure.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;We find that it is possible to improve agreement on steady state viscosity structure between tomographic models by approximately 30%, and reduce its uncertainty by an order of magnitude as compared to a forward-modelling approach. Direct access to temperature structure allows us to estimate lateral variations in lithospheric thickness, geothermal heat flow, and their associated uncertainties.&amp;lt;/p&amp;gt;&amp;lt;p&

Journal article

Bastow I, Merry T, Kounoudis R, Ogden C, Bell R, Goes S, Jenkins J, Jones L, Grant B, Braham Cet al., 2022, Mantle origins of topography, volcanism and the North Anatolian Fault in Anatolia: constraints from seismic tomography, seismic anisotropy and crustal structure

<jats:p>&amp;lt;p&amp;gt;The eastern Mediterranean hosts, within the span of a few hundred kilometres, extensional, strike-slip, and collision tectonics above a set of fragmenting subducting slabs. Widespread Miocene-Recent volcanism and ~2km uplift has been attributed to mantle processes such as delamination, dripping and/or slab tearing/break-off. We investigate this complex region using a variety of broadband seismological techniques, with new P- and S-wave tomographic images in Kounoudis et al. (2020), seismic anisotropy constrained via an updated dataset of SKS shear-wave splitting observations in Merry et al. (2021), and crustal structure imaged by quality-controlled H-&amp;amp;#954; stacking of receiver functions in Ogden &amp;amp; Bastow (2021). Overall, seismic anisotropy and crustal structure are more spatially variable than previously recognised, and such variations correspond well with variations in mantle structure shown by the tomography.&amp;amp;#160;In general, Moho depth is poorly correlated with elevation, suggesting crustal thickness variations do not fully explain topographic differences, and residual topography calculations indicate the requirement for a mantle contribution to Anatolian Plateau uplift. Evidence for such a contribution exists in central Anatolia, where an imaged horizontal tear in the Cyprus slab spatially corresponds with volcanism, a residual topographic high, and a region of reduced splitting delay times and nulls, all consistent with upwelling of asthenospheric material through the tear. Anisotropic fast directions are consistent with flow through the imaged gap between the Cyprus and Aegean slabs, again correlating roughly with both volcanism and high residual topography. Slow uppermost&amp;amp;#8208;mantle wave speeds below active volcanoes in eastern Anatolia, and ratios of P-to-S wave relative traveltimes, indicate a thin lithosphere and melt contributions. Elsewhere, there is more evidence f

Journal article

Bie L, Hicks S, Rietbrock A, Goes S, Collier J, Rychert C, Harmon N, Maunder Bet al., 2022, Fluid migration, deep dehydration, and melt generation in the Lesser Antilles subduction zone

<jats:p>&amp;lt;p&amp;gt;Volatiles play a pivotal role in subduction zones dynamics, associated geological hazards and mineralization, yet their pathways remain partially understood. The Lesser Antilles subduction zone can yield insights to volatile recycling as a global end-member, where old oceanic lithosphere formed by slow spreading slowly subducts. Here we use seismograms from local earthquakes recorded by a temporary deployment of ocean-bottom seismometers in the fore- and back-arc during the VoiLA (Volatile Recycling in the Lesser Antilles) experiment to characterize the 3-D properties of the slab, back-arc and mantle wedge in the north-central Lesser Antilles subduction zone. Along the top of the slab, defined by the underlying Wadati-Benioff seismicity, we find low P-wave velocity extending to 130&amp;amp;#8211;150 km depth, deeper than expected for magmatic oceanic crust. The deep low velocities together with high Vp/Vs at 60&amp;amp;#8211;80 km and 120&amp;amp;#8211;150 km depth are consistent with a significantly tectonised and serpentinised slab top, as expected for lithosphere formed by slow spreading. The most prominent high Vp/Vs anomalies in the slab correlates with two projected fracture zones and the obliquely subducting boundary between Proto-Caribbean and Equatorial Atlantic lithosphere, indicating these structures enhance hydration of the oceanic lithosphere and subsequent dehydration when subducted. Deep dehydration of slab mantle serpentinite is evidenced by high Vp/Vs anomalies in the back-arc offshore Guadeloupe and Dominica. Right above the slab, the asthenospheric mantle wedge is imaged beneath the back-arc as high Vp/Vs and moderate Vp feature, indicative for fluids rising from the slab through the overlaying cold boundary layer. The fluids might be dragged down with the subducting slab before rising upwards to induce melting further to the west. The variation in seismic properties along the subducting slab and

Journal article

Okuwaki R, Hicks S, Craig T, Fan W, Goes S, Wright T, Yuji Yet al., 2022, Illuminating a Contorted Slab with a Complex Intraslab Rupture Evolution during the 2021 Mw 7.3 East Cape, New Zealand Earthquake

<jats:p>The state-of-stress within subducting oceanic plates controls rupture processes of deep intraslab earthquakes. However, little is known about how the large-scale plate geometry and the stress regime relate to the physical nature of the deep-intraslab earthquakes. Here we find, by using globally and locally observed seismic records, that the moment magnitude 7.3 2021 East Cape, New Zealand earthquake was driven by a combination of shallow trench-normal extension and unexpectedly, deep trench-parallel compression. We find multiple rupture episodes comprising a mixture of reverse, strike-slip, and normal faulting. Reverse faulting due to the trench-parallel compression is unexpected given the apparent subduction direction, so we require a differential-buoyancy driven stress rotation which contorts the slab near the edge of the Hikurangi plateau. Our finding highlights that buoyant features in subducting plates may cause diverse rupture behavior of intraslab earthquakes due to the resulting heterogeneous stress state within slabs.</jats:p>

Working paper

Okuwaki R, Hicks SP, Craig TJ, Fan W, Goes S, Wright TJ, Yagi Yet al., 2021, Illuminating a contorted slab with a complex intraslab rupture evolution during the 2021 Mw 7.3 East Cape, New Zealand earthquake, Geophysical Research Letters, Vol: 48, Pages: 1-13, ISSN: 0094-8276

The state-of-stress within subducting oceanic plates controls rupture processes of deep intraslab earthquakes. However, little is known about how the large-scale plate geometry and the stress regime relate to the physical nature of the deep intraslab earthquakes. Here we find, by using globally and locally observed seismic records, that the moment magnitude 7.3 2021 East Cape, New Zealand earthquake was driven by a combination of shallow trench-normal extension and unexpectedly, deep trench-parallel compression. We find multiple rupture episodes comprising a mixture of reverse, strike-slip, and normal faulting. Reverse faulting due to the trench-parallel compression is unexpected given the apparent subduction direction, so we require a differential buoyancy-driven stress rotation, which contorts the slab near the edge of the Hikurangi plateau. Our finding highlights that buoyant features in subducting plates may cause diverse rupture behavior of intraslab earthquakes due to the resulting heterogeneous stress state within slabs.

Journal article

Hicks S, Goes S, Whittaker A, Stafford Pet al., 2021, Multivariate statistical appraisal of regional susceptibility to induced seismicity: application to the Permian Basin, SW United States, Journal of Geophysical Research. Solid Earth, Vol: 126, ISSN: 2169-9356

Induced earthquake sequences are typically interpreted through causal triggering mechanisms. However, studies of causality rarely consider large regions and why some regions experiencing similar anthropogenic activities remain largely aseismic. Therefore, it can be difficult to forecast seismic hazard at a regional scale. In contrast, multivariate statistical methods allow us to find the combinations of factors that correlate best with seismicity, which can help form the basis of hypotheses that can be subsequently tested with physical models. Whilst strong correlations do not necessarily equate to causality, such a statistical approach is particularly important for large regions with newly emergent seismicity comprising multiple distinct clusters and multi-faceted industrial operations. Recent induced seismicity in the Permian Basin provides an excellent test-bed for multivariate statistical analyses because the main causal industrial and geological factors driving earthquakes in the region remain highly debated. Here, we use logistic regression to retrospectively predict the spatial variation of seismicity across the western Permian Basin. We reproduce the broad distribution of seismicity using a combination of both industrial and geological factors. Our model shows that the proximity to neotectonic faults west of the Delaware Basin is the most important factor that contributes to induced seismicity. The second-most important factor is salt-water disposal at shallow depths, with hydraulic fracturing playing a less dominant role. The higher tectonic stressing, together with a poor correlation between seismicity and large-volume deep salt-water disposal wells indicates a very different mechanism of induced seismicity compared to that in Oklahoma.

Journal article

Braszus B, Goes S, Allen R, Rietbrock A, Collier J, Harmon N, Henstock T, Hicks S, Rychert CA, Maunder B, van Hunen J, Bie L, Blundy J, Cooper G, Davy R, Kendall JM, Macpherson C, Wilkinson J, Wilson Met al., 2021, Subduction history of the Caribbean from upper-mantle seismic imaging and plate reconstruction, Nature Communications, Vol: 12, Pages: 1-14, ISSN: 2041-1723

The margins of the Caribbean and associated hazards and resources have been shaped by a poorly understood history of subduction. Using new data, we improve teleseismic P-wave imaging of the eastern Caribbean upper mantle and compare identified subducted-plate fragments with trench locations predicted from plate reconstruction. This shows that material at 700–1200 km depth below South America derives from 90–115 Myr old westward subduction, initiated prior to Caribbean Large-Igneous-Province volcanism. At shallower depths, an accumulation of subducted material is attributed to Great Arc of the Caribbean subduction as it evolved over the past 70 Ma. We interpret gaps in these subducted-plate anomalies as: a plate window and tear along the subducted Proto-Caribbean ridge; tearing along subducted fracture zones, and subduction of a volatile-rich boundary between Proto-Caribbean and Atlantic domains. Phases of back-arc spreading and arc jumps correlate with changes in age, and hence buoyancy, of the subducting plate.

Journal article

Hicks S, Goes S, Whittaker A, Stafford Pet al., 2021, Multivariate statistical appraisal of regional susceptibility to induced seismicity: application to the Permian Basin, SW United States, Publisher: Earth ArXiv

Induced earthquake sequences are typically interpreted through causal triggering mechanisms. However, studies of causality rarely consider large regions and why some regions experiencing similar anthropogenic activities remain largely aseismic. Therefore, it can be difficult to forecast seismic hazard at a regional scale. In contrast, multivariate statistical methods allow us to find the combinations of factors that correlate best with seismicity, which can help form the basis of hypotheses that can be subsequently tested with physical models. Such a statistical approach is particularly important for large regions with newly-emergent seismicity comprising multiple distinct clusters and multi-faceted industrial operations. Recent induced seismicity in the Permian Basin provides an excellent test-bed for multivariate statistical analyses because the main causal industrial and geological factors driving earthquakes in the region remain highly debated. Here, we use logistic regression to retrospectively predict the spatial variation of seismicity across the western Permian Basin. We reproduce the broad distribution of seismicity using a combination of both industrial and geological factors. Our model shows that hydraulic fracturing and/or hydrocarbon production from the Wolfcamp Shale is the strongest predictor of seismicity, although the physical triggering process is unclear due to uncertain earthquake depths. We also find that the proximity to neotectonic faults west of the Delaware Basin is another important factor that contributes to induced seismicity. This higher tectonic stressing, together with a poor correlation between seismicity and large-volume deep salt-water disposal wells indicates a very different mechanism of induced seismicity compared to that in Oklahoma.

Working paper

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