Periodic Reporting for period 4 - NEWTON (NEw Windown inTO Earth's iNterior)
Periodo di rendicontazione: 2022-09-01 al 2023-11-30
One of the principal objectives of Earth science is to understand the internal dynamics, structure and composition of our planet. Because most of the Earth is inaccessible to direct investigation, we must rely on indirect methods, such as seismological methods, and on numerical/analogue modelling to generate a window through which explore the Earth’s interior.
On the one hand, geodynamic models give insights into the complex dynamical behavior of the Earth, where several thermomechanical and petrological processes occur simultaneously at geological timescales. However, the validation of the results relies mainly on comparison with seismological observations, which is often not possible due to the lack of numerical tools allowing to compute mantle elastic properties and perform modelling of seismological synthetics.
On the other hand, seismological methods, which are based on the study of the propagation of seismic waves, are by far the best instrument for studying the Earth's current deep structure and physical properties. In particular, seismic tomography is a technique that allows mapping the lateral variations of the elastic properties (particularly wave-propagation velocity) of the Earth’s interior from seismic travel time and waveform data. As a matter of fact, the interpretation of tomographic models is commonly carried out considering the rocks as seismically isotropic. However, neglecting the existing mechanical anisotropy results in artefacts (i.e. apparent seismic velocity anomalies) that can be easily confused with real velocity anomalies, and thus bias our understanding of the present-day mantle structure. Therefore, assessing the validity and robustness of seismic tomography models is fundamental in order to have a reliable window of the Earth’s interior. Furthermore, the interpretation of real velocity anomalies (due to thermal anomalies or petrological reactions such as melting) in non-unique, and geodynamic modelling can provide the required petrological-thermo-mechanical constraints.
As such, the main objectives of the NEWTON project are:
1) generating a new multidisciplinary window through which the Earth's internal dynamics and structure will be explored by coupling geodynamic and seismological methods in order to decompose velocity anomalies into isotropic (thermo-petrological) and anisotropic (mechanical) components and, at the same time, provide both geodynamic constraints to the nature of these seismic anomalies and seismological constraints to geodynamic models physical parameters. As a major outcome, we expect to provide a new, geodynamically and seismologically constrained perspective of the current deep structure and tectono-magmatic evolution of different tectonic settings (see Figure).
2) Apply the new methodology to the Mediterranean and the Cascadia convergent margins where, despite the abundant observations, large uncertainties about the subsurface structure and tectonic evolution persist.
3) Release an open source and more sophisticated version of existing codes for modelling mantle fabric and subsequently perform inversions of synthetic seismic waveforms. The new software will be designed to be portable across numerical codes of mantle convection, thus providing a useful tool to perform and couple geodynamic and seismological modelling in other tectonic settings.
On the one hand, geodynamic models give insights into the complex dynamical behavior of the Earth, where several thermomechanical and petrological processes occur simultaneously at geological timescales. However, the validation of the results relies mainly on comparison with seismological observations, which is often not possible due to the lack of numerical tools allowing to compute mantle elastic properties and perform modelling of seismological synthetics.
On the other hand, seismological methods, which are based on the study of the propagation of seismic waves, are by far the best instrument for studying the Earth's current deep structure and physical properties. In particular, seismic tomography is a technique that allows mapping the lateral variations of the elastic properties (particularly wave-propagation velocity) of the Earth’s interior from seismic travel time and waveform data. As a matter of fact, the interpretation of tomographic models is commonly carried out considering the rocks as seismically isotropic. However, neglecting the existing mechanical anisotropy results in artefacts (i.e. apparent seismic velocity anomalies) that can be easily confused with real velocity anomalies, and thus bias our understanding of the present-day mantle structure. Therefore, assessing the validity and robustness of seismic tomography models is fundamental in order to have a reliable window of the Earth’s interior. Furthermore, the interpretation of real velocity anomalies (due to thermal anomalies or petrological reactions such as melting) in non-unique, and geodynamic modelling can provide the required petrological-thermo-mechanical constraints.
As such, the main objectives of the NEWTON project are:
1) generating a new multidisciplinary window through which the Earth's internal dynamics and structure will be explored by coupling geodynamic and seismological methods in order to decompose velocity anomalies into isotropic (thermo-petrological) and anisotropic (mechanical) components and, at the same time, provide both geodynamic constraints to the nature of these seismic anomalies and seismological constraints to geodynamic models physical parameters. As a major outcome, we expect to provide a new, geodynamically and seismologically constrained perspective of the current deep structure and tectono-magmatic evolution of different tectonic settings (see Figure).
2) Apply the new methodology to the Mediterranean and the Cascadia convergent margins where, despite the abundant observations, large uncertainties about the subsurface structure and tectonic evolution persist.
3) Release an open source and more sophisticated version of existing codes for modelling mantle fabric and subsequently perform inversions of synthetic seismic waveforms. The new software will be designed to be portable across numerical codes of mantle convection, thus providing a useful tool to perform and couple geodynamic and seismological modelling in other tectonic settings.
To fulfill the NEWTON project’s objectives, several research activities were conducted, which are grouped in 4 different but strongly interconnected Working Activities (WA):
WA1- Macroflow modelling
We have performed the first geodynamic model of the case studies Cascadia and the Mediterranean (main output of WA1; Zhou et al., 2018; Confal et al., 2018; Lo Bue et al., 2021, 2022). In addition, we have (i) tested alternative mechanisms for generating seismic anomalies in the upper and lower mantle in proximity of subducting slabs (Chen and Faccenda, 2019; Yang and Faccenda, 2020), (ii) found a relationship between plate speed and seismic anisotropy in the underlying asthenosphere (Kendall et al., 2022), (iii) discovered that imaged age-independent oceanic plate structure could be an artifact related to the resolving power of tomographic models (Rappisi et al., 2024), and (iv) generated subduction models that explain the presence of seismic anisotropy in the uppermost lower mantle (Ferreira et al., 2019; Sturgeon et al., 2019).
WA2 - Microflow and other types of fabric modelling
A new software package named ECOMAN (Exploring the Consequences of Mechanical Anisotropy in the maNtle) has been released in the project website. The package is intended to provide to the scientific community an efficient numerical tool for modelling the elastic and viscous properties of mantle aggregates and exploring the consequences of mechanical anisotropy in the Earth’s mantle (Faccenda et al., submitted).
The role of extrinsic elastic and viscous mechanical anisotropy on seismic anisotropy and mantle convection has been quantified (Faccenda et al., 2019; de Montserrat et al., 2021).
WA3 - SKS splitting seismology
We have determined the SKS splitting parameters in the Alp-Array and the Central Mediterranean area (Petrescu et al., 2020; Pondrelli et al., 2022, 2023; Confal et al., 2023) . These studies have constrained the large-scale mantle flow in the area, and inferred the source of mantle anisotropy in the sub-lithospheric mantle. A similar exercise has been done for the Hindu-Kush region (Peng et al., 2020).
WA4 - P-wave and S-wave inversions
We have developed and successfully tested new methodologies for jointly inverting seismic anisotropy using multiphase datasets including P-wave and S-wave travel-times and S-wave splitting intensity (VanderBeek and Faccenda, 2021; VanderBeek et al., 2023; Del Piccolo et al., 2024). This new technique allows to invert for arbitrarily oriented anisotropic patterns. The inverse methodologies has been applied to the imaging of the Mediterranean (Confal et al., 2020; Rappisi et al., 2022) and Cascadia (VanderBeek and Del Piccolo, 2023, AGU23) case studies, and also to other tectonic settings like divergent margins and intra-oceanic hotspot settings (Faccenda and Vanderbeek, 2023).
WA1- Macroflow modelling
We have performed the first geodynamic model of the case studies Cascadia and the Mediterranean (main output of WA1; Zhou et al., 2018; Confal et al., 2018; Lo Bue et al., 2021, 2022). In addition, we have (i) tested alternative mechanisms for generating seismic anomalies in the upper and lower mantle in proximity of subducting slabs (Chen and Faccenda, 2019; Yang and Faccenda, 2020), (ii) found a relationship between plate speed and seismic anisotropy in the underlying asthenosphere (Kendall et al., 2022), (iii) discovered that imaged age-independent oceanic plate structure could be an artifact related to the resolving power of tomographic models (Rappisi et al., 2024), and (iv) generated subduction models that explain the presence of seismic anisotropy in the uppermost lower mantle (Ferreira et al., 2019; Sturgeon et al., 2019).
WA2 - Microflow and other types of fabric modelling
A new software package named ECOMAN (Exploring the Consequences of Mechanical Anisotropy in the maNtle) has been released in the project website. The package is intended to provide to the scientific community an efficient numerical tool for modelling the elastic and viscous properties of mantle aggregates and exploring the consequences of mechanical anisotropy in the Earth’s mantle (Faccenda et al., submitted).
The role of extrinsic elastic and viscous mechanical anisotropy on seismic anisotropy and mantle convection has been quantified (Faccenda et al., 2019; de Montserrat et al., 2021).
WA3 - SKS splitting seismology
We have determined the SKS splitting parameters in the Alp-Array and the Central Mediterranean area (Petrescu et al., 2020; Pondrelli et al., 2022, 2023; Confal et al., 2023) . These studies have constrained the large-scale mantle flow in the area, and inferred the source of mantle anisotropy in the sub-lithospheric mantle. A similar exercise has been done for the Hindu-Kush region (Peng et al., 2020).
WA4 - P-wave and S-wave inversions
We have developed and successfully tested new methodologies for jointly inverting seismic anisotropy using multiphase datasets including P-wave and S-wave travel-times and S-wave splitting intensity (VanderBeek and Faccenda, 2021; VanderBeek et al., 2023; Del Piccolo et al., 2024). This new technique allows to invert for arbitrarily oriented anisotropic patterns. The inverse methodologies has been applied to the imaging of the Mediterranean (Confal et al., 2020; Rappisi et al., 2022) and Cascadia (VanderBeek and Del Piccolo, 2023, AGU23) case studies, and also to other tectonic settings like divergent margins and intra-oceanic hotspot settings (Faccenda and Vanderbeek, 2023).
The research activities have progressed beyond the state-of-the-art by:
1. developing a theoretical and computation framework to invert for recovering the anisotropy related to an arbitrarily oriented anisotropic medium, which is required to reconstruct 3D structures, mantle strain patterns and validate geodynamic models.
2. performing the first forward/inverse geodynamic and body-wave anisotropic seismological modelling of the Cascadia and Mediterranean convergent margins, which were the two case studies of the proposals.
3. quantifying the amount of elastic and viscous extrinsic anisotropy in the crustal/mantle rocks and finding that while elastic anisotropy due compositional layering is negligible, extrinsic viscous anisotropy could affect mantle convection patterns.
4. developing and releasing a new software package named ECOMAN (Exploring the Consequences of Mechanical ANisotropy) that is intended to provide to the scientific community an efficient numerical tool for modelling strain-/stress-induced rock fabrics and testing the effects of the resulting mechanical (elastic and viscous) anisotropy on seismic imaging and mantle convection patterns.
1. developing a theoretical and computation framework to invert for recovering the anisotropy related to an arbitrarily oriented anisotropic medium, which is required to reconstruct 3D structures, mantle strain patterns and validate geodynamic models.
2. performing the first forward/inverse geodynamic and body-wave anisotropic seismological modelling of the Cascadia and Mediterranean convergent margins, which were the two case studies of the proposals.
3. quantifying the amount of elastic and viscous extrinsic anisotropy in the crustal/mantle rocks and finding that while elastic anisotropy due compositional layering is negligible, extrinsic viscous anisotropy could affect mantle convection patterns.
4. developing and releasing a new software package named ECOMAN (Exploring the Consequences of Mechanical ANisotropy) that is intended to provide to the scientific community an efficient numerical tool for modelling strain-/stress-induced rock fabrics and testing the effects of the resulting mechanical (elastic and viscous) anisotropy on seismic imaging and mantle convection patterns.