Sensitivity of horizontal surface deformation to mantle dynamics from 3D instantaneous dynamics modeling of the eastern Mediterranean region

Geodetically estimated surface motions contain contributions to crustal deformation from coupled geodynamic processes active at all spatial scales and constitute key data for lithosphere dynamics research. Data interpretation methods should therefore account for the full range of possible processes, otherwise risking misinterpretation of data signal and incorrect estimation of lithosphere rheology, stress, or deformation fields. Here we explore the sensitivity of surface deformation to sub-lithospheric processes such as viscous plate-mantle and slab-mantle coupling, variations in slab pull, and buoyancy-driven mantle flow. To this end, we perform 3D instantaneous-dynamics numerical modelling of an elaborately structured compressible crust-mantle system designed for the Eastern Mediterranean Aegean-Anatolian region. We first determine a reference model driven by the absolute motions of the major plates, regional slab pull, a 3D mantle buoyancy field, and modulated by plate boundary coupling and mantle viscosity. The RMS motion data fit of ~5.9 mm/yr of predicted and observed Aegean-Anatolian horizontal surface motions demonstrates that the bulk amplitude of surface motion can be explained by these combined mantle processes. Next, by systematically perturbing reference model features, we assess the crustal sensitivity to each geodynamic driver and to mantle rheology. We find significant changes in crustal velocity gradient amplitudes, often between 10% and 40% of the reference model, with slab morphology effects of up to 93%. This demonstrates the key importance of carefully accounting for each process in modelling lithosphere dynamics. For the Aegean-Anatolia region, we present geodynamic evidence that the Aegean slab pull is the primary driver of the crustal motion field, as was previously suggested from kinematic analysis.

The Analytical Contribution to the Theory of Solar-induced Earthquakes: the Croatian December 2020 M=6.4 Case Study

Solar-induced earthquakes are a relatively new field of research of possible connection between events originating from Sun, and the Earth's lithosphere dynamics. This is a theory that tries to explain the temporal correlation between the solar activity increase, particularly measured using proton density values, and occurrence of the strongest earthquakes on Earth. In this paper, the case study of Croatian major earthquake in December 2020 was investigated. The increase in proton density as measured by STEREO satellite, by +4.2 standard deviations from the monthly mean value, preceded the main shock of M=6.4 by 16 hours. Such proton density increases, within one day before major earthquake, agrees with previous research where strong temporal correlation of those two events was found.

Impact of upper mantle convection on lithosphere hyperextension and subsequent horizontally forced subduction initiation

Many plate tectonic processes, such as subduction initiation, are embedded in long-term (>100 Myr) geodynamic cycles often involving subsequent phases of extension, cooling without plate deformation and convergence. However, the impact of upper mantle convection on lithosphere dynamics during such long-term cycles is still poorly understood. We have designed two-dimensional upper-mantle-scale (down to a depth of 660 km) thermo-mechanical numerical models of coupled lithosphere–mantle deformation. We consider visco–elasto–plastic deformation including a combination of diffusion, dislocation and Peierls creep law mechanisms. Mantle densities are calculated from petrological phase diagrams (Perple_X) for a Hawaiian pyrolite. Our models exhibit realistic Rayleigh numbers between 106 and 107, and the model temperature, density and viscosity structures agree with geological and geophysical data and observations. We tested the impact of the viscosity structure in the asthenosphere on upper mantle convection and lithosphere dynamics. We also compare models in which mantle convection is explicitly modelled with models in which convection is parameterized by Nusselt number scaling of the mantle thermal conductivity. Further, we quantified the plate driving forces necessary for subduction initiation in 2D thermo-mechanical models of coupled lithosphere–mantle deformation. Our model generates a 120 Myr long geodynamic cycle of subsequent extension (30 Myr), cooling (70 Myr) and convergence (20 Myr) coupled to upper mantle convection in a single and continuous simulation. Fundamental features such as the formation of hyperextended margins, upper mantle convective flow and subduction initiation are captured by the simulations presented here. Compared to a strong asthenosphere, a weak asthenosphere leads to the following differences: smaller value of plate driving forces necessary for subduction initiation (15 TN m−1 instead of 22 TN m−1) and locally larger suction forces. The latter assists in establishing single-slab subduction rather than double-slab subduction. Subduction initiation is horizontally forced, occurs at the transition from the exhumed mantle to the hyperextended passive margin and is caused by thermal softening. Spontaneous subduction initiation due to negative buoyancy of the 400 km wide, cooled, exhumed mantle is not observed after 100 Myr in model history. Our models indicate that long-term lithosphere dynamics can be strongly impacted by sub-lithosphere dynamics. The first-order processes in the simulated geodynamic cycle are applicable to orogenies that resulted from the opening and closure of embryonic oceans bounded by magma-poor hyperextended rifted margins, which might have been the case for the Alpine orogeny.

Seismic anisotropy reveals crustal flow driven by mantle vertical loading in the Pacific NW

Buoyancy anomalies within Earth’s mantle create large convective currents that are thought to control the evolution of the lithosphere. While tectonic plate motions provide evidence for this relation, the mechanism by which mantle processes influence near-surface tectonics remains elusive. Here, we present an azimuthal anisotropy model for the Pacific Northwest crust that strongly correlates with high-velocity structures in the underlying mantle but shows no association with the regional mantle flow field. We suggest that the crustal anisotropy is decoupled from horizontal basal tractions and, instead, created by upper mantle vertical loading, which generates pressure gradients that drive channelized flow in the mid-lower crust. We then demonstrate the interplay between mantle heterogeneities and lithosphere dynamics by predicting the viscous crustal flow that is driven by local buoyancy sources within the upper mantle. Our findings reveal how mantle vertical load distribution can actively control crustal deformation on a scale of several hundred kilometers.

Modelling lithosphere dynamics with robust rheological implementations: Towards 3D

<div>Reliable numerical models of lithospheric deformation require robust solution methods. The latter should account for a complex and realistic rheological model and should also provide convergent and reproducible results.</div><div>Here we present models of crustal-scale deformation that accurately capture the phenomenon of strain localisation in two-dimensions. The use of viscous regularisation yields convergent numerical results. We will compare linearisation methods (consistent tangent, effective viscosity) and discuss the implementation of rheological models (power-law viscous, hardening/softening laws). We will also present three-dimensional models of crustal-scale strain localisation that benefit from both the above-described methods and the computing power of graphical processing units (GPUs).</div>

On formulations of compressible mantle convection

SUMMARY Mantle convection and long-term lithosphere dynamics in the Earth and other planets can be treated as the slow deformation of a highly viscous fluid, and as such can be described using the compressible Navier–Stokes equations. Since on Earth-sized planets the influence of compressibility is not a dominant effect, density deviations from a reference profile are at most on the order of a few percent and using the full governing equations poses numerical challenges, most modelling studies have simplified the governing equations. Common approximations assume a temporally constant, but depth-dependent reference profile for the density (the anelastic liquid approximation), or drop compressibility altogether and use a constant reference density (the Boussinesq approximation). In most previous studies of mantle convection and crustal dynamics, one can assume that the error introduced by these approximations was small compared to the errors that resulted from poorly constrained material behaviour and limited numerical accuracy. However, as model parametrizations have become more realistic, and model resolution has improved, this may no longer be the case and the error due to using simplified conservation equations might no longer be negligible: while such approximations may be reasonable for models of mantle plumes or slabs traversing the whole mantle, they may be unsatisfactory for layered materials experiencing phase transitions or materials undergoing significant heating or cooling. For example, at boundary layers or close to dynamically changing density gradients, the error arising from the use of the aforementioned compressibility approximations can be the dominant error source, and common approximations may fail to capture the physical behaviour of interest. In this paper, we discuss new formulations of the continuity equation that include dynamic density variations due to temperature, pressure and composition without using a reference profile for the density. We quantify the improvement in accuracy relative to existing formulations in a number of benchmark models and evaluate for which practical applications these effects are important. Finally, we consider numerical aspects of the new formulations. We implement and test these formulations in the freely available community software aspect, and use this code for our numerical experiments.

Penerapan Model Pembelajaran Problem Based Learning Untuk Meningkatkan Hasil Belajar Geografi Peserta Didik Kelas X IIS 1 SMA Negeri 9 Sinjai

This research aims to improve the learning results of geography materials lithosphere dynamics and their impact on life through the application of the model of learning problem based learning. Data collection was done through the test results of the study. Using quantitative analysis. The minimum completeness criterion is 70. The results of the analysis show that the learning outcomes of students have increased seen from the average value of learning outcomes in the first cycle, namely 70.00 with the percentage of classical learning completeness which is 51.72% increased in the second cycle with an average value of 85.34 with the percentage of mastery learning in classical is 100%. The conclusion of this research is the application of the model of learning problem based learning can improve the results of studying the geography of the learners.