612 research outputs found
Testing the effects of basic numerical implementations of water migration on models of subduction dynamics
Subduction of oceanic lithosphere brings water into the Earth's upper
mantle. Previous numerical studies have shown how slab dehydration and
mantle hydration can impact the dynamics of a subduction system by
allowing a more vigorous mantle flow and promoting localisation of
deformation in the lithosphere and mantle. The depths at which dehydration
reactions occur in the hydrated portions of the slab are well
constrained in these models by thermodynamic calculations. However,
computational models use different numerical schemes to simulate
the migration of free water. We aim to show the influence of
the numerical scheme of free water migration on the dynamics of the
upper mantle and more specifically the mantle wedge. We investigate
the following three simple
migration schemes with a finite-element model: (1)
element-wise vertical migration of free water, occurring independent
of the flow of the solid phase;
(2) an imposed vertical free water velocity; and
(3) a Darcy velocity, where the free water velocity is
a function of the pressure gradient caused by the difference in density
between water and the surrounding
rocks. In addition, the flow of the solid material
field also moves the free water
in the imposed vertical velocity and Darcy schemes. We first test the
influence of the water migration scheme using a simple
model that simulates the sinking of a cold, hydrated cylinder into
a dry, warm
mantle. We find that the free water migration scheme has
only a limited impact on the water distribution after 1 Myr in these
models. We next investigate slab dehydration and mantle hydration with
a thermomechanical subduction model that includes brittle behaviour
and viscous water-dependent creep flow laws.
Our models demonstrate that the
bound water distribution is not greatly influenced by the water
migration scheme whereas the free water distribution is. We find that a
bound water-dependent creep flow law results in a broader area of
hydration in the mantle wedge, which feeds back to the dynamics of the
system by the associated weakening. This finding underlines
the importance of using dynamic time
evolution models to investigate the effects of (de)hydration. We also
show that hydrated material can be transported down to the base of the
upper mantle at 670 km. Although (de)hydration processes
influence subduction dynamics, we find that the exact numerical
implementation of free water migration is not important
in the basic schemes we investigated.
A simple implementation of water migration
could be sufficient for a first-order impression of the effects of water
for studies that focus on large-scale features of subduction
dynamics
Analogue modelling of basin inversion: a review and future perspectives
Basin inversion involves the reversal of subsidence in a basin due to
compressional tectonic forces, leading to uplift of the basin's sedimentary
infill. Detailed knowledge of basin inversion is of great importance for
scientific, societal, and economic reasons, spurring continued research
efforts to better understand the processes involved. Analogue tectonic
modelling forms a key part of these efforts, and analogue modellers have
conducted numerous studies of basin inversion. In this review paper we recap
the advances in our knowledge of basin inversion processes acquired through
analogue modelling studies, providing an up-to-date summary of the state of
analogue modelling of basin inversion. We describe the different definitions
of basin inversion that are being applied by researchers, why basin
inversion has been historically an important research topic and what the
general mechanics involved in basin inversion are. We subsequently treat the
wide range of different experimental approaches used for basin inversion
modelling, with attention to the various materials, set-ups, and techniques
used for model monitoring and analysing the model results. Our new systematic overviews of generalized model results reveal the diversity of these results, which depend greatly on the chosen set-up, model layering and
(oblique) kinematics of inversion, and 3D along-strike structural and
kinematic variations in the system. We show how analogue modelling results
are in good agreement with numerical models, and how these results help researchers to
better understand natural examples of basin inversion. In addition to
reviewing the past efforts in the field of analogue modelling, we also shed
light on future modelling challenges and identify a number of opportunities
for follow-up research. These include the testing of force boundary
conditions, adding geological processes such as sedimentation, transport, and
erosion; applying state-of-the-art modelling and quantification techniques;
and establishing best modelling practices. We also suggest expanding the
scope of basin inversion modelling beyond the traditional upper crustal
“North Sea style” of inversion, which may contribute to the ongoing search
for clean energy resources. It follows that basin inversion modelling can
bring valuable new insights, providing a great incentive to continue our
efforts in this field. We therefore hope that this review paper will form an
inspiration for future analogue modelling studies of basin inversion.</p
Non-Disruptive Tactics of Suppression Are Superior in Countering Terrorism, Insurgency, and Financial Panics
BACKGROUND: Suppressing damaging aggregate behaviors such as insurgency, terrorism, and financial panics are important tasks of the state. Each outcome of these aggregate behaviors is an emergent property of a system in which each individual's action depends on a subset of others' actions, given by each individual's network of interactions. Yet there are few explicit comparisons of strategies for suppression, and none that fully incorporate the interdependence of individual behavior. METHODS AND FINDINGS: Here I show that suppression tactics that do not require the removal of individuals from networks of interactions are nearly always more effective than those that do. I find using simulation analysis of a general model of interdependent behavior that the degree to which such less disruptive suppression tactics are superior to more disruptive ones increases in the propensity of individuals to engage in the behavior in question. CONCLUSIONS: Thus, hearts-and-minds approaches are generally more effective than force in counterterrorism and counterinsurgency, and partial insurance is usually a better tactic than gag rules in quelling financial panics. Differences between suppression tactics are greater when individual incentives to support terrorist or insurgent groups, or susceptibilities to financial panic, are higher. These conclusions have utility for policy-makers seeking to end bloody conflicts and prevent financial panics. As the model also applies to mass protest, its conclusions provide insight as well into the likely effects of different suppression strategies undertaken by authoritarian regimes seeking to hold on to power in the face of mass movements seeking to end them
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