scholarly journals Implications for melt transport and source heterogeneity in upwelling mantle from the magnitude of S p converted phases generated at the onset of melting

2014 ◽  
Vol 41 (15) ◽  
pp. 5444-5450 ◽  
Author(s):  
C. Havlin ◽  
E. M. Parmentier
Keyword(s):  
Melt Transport ◽  
Converted Phases ◽  
Source Heterogeneity

Extension of forward modeling phase-screen code in isotropic and anisotropic media up to critical angle

Geophysics ◽  
2007 ◽  
Vol 72 (5) ◽  
pp. SM107-SM114 ◽  
Author(s):  
James C. White ◽  
Richard W. Hobbs
Keyword(s):  
Critical Angle ◽  
Model Space ◽  
Anisotropic Media ◽  
Forward Modeling ◽  
Phase Screen ◽  
Computationally Efficient ◽  
Reflection And Transmission ◽  
Transmission Coefficients ◽  
Phase Corrections ◽  
Converted Phases

The computationally efficient phase-screen forward modeling technique is extended to allow investigation of nonnormal raypaths. The code is developed to accommodate all diffracted and converted phases up to critical angle, building on a geometric construction method. The new approach relies upon prescanning the model space to assess the complexity of each screen. The propagating wavefields are then divided as a function of horizontal wavenumber, and each subset is transformed to the spatial domain separately, carrying with it angular information. This allows both locally accurate 3D phase corrections and Zoeppritz reflection and transmission coefficients to be applied. The phase-screen code is further developed to handle simple anisotropic media. During phase-screen modeling, propagation is undertaken in the wavenumber domain where exact expressions for anisotropic phase velocities are available. Traveltimes and amplitude effects from a range of anisotropic shales are computed and compared with previous published results.

Melting and melt transport mechanisms in the dynamic earth: from melt segregation, extraction to the formation of crustal magmatic systems

2021 ◽  
Author(s):  
Harro Schmeling
Keyword(s):  
Continental Crust ◽  
Dynamic Models ◽  
Elevated Temperatures ◽  
Two Phase Flow ◽  
Solidus Temperature ◽  
Phase Flow ◽  
Transport Mechanisms ◽  
Two Phase ◽  
Melt Transport ◽  
Open Question

<p><strong>Introduction</strong></p><p>At various regions within the dynamic earth melts are generated due to decompressional melting, reduction of the solidus temperature due to volatiles or due to elevated temperatures. They segregate from these partially molten regions, rise by various transport mechanisms and may form crustal magmatic systems where they are emplaced or erupt. The physics of various aspects of this magmatic cycle will be addressed.</p><p><strong>Melt transport mechanisms</strong></p><p>Starting from a partially molten region by which mechanism(s) does the melt segregate out of the melt source region and rise through the mantle or crust? The basic mechanism is two-phase flow, i.e. a liquid phase percolates through a solid, viscously deforming matrix. The corresponding equations and related issues such as compaction or effective matrix rheology are addressed. Beside simple Darcy flow, special solutions of the equations are addressed such as solitary porosity waves. Depending on the bulk to shear viscosity ratio of the matrix and the non-dimensional size of these waves, they show a variety of features: they may transport melt over large distances, or they show transitions from rising porosity waves to diapiric rise or to fingering. Other solutions of the equations lead to channeling, either mechanically or chemically driven. One open question is how do such channels transform into dykes which have the potential of rising through sub-solidus overburden. A recent hypothesis addresses the possibility that rapid melt percolation may reach the thermal non-equilibrium regime, i.e. the local temperature of matrix and melt may evolve differently.  Once dykes have been formed they may propagate upwards driven by melt buoyancy and controlled by the ambient stress field. Often in dynamic models the complexities of melt transport are simplified by parameterized melt extraction. The limitations of such simplifications will be addressed.</p><p><strong>Modelling magmatic systems in thickened continental crust </strong></p><p>Once basaltic melts rise from the mantle, they may underplate continental crust and generate silicic melts. Early dynamic models (Bittner and Schmeling, 1995, Geophys. J. Int.) showed that such silicic magma bodies may rise to mid-crustal depth by diapirism. More recent approaches (e.g. Blundy and Annan, 2016, Elements) emplace sill intrusions into the crust at various levels and calculate the thermal and melting effects responsible for the formation of mush zones. Recently Schmeling et al. (2019, Geophys. J. Int.) self-consistently modelled the formation of crustal magmatic systems, mush zones and magma bodies by including two-phase flow, melting/solidification and effective power-law rheology. In these models melt is found to rise to mid-crustal depths by a combination of compaction/decompaction assisted two-phase flow, sometimes including solitary porosity waves, diapirism or fingering. An open question in these models is whether or how dykes may self-consistently form to transport the melts to shallower depth. First models which combine elastic dyke-propagation (Maccaferri et al., 2019, G-cubed) with the two-phase flow crustal models are promising.</p>

Wave conversions from earthquakes and a new velocity model for the South Carolina coastal plain

1987 ◽  
Vol 77 (6) ◽  
pp. 2143-2151
Author(s):  
Susan Rhea
Keyword(s):  
Surface Layer ◽  
South Carolina ◽  
Coastal Plain ◽  
Velocity Structure ◽  
Velocity Model ◽  
Seismogenic Fault ◽  
Impedance Boundary ◽  
High Impedance ◽  
Hypocentral Parameters ◽  
Converted Phases

Abstract Phase conversions from P to SV and from SV to P occur at a high impedance boundary near the surface in Charleston, South Carolina. Four arrivals (P, converted P, converted S, and S) are observed on three-component records of earthquakes in this area. Using arrival-time differences between paired arrivals of direct and converted phases, a shallow surface layer Vp/Vs ratio of 2.9 was determined. Applying the Wadati method to travel times derived at the base of the surface layer yields a Vp/Vs ratio in deeper layers of 1.73. Relocating earthquakes using this more appropriate velocity structure for direct and converted shear waves alters hypocentral parameters such that epicenters diverge and depths converge. It is inferred that these relocated earthquakes are not exclusively associated with a single seismogenic fault.

scholarly journals Crustal Magmatic System Beneath the East Pacific Rise (8°20′ to 10°10′N): Implications for Tectonomagmatic Segmentation and Crustal Melt Transport at Fast‐Spreading Ridges

2018 ◽  
Vol 19 (11) ◽  
pp. 4584-4611 ◽  
Author(s):  
Milena Marjanović ◽  
Suzanne M. Carbotte ◽  
Hélène D. Carton ◽  
Mladen R. Nedimović ◽  
Juan Pablo Canales ◽  
...  
Keyword(s):  
East Pacific Rise ◽  
Magmatic System ◽  
East Pacific ◽  
Spreading Ridges ◽  
Fast Spreading ◽  
Melt Transport

scholarly journals Mantle Source Heterogeneity Inferred from Olivine-Hosted Melt Inclusions

2020 ◽  
Author(s):  
Mischa Böhnke ◽  
Felix Genske ◽  
Andreas Stracke
Keyword(s):  
Mantle Source ◽  
Melt Inclusions ◽  
Source Heterogeneity

scholarly journals Source mechanisms and near-source wave propagation from broadband seismograms

1994 ◽  
Vol 37 (6) ◽  
Author(s):  
J. Virieux ◽  
A. Deschamps ◽  
J. Perrot ◽  
J. Campos
Keyword(s):  
Wave Propagation ◽  
Coordinate System ◽  
Ray Tracing ◽  
Dynamic Range ◽  
Time Derivative ◽  
Quality Data ◽  
Heterogeneous Structure ◽  
Spherical Coordinate ◽  
Seismic Rupture ◽  
Converted Phases

Recording seismic events at teleseismic distances with broadband and high dynamic range instruments provides new high-quality data that allow us to interpret in more detail the complexity of seismic rupture as well as the heterogeneous structure of the medium surrounding the source where waves are initially propagating. Wave propagation analysis is performed by ray tracing in a local cartesian coordinate system near the source and in a global spherical coordinate system when waves enter the mantle. Seismograms are constructed at each station for a propagation in a 2.5-D medium. Many phases can be included and separately analyzed; this is one of the major advantages of ray tracing compared to other wave propagation techniques. We have studied four earthquakes, the 1988 Spitak Armenia Earthquake (Ms = 6.9), the 1990 Iran earthquake (Ms = 7.7), the 1990 romanian earthquake (Ms = 5.8) and the 1992 Erzincan, Turkey earthquake (Ms = 6.8). These earthquakes exhibit in different ways the complexity of the rupture and the signature of the medium surrounding the source. The use of velocity seismograms, the time derivative of displacement, increases the difficulty of the fit between synthetic seismograms and real seismograms but provides clear evidence for a need of careful time delay estimations of the different converted phases. We find that understanding of the seismic rupture as well as the influence of the medium surrounding the source for teleseismically recorded earthquakes requires a multi-stop procedure: starting with ground displacement seismograms, one is able to give a first description of the rupture as well as of the first-order influence of the medium. Then, considering the ground velocity seismograms makes the fit more difficult to obtain but increases our sensitivity to the rupture process and early converted phases. With increasing number of worldwide broadband stations, a complex rupture description is possible independently of field observations, which can be used to check the adequacy of such complicated models.

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