wave tomography
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2022 ◽  
Vol 167 ◽  
pp. 108594
Author(s):  
Guang-Heng Luo ◽  
Jian-Wen Pan ◽  
Jin-Ting Wang ◽  
Feng Jin

2022 ◽  
Vol 2022 (1) ◽  
Author(s):  
Abhay Ashtekar ◽  
Neev Khera ◽  
Maciej Kolanowski ◽  
Jerzy Lewandowski

Abstract It is well-known that blackhole and cosmological horizons in equilibrium situations are well-modeled by non expanding horizons (NEHs) [1–3]. In the first part of the paper we introduce multipole moments to characterize their geometry, removing the restriction to axisymmetric situations made in the existing literature [4]. We then show that the symmetry group $$ \mathfrak{G} $$ G of NEHs is a 1-dimensional extension of the BMS group $$ \mathfrak{B} $$ B . These symmetries are used in a companion paper [5] to define charges and fluxes on NEHs, as well as perturbed NEHs. They have physically attractive properties. Finally, it is generally not appreciated that $$ \mathcal{I} $$ I ±of asymptotically flat space-times are NEHs in the conformally completed space-time. Forthcoming papers will (i) show that $$ \mathcal{I} $$ I ± have a small additional structure that reduces $$ \mathfrak{G} $$ G to the BMS group $$ \mathfrak{B} $$ B , and the BMS charges and fluxes can be recovered from the NEH framework; and, (ii) develop gravitational wave tomography for the late stage of compact binary coalescences: reading-off the dynamics of perturbed NEHs in the strong field regime (via evolution of their multipoles), from the waveform at $$ \mathcal{I} $$ I +.


2021 ◽  
Author(s):  
Constanz Rodriguez Piceda ◽  
Magdalena Scheck-Wenderoth ◽  
Bott Judith ◽  
Maria Laura Gómez Dacal ◽  
Mauro Cacace ◽  
...  

In an ocean-continent subduction zone, the assessment of the lithospheric thermal state is essential to determine the controls of the deformation within the upper plate and the dip angle of the subducting lithosphere. In this study, we evaluate the degree of influence of both the configuration of the upper plate and variations of the subduction angle on the lithospheric thermal field of the southern Central Andes (29°–39°S). Here, the subduction angle increases from subhorizontal (5°) north of 33°S, to steep (~30°) in the south. We derived the 3D temperature and heat flow distribution of the lithosphere in the southern Central Andes considering conversion of S wave tomography to temperatures together with steady-state conductive modeling. We found that the orogen is overall warmer than the forearc and the foreland, and that the lithosphere of the northern part of the foreland appears colder than its southern counterpart. Sedimentary blanketing and the thickness of the radiogenic crust exert the main control on the shallow thermal field (< 50 km depth). Specific conditions are present where the oceanic slab is relatively shallow (< 85 km depth) and the radiogenic crust is thin, This configuration results in relatively colder temperatures compared to regions where the radiogenic crust is thick and the slab is steep. At depths >50 km, the temperatures of the overriding plate are mainly controlled by the mantle heat input and the subduction angle. The thermal field of the upper plate likely preserves the flat subduction angle and influences the spatial distribution of shortening.


Solid Earth ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 2633-2669 ◽  
Author(s):  
Mark R. Handy ◽  
Stefan M. Schmid ◽  
Marcel Paffrath ◽  
Wolfgang Friederich ◽  

Abstract. Based on recent results of AlpArray, we propose a new model of Alpine collision that involves subduction and detachment of thick (∼ 180 km) European lithosphere. Our approach combines teleseismic P-wave tomography and existing local earthquake tomography (LET), allowing us to image the Alpine slabs and their connections with the overlying orogenic lithosphere at an unprecedented resolution. The images call into question the conventional notion that downward-moving lithosphere and slabs comprise only seismically fast lithosphere. We propose that the European lithosphere is heterogeneous, locally containing layered positive and negative Vp anomalies of up to 5 %–6 %. We attribute this layered heterogeneity to seismic anisotropy and/or compositional differences inherited from the Variscan and pre-Variscan orogenic cycles rather than to thermal anomalies. The lithosphere–asthenosphere boundary (LAB) of the European Plate therefore lies below the conventionally defined seismological LAB. In contrast, the lithosphere of the Adriatic Plate is thinner and has a lower boundary approximately at the base of strong positive Vp anomalies at 100–120 km. Horizontal and vertical tomographic slices reveal that beneath the central and western Alps, the European slab dips steeply to the south and southeast and is only locally still attached to the Alpine lithosphere. However, in the eastern Alps and Carpathians, this slab is completely detached from the orogenic crust and dips steeply to the north to northeast. This along-strike change in attachment coincides with an abrupt decrease in Moho depth below the Tauern Window, the Moho being underlain by a pronounced negative Vp anomaly that reaches eastward into the Pannonian Basin area. This negative Vp anomaly is interpreted as representing hot upwelling asthenosphere that heated the overlying crust, allowing it to accommodate Neogene orogen-parallel lateral extrusion and thinning of the ALCAPA tectonic unit (upper plate crustal edifice of Alps and Carpathians) to the east. A European origin of the northward-dipping, detached slab segment beneath the eastern Alps is likely since its down-dip length matches estimated Tertiary shortening in the eastern Alps accommodated by originally south-dipping subduction of European lithosphere. A slab anomaly beneath the Dinarides is of Adriatic origin and dips to the northeast. There is no evidence that this slab dips beneath the Alps. The slab anomaly beneath the Northern Apennines, also of Adriatic origin, hangs subvertically and is detached from the Apenninic orogenic crust and foreland. Except for its northernmost segment where it locally overlies the southern end of the European slab of the Alps, this slab is clearly separated from the latter by a broad zone of low Vp velocities located south of the Alpine slab beneath the Po Basin. Considered as a whole, the slabs of the Alpine chain are interpreted as highly attenuated, largely detached sheets of continental margin and Alpine Tethyan oceanic lithosphere that locally reach down to a slab graveyard in the mantle transition zone (MTZ).


Author(s):  
A.V. Goncharsky ◽  
S.Y. Romanov ◽  
S.Y. Seryozhnikov

This paper is concerned with implementation of wave tomography algorithms on modern SIMD CPU and GPU computing platforms. The field of wave tomography, which is currently under development, requires powerful computing resources. Main applications of wave tomography are medical imaging, nondestructive testing, seismic studies. Practical applications depend on computing hardware. Tomographic image reconstruction via wave tomography technique involves solving coefficient inverse problems for the wave equation. Such problems can be solved using iterative gradient-based methods, which rely on repeated numerical simulation of wave propagation process. In this study, finite-difference time-domain (FDTD) method is employed for wave simulation. This paper discusses software implementation of the algorithms and compares the performance of various computing devices: multi-core Intel and ARM-based CPUs, NVidia graphics processors. В данной статье рассматривается реализация алгоритмов волновой томографии на современных вычислительных платформах SIMD CPU и GPU. Область волновой томографии, которая в настоящее время находится в стадии разработки, требует мощных вычислительных ресурсов. Основные области применения волновой томографии - это медицинская визуализация, неразрушающий контроль, сейсмические исследования. Практические приложения зависят от вычислительного оборудования. Восстановление томографического изображения методом волновой томографии включает решение коэффициентов обратной задачи для волнового уравнения. Такие проблемы могут быть решены с помощью итерационных градиентных методов, основанных на многократном численном моделировании процесса распространения волн. В этом исследовании для моделирования волн используется метод конечных разностей во временной области (FDTD). В статье обсуждается программная реализация алгоритмов и сравнивается производительность различных вычислительных устройств: многоядерных процессоров Intel и ARM, графических процессоров NVidia.


2021 ◽  
Vol 819 ◽  
pp. 229106
Author(s):  
Mohammad Veisi ◽  
Farhad Sobouti ◽  
Sébastien Chevrot ◽  
Madjid Abbasi ◽  
Esmaeil Shabanian

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Grace E. Shephard ◽  
Christine Houser ◽  
John W. Hernlund ◽  
Juan J. Valencia-Cardona ◽  
Reidar G. Trønnes ◽  
...  

AbstractThe two most abundant minerals in the Earth’s lower mantle are bridgmanite and ferropericlase. The bulk modulus of ferropericlase (Fp) softens as iron d-electrons transition from a high-spin to low-spin state, affecting the seismic compressional velocity but not the shear velocity. Here, we identify a seismological expression of the iron spin crossover in fast regions associated with cold Fp-rich subducted oceanic lithosphere: the relative abundance of fast velocities in P- and S-wave tomography models diverges in the ~1,400-2,000 km depth range. This is consistent with a reduced temperature sensitivity of P-waves throughout the iron spin crossover. A similar signal is also found in seismically slow regions below ~1,800 km, consistent with broadening and deepening of the crossover at higher temperatures. The corresponding inflection in P-wave velocity is not yet observed in 1-D seismic profiles, suggesting that the lower mantle is composed of non-uniformly distributed thermochemical heterogeneities which dampen the global signature of the Fp spin crossover.


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