NOLET , G.

International audience

The observed travel times of seismic waves as a function of distance have since long beenused to infer the elastic properties at depth in the Earth, to study the Moon's regolithand more recently the radial structure of the Sun. Once a rst-order radially symmetricstructure has been obtained, small delays that depend on source...

This article summarizes three important methods for seismic transmission tomography:the interpretation of delays in onset times of seismic phases using ray theory, of cross-correlation delays using nite-frequency methods, and of full waveforms using adjoint tech-niques. Delay-time techniques di er importantly in ...

In geology textbooks, the fate of the oceanic crust seems straightforward. The ocean floor is created by upwelling of lighter magma at spreading ridges. The magma cools as it moves away from the ridge, forming a stiff layer or "plate" called the oceanic lithosphere. Having increased in density, it then descends back into the mantle in trench...

The upper mantle is defined as that part of the mantle between the crust and the phase transition of γ-olivine to perovskite. The total mass of the upper mantle is 1.06 × 1024 kg, about a quarter of the total mass of the mantle. Its volume, 2.95 × 1011 km3, is a third of the total volume of the mantle. Until the discovery of a major transition...

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We compare finite-frequency sensitivity kernels computed from ray-theoretical wavefields ("banana-doughnut" kernels) and from full waveform computations (often called "adjoint" kernels) in order to evaluate resolution, accuracy and computational cost. We focus here on body-wave seismic tomography at regional and local scales. Our results show...

We explore the validity of the linear relation between cross-correlation delay times and velocity model perturbations that is required for linearized finite-frequency tomography. We estimate delay times from a large number of 'ground truth' seismograms computed with the spectral element method in 3-D models. We find that the observed...

Geophysical Journal International, v. 174, n. 2, p. 629-648, 2008. http://dx.doi.org/10.1111/j.1365-246X.2008.03833.x

We introduce and compare new compression approaches to obtain regularized solutions of large linear systems which are commonly encountered in large scale inverse problems. We first describe how to approximate matrix vector operations with a large matrix through a sparser matrix with fewer nonzero elements, by borrowing from ideas used in...

We evaluated a comprehensive numerical experiment of finite-frequency tomography with ray-based ("banana-doughnut") kernels that tested all aspects of this method, starting from the generation of seismograms in a 3D model, the window selection, and the crosscorrelation with seismograms predicted for a background model, to the final regularized...

The region of central Chile offers a unique opportunity to study the links between the subducting Juan Fernandez Ridge, the flat slab, the double seismic zone (DSZ), and the absence of modern volcanism. Here we report the presence and characteristics of the first observed DSZ within the intermediate-depth Nazca slab using two temporary seismic...

We simultaneously invert for the velocity and attenuation structure of the North American mantle from a mixed data set: SH wave traveltime and amplitude anomalies, SS wave differential traveltime anomalies, and Love wave fundamental mode phase delays. All data are measured for multiple frequency bands, and finite frequency sensitivity kernels...

An intermediate-depth earthquake (7 January 2003, Mw 5.7) occurred within the subducting Nazca plate at longitude 70.3°W, latitude 33.8°S and depth 113 km. Its focal mechanism shows normal faulting with a slight strike-slip component. We detected 50 aftershocks within January 2003 using a temporary seismic network installed in the zone. Their...

Eastward subduction of oceanic tectonic plates has shaped the geologic history of western North America over the past 150 million years. The mountain-building and volcanism that brought forth the spectacular landscapes of the West are credited to the vast ancient Farallon plate, which interacted mechanically and chemically with the overlying...

Scientists get a window into deep Earth structures by using a method called seismic tomography. Similar to computed tomography (CT) scans of the brain, seismic tomography uses delays in the arrival times of seismic P waves to make scans and three-dimensional images of the variations in seismic wave speed in the Earth's interior. Patterns in the...

Our study compares the seismic properties between the flat and normal subduction regions in central Chile, to better understand the links between the slab geometry, surface deformation and the deeper structures. In comparison with previous studies, we show the most complete 3-D regional seismic tomography images for this region, in which we use...

Full-waveform inversion (FWI) is not yet a mature imaging technology for lithospheric imaging from teleseismic data. Therefore, its promise and pitfalls need to be assessed more accurately according to the specifications of teleseismic experiments. Three important issues are related to (1) the choice of the lithospheric parametrization for...

During the Cenozoic, the geodynamics of the western Mediterranean domain has been characterized by a complex history of subduction of Mesozoic oceanic lithosphere. The final stage of these processes is proposed to have led to the development of the Calabria and Gibraltar arcs, whose formation is still under debate. In this study, we take...

The effects of several nonlinear regularization techniques are discussed in the framework of 3D seismic tomography. Traditional, linear, ℓ2 penalties are compared to so-called sparsity promoting ℓ1 and ℓ0 penalties, and a total variation penalty. Which of these algorithms is judged optimal depends on the specific requirements of the scientific...

Global seismic tomography suffers from uncertainties in earthquake parameters routinely published in seismic catalogues. In particular, errors in earthquake location and origin-time may lead to strong biases in measured body wave delay-times and significantly pollute tomographic models. Common ways of dealing with this issue are to incorporate...

We present methods of data analysis adapted to Mobile Earthquake Recorder in Marine Areas by Independent Divers (MERMAID) seismograms, obtained with hydrophones mounted on moving underwater floats. If the MERMAID float comes immediately to the surface after recording an earthquake signal, the seismogram location is obtained from the first...

The Western Alps, although being intensively investigated, remains elusive when it comes to determining its lithospheric structure. New inferences on the latter are important for the understanding of processes and mechanisms of orogeny needed to unravel the dynamic evolution of the Alps. This situation led to the deployment of the CIFALPS...

We propose a new probabilistic scheme for the automatic recognition of underwater acoustic signals generated by teleseismic P-waves recorded by hydrophones in the ocean. The recognition of a given signal is based on the relative distribution of its power among different frequency bands. The signal's power distribution is compared with a...

We present a new whole mantle P wave tomographic model GAP_P4. We used two data groups; short-period data of more than 10 million picked-up onset times and long-period data of more than 20 thousand differential travel times measured by waveform cross correlation. Finite frequency kernels were calculated at the corresponding frequency bands for...