We consider the quantitative inverse problem of recovering sub-surface Earth’s parameters from measurements obtained near surface. The reconstruction procedure uses the iterative minimization of a misfit criterion that evaluates the discrepancy between the observed and simulated signals, following the principles of Full Waveform Inversion. In the context of passive imaging, the position and characterization of the source signature are unknown, hence increasing the difficulty of inversion. In this work, we propose a new misfit criterion based upon reciprocity formulas, and that allows for source-free inversion, such that no information regarding the probing sources is required, making it an interesting candidate for ambient noise imaging. Our misfit criterion relies on the deployment of new sensing devices such as dual-sensors and distributed acoustic sensing technology, that offer the perspective of measuring different wave fields. It is the combination of these wave fields that makes the essence of our Full Reciprocity-gap Waveform Inversion method, [1, 2]. with two and three-dimensional reconstructions of acoustic and elastic media.

[1] F. Faucher, G. Alessandrini, H. Barucq, M. V. de Hoop, R. Gaburro, E. Sincich. Full Reciprocity-Gap Waveform Inversion, enabling sparse-source acquisition, Geophysics, 85 (6), 2020. https://dx.doi.org/10.1190/geo2019-0527.1

[2] F. Faucher, M. V. de Hoop, O. Scherzer. Reciprocity-gap misfit functional for Distributed Acoustic Sensing, combining data from active and passive sources , Geophysics, 86 (2), 2021. https://doi.org/10.1190/geo2020-0305.1

Traditionally models for the interior structure of giant planets are constrained by spacecraft measurements that fly by a planet at close range and measure its gravitational field with high precision. Still with increasing depth, it becomes more and more difficult with such measurements to uniquely determine what type of layers exist in a giant planet. This is especially true for the cores of giant planets that harbor valuable information on how the planet formed and what the early solar system looked like. Measurements of normal modes on the other hand offer an alternate potentially powerful approach to probing much deeper into a giant planet. While such dynamic measurements are very challenging, a number of such observations have already been reported. Here we review ring seismological measurements of spiral density waves in Saturn’s rings, radial velocity measurements of Jupiter’s atmosphere as well as a recent analysis of time dependent variations in Jupiter’s gravity field. We then compare results from these measurements with predictions from models for the interiors of Jupiter and Saturn that were constrained by gravity measurements alone. We conclude by discussing Jupiter’s dilute core and a recent study that explains how Saturn’s ring formed.

In this presentation I will gather an overview of various inverse problems that have arisen in the context of (passive) terrestrial imaging—including but not limited to earthquakes, that is. At the smallest scale, I will discuss a source-encoded crosstalk-free Laplace-domain elastic Full Waveform Inversion (FWI) method that uses time- domain solvers, which cuts down drastically on computation time even for very data rich environments. This technique has been used in medical ultrasound, but also at the scale of the globe, and is now actively being developed for applications in the oil industry. At the regional scale, I will discuss full-waveform centroid moment tensor (CMT) inversion of passive seismic data acquired at the reservoir scale, for a field application in Tajikistan. At the largest scale, I will show how receiver function techniques are being supplemented by new technology to image mantle transition zone (MTZ) discontinuities in three-dimensional (3-D) heterogeneous background Earth models, and I will show new seismic evidence for a 1000 km mid-mantle discontinuity under the Pacific obtained by imaging via full-waveform reverse-time migration of precursors to surface-reflected seismic body waves, and its interpretation.

The ambient seismic noise has been widely used for surface wave tomography. We present examples of imaging of geological structures of interest at different depths and different scales: the region of the core-mantle boundary and an active fault in the crust. In both cases, we use continuous data from large arrays of sensors. We discuss the global spatial correlation properties of seismic ambient vibrations and their relations with body waves [1-2]. We show the signature of the heterogeneity of the lowermost mantle in contrast to the almost transparent upper core [3]. For the case of the fault systems, a major issue is the strong lateral variations of seismic velocity in the first kilometers that degrade the quality of the imaging. In this case an aberration correction is performed to the data of a dense array through the reflection matrix framework [4].

[1] P. Boué, P. Poli, M. Campillo, P. Roux. Reverberations, coda waves and ambient noise : correlations at the global scale and retrieval of the deep phases, Earth and Planetary Science Let. 391, 137-145, 2014.

[2] L. Li, P. Boué, M. Campillo. Observation and explanation of spurious seismic signals emerging in teleseismic noise correlations Solid Earth 11, 173-184, 2020.

[3] L. Retailleau, P. Boué, L. Li, M. Campillo. Ambient seismic noise imaging of the lowermost mantle beneath the North Atlantic Ocean Geophysical J. Int. 222 (2), 1339-1351, 2020.

[4] R. Touma, T. Blondel, A. Derode, M. Campillo, A. Aubry. A Distortion Matrix Framework for High-Resolution Passive Seismic 3D Imaging: Application to the San Jacinto Fault Zone, California Geophysical J. Int., 226, 780–794, 2021.