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Basini, P.
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Basini, P.
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- PublicationRestrictedForward and adjoint simulations of seismic wave propagation on fully unstructured hexahedral meshes(2011)
; ; ; ; ; ; ; ; ; ; ; ; ; ;Peter, D.; Princeton University, Department of Geosciences, 318 Guyot Hall, Princeton, NJ 08544, USA ;Komatitsch, D.; Université de Pau et des Pays de l’Adour, CNRS & INRIA Magique-3D, Laboratoire de Modélisation et d’Imagerie en Géosciences UMR 5212, Avenue de l’Université, 64013 Pau Cedex, France. Institut universitaire de France, 103 boulevard Saint-Michel, 75005 Paris, France ;Luo, Y.; Princeton University, Department of Geosciences, 318 Guyot Hall, Princeton, NJ 08544, USA ;Martin, R.; Université de Pau et des Pays de l’Adour, CNRS & INRIA Magique-3D, Laboratoire de Modélisation et d’Imagerie en Géosciences UMR 5212, Avenue de l’Université, 64013 Pau Cedex, France ;Le Goff, N.; Université de Pau et des Pays de l’Adour, CNRS & INRIA Magique-3D, Laboratoire de Modélisation et d’Imagerie en Géosciences UMR 5212, Avenue de l’Université, 64013 Pau Cedex, France ;Casarotti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Le Loher, P.; Université de Pau et des Pays de l’Adour, CNRS & INRIA Magique-3D, Laboratoire de Modélisation et d’Imagerie en Géosciences UMR 5212, Avenue de l’Université, 64013 Pau Cedex, France ;Magnoni, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Liu, Q.; Department of Physics, University of Toronto, Ontario, Canada ;Blitz, C.; Université de Pau et des Pays de l’Adour, CNRS & INRIA Magique-3D, Laboratoire de Modélisation et d’Imagerie en Géosciences UMR 5212, Avenue de l’Université, 64013 Pau Cedex, France ;Nissen-Meyer, T.; Institute of Geophysics, ETH Zurich, Sonneggstr. 5, CH-8092 Zurich, Switzerland ;Basini, P.; Institute of Geophysics, ETH Zurich, Sonneggstr. 5, CH-8092 Zurich, Switzerland ;Tromp, J.; Princeton University, Department of Geosciences, 318 Guyot Hall, Princeton, NJ 08544, USA. Princeton University, Program in Applied & Computational Mathematics, Princeton, NJ 08544, USA; ; ; ; ; ; ; ; ; ; ; ; We present forward and adjoint spectral-element simulations of coupled acoustic and (an)elastic seismic wave propagation on fully unstructured hexahedral meshes. Simulations benefit from recent advances in hexahedral meshing, load balancing and software optimization. Meshing may be accomplished using a mesh generation tool kit such as CUBIT, and load balancing is facilitated by graph partitioning based on the SCOTCH library. Coupling between fluid and solid regions is incorporated in a straightforward fashion using domain decomposition. Topography, bathymetry and Moho undulations may be readily included in the mesh, and physical dispersion and attenuation associated with anelasticity are accounted for using a series of standard linear solids. Finite-frequency Fre ́chet derivatives are calculated using adjoint methods in both fluid and solid domains. The software is benchmarked for a layercake model. We present various examples of fully unstructured meshes, snapshots of wavefields and finite-frequency kernels generated by Version 2.0 ‘Sesame’ of our widely used open source spectral-element package SPECFEM3D.239 28 - PublicationOpen AccessThe influence of nonuniform ambient noise on crustal tomography in EuropeAmbient‐noise seismology is of great relevance to high‐resolution crustal imaging, thanks to the unprecedented dense data coverage it affords in regions of little seismicity. Under the assumption of uniformly distributed noise sources, it has been used to extract the Green's function between two receivers. We determine the imprint of this assumption by means of wave propagation and adjoint methods in realistic 3‐D Earth models. In this context, we quantify the sensitivity of ambient‐noise cross‐correlations from central Europe with respect to noise‐source locations and shear wave‐speed structure. We use ambient noise recorded over 1 year at 196 stations, resulting in a database of 864 cross‐correlations. Our mesh is built upon a combined crustal and 3‐D tomographic model. We simulate synthetic ambient‐noise cross‐correlations in different frequency bands using a 3‐D spectral‐element method. Traveltime cross‐correlation measurements in these different frequency bands define the misfit between synthetics and observations as a basis to compute sensitivity kernels using the adjoint method. We perform a comprehensive analysis varying geographic station and noise‐source distributions around the European seas. The deterministic sensitivity analysis allows for estimating where the starting crustal model shows better accordance with our data set, and gain insight into the distribution of noise sources in the European region. This highlights the potential importance of considering localized noise distributions for tomographic imaging, and forms the basis of a tomographic inversion in which the distribution of noise sources may be treated as a free parameter similar to earthquake tomography.
86 22 - ItemRestrictedDevelopment and testing of a 3D seismic 1 velocity model of the Po Plain sedimentary basin, Italy(Seismological Society of America, 2015-12)
; ; ; ; ;Molinari, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Argnani, A.; CNR, Area Ricerca Bologna ;Morelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Basini, P.; University of Toronto Department of Physics 60 St. George St. Toronto, Ontario; ; ; We built a 3D seismic model of the Po Plain and neighboring regions of northern Italy, covering altogether an area about 600 km by 300 km with an approximately 1 km spaced grid. We started by collecting an extensive and diverse set of geological and geophysical data, including seismic reflection and refraction profiles, borehole logs, and available geological information. Major geological boundaries and discontinuities have thus been identified and mapped into the model. We used kriging to interpolate the geographically sparse information into continuous surfaces delimiting geological bodies with laterally varying thickness. Seismic-wave properties have been assigned to each unit using a rule-based system and, VP, VS, and ρ derived from other studies. Sedimentary strata, although with varying levels of compaction and hence material properties, may locally reach a thickness of 15 km and give rise to significant effects in seismic-wave propagation.We have used our new model to compute the seismic response for two recent earthquakes, to test its performance. Results show that the 3D model reproduces the large amplitude and the long duration of shaking seen in the observed waveforms recorded on sediments, whereas paths outside the basin may be well fit by more homogeneous (1D) hard rock structure. We conclude that the new model is suited for simulation of wave propagation, mostly for T > 3 s, and may serve well as a constraint for earthquake location and further improvements via body- or surface-wave inversion.161 77