Foundations for a multiscale collaborative Earth model

Abstract

It is assembled from a long-wavelength 3-D global model into which several regional-scale tomographies are embedded. We illustrate the CSEM workflow of successive updating with two examples from Japan and the Western Mediterranean, where we constrain smaller scale structure using full-waveform inversion. Furthermore, we demonstrate the ability of the CSEM to act as a vehicle for the combination of different tomographic techniques with a joint fullwaveform and traveltime ray tomography of Europe. This combination broadens the exploitable frequency range of the individual techniques, thereby improving resolution. We perform two iterations of a whole-Earth full-waveform inversion using a long-period reference data set from 225 globally recorded earthquakes. At this early stage of the CSEM development, the broad global updates mostly act to remove artefacts from the assembly of the initial CSEM. During the future evolution of the CSEM, the reference data set will be used to account for the influence of small-scale refinements on large-scale global structure. The CSEM as a computational framework is intended to help bridging the gap between local, regional and global tomography, and to contribute to the development of a global multiscale Earth model. While the current construction serves as a first proof of concept, future refinements and additions will require community involvement, which is welcome at this stage already.

Global‐Scale Full‐Waveform Ambient Noise Inversion

“…In order to facilitate the interpretation and the identification of structural features, we plot S20RTS (Ritsema et al, ) in Figure b and a comparison to the Collaborative Seismic Earth Model, CSEM (Afanasiev et al, ; Fichtner et al, ) in Figure . The depth of 100 km for the comparison could be chosen differently to better match the depth sensitivity of Rayleigh waves (Boschi et al, ), but we expect a strong imprint of the crust and upper mantle, since we do not account for its variability in our 1‐D starting model.…”

“…Describing reality more accurately and quantifying inevitable source‐structure trade‐offs have the potential to connect correlations more consistently with other data sets. With this successful proof of concept, we follow this line of thought and take the opportunity to contribute to the CSEM (Afanasiev et al, ; Fichtner et al, ). The first‐generation CSEM contains 12 regional refinements built from waveform data with varying minimum period.…”

The Collaborative Seismic Earth Model: Generation 1

“…Though being per se application independent, the general development is exemplified by the CSEM, which serves as a large‐scale use case that allows us to identify bottlenecks. In this context, we abandoned an earlier prototype based on a whole‐Earth refinable tetrahedral mesh (Afanasiev et al, ). While elegant in theory, it was too difficult to handle in practice, already requiring supercomputing resources for trivial tasks such as visualization and the addition of a refinement region.…”

Automated Large‐Scale Full Seismic Waveform Inversion for North America and the North Atlantic

“…Gradient-based optimization mandates a good starting model, which has been extracted from the Collaborative Seismic Earth Model (CSEM; Afanasiev et al, 2016). It consists of a global 1-D background model based on Preliminary reference Earth model (PREM; Dziewoński & Anderson, 1981) including its attenuation model with the discontinuity at a depth of 220-km being replaced by a linear gradient, superimposed by 3-D perturbations of S velocity from S20RTS (Ritsema et al, 1999).…”