Detecting the co-seismic and post-seismic gravity signal of large thrust earthquakes with Quantum Space Gravimetry mission concepts

Co-seismic dislocation and post-seismic relaxation are mass transport processes that can be sensed by a broad array of seismological and/or geodetic techniques. Gravity observations through time have the potential of improving the amount of available information on these processes, especially when the dislocation is a-seismic and when its surface expression occurs mostly in areas that are difficult or impossible to sense with space geodesy (such as GNSS, DInSAR), as is the case for off shore areas. New mission concepts, such as those proposed for the Mass change And Geosciences International Constellation (MAGIC), have been recently assessed as capable of providing significant enhancements in the spatial and temporal resolution of gravity field products, resulting in turn in unprecedented impact on the scientific applications, including earthquake gravimetry 1. The evolution of sensors beyond classic electrostatic accelerometers, such as future applications of Cold Atom Interferometry (CAI) on space borne platforms, has the potential to allow further steps forward in sensing the mass transport in the Earths system. In this context, we aim at assessing the impact of Quantum Space Gravimetry (QSG) to earthquake detectability, by modelling a database of synthetic earthquake gravity signal, including the effect of post-seismic viscoelastic relaxation, and setting up a strategy do assess their detectability in simulated time-varying gravity field products. We compute the gravity change in time using the QSSPSTATIC 2 code and a workflow we developed to obtain the spherical harmonics (SH) expansion of the geopotential change through time. We designed the structure of this synthetic earthquake data to be easily included as part of time-varying signals used in simulations, improving the solid-Earth component of models such as AOHIS 3. In this contribution we present the detection threshold of different events, real earthquakes ranging from Mw 9.2 to 7.6 with an assortment of depths, locations and focal mechanisms, using an SNR assessment in the spectral domain, between the modelled signal and retrieval errors (residuals) obtained from mission simulations. This work is supported by the ESA QSG4EMT study, a collaboration between Technical University of Munich, Politecnico di Milano, Delft University of Technology, HafenCity University Hamburg, University of Bonn and University of Trieste. 1 Daras I., March G., Pail R., Hughes C. W., Braitenberg C., Gntner A., Eicker A., Wouters B., Heller-Kaikov B., Pivetta T., Pastorutti, A. (2023). Mass-change And Geosciences International Constellation (MAGIC) expected impact on science and applications. Geophysical Journal International, 12881308. https://doi.org/10.1093/gji/ggad472 2 Wang, R., Heimann, S., Zhang, Y., Wang, H., Dahm, T. (2017). Complete synthetic seismograms based on a spherical self-gravitating Earth model with an atmosphere-ocean-mantle-core structure. Geophysical Journal International, 210(3), 17391764. https://doi.org/10.1093/gji/ggx259 3 Dobslaw, H., Bergmann-Wolf, I., Dill, R., Forootan, E., Klemann, V., Kusche, J., Sasgen, I. (2015). The updated ESA Earth System Model for future gravity mission simulation studies. Journal of Geodesy, 89(5), 505513. https://doi.org/10.1007/s00190-014-0787-8