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Conference Paper

Temporal variations of seismic velocities from ambient noise: monitoring groundwater in the Maltese islands

Authors

Laudi,  Luca
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Galea,  Pauline
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Agius,  Matthew R.
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

D'Amico,  Sebastiano
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Schimmel,  Martin
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

Lecocq,  Thomas
IUGG 2023, General Assemblies, 1 General, International Union of Geodesy and Geophysics (IUGG), External Organizations;

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Citation

Laudi, L., Galea, P., Agius, M. R., D'Amico, S., Schimmel, M., Lecocq, T. (2023): Temporal variations of seismic velocities from ambient noise: monitoring groundwater in the Maltese islands, XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG) (Berlin 2023).
https://doi.org/10.57757/IUGG23-2118


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5018715
Abstract
The Maltese islands, approximately 314 km2 in area with a high population density, face high levels of water stress due to low amounts of rainfall and a dependence on groundwater abstraction. Until now, in-situ borehole readings have been the only method utilised to monitor the quantitative status of groundwater in the Maltese islands. This study investigates an innovative, cost-effective approach to groundwater monitoring in a small island environment by computing cross-correlations and autocorrelations of ambient seismic noise recorded on seismic networks of broadband and short-period stations in the Maltese islands. We compare the borehole readings of groundwater levels ranging from 0.28-3.39 m above mean sea level with the variations in seismic velocity (δv/v). We apply appropriate filters for the broadband and short-period stations of 0.1-1 Hz and 0.3-3 Hz, respectively. The results demonstrate clear seasonal changes in the seismic velocities, which can be correlated with changes in groundwater levels in nearby boreholes. We find that variations of the δv/v from autocorrelations are more pronounced than the cross-correlation, with maximum seismic velocity changes of ~2% and ~0.3% respectively. The quality of the δv/v deteriorates at longer interstation distances where seasonal variations are less noticeable. Presumably, this is because longer interstation paths tend to traverse more complex geology, different types of aquifers, or even the sea.