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Monitoring Land-Based Gravity Changes Using Absolute and Superconducting Gravimeters

This study presents findings from land-based gravity measurements conducted using absolute and superconducting gravimeters, focusing on data from the Royal Observatory of Belgium and the University of Luxembourg. The analysis reveals average gravity change rates of 1.2 ± 1.4 nm/s²/yr and subsidence of 0.6 ± 0.7 mm/yr. The research highlights the importance of collocated measurements and concludes that hydrological effects should not hinder the detection of slow tectonic processes. This work aims to improve the reliability of long-term gravity change monitoring.

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Monitoring Land-Based Gravity Changes Using Absolute and Superconducting Gravimeters

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  1. land-based gravity measurements using absolute and superconducting gravimeters M. Van Camp1 & O. Francis2 1Royal Observatory of Belgium 2U. Luxembourg NGS, October 2009

  2. Example of repeated AG measurements 403 nm/s²/yr Slow oscillations? Cause: Hydrology? (see poster) • Average (Jülich not included) : 1.21.4 nm/s²/yr • Subsidence of 0.60.7 mm/yr • (1 nm/s²  0.5 mm) (1 s)

  3. The Membach Geodynamic Station SG: continuously since 1995 AG: since 1996: 1 measurement /1 month

  4. PSDs of AG and SG (Membach) 100 days 10 days 1 day Fractional Brownian noise: k = -1.25 AG & SG provide same information Toward FOGM? (see poster) AG meets SG at 1 day Probably white AG instrumental noise : 100 nms-2 Hz-0.5 @ 5 s period : resolution = (1.0E4/(2*5))0.5 =30 nm/s² • White SG instrumental noise : 2.2 nms-2 Hz-0.5 • e.g. : • @ 1 h period : resolution = (5/(2*3600))0.5 = 0.03 nm/s² • @ 100 s period : resolution = (5/(2*100))0.5 = 0.2 nm/s² Van Camp et al., JGR, 2004

  5. Conclusions  Based on collocated SG/AG measurements : AG “set-up” noise ~16 nm/s²;  At periods longer than ~1-2 months : both the AG and SG tell the same story;  In Belgium and Germany : no significant gravity rates of change > 3 nm/s²/yr  1.5 mm/yr (2 s);   Hydrological effects should not prevent one to measure slow tectonic processes (unless climate changes?) (Van Camp et al., JGR, in review);  Worst case: 1 nm/s²/yr needs 16 years Conservative result based on 18 short SG time series (spanning 5-13 years); This may be revised when similar analyze performed on longer time series;    Measuring slow processes using AGs should not be hopeless (the AG profile in Belgium and Germany seems to confirm this).

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