Comparative study of superconducting gravimeters and broadband seismometers STS-1 / Z in seismic and subseismic frequency bands

High‐resolution analysis of the gravest seismic normal modes after the 2004 Mw = 9 Sumatra earthquake using superconducting gravimeter data

“…The necessity to correct seismometer and SG data for local atmospheric pressure at frequencies below 1 mHz has been demonstrated by many authors [e.g., Zürn and Widmer, 1995;Freybourger et al, 1997;Rosat et al, 2003a]. We first compare this earthquake to the 2001 Peruvian event.…”

OSG-057 Superconducting Gravimeter Noise Levels in Lhasa (China)

“…Furthermore, on the one hand, the above results were confirmed and the better quality of the OSG-057 data in the long-period seismic band underlined, owing to the observations of its larger signal-to-noise ratio amplitude spectra versus that of the STS-1/Z data below 1 mHz, where the Eigen frequencies of the low-order free oscillation modes (which are not excited to large amplitudes even by very large earthquakes) are located (Richter et al 1995;Freybourger et al 1997). Herein the STS-1/Z is the only available seismometer in Lhasa for the study of free oscillation modes excited by earthquakes and is about 11 km away from the OSG-057 (cf.…”

“…4). Given the wavelengths of the gravity signals we are interested in (e.g., about 20000 km for the fundamental mode 0 S 2 ), the SG and STS-1/Z stations are actually close enough to make the observed signals similar and comparable in both waveforms and amplitudes (Freybourger et al 1997). Both the SG and STS-1/Z data records were one-second decimated and the STS-1/Z data records were corrected for the instrumental response to recover ground acceleration.…”

“…The noise levels estimated from the Fourier spectral analysis of the OSG-057 residual records at different tidal frequencies are listed in Table 3 [0.1, 1, 2, 3, and 4 cycles day -1 (cpd) represent long-periodic (periods between 0.007 and 0.193 cpd), diurnal, semidiurnal, terdiurnal, and quaterdiurnal tidal waves, respectively]. The standard deviations after highpass filtering were also computed {0.437 nm s -2 for 2010, Freybourger et al (1997) and Table 1 of Rosat et al (2004)]. …”

Application of a non-linear damped harmonic analysis method to the normal modes of the Earth

“…SGs have proved to be well-suited for the study of the long-period seismic and sub-seismic modes (e.g. Freybourger et al, 1997;Van Camp, 1999;Widmer-Schnidrig, 2003;Rosat et al, 2004). The precise estimation of the frequencies and damping of the seismic modes of the Earth below 1 mHz, is fundamental as they are very sensitive to the density structure inside the Earth.…”