Determination of Phase-Velocity Dispersion Curves of Rayleigh Surface
Waves from Tidal Gravimetric Recordings of Earthquakes
Abstract
This study presents the novel application of tidal gravimetric data in
the determination of phase-velocity dispersion curves of Rayleigh
surface waves. Tidal gravimeters are capable to detect surface waves of
periods even up to 500−600 s, while a typical broad-band seismic sensor
can detect them up to the periods of 200−300 s due to its mechanical
limitation. The capability of using tidal gravimeters as long period
seismometers has already been analyzed since the late ’90s. These
researches were mainly focused on the comparison of the power spectral
density of noise level of gravimeters and seismometers and the analysis
of normal modes of the largest earthquakes recorded by gravimeters. The
first steps in the calculation of group velocity dispersion curves of
Rayleigh surface waves were carried out lately. The Wiener deconvolution
technique was used to calculate the phase-velocity dispersion curve by a
two-stations method, from two pre-processed traces recorded in two
different stations, located at the same great circle that the epicentre.
The Incorporated Research Institutions for Seismology (IRIS) database
were searched in terms of availability of at least 1 Hz data recorded by
a co-located broad-band seismometer and tidal gravimeter. Additionally,
the IRIS database provides the information about the transfer function
of instruments, what is necessary in the two-stations method. Only,
three sites met the above conditions: Black Forest, Membach and
Rochfort, all located in Western and Central Europe. The compatibility
of gravimetric and seismic data in the period range of 20-100 s are
shown. Tidal gravimeters, because of their higher sensitivity, can
better detect weaker earthquakes, which results in a higher number of
recordings. However, to explore all advantages of gravimetric recordings
of earthquakes, especially up to the periods of 500-600 s, above
analysis must be applied to tidal gravimeters with higher inter-station
distances and evaluated transfer functions. This work was done in the
research project No. 2017/27/B/ST10/01600 financed from the funds of the
Polish National Science Centre.