Exploring the Earth's mantle structure based on joint gravimetric and seismometric group-velocity dispersion curves of Rayleigh waves

Gravimetric data show excellent capabilities in long-period seismology. Tidal gravimeters can detect surface waves of periods even up to 500-600 s, while a typical broad-band seismic sensor, due to its mechanical limitation, can detect them only up to the periods of 200-300 s. Consequently, gravimetric data can complement seismic recordings for longer periods, depending on what seismometer the station is equipped with and what seismometer’s cut-off period is. A superconducting gravimeter can act as a single-dimension (only vertical component) of a very broad-band seismometer. 

We selected over a dozen stations worldwide with co-located typical broad-band seismic sensors and superconducting gravimeters. A time series from broad-band seismometers have been downloaded from Incorporated Research Institutions for Seismology (IRIS) database. The raw gravimetric data (1-Hz or 1-min) are available in the International Geodynamics and Earth Tide Service (IGETS) database. Some of the data were made available courtesy of the station’s operators. 

This study presents a joint analysis of the gravimetric and seismometric data to determine group-velocity dispersion curves of Rayleigh surface waves. We created a database of recordings of earthquakes for all stations and instruments. Following, we calculated the individual group-velocity dispersion curves of fundamental-mode Rayleigh waves. Simultaneous seismic and gravity recordings at the same location allow exploring a broader response for incoming seismic waves. In this way, one joint group-velocity dispersion curve of Rayleigh surface waves for a broader range of periods has been estimated for all stations. All curves were then inverted by linear inversion and Monte Carlo methods to calculate a distribution of shear-wave seismic velocity with depth in the Earth’s mantle.    

This work was done within the research project No. 2017/27/B/ST10/01600 financed from the Polish National Science Centre funds.