Seismic prompt gravity strain signals in a layered spherical Earth

Seismic waves generated by an earthquake can produce dynamic perturbations in the Earth’s gravity field before the direct arrival of P-waves. Observations of these so-called prompt elasto-gravity signals by ground-based gravimeters and broadband seismometers have been reported for some large events, such as the 2011 M_W9.1 Tohoku earthquake. Recent studies have introduced prompt gravity strain signals (PGSSs) as a new type of observable seismic gravity perturbation that can be used to measure the spatial gradient of the perturbed gravity field. Theoretically, these types of signals can be recorded by in-development instruments termed gravity strainmeters, although no successful detection has been reported as yet. Herein, we propose an efficient approach for PGSSs based on a multilayered spherical Earth model. We compared the simulated waveforms with analytical solutions obtained from a homogeneous half-space model, which has been used in earlier studies. This comparison indicates that the effect of the Earth’s structural stratification is significant. With the help of the new simulation approach, we also demonstrated how the PGSSs depend on the magnitude of the seismic source. We further conducted synthetic tests estimating earthquake magnitude using gravity strain signals to demonstrate the potential application of this type of signal in earthquake early warning systems. These results provide essential information for future studies on the synthesis and application of earthquake-induced gravity strain signals.