Seismic Prompt Gravity Strain Signals in a Layered Spherical Earth

Abstract

Seismic waves generated by an earthquake can produce dynamic perturbations in the Earth’s gravity field, appearing before the direct P-wave arrival. The observations of this so-called prompt elasto-gravity signals by ground-based gravimeters and broadband seismometers have been reported for some large events, such as 2011 Mw9.1 Tohoku-Oki earthquake. Recent studies have introduced a new type of observables for seismic gravity perturbations, the prompt gravity strain signals, which measure the spatial gradient of the perturbed gravity field. Theoretically, this kind of signals can be recorded by the in-development instruments termed gravity strainmeters, even though no successful detection has been reported till now. Here we propose an efficient approach to simulate the prompt gravity strain signals based on a multi-layered spherical Earth model. We compare the simulated waveforms with analytical solutions for a homogeneous half-space model, which have been used in earlier studies. The comparison indicates that the effect of the Earth’s structure stratification is significant. With the help of the new simulation approach and the advanced detection method, we also illustrate how the prompt gravity strain signals depend on the magnitude of the seismic source. In this respect, we further conduct synthetic tests on estimating the earthquake magnitude by the gravity strain signals to demonstrate the potential application of this kind of signals to earthquake early warning systems. The results provide essential information for future studies involving synthetics and applications of earthquake-induced gravity strain signals.

Keywords: gravity strain, synthetic seismogram, earthquake early warning system