Transient gravity perturbations induced by earthquake rupture

Abstract

S U M M A R YThe static and transient deformations produced by earthquakes cause density perturbations which, in turn, generate immediate, long-range perturbations of the Earth's gravity field. Here, an analytical solution is derived for gravity perturbations produced by a point double-couple source in homogeneous, infinite, non-self-gravitating elastic media. The solution features transient gravity perturbations that occur at any distance from the source between the rupture onset time and the arrival time of seismic P waves, which are of potential interest for real-time earthquake source studies and early warning. An analytical solution for such prompt gravity perturbations is presented in compact form. We show that it approximates adequately the prompt gravity perturbations generated by strike-slip and dip-slip finite fault ruptures in a half-space obtained by numerical simulations based on the spectral element method. Based on the analytical solution, we estimate that the observability of prompt gravity perturbations within 10 s after rupture onset by current instruments is severely challenged by the background microseism noise but may be achieved by high-precision gravity strainmeters currently under development. Our analytical results facilitate parametric studies of the expected prompt gravity signals that could be recorded by gravity strainmeters.

Prompt gravity signal induced by the 2011 Tohoku-Oki earthquake

“…These changes are consistent with theoretical predictions267. In addition to the static signal, a transient gravity change is expected to appear everywhere during the rupture, before the arrival of seismic waves8. Such a prompt gravity signal is in general expected to be very small compared with the background seismic noise that affects all gravity sensors (see section 4.1 of ref.…”

“…1a). Based on the theory developed by Harms, J. et al 8. (see also the ‘Discussion' section), we expect a prompt gravity signal amplitude of a fraction of μGal at ∼65 s after the rupture onset, just before the arrival of the seismic P-waves at the instruments.…”

“…Such a prompt gravity signal is in general expected to be very small compared with the background seismic noise that affects all gravity sensors (see section 4.1 of ref. 8). Thus, to maximize the chance of detection, it is necessary to consider a very large earthquake recorded in a low-noise environment at distances large enough to capitalize on the time between rupture onset and arrival of seismic waves, but short enough to not be challenged by the rapid distance decay of the gravity field.…”

SOGRO (Superconducting Omni-directional Gravitational Radiation Observatory)

“…A recent study [17] shows that a gravity strain sensor with 10 −20 Hz −1/2 sensitivity at 0.1 Hz would detect an early gravity perturbation induced by an earthquake of magnitude M > 6 with SNR > 5 at epicentral distances up to 500 km. The prompt detection of earthquakes would enable an early warning to be issued before destructive seismic waves reach populated areas.…”

Improving parameter estimation accuracy with torsion-bar antennas

“…In addition, this work is considered to be applicable not only for the GW detection but also for a prompt earthquake detection [27]. TOBA is sensitive to the gravity gradient caused by the earthquake.…”