Sensitivity of the MAGIC satellite instrumentation to the gravity rate of change due to rifting in the Gulf of Aden

Summary

Tectonic gravity anomalies are commonly assumed as static, except during major geodynamic events like earthquakes or plate reorganizations. This study challenges such an assumption at the regional scale by examining the ongoing rifting in the Gulf of Aden. Using 3D finite element and gravitational modelling, it can be shown that horizontal motion between oceanic and continental crusts – characterized by a density contrast of 400 kg/m3 and a divergence rate of 1.25 cm/yr – generates a potentially measurable gravity rate of change, forming a dipolar pattern with peak amplitudes of ±40 nGal/yr. Numerical simulations were conducted to evaluate whether this signal could be actually measured by the forthcoming MAGIC satellite mission. To this aim, the time-variable gravity field derived from the 3D finite element was propagated into orbit simulations, considering only instrumental noise. A series of 1-year least squares solutions were computed from the simulated data in terms of spherical harmonics. Then gravity disturbance grids at 5 km height covering the Gulf of Aden were derived and the gravity rate was estimated at each point of the grid, considering different maximum harmonic degree. Results indicate that the noise level of the MAGIC instrumentation is low enough to make it sensible to this signal, despite spatial resolution limitations. The two opposing gravity stripes cannot be distinguished, but a central bump of gravity rate with an amplitude of about 6 nGal/yr can be well identified by considering a maximum harmonic degree of 70. Of course, the detectability of such a signal from MAGIC observations becomes unfeasible when considering the temporal aliasing induced by other geophysical phenomena involving stronger and faster mass transport. Nevertheless, these findings suggest that tectonic processes associated with rifting can induce measurable gravity variations (given the accuracy level of MAGIC instrumentation), even in the absence of episodic seismic activity, offering new prospects for satellite gravimetry in monitoring active plate boundaries.