SHmax Orientation in the Northern Alpine Foreland from Stress-Induced Anisotropy in Nonlinear Elasticity

Abstract

<p>The orientation of SHmax is commonly estimated from in-situ borehole breakouts and earthquake focal mechanisms. Borehole measurements are expensive, and therefore sparse, and earthquake measurements can only be made in regions with many well characterized earthquakes. Here we derive the stress-field orientation using stress-induced anisotropy in nonlinear elasticity. In this method, we measure the strain derivative of velocity as a function of azimuth. We use a pump-probe method which consists of measuring elastic wave speed using empirical Green’s functions (probe) at different points of the tidal strain cycle (pump) as in Delorey et al. (2021). The approach is applied to data from the AlpArray in the Alpine foreland region, where the orientation of maximum horizontal compressive stress is well-known from borehole breakouts and drilling-induced fractures.</p><p>Delorey, A., Bokelmann, G., Johnson, C., Johnson, P. Estimation of the orientation of stress in the Earth's crust without earthquake or borehole data. Nature Comm. Earth Environ. 2, 190 (2021). https://doi.org/10.1038/s43247-021-00244-1</p>