Lithological and stress anisotropy control large-scale seismic velocity variations in tight carbonates.

摘要: Our knowledge of subsurface structures often derives from seismic velocities that are measured during acquisition surveys. These can greatly change due to lithological, fracture frequencies and/or effective pressure/temperature variations. However, the influence such intrinsic lithological properties and environmental conditions at large scale is poorly understood lack comprehensive datasets. Here, we analyze 43 borehole-derived velocity datasets 3 end-member tight carbonate sequences Central Italy, including massive pure limestone (Calcare Massiccio, CM), thick-layered (20-50 cm) (Maiolica, MA), thin-layered (2-20 cm) marly (Calcareous Scaglia, CS). results show main rock parameters driving variations bedding paleostresses, while mineralogical composition current tectonic stress also play a role. For each end-members, VP values vary differently with depth, as CS units clear increase in Vp, slightly increases remains constant for MA CM units, respectively. Such observations affected by specific characteristics discontinuities, thickness bedding. Counterintuitively, larger Vp were recorded deformed mountain range than undeformed foreland suggesting higher paleo-stresses enhancing diagenesis healing discontinuities. thus demonstrate strictly related variation geological history an area. We suggest controls should be taken into account when developing mechanical models tectonically active regions Mediterranean Area, where earthquakes mostly nucleate propagate through formations, resource exploration fractured reservoirs.