%0 Journal Article %T Depth dependent stress revealed by aftershocks %+ Institut de Physique du Globe de Paris (IPGP) %A Shebalin, Peter %A Narteau, Clément %< avec comité de lecture %@ 2041-1723 %J Nature Communications %I Nature Publishing Group %V 8 %P 272, p. 44-49. %8 2017 %D 2017 %Z 2017NatCo...8.1317S %R 10.1038/s41467-017-01446-y %Z Sciences of the Universe [physics]Journal articles %X Characterising the state of stress in the brittle upper-crust is essential in mechanics of faulting, industrial production processes, and operational earthquake forecasting. Nevertheless, unresolved questions concern the variation of pore-fluid with depth and the absolute strength on tectonically active faults. Here we show that, along the San Andreas fault system, the time-delay before the onset of the power-law aftershock decay rate (the c-value) varies by three orders of magnitude in the first 20 km below the surface. Despite the influence of the lithostatic stress, there is no continuous change in c-value with depth. Instead, two decay phases are separated by an abrupt increase at an intermediate depth range of 2-5 km. This transitional regime is the only one observed in fluid-injection-induced seismic areas. This provides strong evidence for the role of fluid and a porosity reduction mechanism at depth of few kilometres in active fault zones. Aftershock statistics can then be used to predict changes in differential shear stress with depth until the brittle-ductile transition is reached. %G English %2 https://insu.hal.science/insu-03748825/document %2 https://insu.hal.science/insu-03748825/file/s41467-017-01446-y.pdf %L insu-03748825 %U https://insu.hal.science/insu-03748825 %~ INSU %~ UNIV-PARIS7 %~ AFRIQ %~ CNRS %~ IPGP %~ USPC %~ SORBONNE-UNIVERSITE %~ UNIV-PARIS %~ SU-TI %~ ALLIANCE-SU