hydroseis-en hydroseis-fr
Publications 2016

Goebel T.H.W., Hosseini S. M., Cappa F., Hauksson E., Ampureo J.-P., Aminzadeh F. et Saleeby J. B.,
Wastewater disposal and earthquake swarm activity at the southern end of the Central Valley, California,
Geophysical Research Letters, vol. 43, n°3, pp. 1092–1099,
Nature Research Highlight, 2016.






Fluids in the Earth’s crust have long been recognized as playing an important role in the mechanics of faults and earthquakes, but the influence on seismic rupture has not been precisely determined yet mainly due to the lack of observations near the seismogenic zone and multiphysics modeling. In this project, we propose to explore jointly the mechanical and seismological response of faults to fluid pressures, using a combined in-situ experimental and modeling approach. The main goal is to provide new observations in a seismogenic area and the appropriate theoretical models for a better understanding of the hydromechanical and seismic/aseismic behavior of fault zones under the different fluid pressure conditions operating in the brittle crust. The main questions addressed in this project are: (1) how do faults with fluids slip?, (2) do the fluids participate only in the rupture triggering phase or in the entire rupture process?, (3) are the fluid pressures and seismic waves measured in the near-surface part of active faults a good marker of deformation and a precursor of rupture at depth?, and (4) what are the processes generating the seismic and mechanical observations on faults which can be used to improve the rupture forecasting?

To address these fundamental questions, a complete approach from field observation, in-situ experiments to fault modeling is proposed with: (1) the assessment of the fluid effect on the mechanical and seismic behavior of a fault, from in-situ, 10-m scale, experiments under constrained mechanical and hydraulic conditions in the seismogenic zone (Task 2); (2) the development of hydromechanical models reproducing the in-situ measurements at meter-scale, and upscaling the inferred physical mechanisms to crustal scale (Task 3). The models will include the fully coupled nature of fluids, rupture and rock damage; (3) finally, we will assess how the evolution of the fluid pressure, rupture and hydromechanical properties of fault system observed during in-situ experiments can explain the complex observations (deformations, fluid pressures, seismic velocity changes, micro-seismicity scaling laws) recorded around several active crustal scale fault systems worldwide (Task 4).

Thus, our first step will be to seek the links between transient fluids, strain and seismicity before, during and right after the rupture of a fault within the seismogenic area. To do that, we will use the continuous and simultaneous measurements of fluid pressure, mechanical displacement and high-resolution seismology recorded during a field experiment at 0.3-km depth in which we will nucleate, in a controlled manner, both slow and rapid slips through the artificial pressurization of a fault already well documented thanks to galleries and boreholes into the LSBB facilities in France, a “Site Instrumenté” supported by CNRS/INSU along its observatory leadership. We define and conduct a new experiment specifically dedicated to the monitoring of multiphase fluid processes during the fault seismic rupture using the results of a feasibility experiment of fault activation performed within a previous project ANR-07-PCO2-002-01. Joint analysis of the seismological and hydromechanical data will help to constrain processes accounting for the effect of fluid pressure on the fault behavior, especially on the preparation process of rupture and induced seismicity. These constraints will be integrated in hydromechanical models describing how the coupling between fluids and fault mechanics occurs and evolves in the different parts of faults, from the granular core to the fractured damage zone. The key ideas will be to identify seismic or hydrologic proxies of fault rupture processes that could be implemented in crustal scale analyses. Then, we aim at comparing our meter-scale controlled in situ and numerical experiments to crustal fault datasets, in order to bridge the gap between experimental data, field observations and crustal earthquake processes.