ANR AlterAction

This ANR project will focus on the process of maturation of active faults in the upper crust by chemical alteration of their fault walls, and on the feedback between alteration and tectonic activity.

The main research hypothesis is that the fault activity induces new fractures that enhance fluid-rock interactions and associated fault zone alteration. This feedback forcing would accelerate the maturation of active faults, by creating clay gouges that weakens the fault and decreases its core permeability over time.

Our focus is on granitoid rocks, which is the lithology of both the Rhine Valley geothermal reservoirs and that of the wall rocks of the Nojima fault responsible for the 1995 Nanbu-Kobe earthquake in Japan. Dynamic loading pulverizes granitoid rocks, which enhances their permeability. That facilitates laboratory alteration of centimetric samples, as shown by preliminary experiments.

We will use core samples from the GSJ-Hirabayashi scientific borehole intersecting the Nojima fault to (1) obtain a continuous alteration profile through the fault by combining core and downhole geophysical data and (2) perform laboratory alteration experiments at various differential stresses to assess the intertwined effects of tectonic loading and fault alteration.