Ambient seismic noise tomography using the dense array “EstOf” for deep geothermal exploration, Alsace, France

Abstract

In September 2014, a dense temporary network (EstOf) including 288 geophones was deployed during 30 days in the Outre-Forêts region of the Upper Rhine Graben, where two deep geothermal projects have been settled (Soultz-sous-Forêts and Rittershoffen, France). We use the ambient noise cross-correlation technique to determine the station-tostation Rayleigh wave travel times and to build a tomographic image of the area (~500 km2). We show that the fundamental mode and first overtone of the Rayleigh waves can be identified between almost all the ~41000 station pairs of the network in a period band ranging from 1 to 5 seconds. These waves are used to build a preliminary group-velocity model of the area. We also show that P-waves emerge from the cross-correlation functions and could bring additional information about the structures in the geothermal reservoir. In the future, similar networks might be used in an industrial context for the exploration of geothermal resources and for reservoir characterization.