Deep EarthShape - Geophysical Imaging: Imaging weathering fronts in deep regoloth with seismic and electromagnetic methods (GIDES)

 

Investigator Names and Contact Info:

• Charlotte Krawczyk (Seismics / Geophysics). German Research Centre for GeoSciences (GFZ) Potsdam, Germany
• Ute Weckmann (Magnetotellurics / Geophysics). German Research Centre for GeoSciences (GFZ) Potsdam, Germany
• Klaus Bauer (Seismics / Geoinformatics). German Research Centre for GeoSciences (GFZ) Potsdam, Germany

 

Chilean Collaborators Involved:

• Jaime Araya Vargas (Magnetotellurics, electromagnetic and potential field methods). Universidad de Atacama, Copiapó, Chile
• Klaus Bataille (Seismology). Universidad de Concepción, Concepción, Chile

 

Post-Doc:

Electromagnetic imaging using Radio-Magnetotelluric (RMT) methods.

• José Alejandro Cruces Zabala. GFZ Potsdam, Germany
• supervisor: PD Dr. Ute Weckmann

 

Post-Doc:

Electromagnetic imaging using Radio-Magnetotelluric (RMT) methods.

• Cedric Patzer. GFZ Potsdam, Germany
• supervisor: PD Dr. Ute Weckmann

 

PhD:

Seismic imaging using surface wave methods.

• Rahmantara Trichandi. GFZ Potsdam, Germany
• supervisor: Dr. K. Bauer, co-supervisor: Prof. Charlotte Krawczyk

 

 

Project summary:

This project is part of the interdisciplinary DeepEarthshape package, newly proposed in Earthshape phase 2. The DeepEarthshape concept arose from the multi-disciplinary soil characterisation carried out in Earthshape phase 1. In all four primary study sites the weathering zone was found to be much deeper than expected (possibly > 30 m), such that unweathered rock was never encountered in the soil pits. In parallel, appreciable amounts of microbial biomass and DNA counts were observed at depths of 1-2 m. Bacteria and archaea colonizing rock surfaces are closely related to those from deeper soil zones. These findings led us towards new research questions: In particular, we identified the need to know (i) the depth of weathering; (ii) the biotic, geochemical and geophysical processes advancing the weathering front; (iii) whether this zone constitutes a habitat and interacts with the surface biosphere.

Application of geophysical techniques can probe the deep subsurface and thus quantify physical properties of the critical zone. While seismic data is sensitive to elastic parameters that are mainly controlled by the rock matrix, the electrical conductivity is sensitive to smaller compounds within the pores and their interconnectivity. Drilling campaigns at all four study sites will yield detailed data and calibration.

We will (i) map the depth of the weathering zone with seismics and RMT; (ii) derive the density of (large scale) faults; (iii) determine the depth of the water table - resp. the depth to weathering; (iv) evidence the presence of fluid/moisture in regolith. The latter provides geochemists with a crucial hint for ongoing weathering processes, and microbiologists for the essential ingredient for recent microbial growth at depth.