Section 2.7: Near-surface Geophysics

Constrained modelling of electromagnetic and potential field data to investigate the Walvis Ridge magmatism and its interaction with the Kaoko Mobile Belt, Namibia.

The area around Nový Kostel/NW-Bohemia is part of the geodynamically active Variscan orogenic belt in Europe, and experiences repeated occurrence of intra-plate earthquake swarms and is characterized by numerous mineral springs and CO2 emissions.

The objective of the MT part of the observatory is to monitor and analyse electromagnetic data to decipher possible changes in the subsurface electrical resistivity distribution. After elimination of a geomagnetic source field effect which strongly affects the measurements, we examine remaining temporal electromagnetic field variations.

The Posedonian (Lower Jurassic) black shale is studied as a prominent example for this type of unconventional reservoir rock. Controlled-source seismic reflection and tomography experiments are conducted near Minden (Lower Saxony) to follow black shale horizons from outcrops into the deepening North German basin. A wide range of conventional and advanced processing and imaging techniques will be applied to determine the distribution and the inherent seismic properties of the Posedonian black shales and surrounding sediments.

The Mérida Andes (MA) are the main mountain chain of western Venezuela. GFZ acquired two 240 km and 160 km long magnetotelluric profiles in March and April 2015.

Development and testing of electromagnetic geophysical methods to monitor the distribution of a biopolymer in the underground in the context of enhanced oil recovery.

The San Andreas fault (SAF) is one of the most studied strike-slip faults in the world - yet its subsurface geometry is still uncertain in most locations. The Salton Seismic Imaging Project (SSIP) was undertaken to image the structure surrounding the SAF and also its subsurface geometry. Such data are useful as input for modeling scenarios of strong ground shaking in the surrounding high-population areas. As part of long-term cooperations between GFZ and partners in the U.S. we apply pre-stack depth migration methods to obtain images of steeply dipping structures around the SAF in southern California.

The joint project SIMULTAN aims to develop and apply an early recognition system of sinkhole instability, unrest and collapse in Germany.

In the area of the former airport Berlin-Tempelhof/Germany a vibroseismic pilot study to test feasibility and limits of seismic exploration in the heart of a mega city with its enormous noise background was successfully conducted. New high-resolutional images of local subsurface structures were achieved down to 4 km depth as well as valuable findings with respect to necessary field and processing techniques and corresponding parameters for possible future intra-urban surveys in the presence of high noise, coverage irregularities and safety requirements.

In a series of geophysical experiment we study deep structures and geodynamic processes in the Tien Shan and Pamir collision zones, central Asia. The magnetotelluric (MT) component addresses topics such as middle crustal flow, stress relaxation due to partial melting and fluid release in continental subduction processes.

As part of the project "WeatherSeis" a seismic survey has been carried out to explore shallow subsurface structures at the location "Waldschadensstandort Konventwald" in the Black Forest near Freiburg, Germany in July 2014.