Geophysical Investigation of a Diatreme Structure Near Ebersbrunn/W-Saxony in Germany

From 2003 to 2006 an extensive geophysical survey, including gravimetry, magnetics, and electromagnetics, of the structure characterized as a tuff chimney was carried out. This fossile fluid migration zone which is located near Ebersbrunn/West-Saxony in Germany is afresh of geoscientific interest as it is near an area in which unexpectedly swarm earthquakes occurred in the last years. From the gravimetric survey an elliptical Bouguer-anomaly emerges with a gravity minimum of -3 mGal and a diameter of about 1000 m. In agreement with the meas-urements of the vertical intensity in the 1960s a dissected anomaly of the magnetic total field intensity is found. The anomalies are characterized by variations of several 100 nT with al-most no recognizable minima. The degree of weathering appearently affects the presence of maxima in the total field since visibly reduced magnetic susceptibility values were found in areas in which strong weathering occurred. From the conductivity map the diatreme border could be derived which beforehand was deduced from near-surface wells. By a 3d gravimetric and magnetic modeling including the results from the other geophysi-cal surveys as well as information from geological and petrographic studies, core analyses, and well logging, details on the diatreme structure could be determined.