Inst. f. Geoscience of CAU Kiel :

Seismics - ICDP/KTB

People Projects ICDP/KTB ICDP-KTB-Schwerpunktprogramm

ICDP / KTB - International Continental Drilling Program /
Kontinentale Tiefbohrung der Bundesrepublik Deutschland

A new project campaign under the roof of the ICDP is finally being carried out this year at the KTB-location (KTB site map) close to Windischeschenbach, Bavaria, Germany. Active borehole seismics i.e. VSP (vertical seismic profiling), MSP (moving source profiling), a channel wave experiment, and a so called Erbendorf Body Endoskopy with an additional surface array at the KTB site have been planned.

The objective is to obtain essentially new information for understanding crustal processes. In particular, the effect of fluids on seismic wave propagation (and the ability to recognize it) is of critical importance because of the great effect of even small amounts of fluids on crustal processes. At 7 km depth the borehole intersects a major reflective structure, the so called SE1 reflection (Altenparkstein Fault Zone). KTB offers the chance to quantify the reflectivity of this large thrust related fault at mid-crustal depth. It provides a unique scientific datum, which would also allow to estimate the reflection coefficients of the lower crust. To get an idea of the target of exploration you may want to take a look at the geologic setting of the region or at some photos taken on different occasions.

In April and September 1999 the first part of these experiments, the VSP, has been accomplished by using explosives. A depth interval from 3000 to 8500 m has been examined. First seismograms of the April campaign show the trace normalized, notch filtered, and inline rotated inline, crossline, and vertical component of the zero offset data. A combination of the zero offset April/September VSP data is clickable only for the vertical component so far. The varying trace spacing is due to a change of depth intervals during the experiment.
The MSP and the channel wave experiment have been carried out in the first half of November 1999. The experiment consisted of six 8 km long MSPs with geophone depths of 7800 and 8490 m and a channel wave experiment with two short VSPs with source locations within and outside the shear zone of the SE1 (Altenparkstein Fault Zone).
A last experiment, the so called "Erbendorfkoerper Endoskopie" with shot to receiver offsets between 40-50 km and charges of 90 kg is going to be carried out at the end of May 2000.

A new high temperature/high pressure (HT/HP) borehole geophone (GFZ Potsdam) has been used for the experiments. An example of the test data collected in April 1998 and an outline of the planned experiments have been summorized in a poster shown at the ICDP/KTB-Kolloquium at Bochum, Germany, on June 4th and 5th 1998. (Postscript-copies of the poster are available, each about 2.5 MByte gzipped files. There are two options in papersize DIN-A4 (about 21 x 30 cm) or DIN-A0 (about 84 x 119 cm).)

The main problem with the geophone sonde we have come across can best be described by an about 25 seconds long movie (about 9 Mbytes! You will need Java to take a look). In this movie you can first watch noise spikes on different channels of the geophone sonde followed by the sampling of a shot. We do not know yet where the noise comes from. It could be triggered by mechanical instabilities within the geophone sonde due to pressure and/or temperture or by the sonde electronics. We prefer the first explanation, but have no proof yet. We have worked on a processing utility to get rid of these spikes before correlating seismic sweeps and have finally come across a method to suppress them. These spikes are one of the reasons for using explosives in the VSP.

The following persons are involved in this campaign:

Rabbel, W. and Beilecke, Th. from the University of Kiel,
Bram, K. from GGA Hannover
Smithson, S. from the University of Wyoming,
Borm, G. and Giese, R. from the GFZ Potsdam,
Ge, X. from the Engineering Acadamy in Wuhan,
Gebrande, H. and Lüschen, E. from the University of Munich,
Hubral, P. and Wenzel, F. from the University of Karlsruhe,
Pujol, J. from the University of Memphis

Funding of the scientific work and the data aquisition is shared between the International Continental Drilling Program (ICDP), the Deutsche Forschungsgemeinschaft (DFG), the National Science Foundation (NSF), the GeoForschungsZentrum Potsdam (GFZ), and the Geowissenschaftliche Gemeinschaftsaufgaben (GGA), Hannover.

comments, suggestions & questions: Thies Beilecke
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