Gravity Investigation of Deep Crustal Structures by Linsser-Filtering

Robert Trzebski and Jan Svancara

Investigation of tectonic structures is an essential part of geophysical exploration. Seismic surveys are usually performed along predetermined profile lines, so that an adequate areal mapping of faults can be obtained only by costly 3D-seismics at the end of the investigation. In contrast, gravity data can be easily aquired in the early phase of geophysical exploration by area wide spot coverage. Detailed mapping of fault patterns requires the analysis of the smallest anomalies on the Bouguer gravity map. The conventional interpretation of residual and derivative gravity maps generally assumes spherical bodies in deep crustal levels to explain the gravity effects. The Linsser-filtering, in contrast, uses tectonic elements as source for the gravity effects produced by fau t-induced density contrasts.

The original digital template Linsser-filtering has been recomputerized as PC-program LIN 2 for depth-selective analysis of Bouguer gravity gradients. The principle of the method is based on testing gravity maps for the effects o faults by comparing observed gravity data with calculated master curves. The program calculates depth-related gravity effects of fault-induced density boundaries indicated by gradients. The geometry, depth and orientation of faults can consequently be derived by stacking the resulting Linsser-indication maps of different crustal levels and correlating with surface geology and tectonic structures.

Besides applications in mapping of faults in soft-rock environment the Linsser-filtering is used to determine the morphogenesis and tectonic position of granitic intrusions in metamorphic complexes. Examples from mid-European Variscides demonstrate that the Linsser-filtering is a useful tool for 3D-modeling of deep crustal structures.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California