CRC 526 | Project area A

The strength of the upper crust and its role as a stress conducter

A10 Fluid transport and frictional strength of jointed or faulted rocks

Song, Renner, Bruhns

Summary
We propose to continue our study into the relation between bulk frictional strength and hydraulic properties of jointed or faulted rocks. The study aims to provide basic constitutive equations for the frictional and fluid transport properties of faulted rocks relevant for the brittle upper crust. On the experimental side, we will focus on recognizing the scales of heterogeneities by determining the frequency dependence of permeability and storage capacity and performing flow analysis in addition to the traditional pressure interpretation. We will investigate the influence of fault orientation and surface properties (i.e., smooth, rough, and gauge-filled) on frictional strength at true triaxial stress states. We will further investigate whether the hydraulic diffusion radius constitutes a characteristic length scale of the coupling between frictional strength and fluid transport. In the theoretical part of the project, global material descriptions of jointed/faulted rocks will be determined introducing general assumptions about the heterogeneity and anisotropy of the material. Then, the assumptions will be verified using the experimental observations. Different methods of homogenization will be tested and applied during this iterative process. Improved constitutive equations for jointed/faulted rocks will constrain the conditions for activation of existing faults and fluid flow in the brittle upper crust on different spatial scales and thus provide the basis for substantial modeling of the strength envelope of the brittle upper crust. The results of the study will further aid in developing tools for the determination of characteristic scaling parameters from field experiments.

A11 Strength of upper crustal rocks on different scales - from fracture experiments in the lab to mining-induced seismicity

Alber, Meier

Summary
The strength of upper crustal rocks may be evaluated in the lab e.g. by deformation and fracture experiments. However, conditions of these experiments differ considerably in scale from in-situ conditions. We propose to study the response of upper crustal layers to stresses caused by mining in order to investigate the strength of the upper crust and to bridge the gap between laboratory scales and crustal scales of tectonic processes. The rheology of the upper crust is studied in a volume of about 4 km3 using the special opportunities offered by mining activity in the vicinity of the Ruhr-University Bochum.

Mining induced seismic events are supposed to result from failure of seismogenic strata (Hamm) as well as from the activation of preexisting faults (Ibbenbüren). Therefore, we propose to

  1. identify seismogenic strata by localization of mining induced events as well as by laboratory tests of rock samples,
  2. to compare source parameters of seismic events with parameters of the stress-strain curves of rock samples and
  3. to study the influence of faults on mining induced seismic activity by conducting numerical studies and subsequently shear tests on discontinuities in the lab.


nach oben

A1 (2005/2-2008/1)

Prof. Th. Triantafyllidis, Dr. D. König


A4 (1999/2-2005/1)

Prof. O. Bruhns


A6 (1999/2-2002/1)

Dr. F. Rummel


A7 (1999/2-2005/1)

Prof. J. Kalthoff


A12 (2005/2-2008/1)

Prof. B. Stöckhert