3-DIMENSIONAL COMPRESSIONAL DEFORMATIONS IN THE ZAILISKI-ALATAU MOUNTAINS, KAZAKHSTAN

The classical model of faulting predicts that slip planes occur in two conjugate sets. Theoretically, more sets can be contemporarily active if pre-existing structures are reactivated in a three-dimensional str ain field. Four to six sets of faults have been active in the Holocene in the Zailiski Alatau mountain range, Kazakstan. Faults strike with the highest frequency ENE and ESE and show mostly left-lateral reverse and right-lateral reverse motions, respectively. These faults have a bimodal distribution of dips, forming four sets arranged in orthorhomb ic symmetry. Locally, NNW- to NNE-striking vertical faults have also b een active in the Holocene and show right-lateral strike-slip and left -lateral strike-slip motions, respectively. All these fault sets accom modated the general three-dimensional deformation, given by N-S-direct ed horizontal shortening, vertical extension, and E-W-directed horizon tal extension. Field evidence also shows that the reverse motions, eve n if with a minor strike-slip component, occurred on high-angle planes with inclination of 65 degrees-85 degrees. ENE-and ESE-striking fault s reactivated older fracture zones, whereas the other sets are newly f ormed. Comparison of these field results with the structures obtained from published analogue models shows a strong similarity of fault geom etry and kinematics.