Strike-slip fault and its related structure

1. Strike-slip fault and its related structure 01003117 LuoMao

2. Strike-slip fault • Definition : a kind of fault that the two blocks move along the strike direction of fault plane. It can be subdivided into two kinds. sinistral(left lateral)-----the opposite block moves to the left dextral(right lateral)-----the opposite block moves to the right.

3. Mechanism of strike-slip fault Fault is the result of force and stress. Different force situations would generate different faults. The force system of strike-slip fault is plotted as follows The greatest stress is horizontal, the smallest stress is horizontal, two sets of strike-slip fault inter- sect along the intermediate Picture in two dimension stress,each dipping vertically. (Down plunge view) σ3 σ1

4. Fault orientation in relation to principal stress axes (After E.M.Anderson, 1951) A Normal fault sets. B Thrust fault sets. C Strike-slip fault sets

5.  Fault plane  Fault zone • Fault plane usually is a plane and the dip angle is approximate 90 degree. The strike line on the ground extends straightly in a region(picture A).But there are some exceptions. Sometimes the strike line curves(B). because of the characteristics of adjacent blocks and even form a zone(C). A B C

6. Flower structure • If the fault plane curves,under the effect of greatest stress,it would bear movement along two direction. Part A combines both strike-slip movements and compression.It would move upwards to form positive flower structure,as to part B,the extension and the gravity prompt block to fall downwards,thus form negative flower structure. A B C

7. Strike-slip faultsystem A- Local compressional and extensional struc- tures produced by fault terminations and fault overlaps. B-Formation of raised and depressed wedge- shaped blocks by local transpression and transtension. C- Positive and negative flower structures produ- ced by convergence and divergence respectively in strike-slip motion D-Strike-slip duplex

8. FLOWER STRUCTURE IN STRIKE-SLIP FAULTS Positive flower structure for uplift blocks Negative flower structure for depressed blocks

9. Analysis of flower structure • We observe the structure carefully,it can be inferred that positive flower structure is a combination of reverse fault, whereas the negative consists of a group of normal fault. Several methods can be used to identify the structure  displacement  joint  attitude of fault plane  breccia  slikenline

10. Kink band&Fault zone It is a kind of chevron fold which possesses planar limbs and sharp angular hinges.If it is symmetrical,we call it conjugate kink ,and if not,we call it monoclinal Kink band. Fault zone developed in strike-slip fault is between two boundings,As slip occurs along the fault bounding the rock between them develops parallel en-echelon tension cracks that give the zone an oblique foliation.

11. Conjugate folds(A,B) with opposite sense of asymmetry and polyclinal folds(C) with variable axial surfaces

12. 不同膝折带形成的应力状态 （据Johnson，1977） A.对称共轭膝折带；B.非对称共轭膝折带；C.单斜膝折带；σ1.最大主应力； σ3.最小主应力

13. The band is the zone in which the common short straight limb bounded by the two adjacent fold surfaces Markedly asymmetric chevron with a very long limb and a very short limb Kink band

14. Analysis • In fact,the mechanism of en-echelon formed by strike-slip fault and the kink band is the same,though result is different.The key to this problem I think is the rock character. One situation is that the block is a whole that every parts is the same,when undergoing the slides,en-echelon is formed. Another situation is that the block has planar features. Slides would occur between two strata,thus make the stress outlet,and prevent it from cracking.

16. That’all for my presentation Thank you very much!