Fault growth & linkage

Transcription

1 Fault growth & linkage Important to understand fault growth, interaction & linkage Continental extension and basin formation Controls on subsurface fluid flow Hydrocarbon exploration & production Minerals Groundwater Waste management/disposal Hazard assessment EARS5136 slide 1

2 3D Fault Array: Continuity EARS5136 slide 2

3 3D Fault Array: Reservoir models EARS5136 slide 3

4 EARS5136 slide 4

5 Displacement pattern on an isolated normal fault - after Barnett et al. (1987) Reverse drag r Displacement not to scale EARS5136 slide 5

6 Normal fault Coal field EARS5136 slide 6

7 Gulf Coast normal fault EARS5136 slide 7

8 Single fault North Sea seismic data a b EARS5136 slide 8

9 Fault surface topography EARS5136 slide 9

10 Normal fault - Oregon Throw and Separation Single fault from surface exposure in central Oregon Maximum separation (throw) near centre of fault. Gradual taper of separation profile from a maximum separation to zero at the fault tips. EARS5136 slide 10

11 West Africa: lower fault tips & conjugate faults EARS5136 slide 11

12 Low throw normal faults EARS5136 slide 12

13 Fault dimensions Aspect ratios average 2:1 but variable Linear throw gradients on isolated faults Non-linear on restricted faults Steeper gradients near overlapping tips EARS5136 slide 13

14 Fault aspect ratios Location Average aspect ratio Derbyshire coalmines UK 2.3 Timor Sea 2.2 Gulf Coast, USA 1.6 North Sea 2.4 From Nicol et al. (1996) EARS5136 slide 14

15 Fault dimensions From Nicol et al. (1996) EARS5136 slide 15

16 Restricted faults EARS5136 slide 16

17 Structure contours Beatrice field Map view Footwall anticline: Cross-section A-A shows form of footwall anticline. Maximum uplift near center of fault. Transverse section through hanging wall Hangingwall syncline: Maximum structural low near center of fault. Schlische, 1995 EARS5136 slide 17

18 Deformation around a fault Large scale faults generate isostatic footwall uplift and hangingwall subsidence Strain around the fault produces reverse drag Normal drag localized around the fault Flexural isostatic effects. EARS5136 slide 18

19 Isostasy EARS5136 slide 19

20 Flexural cantilever EARS5136 slide 20

21 Footwall uplift: Gullfaks field From: Husmo et al.(2002) EARS5136 slide 21

22 North Viking Graben From: Husmo et al.(2002) EARS5136 slide 22

23 Deformation around a fault Reverse drag profiles generate: footwall uplift hangingwall subsidence Relationship of structure contours to fault vary with slip direction Reverse drag does not imply a listric fault Earthquake related elastic strains relax to permanent bed deformation EARS5136 slide 23

24 Earthquake induced deformation < Imperial Valley earthquake 1940 Slip = e -3.5dist 0.03dist Strike-slip illustrates offsets Borah Peak earthquake 1983 > Lost River fault, Idaho EARS5136 slide 24

25 Deformation around a fault Radar interferometry image of ground deformation induced by Hector Mine earthquake Magnitude: 7.1 Depth 5±3 km Right-lateral strike-slip Length of surface rupture: 41 km Maximum surface offset 5.2 m EARS5136 slide 25

26 Fault drag profiles Empirical relationships for: Single event: Slip = e -3.5dist 0.03dist Multiple event steady state: Slip = e -5.5dist 0.004dist From Gibson et al. (1989) EARS5136 slide 26

27 Modelling bed contours Around blind faults (a-e) and synsedimentary fault (f). From Gibson et al. (1989) EARS5136 slide 27

28 Structure contours around an isolated normal fault EARS5136 slide 28

29 Hangingwall & footwall displacement Same in hangingwall and footwall for blind faults Greater hangingwall subsidence than footwall uplift for synsedimentary faults Percentage contribution of hangingwall displacement (HW) is given by: HW = 110 2θ/3 Where θ is fault dip and dip exceeds 30 degrees EARS5136 slide 29

30 Patterns around synsedimentary faults EARS5136 slide 30

31 Patterns around synsedimentary faults: a local example The Craven fault zone EARS5136 slide 31

32 Normal drag in footwall to a 6m throw normal fault: Carboniferous, Anglesey Normal drag profiles often highly localised around fault EARS5136 slide 32

33 Fault shape & linkage EARS5136 slide 33

34 Possible modes of fault linkage after Childs et al. (1995) a b c EARS5136 slide 34

35 a Displacement pattern correlated single fault 2D-seismic data set Middle East b EARS5136 slide 35

36 Displacement pattern correlated multiple faults 2D-seismic data set Middle East a b EARS5136 slide 36

37 Displacement patterns on overlapping faults from Childs et al. (1995) EARS5136 slide 37

38 Relay ramp structure and displacement patterns on overlapping faults from Huggins et al. (1995) A B Relay ramp structure and displacement patterns on overlapping faults. Summed throws give a coherent pattern. From Huggins et al. (1995) EARS5136 slide 38

39 Fault displacement and linkage patterns differences between higher and lower mapped horizons from Childs et al. (1995) EARS5136 slide 39

40 Segmented fault zone, Timor Sea from Childs et al. (1995) EARS5136 slide 40

41 Displacement patterns on overlapping faults from Childs et al. (1995) Fault 1 Fault 2 Aggregate throw EARS5136 slide 41

42 Relay zone structure from Peacock & Sanderson (1994) EARS5136 slide 42

43 Hard linked faults (Krantz 1988) Fault map Vertical separation EARS5136 slide 43

44 Relay ramps seismic mapping EARS5136 slide 44

45 Relay ramps seismic mapping EARS5136 slide 45

46 Relay ramp EARS5136 slide 46

47 Relay zone structure from Peacock & Sanderson (1994) EARS5136 slide 47

48 Fault displacement profiles From Nicol et al. (1996) EARS5136 slide 48

49 Geometric coherence From Walsh et al. (2003) EARS5136 slide 49

50 Different styles of transfer zones (Morley 1990) EARS5136 slide 50

51 NE-SW Cross-cutting faults NW-SE Interacting EARS5136 slide 51

52 Cross-cutting faults EARS5136 slide 52

53 Hard-linked splays EARS5136 slide 53

54 Conjugate faults EARS5136 slide 54

55 Conjugate faults EARS5136 slide 55

56 EARS5136 slide 56

57 Growth rates & slip rates Higher strain rate basins have higher slip rates on faults rather then more faults Large faults grow faster Large faults relatively large throughout growth of fault system Rates to 1.0mmyr -1 : 0.188mmyr -1 (GOM) 0.030mmyr -1 (North Sea) 0.074mmyr -1 (Timor Sea) 0.248mmyr -1 (Aegean) 0.098mmyr -1 (Basin & Range) 0.049mmyr -1 (Kenya Rift) EARS5136 slide 57