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Dynamic Earth Class 15 28 February 2005.

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Presentation on theme: "Dynamic Earth Class 15 28 February 2005."— Presentation transcript:

1 Dynamic Earth Class 15 28 February 2005

2 The Flow of the Continents (Chapter 5) Building Mountains: Rock Deformation and Earthquakes

3 Rock Deformation Large scale deformation of the Earth’s crust = Plate Tectonics Smaller scale deformation = structural geology

4 Deformation Changes in volume or shape of a rock body = strain

5 Deformation of rocks Folds and faults are geologic structures Structural geology is the study of the deformation of rocks and the effects of this movement

6 Small-Scale Folds

7 Stress The force that acts on a rock unit to change its shape and/or its volume Causes strain or deformation Stress Compression Tension Shear

8 Compression Action of coincident oppositely directed forces acting towards each other

9 Tension Action of coincident oppositely directed forces acting away from each other

10 Shear Action of coincident oppositely directed forces acting parallel to each other across a surface in a couple

11 Differential stress

12 Strength Ability of an object to resist deformation
Compressive or tensile

13 Strain Any change in original shape or size of an object in response to stress acting on the object

14 Kinds of deformation Elastic vs Plastic Brittle vs Ductile

15 Elastic Deformation Temporary change in shape or size that is recovered when the deforming force is removed


17 Ductile (Plastic) Deformation
Permanent change in shape or size that is not recovered when the stress is removed Occurs by the slippage of atoms or small groups of atoms past each other in the deforming material, without loss of cohesion

18 Increasing stress Increasing strain

19 Brittle Deformation (Rupture)
Loss of cohesion of a body under the influence of deforming stress Usually occurs along sub-planar surfaces that separate zones of coherent material

20 Increasing stress Increasing strain

21 Factors that affect deformation
Temperature Pressure Strain rate Rock type The variation of these factors determines if a rock will fault or fold.

22 Rocks are: Elastic and brittle near the earth's surface
More plastic and ductile deeper in the crust Because of the increasing temperature and pressure

23 Folds Most common ductile response to stress on rocks in the earth's crust

24 Experimental Deformation of Marble
Brittle Deformation (low confining pressure) Ductile Deformation (high confining pressure)

25 Tectonic Forces and Resulting Deformation

26 Geometry of Anticlines & Synclines

27 Types of Folds (bent planar structures)
anticline: older rocks on the inside syncline: older rocks on the outside (scale - from mm to tens of km)

28 Anticlines and Synclines

29 Syncline

30 Fold Terms axial plane: the plane of mirror symmetry dividing the fold into two limbs axis: line formed by the intersection of the axial plane and a bedding plane horizontal fold: where the fold axis is horizontal plunging fold: where the fold axis is not horizontal

31 Fold Terminology

32 Symmetrical, Asymmetrical and Overturned Folds

33 Asymmetric Folds

34 Overturned Folds

35 Map View of Plunging Folds

36 Oil Field at Crest of Plunging Anticline




40 Fracture Most common brittle response to stress
With No displacement = Joint With displacement = Fault

41 Joints commonly form when the surface of a volcanic rock cools and contracts


43 Devil’s Tower, Wyoming

44 Faults Occur when large stresses build up in the crust, often due to lava movement into shallow magma chambers Classified according to the kind of movement that has occurred along them


46 Normal Fault Hanging wall drops down

47 Tom Bean


49 Rift Valley Formed by Extension


51 Wildrose Graben, Southern California

52 Reverse Fault Hanging wall moves up

53 Reverse Fault

54 Large-Scale Overthrust Sheet

55 Keystone Thrust Fault, S. Nevada
Cambrian Limestone Jurassic Sandstone

56 Cross Section of the Keystone Thrust West of Las Vegas

57 French Thrust, Wyoming Mississippian Limestone Cretaceous Shale

58 Strike-slip Fault




62 Faults may move several meters in a second or so
This movement within the earth's crust usually generates an earthquake

63 Global Locations of Earthquakes

64 First-motion studies of earthquakes indicate direction of movement on faults

65 Tuesday Continue with reading for Chapter 5

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