Physical Geology 1330
116-S&R 1
Crustal Deformation
Dr. Mike Murphy
mmurphy@mail.uh.edu
333-S&R-1
www.uh.edu/~mamurph2/homepage.html
Today’s Outline
 Describing geologic features – strike and dip
 Stress and Strain
 Types of Deformation – Elastic
Ductile
Brittle
 Types of Folds and Faults
Strike: bearing of a line defined by the intersection of the plane in question and
the horizontal
Dip: acute angle between the plane and the horizontal, measured perpendicular
to strike.
Stress – Force per unit area
Confining stress (pressure)
Equal forces acting on all sides of an object
Deviatoric Stress – unequal forces acting on an object
Compression – oppositely directed forces acting towards each other
Tension – oppositely directed forces acting away from each other
Shear – oppositely directed forces acting parallel to one another on a surface. Together
they form a shear couple.
Strength – the ability for an object (material – e.g. rock) to resist deformation
Strain – the change in shape of an object.
Three Types of Strain: Elastic, Ductile, and Brittle
Elastic Deformation –
Ductile Deformation –
Brittle Deformation –
Factors Determining the Style of Deformation
Pressure –
Temperature –
Strain Rate –
Rock Composition –
Relationship between Stress, Strain, and Deformation -
Tectonic Forces and Resulting Deformation
Fig. 10.6
Folds – Bent planar features
Anticline –
Syncline –
Axial plane – an imaginary surface that divides the fold as symmetrically as possible.
Fold axis – the line that is defined by the intersection of the folded strata and the axial
plane.
Horizontal Fold – a fold where the fold axis is horizontal.
Plunging Fold – a fold where the fold axis is not horizontal.
Fault – a fracture along which movement has occurred.
Dip-Slip Faults – Faults in which the adjacent sides have moved in the dip direction of
the fault.
Normal faults –
Reverse Faults –
*Thrust fault –
Strike-Slip faults – faults in which movement of the adjacent sides has moved in the
strike direction, i.e. horizontally passed one another.
Right-slip fault –
Left-slip fault –