GEOLOGICAL STRUCTURESForces acting on the lithosphere generate stresses that cause rocks to DEFORM for example:- folding faulting.

http://www.uky.edu/AS/Geology/howell/goodies/elearning/module10swf.swf

A variety of forces act upon plates generate tectonic stresses that are transmitted through the lithosphere.Activity find the definitions of:-STRESS

STRAIN

TECTONIC FORCES:-Generate extensional or compressional stress fields leading to fold and fault formation. Fold formation is by buckling or by ductile flow. Folds can be studied by analysis of the FOLD GEOMETRY:- limbs hinges axis axial plane, plunge , upright, over turned, recumbent. Faults result from brittle rock failure when applied stresses exceed fracture strength. Faults can be analysed by FAULT GEOMETRY:- Dip throw displacement, fault types normal, reverse, thrust, strike, slip.

Applying stress to a rock or soil causes strain resulting in change in volume and length at right angles to principal stress axis (ie where stress applied is greatest)

Pmax Pmax

PminPmax

Pmax

Pmin

PmaxPmax

Pmin

Pmin

Principal Stress Axis (Pmax)Minimum l Stress Axis(Pmin)

ActivityFor the following situations place the correct resultant deformation into the box by copying and pasting.

Geological StructuresUse the following resources to fill in the blankshttp://earthsci.org/education/teacher/basicgeol/deform/deform.html#StressandStrain

http://earth.leeds.ac.uk/learnstructure/

Activity Label the features of a fault. Hanging WallFoot WallThrowFault Plane

Faults are fractures that have displacement of rock along them.Features of faults: -

Create zones of broken ground-weaker and less stable, with implications for foundation bearing, slope stability and tunnel roof integrity.

Sudden movement alone faults produce earthquakes.

Allow movement of liquids and gases (radon). Implication for tunnelling, reservoirs.

Types of FaultsActivity Name the faults, mark on the direction of movement. Measure the throw (1cm = 1 metre)

JointsAre rock fractures with no movement along them. They are formed by tectonic stressing and are developed in nearly all rocks.

Groups of sub parallel joints or joint systems are known as JOINTS SETS.

All joints are structural weaknesses, whose density, extent and orientation are major influences on rock mass strength.Activity How many joint sets?

Measure the throw if 1cm = 1 m

Measurements:-If(m) Fracture Spacing IndexFracture spacing: - given as index, significance of spacing controls stability of slope or tunnel for example closely spaced joints speed up tunnelling but give more potential for collapse. Extremely High >2m to extremely low 0.006m

RQD

Dominant Feature in sedimentary rocks is the bedding plane, mark on the DIP and STRIKEActivity label the Dip and strike

FOLDS

FOLDSFold animation

http://www.geology.sdsu.edu/visualstructure/Geo306_webmaterial/foldelements.html

Activity Label the fold.

Horizontal

Activity Identify the types of folds

LimbAxisAxial PlaneDip Angle