Download Types of Faults

Types of Faults
Stress, Strain and Faulting
Faults and strain
• Faults form when stress causes the two
opposing sides of a rock formation
(called fault blocks) to break apart
and move in different directions. Stress
falls into 3 categories:
1. Tension
2. Compression
3. Shear
3 Types of Stress
1.
2.
3.
Tension – caused by tectonic forces
pulling the fault blocks apart
Examples: # 1, 5, 6, 7 and 9a
Compression – caused by tectonic
forces pushing the fault blocks
together Examples: # 2, 8 and 9b
Shear – caused by tectonic forces
which cause the fault blocks to slide
past each other sideways –
Examples: # 3, 4, 9a & 9b
3 Types of Stress
I. Rock Deformation
A. Stress is the force that tries to change the
shape of a rock.
There are 3 types of stress:
1) Tension (
) - forces are
pulling the rock apart
2) Compression (
) - forces are
pushing (compressing) the rock
3) Shear (
) forces are trying to slide
or snap off the rock
3 Types of strain
B. Strain is the effect that stress has on the rock.
There are 3 types of strain:
1) Elastic Deformation - when stress is
removed, the strain goes back to zero
(rock or object returns to its original
shape);
Ex: rubber band, ruler
3 Types of strain
B. Strain is the effect that stress has on the rock.
There are 3 types of strain :
2) Plastic Deformation - when stress is
removed, the rock remains deformed;
Ex: Silly Putty.
Rocks deep in the crust are subject to the
high confining pressures required for plastic
deformation.
3 Types of strain
B. Strain is the effect that stress has on the rock.
There are 3 types of strain :
3) Brittle Deformation - stresses are so great that
the rock breaks or ruptures.
Example: Pencil, twig, window glass
C. Rocks that undergo plastic deformation deep in
the crust become folded.
Rocks that undergo rupture and move form
faults:
1
Reverse Fault –
due to
Compression
2
Normal
Fault –
due to
Tension
and
Gravity
Vertical Faulting - more damaging
Normal Fault
Reverse Fault
1
2
Normal
Fault –
due to
Tension
and
Gravity
1
2
Reverse Fault –
due to
Compression
Lateral Faults
Called Transform Faults or Strike-Slip Faults
3
Right Lateral
Transform
Fault – due to
Shear
Left Lateral
Transform
Fault – also
due to Shear
4
Lateral Faults
Left Lateral
Transform Fault
Right Lateral
Transform Fault
3
4
Lateral Faults
4
3
Left Lateral
Transform
Fault –due to
Shear
Right Lateral
Transform
Fault – also
due to Shear
6
5
Normal
Faults –
due to
Tension
and
Gravity
Horst and graben
Owens Valley,
Eastern California
7 Block Faults –
due to Tension
and Gravity
A Classic
Block Fault
Mountain Range
Front View
Side View
8
Thrust Faults
Low Angle
Reverse faults occur due to
Compression
Blind Thrust – buried under
new rock layers
8
Strike-Slip San Andreas
Fault (caused by shear)
is 90 miles east.
Blind Thrust Faults
(caused by compression)
are under Los Angeles
Faulting
Ground offset by faulting
can be minor…
…or it can cause major
disruptions of the ground
surface
vertical fault damage
• Alaskan Earthquake,
1964
• Buildings and streets
heavily damaged by
vertical surface waves
(Rayleigh Waves) and
vertical faulting
Lateral fault damage
Railroad Tracks
distorted by
horizontal
surface waves
(Love Waves)
Body Seismic Waves
Seismic Waves are
shock waves given
off by earthquakes.
There are 2 types:
1. Body Waves:
• Originate from
the focus (F)
• Travel through the
body of the earth.
• Used to locate
epicenters (E.)
Surface
Waves
2 Types of Body Waves
1) Primary (P) Waves:
• compression waves
• travel fastest
through solids
• first waves to arrive
2 Secondary (S)
Waves
• shear waves
• cannot travel through
liquids
• second to arrive
• only half as fast as P
waves
Surface
Waves
2 Types of Body Waves
1) P Waves –
Compressional
(or Longitudinal)
Waves
2) S Waves –
Shear
(Transverse)
Waves
Surface Seismic Waves
Seismic Waves are
shock waves given
off by earthquakes.
There are 2 types:
2. Surface Waves:
• Originate from
the epicenter (E)
• Travel slowly on
the surface.
• Cause a lot of
damage
Surface
Waves
2 Types of Surface Waves
1) Love Waves –
Horizontal Shear
Waves
2) Rayleigh Waves –
Vertical Shear
Waves
Locating Earthquakes
S wave
arrives
P wave
arrives
1. Epicenter could be ANYWHERE on the blue circle!!
Locating Earthquakes
S wave
arrives
1. Epicenter has to
P wave arrives
be at one of the two intersections
of blue and green circles.
Locating Earthquakes by Triangulation
S wave arrives
P wave arrives
1. Epicenter can only be at the point where
all 3 circles intersect!
Seismic Gaps – Strain Builds Up
7. Seismic Gaps are regions along an active faultline that are overdue to
have a quake. (Short-term prediction is not possible yet.)