Transcript GSC 1530 Chapter 15 - Oakland Community College

GSC 1530: Chapter 10
Crustal Deformation
Crustal Deformation
• Crustal deformation
processes have produced
some of the world’s most
beautiful scenery (e.g.,
the Himalaya Mountains)
but also some of its most
deadly events (e.g., the
earthquake which induced
the massive 2004 Indian
Ocean tsunami)
Terminology
• Stress – amount of force applied to a given area
of a body
• Three main types of non-uniform (differential)
stress: compressive (
),
tensional (
) and shear (
)
• Strain – change in shape of a body resulting from
the applied stress
• Three main types: brittle, elastic and plastic
(ductile); see classroom examples and slides
Joints and Faults
Joints and faults
result from brittle
rock behavior
Joints – rock
fractures along
which no
appreciable
displacement has
occurred
Earthquake Origin?
• Fault – a crack in rock along which rock shifting
(displacement) has occurred
• Earthquakes result from brittle rock behavior which
produces faults
• Elastic Rebound Theory: earthquakes result from the
rapid release of elastic strain energy that produces rock
rupture and displacement (shifting)
• See classroom examples, including slide illustrating the
elastic rebound theory
Elastic Rebound
Phenomenon
and Earthquake
Production
Elastic Rebound
Earthquakes and Faults
• An initial earthquake produces the fault
and subsequent movement can occur along
the fault if sufficient strain energy
accumulates to cause brittle behavior
More Earthquake Terminology
• Focus – subsurface origin point of earthquake;
earthquake (seismic) energy radiates outward in
all directions from the focus
• Epicenter – point on the Earth’s surface directly
above the focus; seismic surface waves radiate
outward from this point
• Fault scarp – relatively steep landform produced
from fault motion with a substantial vertical
component
• Seismic waves – the vibrational energy produced
during an earthquake
Fault Types
• Faults can be broadly classified as dip-slip (rock
displacement is primarily vertical) and strike-slip
(rock displacement is primarily horizontal)
• Dip-slip faults can be further subclassified as
reverse or normal faults
• To correctly subclassify a dip-slip fault, you need
to know the relative motion of the hanging wall
and footwall blocks (see slide)
Hanging Wall
Footwall
Footwall
Hanging Wall
Reverse fault – hanging
wall block moves upward
relative to the footwall
block; typically results from
compressive stress
Normal fault – hanging
wall block moves
downward relative
to the footwall
block; typically results from
tensional stress
Normal Fault
Reverse Fault
Faults
Thrust fault – low
angle reverse
fault
Type of dip-slip fault?
Type of dip-slip fault?
Major landforms produced by normal faulting
Horst – uplifted block of crust bounded by normal faults that diverge
with depth
Graben – a basin (valley ) formed by a subsided block of crust
bounded by normal faults that converge with depth
Strike-slip fault
Faults
Lateral displacement (~8.5 feet) of fence during the 1906 San Francisco Earthquake
Major Fold Types
• Rocks, under certain conditions, may fold
(ductile deformation) instead of faulting
• What are the four major factors that determine
whether a rock will fold or fault?
• Rock temperature
• Amount of stress exerted upon rock
• Rate stress is exerted upon the rock
• Rock composition
Major Fold Types
• There are three major folds you should be
able to describe: anticlines, synclines and
monoclines
• Anticline – an arch-like package of folded
rocks
• Syncline – a trough-like package of folded
rock
This pattern of rock deformation is characteristic of what region
east of Michigan?
Major Fold Types
• Monoclines – strata exhibiting a single inclination
direction (see slides)
monoclines
Related Fold Types
• Domes - large-scale upwarping of
sedimentary rocks
• Basins - large-scale downwarping of
sedimentary rocks (see slides)
Michigan’s
Lower
Peninsula is
often described
by geologists
as the Michigan
Basin
Folds and Faults
• Folded and faulted rock often coexists; the
rocks fold until their brittle strain threshold
is exceeded and then fault (see slide)
Folded and Faulted
Sedimentary Rock