Transcript Lab 3 - Geologic Structures, Maps, and Block Diagrams

Lab 3 – Structural Geology and
Earthquakes
Definitions
• Structural Geology
– study of how
geologic units
(bodies of rock or
sediment) are
arranged when first
formed and how they
are deformed
afterward.
Geologic Map
• Geologic map – shows
the distribution of rocks at
the Earth’s surface.
– Formations – mappable rock
units
• Beds – subdivisions of
formations
• Example: Cretaceous Kootenai = sandstone
formation, Gastropod Limestone = bed within
Kootenai
– Contacts – boundaries
between geologic units
Geologic Cross Section
• Geologic cross
section – a drawing
of a vertical slice
through the Earth.
Geologic Block Diagram
• Block
diagram – a
combinations
of the geologic
map and cross
section.
Strike and Dip
• Attitude – the orientation of a rock unit or surface.
– Strike – the compass bearing (direction) of a line formed by the
intersection of a horizontal plane and an inclined layer
(bed/stratum) of rock, fault, or fracture.
– Dip – the angle between a horizontal plane and the inclined
(tilted) stratum, fault, or fracture.
• Dip direction – perpendicular to the line of strike, direction in which
water will run downhill.
• Dip angle – inclination of dip down from the horizontal line.
Unconformities
• Disconformity – an unconformity
between parallel strata.
• Angular unconformity – an
unconformity between nonparallel
strata.
• Nonconformity – an unconformity
between sedimentary rock/sediment
and non-sedimentary (ign./met.)
rock.
Faults
• Types: normal, reverse (high angle), thrust
(low angle), transverse (strike-slip)
• Remember:
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Stress fields
Angles
Hanging wall
Foot wall
Folds - Antiforms
• Antiform – “upfold” or “convex folds”
– Anticlines - Oldest rocks in the middle
young
old
young
Folds – Synforms
• Synform – “downfolds” or “concave fold”
– Syncline – youngest rocks in the middle
old
young
old
Other types of folds
Basins
Domes
Earthquakes
• Earthquakes – shaking motions and vibration caused by
release of energy in the Earth.
• Epicenter – point on Earth surface directly above the focus
(origin of earthquake)
• Seismic waves – elastic waves of vibration and shaking cause
by stain.
– P-waves – primary waves, compressional
– S-waves – secondary waves, shear
– Rayleigh/Love waves –move along Earth’s surface
• Seismograph – instrument to record seismic waves
• Seismogram – record of seismic waves
Earthquake Damage
• Damage related to:
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Energy
Amplitude
Soil strength
Building strength
• Unconsolidated sediment amplifies waves.
Earthquake location