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:– Stress fields– Angles– Hanging wall– Foot wall
Folds - Antiforms
• Antiform – “upfold” or “convex folds”– Anticlines - Oldest rocks in the middle
oldyoung young
Folds – Synforms
• Synform – “downfolds” or “concave fold”– Syncline – youngest rocks in the middle
youngold old
Other types of foldsBasins 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:– Energy– Amplitude– Soil strength– Building strength
• Unconsolidated sediment amplifies waves.
Earthquake location