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