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 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: Energy Amplitude Soil strength Building strength Unconsolidated sediment amplifies waves.

Earthquake location