Geology Study Guide 2

# Represent rock strained in a ductile manner usually

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Represent rock strained in a ductile manner, usually under compression Axial plane divides a fold into its two limbs Hinge line: surface trace of an axial plane Types : Anticlines : upward-arching folds & Synclines : downward-arching folds Plunging Folds: If the entire fold structure is inclined, the fold is plunging (the hinge line is not horizontal) Varieties of Folds Open : folds in which the limbs dip gently Isoclinal : folds with parallel limbs Overturned : have limbs that dip in the same directions Recumbent : overturned to the point of being horizontal Hanging Wall - side of the fault above the inclined fault surface Footwall - the side below the fault Dip-Slip : movement parallel to the dip of the fault plane Normal: where the hanging wall moves down relative to the footwall Reverse: fault where the hanging wall moves up relative to the footwall Strike-Slip : horizontal movement parallel to the strike of the fault plane Movement that is predominantly horizontal and parallel to the strike of the fault plane Oblique-Slip : both strike-slip & dip-slip components Movement with both vertical and horizontal components Chapter 16 Number of seismic stations need to determine epicenter of an earthquake

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Plotting distances from 3 stations on a map, as circles with radii equaling the distance from the quake, locates earthquake epicenter Elastic Rebound Theory - earthquakes are a sudden release of strain progressively stored in rocks that bend until they finally break and move along a fault P-waves Compressional (longitudinal) Rock vibrates back and forth parallel to the direction of wave propagation Fast (4 to 7 km/sec), primary wave to arrive following earthquake Pass through solids and liquids S-waves Shearing (transverse) Rock vibrates back and forth perpendicular to the direction of wave propagation Slower (2 to 5 km/sec), secondary wave to arrive following earthquake Pass through solids only Surface waves - travel along Earth’s surface away from the epicenter; slowest type of seismic waves Love waves - Side-to-side motion of the ground surface & Pass through solids Rayleigh waves- Ground moves in an elliptical path opposite the direction of wave motion & Extremely destructive to buildings Benioff Zones Distinct earthquake zones that begin at oceanic trenches and slope landward and downward into Earth at an angle of 30°-60° Most intermediate- and deep-focus earthquakes occur in these subduction zones Measures of earthquake size Intensity : measure of earthquake’s effect on people and buildings Modified Mercalli Scale Depends on location of earthquake, strength of structures, subjective memory Magnitude : measure of the energy released during the earthquake Richter Scale Uses amplitude of seismograms Not good for > 7 Moment Magnitude Scale

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