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Earthquakes and Faults. 1. Faults. A fault is a break or fracture between two blocks of rocks in response to stress. Three types of stresses produce faults Tension Compression Shear One block has moved relative to the other block.
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1. Faults • A fault is a break or fracture between two blocks of rocks in response to stress. • Three types of stresses produce faults • Tension • Compression • Shear • One block has moved relative to the other block. • The surface along which the blocks move is called a fault plane.
2. Components of Faults • STRIKE – a horizontal line along the direction of a fault plane. • DIP – the angle between the fault plane and the horizontal.
2. Components of a Fault • Fault plane – line of intersection between the fault line and the earth’s surface • Fault scarp – cliff of exposed fault plane above the surface of the earth.
2. Components of Faults • Foot wall – bottom layer of the fault. This is where your feet would be located. • Hanging wall – upper layer of the fault, where the lantern would be located. • Terminology comes from mining.
3. Types of Faults • Dip slip faults – movement of the faults is vertical. • Normal fault – footwall moves up, hanging wall moves down. Caused by tension. • Reverse fault – footwall moves downwards. Hanging wall moves upwards. Caused by compression.
3. Types of Faults • Strike Slip Faults – movement is horizontal • Left Lateral - opposing block moves to the left. • Right lateral – opposing block moves to the right.
3. Types of Faults c. Oblique Fault – block moves vertically and horizontally.
4. Earthquakes • An earthquake is a sudden release of energy in the earth’s crust that causes seismic waves. (In other words, the earth shakes.) • The main parts of an earthquake are: • focus – point where the crust moved or slipped • Epicenter – point on the earth’s surface above the focus.
5. Seismic Waves -Shock waves given off by earthquakes • Primary waves – originate from the focus and travel through the earth. They are used to locate the epicenter. • P waves – compression waves, travel faster through solids than liquids, arrive first. • S waves – shear waves; can’t travel through liquids, only half as fast as P waves.
5. Seismic Waves-Shock waves given off by earthquakes • L waves – start when body waves reach the surface at the epicenter. Cause the most damage. • Love waves – horizontal shear • Rayleigh waves – vertical shear • The combined effect of horizontal and vertical shear causes damage.
