GEOL 101 Earthquakes I &II
GEOL 101 Earthquakes I &II 101-017
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This 4 page Bundle was uploaded by Natalee Stanton on Wednesday March 2, 2016. The Bundle belongs to 101-017 at University of South Carolina taught by in Winter 2016. Since its upload, it has received 22 views. For similar materials see Geology 101-017 in Geology at University of South Carolina.
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Date Created: 03/02/16
GEOL 101 Earthquakes Earthquake – vibration of earth produced by a rapid release of energy Fault large fracture in the earth, locus of the earthquake movement o Faults come at all scales, from tiny fracture to plate boundaries Stress – forces per unit area Compression ( convergent Tension (divergent) Shear (strike – slip) Strain – measure of the amount of deformation Any change in any change in original shape or size of an object in response to stress acting on it I. Elastic rebound Stress builds up in rocks until it exceeds the strength of the rocks and the rocks break Elastic deformation is expressed in rocks between earthquakes Elastic rebound – return of rocks to original shape after an earthquake Focus – site of initial rupture, where the slip initiates during an earthquake Epicenter point on surface above the focus Foreshocks – small earthquakes that occur in the vicinity of, but before, a main earthquake Aftershocks – follow the main earthquake in sequences, and their foci are distributed in and around the rupture The size of the aftershocks depends on the size of the initial large earthquake II. Seismology – study of the propagation of mechanical energy that is released by earthquakes When energy is released, waves of motion move through the rocks surrounding the focus Seismic waves – vibrations form earthquakes that travel through the earth Ground vibrations caused by rocks slipping along opposite sides of a fault Instruments used to measure seismic waves are called seismographs III. Two types of body waves 1. Body waves – travel through the earth a. P waves – primary/ compressional Travel as a series of contractions and expansion, pushing and pulling particles in the direction of their path of travel Highest speeds b. S waves secondary/ shear Travel a little slower Push material at right angles to their path of travel Horizontal and vertical planes Do not pass through liquids 2. Surface waves Travel along the earth’s surface Retrograde elliptical motion Transverse movement a. Most devastating waves GEOL 101 Earthquakes II IV. Seismographs – instruments that record the seismic waves generated by earthquakes Vertical and horizontal ground movements Seismic waves form an earthquakes move out concentrically from the focus. The difference between the arrival times of the P and S waves at a recording station is a function of the distance from the epicenter V. Sizing up Earthquakes Duration of shaking o Up to tens of second Intensity scales (qualitative) o Based on damage and human perception Magnitude scale (quantitative) o Based on amount of energy released Modified Mercalli scale Intensity measures the amount of destruction caused by an earthquake VI. Richter scale – magnitude Measures of the amount of energy released by earthquakes Measures of wave amplitude )logarithm of amplitude Largest earthquake – 9.5 Micro earthquake = less than 2 VII. Damage due to earthquakes Ground movement Fire Tidal waves (tsunami) o Speeds up to 5008—km/hr o Triggered by submarine earthquakes Landslides o All kids of mass waist o Liquefaction – sudden loss Floods Tsunamis – triggered by submarine earthquakes / landslides, and the eruption of submarine volcanoes o Are imperceptible in open ocean o Direct expression of the seismic energy traveling through water Recurrence interval the average time between large earthquakes on a fault Number of years required to accumulate the strain that will be released by fault slip in a future earthquake Calculated form fault slip rate and size of the expected VIII. Earthquake predictions Longer term – imprecise (but possible) Short term – precise (very difficult) o Seismic risks can be reduced, but seismic hazards cannot Seismic risk – describes the potential for earthquake damage over a long term for a specific region Seismic hazard – describes the intensity of seismic shaking and ground disruption over a long time in a specific region Sample Exam Questions The amount of ground displacement is an earthquake is called a ___. a. Dip b. Epicenter c. Focus d. Slip Which set of waves are most likely surface waves? a. Set a b. Set b c. Set c d. Set a, b, and c are all surface waves What is the maximum amount of slip on a fault during an earthquake? a. About 1 meter b. About 20 meters c. About 100 meters d. About 200 meters Earthquakes that originate at depths greater than 10KM are associated with __ plate boundaries. a. Convergent b. Divergent c. Transform d. Convergent, divergent, and transform The Mercalli intensity scale measures ___. a. The amount of destruction caused by an earthquakes b. The amount of slip on a fault plan caused by an earthquake c. The amplitude of the surface waves d. All of the above The average time between large earthquake events along a fault is known as the __ interval. a. Seismic b. Hazard c. Fault slip d. Recurrence
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