Geology Department

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Geology 110 Syllabus

EARTHQUAKES

 

Geological Time Hydrogeologic Cycle

 

I. SEISMOLOGY--study of earthquakes

A. Earthquakes produce earth waves
1. Two types of earth waves
a. Body wave-propagate through earth's interior
    - P-wave (push-pull)-- compressional wave

      * Compressed and rarefied

      * Pass through any medium- solid, liquid, or gas
      * Most energetic

    - S-wave or shear wave--particles move at right angles to direction of propogation

      * Liquids and gases can not be sheared
b. Surface wave--propagates along earth's surface
    - Particle movement is mainly up and down
2. Why are earthquake waves able to travel through rocks?

II. SEISMOGRAPH--instrument used to monitor earthquakes

A. 3 seismographs compose a seismic station
1. Vertical movements

2. Horizontal movements, N-S

3. Horizontal movements, E-W
B. Seismic network--numerous seismic stations worldwide

C. Regular travel schedule is disrupted at 11,000 km from epicenter

III. Earthquake scales

A. Intensity--measure of damage produced by an earthquake
1. Mercalli Scale (1902)--intensity scale, considers all type of construction, I-XIII based on obervations, U.S.G.S uses this
a. New Madrid, 1811
B. Magnitude--actual measure of the energy generated by an earthquake
2. Richter Scale--madnitude of an earthquake, based on computations of the amount of motion of certain waves

log scale Richter # each Richter #
represents 10x
the amount of
ground motion of the
next lower #
101=10 1
102=100 2
103=1,000 3
C. Rough comparison
Mercalli   Richter   Results
I 0-3 usually not felt by people
II-III 3-4 felt by people
IV-VI 4-5.5 wakes you, trees way, cars rock
VII 5.5-6 plaster wall crack, window crack
VIII-IX 6-7 weaker houses collapse
X-XI 7-8 few building remains, bridges collapse
XII 8.3 everything distroyed
* magnitude 5 ~ 1st atomic bomb

IV. EARTHQUAKE CAUSE

A. Sudden rupture of rocks stressed beyond their strength

B. Elastic rebound hypothesis

C. San Andreas model
1. Foci are < 15 km deep

V. ASSOCIATED FEATURES

A. Tsunami ("tidal waves")--large sea wave generated by displacement of the ocean floor

B. Liquefaction-- process of changing soil and unconsolidated sediments into a watery mixture immediately following and earthquake

VI. CONTROL OF EARTHQUAKES

A. Rocky Mtn. Arsenal, Denver, CO
1. Injection wells

2. Lab studies show the same thing