Lab 16:
Earthquake Hazards and Human Risks
Objectives:
- Review types of faults and plate boundaries
- Discuss earthquake terminology
- Differentiate between different body waves
- Discuss reading a seismogram
Introduction:
Earthquakes: shaking and vibrations of the Earth, caused by large releases of energy
- accompany volcanic eruptions, explosions, and movement along faults
Richter scale: logarithmic scale for measuring the strength of earthquakes
Focus (foci): point of origin for an earthquake
- radial expansion from focus
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Hazards: destruction of buildings, breakage of pipes, electrical lines, development of
fissures, change in the course of streams, generation of tsunamis
Strength of wave dependent on material it is passing through
- loose unpacked sediments will shake more, cemented sediments will not
- control high or low damage from the same strength earthquake
Graphing seismic data and locating epicenters:
Epicenter: the point on the Earth’s surface at or above the earthquake’s focus
Seismogram: a record of seismic wave motions obtained at a specific recording station
Body waves: seismic waves that travel through the Earth’s interior
P-wave: primary, travel fastest, arrive first (compressional, push-pull waves)
S-wave: secondary, travel slower, arrive after P waves (shear, side to side waves)
L-wave: love waves, travel slowest, arrive after S waves, travel along the surface
Arrival time: time when each wave reaches a seismic station
Travel time: time from start of wave to measuring destination
Distance from epicenter: distance from seismic station to epicenter
Can calculate rate of travel (rate = distance/time)
Other analyses:
Active faults: faults that can move and generate earthquakes at the present time
First motion: can be identified as compressional or dilational based on P wave
- P-wave up, compression
- P-wave down, dilational
Blind faults: faults that do not emerge at the Earth’s surface