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GEOL 106 Lecture Notes - 1989 Loma Prieta Earthquake, Acapulco, Seismic Wave

Geological Sciences and Geological Engineering
Course Code
GEOL 106

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Readings from textbook
Chapter 2 Earthquakes and From chapter 9 – Section on
Tsunami Pages 259 to 267
What exactly causes the damage?
1. Surface Faulting
o Structures on the fault will be disrupted by the tearing
o So don’t build right on ACTIVE faults
But people do! Eg. San Francisco, and other parts
of San Andreas fault
2. Ground Shaking
o this is generally the greatest threat to buildings and
o in a big earthquake, the shaking can be severe even
100’s ok kilometers away from the epicenter
o The amount of shaking also depends on the nature of
the soil/rocks in the area
Soft soils (eg. Clays ) shake more than ….
Stiff soils (eg sand) which skakes more than….
EG, Loma Prieta earthquake near San
Francisco (1989)
EG. 1985 Earthquake near Acapulco, Mexico
In general
1. The closer you are to the quake, the greater the damage …
2. The greater the magnitude of the quake, the greater the
But-> this is modified by natural and anthropogenic conditions
Natural : nature of soils/rocks
Anthropogenic: nature of the structures that we build
Material Amplification Effect
Seismic waves: velocity changes when going from one
medium to another
As P and S waves slow, some of their energy is transferred to
surface wave motion (ie, increased shaking)
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