Environmental Geology lecture outline -
"A bad earthquake at once destroys our
oldest associations: the earth, the very emblem of solidity, has moved beneath
our feet like a thin crust over a fluid: one second of time has created
in the mind a strange idea of insecurity, which hours of reflection would
not have produced. .... it is a bitter and humiliating things to see works,
which have cost man so much time and labour, overthrown in one moment. "
Darwin 1845, on his experience of an earthquake in Concepcion, South America
Given difficulty or even inability to predict earthquakes
an alternate approach is simply to learn to live with them. Most critical
in such approach is to build structures so that they can survive an earthquake.
Example of design criteria (the goal):
- < 5.5 RM little or no damage.
- 5.5-7 RM damage should be repairable.
- > 7 RM the building should remain standing, but
may not be repairable.
- cost factor?
- possibility of liquefaction or mass wasting, possible
site may be unacceptable.
- will determine accelerations.
- earthquake hazard maps for expected earthquakes.
- inertial forces: Newton's first law; "Every body
persists in its state or rest or uniform motion in a straight line unless
it is compelled to change that state by forces impressed on it."
- center of mass for a building, tall vs. squat.
- best fit equations for expected accelerations: e.g.
a=(1080 e ** .5M)/ R+25 **1.32, where M is the magnitude and R is the hypocentral
distance. This equations is only good for bedrock in the California region.
Importance of building material and flexibility, and
the concept of cyclic loading.
Importance of building shape:
- height, and resonance, positive versus negative feedback.
- Mexico city earthquake: ground movement had a cycle
of 2 seconds, up to 3 minutes long, 5-20 story buildings resonated.
- swaying vs. twisting and adjoining building sections.
Approaches in increasing safety of building:
- shear walls.
- continuous columns.
- base isolation.
- juncture reinforcement.
Types of building failure typical during an earthquake:
- base column shear.
- column punching.
- column buckling.
- collapse due to asymmetric structural failure.
- collapse due to foundation failure (e.g. liquefaction).
What to do for domestic abodes?
- anchor tall things (e.g. bookshelves) to wall.
- rolling desks for computers.
- shutoff valves for gas.
- bolt house to foundation.
- practice EQ response.
- possible survival kit.
For large pipelines -> shutoff valves connected to
accelerometers, flexible sections were cross fault.
Cost? 5% of original without, 50-100% as retrofit.
- those that support emergency services, including transportation
- those that pose much greater risk if damaged (e.g.
- those that house people who can not care for themselves:
schools, hospitals, nursing homes.
- those important to functioning of society (e.g. courthouses).
Legal codification of earthquake engineering?
- building codes exist in California, Arkansas, Illinois,
Indiana, Kentucky, Mississippi, Missouri and Tennessee. FEMA (Federal Emergency
Management Agency) issues present guidelines.
- zoning: this approach while not usually taken could
be very useful. A 1972 law requires that no structure be within 15 m of
a known active fault (and has a grandfather clause).
- we will likely see a flurry of activity after the
next big earthquake.
In class seismic hazard assessment exercise:
Split up, self-organize into groups of 4 to 5 people to
complete the exercise. Each group willbe given a section of Omaha to cover
The scenario is a Richter magnitude 6.8 has occurred just
S of Omaha. Remember that such an occurrence is unlikely, although not impossible.
Consider the assigned area and think of the following questions
for 5-10 minutes or so:
- What geologic events associated with the earthquake would
be of specific concern?
- Where would structural damage be concentrated? What type
of structural failure might you expect?
- What specific information would be helpful for a more
- To what should emergency response crews be ready to respond?
- What might be major losses?
- How might some of them be prevented?
Write out a list of conclusions on the sheet provided,
and pick a spokesperson to present them.
Try to be realistic, and not over dramatize. The idea is
to scientifically evaluate to the best of your ability.
Areas to consider:
- Eppley airport.
- Florence water treatment plant.
- Sewage treatment plant.
- University Hospital.
- dam sites N and W of Omaha
- old Market area
- Creighton University
H.D. Maher Jr., 3/9/98
Environmental Geology course index.
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