Journal assignment: The odds that Omaha will suffer the effects of a good
sized earthquake are low, but not zero. Use what you have learned
in class and in your readings, and from what you can learn from
the web, and what you know of Omaha to explore the following question.
What distinct areas and/or facilities might suffer the greatest
amount of damage during such a rare earthquake and why?
Peruse for two hours the USGS
site on earthquakes. Focus on the general info and hazards
"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
Gambling with nature.
- The definition of risk.
- Do we know the odds?
- Defining the gamble - for natural hazards,
what size event do we prepare for?
What happens during an earthquake?
as a geologic event: it is a much more complex
event than many initially imagine.
- the nature of stick-slip vs. creep
behavior along geologic faults.
- an earthquake is a slip event on a fault
- earthquake size is a function of the fault
surface area that moves during an earthquake.
- release of seismic waves.
- surface versus
- important aspects of surface waves from an
environmental perspective: associated vertical and horizontal
ground accelerations, duration and period of shaking.
- associated surface geologic events:
- for big earthquakes - grand breakage.
of wet sediments.
- mass wasting.
- seiche waves.
- permanent land elevation or subsidence.
- alteration of ground water flows.
as a human and engineering event:
- buildings are damaged, can collapse.
- dependent on type of building material (flexibility
good -rigidity bad).
- dependent on natural resonant frequency
and the period of the earthquake ground motion.
- gas and electrical lines break and fires
- roads and bridges can be destroyed interrupting
- water mains and sewage lines break potentially
leading to outbreaks of disease.
- structures along the shoreline can be wiped
out by tsunamis.
- panic and looting.
some famous case histories:
- 1811-1812 New Madrid earthquakes. USGS
- 1904 San Fransisco earthquake. USGS
- "The Marina in 1906 was a salt lagoon.
... in 1914 San Francisco planned its Panama-Pacific exposition
.... The site chosen for the Exposition was the lagoon. To fill
it up, fine sands were hydraulically pumped into it and mixed
with miscellaneous debris. .... Nearly a minute has passed since
the rock slipped at the hypocenter. In San Francisco, the tremors
this time will last fifteen seconds. As the ground violently
shakes and the sand boils of the Marina discharge material from
the liquefying depths, the htings they spit up include tarpaper
and bits of redwood - the sharred remains of houses from the
earthquake of 1906." McPhee, Annals of the Former World,
- 1964 Good Friday Alaska earthquake.
January 17, 1995, case history.
- 6.9 on Richter scale.
- 10 km deep hypocenter, local ground motion
of 5 m, 40 km long rupture.
- 5,480 fatalities, 94,900 injured; $100 billion
- tectonic setting -> arc-subduction complex.
Geophysical Union site on Kobe.
Can earthquakes be predicted?
Types of predictions and forecasts.
Predicting by precursors.
Forecast by past history - this way to fractals.
The Meers fault in Oklahoma - a different type
of earthquake behavior?
Real time warnings?
- in place for tsunamis, but many false positives.
- possible for facilities farther away from
be prepared for and how?
Two basic approaches: earthquake engineering
and earthquake education.
What are critical facilities?
- < 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.
- zoning. For these and other purposes earthquake
hazard maps are crucial.
- reinforcement of junctures.
- shear walls - a spine of strength.
- base isolation.
- accelerograph cutoff devices (for gas lines
to bullet trains).
- cost - much more to retrofit.
- how should you prepare your house, business
for an earthquake.
- computers on rolling desks (simple form of
- what should you do and not do during an earthquake.