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Earthquake damage
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Ground motion due to seismic waves
Fault rupture of the ground surface
Fire
Liquefaction
Tsunami
Earthquake Risk
• The risk that an earthquake will occur close to where you live
depends on whether or not tectonic activity that causes
deformation is occurring within the crust of that area.
• For the U.S., the risk is greatest in the most tectonically active
area, near the plate margin in the Western U.S.
• The San Andreas Fault which forms the margin between the
Pacific Plate and the North American Plate, is responsible for
about 1 magnitude 8 or greater earthquake per century.
• Historically, large earthquakes have also occurred in the area
of New Madrid, Missouri; Charleston, South Carolina; and an
area extending from New Jersey to Massachusetts.
Earthquake Damage
• Earthquakes don't kill people, buildings do. This
is because most deaths from earthquakes are
caused by buildings or other human construction
falling down during an earthquake.
• Earthquakes located in isolated areas far from
human population rarely cause any deaths.
• Damage from earthquakes can be classified as follows:
1-Ground Shaking - Shaking of the ground caused by the
passage of seismic waves near the epicenter of the
earthquake is responsible for the collapse of most
structures. The intensity of ground shaking depends on
distance from the epicenter and on the type of bedrock
underlying the area.
– In general, loose unconsolidated sediment is subject to
more intense shaking than solid bedrock.
– Damage to structures from shaking depends on the type
of construction. Concrete and masonry structures,
because they are brittle are more susceptible to damage
than wood and steel structures, which are more flexible.
Ground shaking is amplified in unconsolidated materials
• 2-Ground Rupture - Ground rupture only occurs along the fault
zone that moves during the earthquake.
– Thus structures that are built across fault zones may
collapse, whereas structures built adjacent to, but not
crossing the fault may survive.
• 3-Fire - Fire is a secondary effect of earthquakes. Because
power lines may be knocked down and because natural gas
lines may rupture due to an earthquake, fires are often started
closely following an earthquake.
– The problem is compounded if water lines are also broken
during the earthquake since there will not be a supply of
water to extinguish the fires once they have started. In the
1906 earthquake in San Francisco more than 90% of the
damage to buildings was caused by fire.
• 4-Liquefaction - Liquefaction is a processes that
occurs in water-saturated unconsolidated sediment
due to shaking.
• In areas underlain by such material, the ground
shaking causes the grains to loose grain to grain
contact, and thus the material tends to flow.
5-Tsunamis - Tsunamis are giant ocean waves that
can rapidly travel across oceans. Earthquakes that
occur along coastal areas can generate tsunamis,
which can cause damage thousands of kilometers
away on the other side of the ocean.
Tsunamis
• Tsunamis, or seismic sea waves
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Earthquakes under the ocean
Destructive waves called “tidal waves”
Result from “push” of fault block
In open ocean height is > 1 meter
In shallow coast water wave can be > 30
meters
• Very destructive
Formation of a tsunami by displacement of the
ocean floor
The speed of a wave moving across the ocean correlates
with the ocean depth.
Tsunamis
Indonesia, 1992
Alaska, 1964
Niigata, 1964
Tsunami travel
times (in hrs) to
Hawaii from
various points in
the Pacific Basin
6-Rapid Mass-Wasting Processes - In
mountainous regions subjected to earthquakes
ground shaking may trigger rapid mass-wasting
events like rock and debris falls, rock and debris
slides, slumps, and debris avalanches.
Eartquake’s Forecasting
• Historic and prehistoric records of past major
earthquakes should reflect that periodicity,
allowing one to forecast the time window for the
next earthquake.
Major seismic gaps (Stretches with little or no seismic activity)
in the Western Hemisphere
Studies of the dates of large historic and prehistoric earthquakes along major
Fault zones have suggested that they may be broadly periodic, occurring at
more or less regular interval.
On average, major
earthquakes occur
every 20 yrs, and
the last one in 1966
The Earthquake Cycle
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Quiescence, building up of energy.
Foreshocks minutes to days before main shock.
Main shock, largest event in the cycle.
Aftershocks occur in the following days to weeks.
Adjustment activity may last years to centuries, and cover the
area surrounding the main shock.
• Quiescence again, lasting much longer than the other phases
(hundreds of years in active area to millions of years).
• The cycle is not periodic (earthquakes do not occur after equal
time periods) because stress build-up at any given site is affected
by the earthquake activity in the surrounding area.
Fluid Injection to minimize major
Earthquakes
• The idea is that, because increased pore pressure
decreases friction and shear strength, facilitating slip
along fault zones, faults “lubricated” by fluid injection
could release built-up stress by slipping. However, in
locked fault zones along which considerable stress had
already built up, the result might be a major earthquake
induced by human activity. There is also no simple
correlation between pore pressure and resultant
earthquake intensity. The method might best be applied,
at least initially, to sections of faults not long quiescent,
so that the stress could be released continually before it
builds to dangerous levels.
Sand boils are caused by soil losing its internal cohesion
(friction between soil particles) during the strong shaking of a large
earthquake, a process called liquefaction
How to Avoid Earthquake
Hazards
• Primary earthquake-related hazards include: landslides
(avoid areas historically prone to landslides; undertake
slope-stability studies); ground motion (stay away from
fault zones, and especially filled land near fault zones;
also, bedrock is safer material to build on than is
unconsolidated sediment; alternatively, try earthquakeresistant structural designs); tsunamis (listen for
warnings; avoid coastal areas); liquefaction (avoid areas
known to be prone to it); coastal flooding from tectonic
movements (not much can be done in this case). A
secondary hazard is fire (build valving systems into
pipelines and water lines to minimize the risks).