Download Earthquake Hazards

Earthquake Hazards
Key ideas:
The amount of damage an earthquake causes
depends on its magnitude, and where it occurs.
Safe building practices can limit loss of life and
damage to property.
Damage from Earthquakes
Earthquakes have a tremendous
destructive power; they strike quickly,
and many, many times unexpectedly.
Within seconds or minutes thousands of
people can die, and buildings turn into
piles of debris.
 Most earthquakes occur at the boundaries
of plate tectonics, or faults. (Faults are
planes along which masses of rocks are
displaced)

Damage from Earthquakes
An earthquake can destroy any man
made structure (buildings, bridges,
roads, etc) in several ways:
1. Ground shaking
2. Aftershocks and fire
3. Tsunamis
Ground Shaking
Ground shaking is caused by the P
waves (the ground is shook side
to side) and the S waves (the
ground is shook up and down).
Most buildings can withstand up
and down shaking, but few will
resist to side to side vibration.
Ground Shaking


Buildings that are built on solid rock have better
chances to remain intact than buildings that are
built on soft rocks. Soft rocks or loose soil can
temporarily take some of the properties of a
liquid during an earthquake. This is called
liquefaction.
For example, San Francisco’s Marina district sits
on a landfill which was used to extend the city
into San Francisco Bay. In the 1989 Loma Prieta
earthquake this landfill liquefied, shaking
buildings off their foundations. Liquefaction
caused great loses in Turkey (1999), Alaska
(1964) Mexico City (1985).
Ground Shaking
Ground Shaking
Aftershocks and Fire

Most earthquakes are followed by a series
of smaller ones, originating close to the
focus of the large earthquake. These
smaller earthquakes are called
aftershocks. Although the magnitude of
these aftershocks is considerably smaller
than the initial earthquake, many still
standing but weakened buildings might
collapse during the aftershocks..
Fires
Imagine that an earthquake affects a
heavily populated area, with miles and
miles of gas pipes running under the
ground. The ground movement breaks
apart the gas lines, and a spark is enough
to start a devastating fire.
 After the 1906 San Francisco earthquake
the fires destroyed about 3000 buildings
and burned about 11 square Km of the
city.

Northridge 1994, the fire after the
quake
San Francisco 1906
Tsunamis
 Tsunamis
are huge waves created
by a displacement of water - a
landslide, volcanic eruption, or
slippage of the boundary between
two of the earth's tectonic plates –
thick slabs of rock that carry the
Earth's continents and seas on an
underground ocean of much hotter,
semi-solid material.
Tsunamis
 Tsunamis
can travel up to 600 mph
(965 km/hour, or 521 knots) at the
deepest point of the water, but slow
down as they get near the shore,
eventually hitting the shore at 30 to
40 mph (48 to 64 km/h or 26 to 35
knots). The energy of the wave's
speed is transferred to height and
sheer force as it approaches the
shore.
Tsunami
Earthquakes Facts
 On
of the most destructive
earthquakes recorded since 1900
occurred on July 27, 1976, in
Tangshan, China, when the official
death count reach 255,000 for a 7.5
magnitude quake. Estimated death
counts, however, reached as high as
655,000.
Earthquake Facts
The highest toll for an earthquake-tsunami
combination since 1900 took place on
December 28, 1908, when a 7.2
magnitude quake struck Messina, Italy,
killing an estimated 70,000 to 100,000
people.
 The deadliest earthquake ever recorded is
believed to have occurred on January 23,
1556, in Shansi, China, killing 830,000
people.

Earthquake facts
 The
worst tsunami in recent history
followed the August 27, 1883, the
eruption of the volcano Krakatau.
The resulting wave swept over the
Indonesian islands of Java and
Sumatra, ultimately killing 36,000
people.
Sources
 U.S.
Geological Survey www.usgs.gov
 Pacific Tsunami Warning Center www.prh.noaa.gov/ptwc
 University of Oregon Seismology
Dept - www.geophys.washington.edu
 http://earthquake.usgs.gov/eqcenter
/recenteqsus/
Earthquake Risk
Where do major earthquakes occur? What
areas in the world are at risk?
To answer this question, let’s remember
that earthquakes are closely related to
movement of plate tectonics or movement
of packs of rocks along faults.
Hence, earthquakes happen everywhere in
the world where these conditions are met.

Earthquake risk in the US
Earthquake risk in the US
 The
west coast of the United States
is the most tectonically active.
 Notice that California has the highest
risk for major earthquakes to
happen. Los Angeles and San
Francisco, two of the largest cities in
the US are close to one of the most
active faults in the world: the San
Andreas Fault.
Europe’s seismic map
South Asia’s seismic map