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Comparison of February 2010 Chile,
January 2010 Haiti, and December
2004 Sumatra Earthquakes.
Earthquake
Chile
Haiti
Sumatra
Magnitude*
8.8
7.0
9.0
Focal Depth
35 km
13 km
30 km
Tsunami
“minor”
minor
major
Deaths
~900
~230,000
~226,000
Energy of earthquake ~32 times with each increase in magnitude.
Chile and Sumatra earthquakes are known as “megathrust” earthquakes, that is,
earthquakes that occur on major subduction zones . Such a zone , the Cascadia
Subduction Zone (or Cascadia “Megathrust”) exists off the coast of northern California
through Oregon to southern British Columbia.
*Magnitude = Moment Magnitude (Mw)based on area fault rupture as well as bedrock
rigidity and energy released.
1960 Chile earthquake = 9.5 Mw; 1964 Alaskan = 9.2Mw; 1906 San Francisco = 7.8Mw.
Subduction beneath a volcanic Island Arc such as in Indonesia (left)
and Continental Arc like the Andes (right). Figures from Tarbuck &
Lutgens.
Oblique subduction of the
Australian-Indian Plate
beneath the Eurasian Plate.
Note the presence of a
right-lateral, strike-slip fault
cutting through Sumatra.
The location, date, & Richter
magnitude for large seismic
events are identified on the
map. The December 26,
2004 earthquake also
occurred in association with
the subduction zone off the
west coast of Sumatra.
Figure from the United
States Geological Survey.
Plate Movement: note that the Caribbean Plate moves laterally along the faults which
cut through Haiti. Note the direct subduction of the Nazca Plate beneath South
America. Also note the oblique convergence of the Australian-Indian Plate into the Java
trench. Tarbuck and Lutgens, 2009.
Chile
Sumatra
Samoa
Haiti
Comparison of Earthquake Magnitude and energy released.
Courtesy of USGS.
Location of epicenter and
related aftershocks. Black line
with barbs off the coast
represents the location of the
subduction zone. Purple
triangles represent volcanoes.
Predicted shaking intensity
related to substrate. Note
that shaking intensity is
greatest away from the
epicenter (star symbol) where
the substrate consists of
thicker alluvial material rather
than bedrock.
Megathrust
(subduction
zone)
Long period waves produced in
“megathrust” event results in
greatest damage to taller
buildings (short ones damaged by
short period wavelengths).
Most loss of life was due to
tsunami in coastal areas (>6m =
18’ high). Maritime radio (Chilean
navy) initially said there wouldn’t
be a tsunami which contributed to
great loss of life.
Seismogram from Umqua Community College. Earthquake P-wave recorded at
6:47:20 UTC (6:34:14 UTC in Chile; wave took 13min 6 sec to reach Roseburg).
Roseburg “shook” for ~13 minutes.
ShakeMap: actual
shaking during 8.8
earthquake. Note that
the intensity of shaking
didn’t reach the violent
or extreme (red) part of
the Modified Mercalli
Intensity scale as was the
case in the 7.0 Haitian
earthquake. The reason
was due to the depth of
the earthquake plus the
type of bedrock.
Earthquake occurred in
the “seismic gap” area
between the 1906 (M8.2)
and 1960 (M9.5) quakes.
400 mile long rupture.
Dip of subduction zone as inferred from
aftershocks (orange=shallow; blue=deep)
North American Plate
Caribbean Plate
Earthquake Probability map, pre-2010 Haiti earthquake.
Magenta and green lines
represent left-lateral
strike-slip faults. The
southern part of the
Caribbean Plate is moving
west while the North
American Plate to the
north is moving east (see
red arrows).
Haiti region: Historic Earthquakes, 1990 to January 12, 2010.
Magenta and green lines are lateral faults.
Haiti earthquake: Tuesday, January 12, 2010; 4:53 PM; Magnitude 7.0;
13 km depth (shallow); 25 km WSW of Port-Au-Prince;
Occurred along a left lateral fault between Caribbean and North
American Plate. That fault moves about 7mm/year.
Note “shake intensity”
of this M 7.0 ‘quake as
compared to the M 8.8
‘quake in Chile. Much
more intensity of
shaking in Haiti even
though the ‘quake was
less intense. Why?
Tsunami!
Elevation of the ocean
surface measured by
satellite 2 hours after
the December 26,
2004 earthquake off
the coast of Sumatra.
Figure from U.S.
National Oceanic &
Atmospheric
Administration & U.S.
National Tsunami
Hazard Mitigation
Program.
Elevation of the ocean
surface measured by
satellite 7 hours after
the December 26, 2004
earthquake off the coast
of Sumatra. Figure
from U.S. National
Oceanic & Atmospheric
Administration & U.S.
National Tsunami
Hazard Mitigation
Program.
Around 25-30 minutes
notice to coastal areas
would be available after a
mega-thrust event on the
Cascadia subduction zone.
Comparison:
Loss of life and damage to property was great for the Sumatra ‘quake because of the
magnitude (9.0) of the earthquake, inadequate tsunami warning ,and poor building
construction even though people were cognizant of earthquake dangers.
Loss of life and damage to property was extensive in the Port-Au-Prince, Haiti
earthquake even though the magnitude (7.0) was less because it had been about
200 years since the last devastating ‘quake, the quake was shallow (13 km) hence
earthquake energy wasn’t as dissipated as in deeper ‘quakes, buildings were poorly
constructed, and the main city (Port-Au-Prince) was built on unstable ground.
Loss of life and damage was “minimal” in the Chilean ‘quake even though the ‘quake
was large (8.8) because Chile is a more affluent country able to construct most
buildings according to earthquake standards, earthquakes are frequent (public is
attuned to them and most know what to do), the ground is a bit more stable, and
the earthquake was deeper than in Haiti. Much of loss of life was from tsunami in
the coastal areas as well as collapsed buildings. Chilean government is looking into
likely shoddy construction even in buildings constructed according to earthquake
standards.