Page 443 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

taBLE 13.2.1 Summary of Three Major Earthquakes in 2010 and 2011
Location, Date, and Local time
Moment Magnitude*
Focus Depth
Epicentre Distance to Nearest City
Port-au-Prince, Haiti, M 7.0 13 km 15 km southwest from 222 750 killed, 300 000 injured, $25 billion Jan. 12, 2010, 4:53 p.m. Ocean Port-au-Prince 1.3 million displaced
Chapter 13 Tectonics, Earthquakes, and Volcanism 407
Human Dimension
Damage Cost (USD)
Maule, Chile, M 8.8 35 km 95 km from Santiago 521 killed, 12 000 injured, $30 billion Feb. 27, 2010, 3:34 a.m. Ocean 800 000 displaced
Tohoku, Honshu, Japan, M 9.0 32 km 129 km from Sendai 16 000 deaths, 6100 injured, ~$325 billion (maybe Mar. 11, 2011, 2:46 p.m. Ocean and 2600 missing as high as $500 billion)
*Reported by USGS.
150 km snapped and was abruptly lifted as much as 80 m, the ocean was dis- placed above it. This disturbance caused the tsunami, in which the largest wave averaged 10 m along the coast of Honshu (Figure 13.2.1d). Where it entered narrow harbours and embayments, wave height reached nearly 30 m. Although Japan’s tsunami warning system sent out immedi- ate alerts, there was not enough time for evacuation. This event illustrates the damage and human cost associated with an earthquake and tsunami, even in a country with strict and extensive earth- quake preparedness standards.
Faulting and Plate interactions
The Chile and Japan quakes both oc- curred along subduction zones. Along the coast of Chile, the Nazca plate is moving eastward beneath the westward- moving South American plate at a rela- tive speed of 7 to 8 cm per year. This is the same subduction zone that produced the M 9.6 that hit Chile in 1960, the larg- est earthquake of the twentieth century. Off the coast of Japan, the Japan Trench defines the subduction zone in which the westward-moving Pacific plate is pulled beneath the North American plate at a rate averaging 8.3 cm per year. Several microplates form this plate boundary, vis- ible on the ocean-floor map that begins this chapter, and in Figure 12.19.
The Haiti earthquake involved more complex fault interactions. Scientists first thought that this earthquake occurred along a 50-km section of the Enriquillo– Plantain garden strike-slip fault, where the Caribbean plate moves eastward relative to the North American plate’s westward shift. After extensive analysis,
from slip along multiple faults, primarily along a previously unknown subsurface thrust fault.
Key data for the analysis came from radar interferograms, remotely sensed images produced by comparing radar topography measurements before and after earthquake events. The Haiti inter- ferogram shows surface deformation in the area of the fault rupture; the narrow rings of colour represent contours of ground motion (Figure 13.2.2). Overall, the earthquake displaced Léogâne
upward about 0.5 m. Scientists found no evidence of surface rupture after a field survey along the Enriquillo fault. Because the slip was not near the surface, scien- tists believe that strain is continuing to accumulate, making future rupture at the surface likely.
For a listing and details of the 10 big- gest earthquakes in history, including the Chile (ranked 6th) and Japan (ranked 4th) events, go to earthquake.usgs.gov/ earthquakes/world/10_largest_world.php.
74°W ATLANTIC OCEAN 20°N
Area of image
19°N
18°N Caribbean Sea 74°W 73°W 72°W
experts now think that the quake resulted from topographic surveys before and after the earthquake. [NASA/JPL/JAXA/METI.]
HAITI
NORTH AMERICAN PLATE
CARIBBEAN PLATE
Léogâne
HAITI
▲Figure 13.2.2 Radar image of Haiti earthquake faults. Synthetic-aperture radar image shows ground deformation near Léogâne, west of Port-au-Prince; narrow bands of colour are contours, each representing 11.8 cm of ground motion. This radar interferogram combines data
Port-au-Prince
0 5
10 KILOMETRES
Enriquillo Fault