COMPLEX PLATE BOUNDARY ZONE IN SOUTHEAST ASIA

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COMPLEX PLATE BOUNDARY ZONE IN SOUTHEAST
ASIA Northward motion of India deforms large
region Many small plates (microplates) and blocks
Davidson p304
Molnar Tapponnier, 1977
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COLLISION BETWEEN INDIAN AND EURASIAN PLATES GPS
MOTIONS.
Mountain building by continental collision
produced boundary zone extending 1000s of km
northward from the nominal plate boundary at the
Himalayan front. Total plate convergence taken
up several ways. About half (20 mm/yr) occurs
across locked Himalayan frontal faults such as
the Main Central Thrust These faults are part of
the interface associated with the underthrusting
Indian continental crust, which thickens crust
under high Himalayas.
Larson et al., 1999
Larson et al., 1999
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COLLISION BETWEEN INDIAN AND EURASIAN PLATES GPS
MOTIONS.
GPS data also show along-strike motion behind the
convergent zone, in the Tibetan Plateau,
presumably because the uplifted and thickened
crust spreads under its own weight. Extension
is part of a large-scale process of crustal
"escape" or "extrusion" in which large fragments
of continental crust are displaced eastward by
the collision along major strike-slip faults.
Larson et al., 1999
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COLLISION BETWEEN INDIA AND EURASIA PLATES
EARTHQUAKES Large destructive thrust earthquakes
reflect convergence on Himalayan frontal faults
such as Main Central Thrust Normal faulting
earthquakes occur behind convergent zone in the
Tibetan Plateau, due to along strike extension
from gravitational collapse Strike slip
earthquakes occur further north
Ni and Barazangi, 1984
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Collision process is thought to involve a complex
interplay between forces due directly to the
collision, gravitational forces due to the
resulting uplift and crustal thickening, and
forces from the resulting mantle flow Crustal
"escape" or "extrusion" in which large fragments
of continental crust displaced eastward by the
collision along major strike-slip faults has been
modeled assuming that India acts as a rigid block
indenting a semi-infinite plastic medium (Asia),
giving rise to a complicated faulting and slip
pattern. Also modelled numerically as thin
viscous sheet flow
Tapponnier et al., 1982
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Himalayan earthquakes are caused by the slip of
India beneath Tibet.
Tibetan Plateau
R. Bilham
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Every few hundred years part of the Himalaya
approaches failure
critical stress
Tibet
R. Bilham
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and a great earthquake ruptures the plate
boundary.
great earthquake
Tibet
R. Bilham
9
R. Bilham
10
R. Bilham
11

R. Bilham
India/Tibet convergence (m)
convergence rate 18 mm/yr
2000
1900
1800
1700
1600
time
The longer we wait the bigger the 'quake.
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FUTURE EARTHQUAKE POTENTIAL
Bilham, R., V. K. Gaur and P. Molnar, Himalayan
Seismic Hazard, Science, 293, 1442-4, 2001
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(No Transcript)
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SLIP DISTRIBUTION
USGS
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The death toll now stands at 30,800 in the
aftermath of a massive earthquake in Pakistan, as
nations around the world try to get aid to the
northern parts of the devastated country and to
Kashmir. "This could get very close to tsunami
levels," an Islamic Relief spokesman said. "It's
horrific. It really is terrible." Many survivors
have been wading through mountains of rubble in
search of survivors, food and clean water.
An aerial view of the town of Balakot. (NY Times)
Two members of the British Rescue and
Preparedness in Disasters team, center, inspect
the site in Islamabad where a 10-story apartment
building collapsed a day earlier. (CNN)
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STRONG GROUND MOTION DECAYS RAPIDLY WITH DISTANCE
Pakistan M 7.6 earthquake?
0.2 g
Stein Wysession, 2003
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(No Transcript)
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DAMAGE DEPENDS ON BUILDING TYPE RESISTANT
CONSTRUCTION REDUCES EARTHQUAKE RISKS
Pakistan earthquake?
0.2 g Damage onset for modern buildings
Coburn Spence 1992
Earthquakes don't kill people buildings kill
people."
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MODERN CONSTRUCTION WITHOUT SEISMIC STRENGTHENING
Non-ductile concrete buildings
USGS
40,000 in California. 8,000 are schools,
including 239 in the Los Angeles Unified School
District. Downtown Los Angeles has about 500 of
the buildings.
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RETROFIT FOR SEISMIC STRENGTHENING
USGS
Problem cost of retrofits can come close to that
of razing a building and starting over. 24 B
needed for California hospital retrofits!