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
Mountain building by
continental collision
produced boundary
zone extending 1000’s of
km northward from the
nominal plate boundary
at the Himalayan
front.
COLLISION BETWEEN INDIAN AND EURASIAN
PLATES: GPS MOTIONS.
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
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
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
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
Himalayan earthquakes are
caused by the slip of India
beneath Tibet.
India
Himalaya
Tibetan Plateau
India
R. Bilham
Every few hundred years part of
the Himalaya approaches failure
critical stress
Tibet
India
R. Bilham
… and a great earthquake
ruptures the plate boundary.
2-8 m
surface rupture
great earthquake
1.5 m co-seismic
subsidence
Tibet
India
R. Bilham
R. Bilham
R. Bilham
R. Bilham
10 m
M=8.2
8m
M=8
6m
M=7.8
2m
M=7.4
1600
4m
M=7.6
1700
1800
1900
2000
time
The longer we wait the bigger the 'quake.
FUTURE EARTHQUAKE POTENTIAL
Bilham, R., V. K. Gaur and P. Molnar, Himalayan Seismic Hazard, Science, 293, 1442-4, 2001
SLIP DISTRIBUTION
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
USGS
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)
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
STRONG GROUND MOTION DECAYS RAPIDLY WITH DISTANCE
Pakistan M 7.6
earthquake?
0.2 g
Stein & Wysession, 2003
DAMAGE DEPENDS ON BUILDING TYPE
RESISTANT CONSTRUCTION REDUCES EARTHQUAKE RISKS
0.2 g
Damage
onset for
modern
buildings
Pakistan
earthquake?
“Earthquakes don't kill people; buildings kill people."
Coburn &
Spence 1992
MODERN CONSTRUCTION WITHOUT SEISMIC STRENGTHENING
Non-ductile concrete buildings
USGS
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
~ 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.
RETROFIT FOR SEISMIC STRENGTHENING
USGS
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Problem: cost of retrofits can come close to that of razing a building
and starting over. $24 B needed for California hospital retrofits!