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COMPLEX PLATE BOUNDARY ZONE IN SOUTHEAST ASIA Northward motion of India deforms large region

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. COLLISION BETWEEN INDIAN AND EURASIAN PLATES: GPS MOTIONS.

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COMPLEX PLATE BOUNDARY ZONE IN SOUTHEAST ASIA Northward motion of India deforms large region

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  1. 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

  2. COLLISION BETWEEN INDIAN AND EURASIAN PLATES: GPS MOTIONS. Mountain building by continental collision produced boundary zone extending 1000’s 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

  3. 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

  4. 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

  5. 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

  6. India Himalaya India Himalayan earthquakes are caused by the slip of India beneath Tibet. Tibetan Plateau R. Bilham

  7. India Every few hundred years part of the Himalaya approaches failure critical stress Tibet R. Bilham

  8. 2-8 m surface rupture 1.5 m co-seismic subsidence India … and a great earthquake ruptures the plate boundary. great earthquake Tibet R. Bilham

  9. R. Bilham

  10. R. Bilham

  11. 10 m M=8.2 8m M=8 6 m M=7.8 4 m M=7.6 2 m M=7.4 R. Bilham India/Tibet convergence (m) convergence rate 18 mm/yr 1600 1700 1800 1900 2000 time The longer we wait the bigger the 'quake.

  12. FUTURE EARTHQUAKE POTENTIAL Bilham, R., V. K. Gaur and P. Molnar, Himalayan Seismic Hazard, Science, 293, 1442-4, 2001

  13. SLIP DISTRIBUTION USGS

  14. 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)

  15. STRONG GROUND MOTION DECAYS RAPIDLY WITH DISTANCE Pakistan M 7.6 earthquake? 0.2 g Stein & Wysession, 2003

  16. 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."

  17. 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.

  18. 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!

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