EARTHQUAKE AND TSUNAMI

BASIC CONCEPTS: THERMAL EVOLUTION OF OCEANIC LITHOSPHERE Warm mantle material upwells at spreading centers and then cools Because rock strength decreases with temperature, cooling material forms strong plates of lithosphere Cooling oceanic lithosphere moves away from the ridges, eventually reaches subduction zones and descends in downgoing slabs back into the mantle, reheating as it goes Lithosphere is cold outer boundary layer of thermal convection system involving mantle and core that removes heat from Earth's interior, controlling its evolution Stein & Wysession 2003

Gordon & Stein, 1992 INDIAN PLATE MOVES NORTH COLLIDING WITH EURASIA

COMPLEX PLATE BOUNDARY ZONE IN SOUTHEAST ASIA Northward motion of India deforms all of the region Many small plates (microplates) and blocks Molnar & Tapponier, 1977

India subducts beneath Burma microplate at about 50 mm/yr Earthquakes occur at plate interface along the Sumatra arc (Sunda trench) These are spectacular & destructive results of many years of accumulated motion

Japan 2011

INTERSEISMIC: India subducts beneath Burma microplate at about 50 mm/yr (precise rate hard to infer given complex geometry) Fault interface is locked EARTHQUAKE Fault interface slips, overriding plate rebounds, releasing accumulated motion HOW OFTEN: Faults aren’t exactly periodic for reasons we don’t understand (Video) Stein & Wysession, 2003

TWO VIEWS OF THE PART OF THE SUMATRA SUBDUCTION ZONE THAT SLIPPED Seismogram analysis shows most slip in southern 400 km Aftershocks show slip extended almost 1200 km C. Ji ERI

Earthquakes rupture a patch along fault's surface. Generally speaking, the larger the rupture patch, the larger the earthquake magnitude. Initial estimates from the aftershock distribution show the magnitude 9.3 Sumatra- Andaman Islands Earthquake ruptured a patch of fault roughly the size of California For comparison, a magnitude 5 earthquake would rupture a patch roughly the size of New York City's Central Park.

TSUNAMI - water wave generated by earthquake NY Times Click Ship click vid

NOAA

IN DEEP OCEAN tsunami has long wavelength, travels fast, small amplitude - doesn’t affect ships AS IT APPROACHES SHORE, it slows. Since energy is conserved, amplitude builds up - very damaging

Because seismic waves travel much faster (km/s) than tsunamis, rapid analysis of seismograms can identify earthquakes likely to cause major tsunamis and predict when waves will arrive TSUNAMI WARNING Deep ocean buoys can measure wave heights, verify tsunami and reduce false alarms LINK DARTLINK DART

Tsunami Warning Centers Hawaii and Alaska When EQ considered capable of generating tsunami, send warning with estimated arrival time  Once tsunami hits somewhere, tsunami watch established to monitor tide gauges and ocean buoys

Tsunami Monitoring Systems Locations of NOAA’s National Data Buoy Center (NDBC) DART stations comprising the operational network.

Tsunami Warning When warning is issued – low lying areas are evacuated U.S. Coast guard issues warnings over marine frequencies Some places have sirens

Tsunami wave propagation characteristics – note that as water depth becomes smaller, waves slow down, become shorter wavelength, and have larger amplitude When the water is 10 m deep, what is the separation of the waves in minutes? NOAA

Damage in Banda Aceh