Tsunami aav lecture

Information about Tsunami aav lecture

Published on February 14, 2008

Author: Rainero

Source: authorstream.com

Content

Dec 26, 2004 Tsumani Disaster:  Dec 26, 2004 Tsumani Disaster What happened and why The Source: A Great Earthquake:  The Source: A Great Earthquake In order to understand what happened and why it happened, we must understand the Earth, its processes, and the nature of waves: Physical Geology What happened A very large earthquake (great earthquake) moved the ocean floor The movement of the ocean floor, displaced a large amount of water The water wave generated by the displacement propagated throughout the ocean The wave, similar to a very fast tide, overcame many low lying areas Plate tectonics:  Plate tectonics Earth's outer shell made up of ~15 major rigid plates ~ 100 km thick Plates move relative to each other at speeds of a few cm/ yr (about the speed at which fingernails grow) Plates are rigid in the sense that little (ideally no) deformation occurs within them, Most (ideally all) deformation occurs at their boundaries, giving rise to earthquakes, mountain building, volcanism, and other spectacular phenomena. Style of boundary and intraplate deformation depends on direction & rate of motion, together with thermo-mechanical structure Earth’s Tectonic Plates:  Earth’s Tectonic Plates At boundaries: earthquakes, volcanoes, mountains Each drifting in different directions The Earthquake:  The Earthquake 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 Slide6:  INTERSEISMIC: India subducts beneath Burma microplate at about 50 mm/yr Fault interface is locked EARTHQUAKE (COSEISMIC): Fault interface slips, overriding plate rebounds, releasing accumulated motion HOW OFTEN: Fault slipped ~ 10 m = 10000 mm; 10000 mm / 50 mm/yr = 200 yr Longer if some slip is aseismic Faults aren’t exactly periodic for reasons we don’t understand Stein & Wysession, 2003 Displaces Water in Ocean The Size: Magnitude 9:  The Size: Magnitude 9 Earthquakes rupture a patch along fault's surface (like a crack in a mirror). Generally speaking, the larger the rupture patch, the larger the earthquake magnitude. Initial estimates from the aftershock distribution show the M 9.0 Sumatra-Andaman Islands Earthquake ruptured a patch of fault roughly the size of California, and modeling seismic waves show that most of the slip occurred in the southern 400 km of the patch. For comparison, a magnitude 5 earthquake would rupture a patch roughly the size of New York City's Central Park Slide8:  EARTHQUAKE MAGNITUDE 9 One of the largest earthquakes since seismometer invented ~ 1900 Stein & Wysession after IRIS Slide9:  TSUNAMI - water wave generated by earthquake NY Times Slide10:  Tsunami generated along fault, where sea floor displaced, and spreads outward Reached Sri Lanka in 2 hrs, India in 2-3 Slide11:  NOAA Movies:  Movies Slide13:  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 Slide14:  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 The Damage: Banda Aceh, North Shore:  The Damage: Banda Aceh, North Shore After Before Gleekbruk Village:  Gleekbruk Village IK Aceh:  IK Aceh Slide18:  “CIVILIZATION EXISTS BY GEOLOGICAL CONSENT” The same geologic processes that make our planet habitable also make it dangerous Can We Predict Earthquakes?:  Can We Predict Earthquakes? Because little is known about the fundamental physics of faulting, many attempts to predict earthquakes searched for precursors, observable behavior that precedes earthquakes. To date, search has proved generally unsuccessful Best to develop hazard reduction United States Geological Survey National Earthquake Hazard Reduction Research Program Seismic Networks: Volcanic and Eartquake Warning Systems National Oceanic and Atmospheric Administration (NOAA) National Warning Centers Pacific Tsunami Warning Center in Ewa Beach, Hawaii The Alaska Tsunami Warning Center ATWC) in Palmer, Alaska Slide20:  PLATE TECTONICS IS DESTRUCTIVE TO HUMAN SOCIETY Mt Saint Helens 1980 eruption USGS 1989 Loma Prieta earthquake Slide21:  Plate boundary volcanism produces atmospheric gases (carbon dioxide CO2 ; water H2O) needed to support life and keep planet warm enough for life ("greenhouse" ) May explain how life evolved on earth (at midocean ridge hot springs) Plate tectonics raises continents above sea level Plate tectonics produces mineral resources including fossil fuels BUT PLATE TECTONICS IS ALSO CRUCIAL FOR HUMAN LIFE Press & Siever Understanding the Source:  Understanding the Source Source time functions of the earthquake Determined by deconvolving synthetics from data for Rayleigh waves Using body waves is problematic due to duration (interference causes by other phases) Used both empirical and theoretical Green’s functions Inverse Radon Transform:  Inverse Radon Transform Solve for moment release as a function of time and distance along a fault

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