Dec 26, 2004 Tsumani Disaster What happened and why

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 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 Earth's outer shell made up of ~15 major rigid plates ~ 100 km thick 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 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, 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. 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 Style of boundary and intraplate deformation depends on direction & rate of motion, together with thermo- mechanical structure

Earth’s Tectonic Plates At boundaries: earthquakes, volcanoes, mountains At boundaries: earthquakes, volcanoes, mountains Each drifting in different directions

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

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 = mm; 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 Earthquakes rupture a patch along fault's surface (like a crack in a mirror). 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. 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. 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 For comparison, a magnitude 5 earthquake would rupture a patch roughly the size of New York City's Central Park

EARTHQUAKE MAGNITUDE 9 One of the largest earthquakes since seismometer invented ~ 1900 Stein & Wysession after IRIS

TSUNAMI - water wave generated by earthquake NY Times

Tsunami generated along fault, where sea floor displaced, and spreads outward Tsunami generated along fault, where sea floor displaced, and spreads outward Reached Sri Lanka in 2 hrs, India in 2-3 Reached Sri Lanka in 2 hrs, India in 2-3

NOAA

Movies

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

The Damage: Banda Aceh, North Shore After Before

Gleekbruk Village

IK Aceh

“CIVILIZATION EXISTS BY GEOLOGICAL CONSENT” The same geologic processes that make our planet habitable also make it dangerous

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 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 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

PLATE TECTONICS IS DESTRUCTIVE TO HUMAN SOCIETY Mt Saint Helens 1980 eruption USGS 1989 Loma Prieta earthquake

Plate boundary volcanism produces atmospheric gases (carbon dioxide CO 2 ; water H 2 O) 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 Source time functions of the earthquake Source time functions of the earthquake Determined by deconvolving synthetics from data for Rayleigh waves Determined by deconvolving synthetics from data for Rayleigh waves Using body waves is problematic due to duration (interference causes by other phases) Using body waves is problematic due to duration (interference causes by other phases) Used both empirical and theoretical Green’s functions Used both empirical and theoretical Green’s functions

Inverse Radon Transform Solve for moment release as a function of time and distance along a fault Solve for moment release as a function of time and distance along a fault