Earthquake research on coral reefs, Sumatra - Talk by Prof Sieh, NTU-SST Programme, June 2012


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  • So here is a summary of the past decade of big megathrust ruptures offshore Sumatra, as well as a summary of how our understanding has progressed, thanks to GPS geodesy and coral measurements.
  • Do sample the fossil corals, we cut big slabs out of them with a chain saw that is equipped to cut under water. Good exercise for an earthquake scientist!
  • A map-view history of what we call “super-cycles” of rupture on this section of the Sumatran megathrust
  • Earthquake research on coral reefs, Sumatra - Talk by Prof Sieh, NTU-SST Programme, June 2012

    1. 1. Earthquake Research on the Coral Reefs of SumatraKerry SiehNTU-SST FlagshipProgram4 June 2012
    2. 2. The earthquake cycle and generation of tsunamis
    3. 3. Stratigraphy and sedimentology tell us about past tsunami. Here we are studying the2004 tsunami sands on Nias island, Sumatra
    4. 4. We can see four separate waves of the tsunami and an older tsunami sand layer aswell
    5. 5. Along the coast of Aceh, Sumatra, is a cave that contains a remarkable record oftsunami over >10,000 years
    6. 6. We collect the layers to determine their age and to determine whether they are from a tsunami
    7. 7. >10,000- Years BPyear record 2004 of sand 2,900-3,200 deposition 4,800-5,300in a coastal 3,210-3,900 cave about 4,900-5,30060 south of Banda 9,500-10,300 Aceh. Sands areinterbedded Tsunami with bat sand beds guano. Dates (before AD 1950) are from
    8. 8. Recall that the islands get dragged down between earthquakes
    9. 9. Here’s an example of ongoing submergence on one of the
    10. 10. Nias island sinking before March 28, 2005 earthquakeThe island rose about2.5 meters during the earthquake
    11. 11. Old high tide Old low tide Examples from Nias, Simeulue and the Banyak islandsOld high tideNew high tide
    12. 12. We use the Global Positioning System (GPS) to measure tectonic deformationConstructing a GPS station on a village green on a Sumatran island
    13. 13. If you want goodphysical exercise inyour profession, earthscience is a goodoption!
    14. 14. A GPS station on a mountaintop at the Equator
    15. 15. We now have48 GPS The Sumatranstations GPS ArraythroughoutSumatra.We callstations 48 this installednetwork theSumatran 2002 between and 2011GPS Array, orSuGAr
    16. 16. Here is an example of what it showed, during a M 7.8 Progression of the 25 Oct 2010 Tsunami earthquake, from the SuGArearthquake in October 2010 An arrow this long means 10 centimeters of horizontal motion Time since the beginning of the
    17. 17. Model forfault slipbased on GPSand tsunamifield surveydataThe piece of megathrustthat ruptured was ~30-kmwide, 100-km long andvery close to the trenchwith max slip of ~10metersBased upon 24-hour solutions scaled by the 1-Hz data Hill and others, in press
    18. 18. This is our interpretation of the deformed layers above themegathrust, from data collected by the oil industry.
    19. 19. We also measureuplift and subsidence using coralsSea-level before 26 Dec 2004 uplift Sea-level after 26 Dec 2004
    20. 20. From GPS and coral measurements we could tell from Rich Briggs, after what part ofthe megathrust ruptured to produce the great earthquake et al 2006 Briggs and tsunami of 2005
    21. 21. Southern extent ofthe Dec 2004 ruptureIn the monthsfollowing December2004, we warned thatthese regions werenow at increased riskfrom greatearthquakes andtsunami
    22. 22. This sectiondid, indeed, fail justa few months laterAll that was now leftwas this onesection, which werefer to as theMentawai patch
    23. 23. A portion of this lockedpatch (in red) broke in a rapid series of 3 large earthquakes on Sept 12-13, 2007Another little patch (in yellow) broke in October 2010 and produced a deadly tsunami
    24. 24. How were we able tomake these forecasts?When will the rest ofthe Mentawai patchfail?
    25. 25. We use ancient corals and the SuGAr to makeforecastsThis coral died due to uplift during a big earthquake in
    26. 26. Here’s another one that records the great earthquakes of1797 and 1833.We know the ages of the corals from radiometric dating, usingthe decay of Uranium to Thorium
    27. 27. NEXT
    28. 28. Other than just curiosity,is a Padang thereare good reasons to studycity sprawlinggeohazards such as about ofearthquakes. 800,000 people. Most of theHere is Padang, a town is less city of than 10 metersnearly a million people, sea level above on thewest coast of Sumatra.We are making forecasts,based on physics(hydrodynamics) andengineering of the effects ofthe coming tsunami on the city
    29. 29. Your profession as a “medium”
    30. 30. Sailors and staff playing cards after a hard days work on the reef
    31. 31. Plenty of time to play the guitar
    32. 32. Collecting a few coconuts for a lunch drink
    33. 33. Five good reasons do understand earthquakes and tsunami