University Park ONLY: Formative Assessment 2: 2004 Sumatran Tsunami Analysis

This exercise represents the second part of your formative assessment for this module. The goal of this assignment is to explore the geology behind tsunami generation, how tsunamis travel, and how they impact coastlines.

Instructions:

You will need to read and explore the following websites in order to answer the questions. The first website explores the details of the earthquake, and the second website explores the data produced by the first international team of geoscientists that investigated the impacts of the tsunami while on the ground in northern Sumatra.

• USGS: Tsunamis and Earthquakes: Tsunami Generation from the 2004 M=9.1 Sumatra-Andaman Earthquake
• USGS: Tsunamis and Earthquakes: The 26 December 2004 Indian Ocean Tsunami: Initial Findings from Sumatra

Files

Download the Worksheet (Microsoft Word 2007 (.docx) 132kB Sep7 16)

Download the Rubric (Microsoft Word 2007 (.docx) 16kB Sep7 16)

Questions

1. What was the magnitude of the earthquake that produced the 2004 Sumatran tsunami?
   1. 8.6
   2. 9.1
   3. 7.3
   4. None of these
      
2. What tectonic plates generated the earthquake that produced the tsunami? Be specific by filling in the blanks. The earthquake occurred between the _________ plate (the subducting plate) and the _________ microplate (the overriding plate).
   
3. The earthquake fault zone that ruptured was massive and extended from northwest Sumatra northward to the Andaman Islands. The rupture front for this earthquake was approximately ______ km long and it took only about 8 minutes for the rupture to travel this entire distance. Make sure you watch the video animation of the rupture front as it propagates and moves northward. Follow instructions on the site if you have difficulty with the video as it is rather large and is a .mov file that plays in QuickTime on most browsers, but you can also download the video if need be and play it on another video tool.
   
4. Once you have watched how the seafloor itself moved,then watch the video where geologists have added water back into the simulation to see how the earthquake led to generation of the tsunami wave. Answer the following:

• A) In the film, you will notice that during the earthquake, the seafloor had two areas of subsidence separated by an area of uplift. This combined motion of the seafloor translated to motion of the overlying water column so that water at the ocean's surface immediately above the fault rupture sank above the areas of subsidence and went up above the area of uplift. This produced a 1200 km-long w-shaped (down-up-down) wave. Once it formed, the wave split and moved outward. The wave then led to both local and long-distance wave impacts. The velocity of the tsunami about six minutes after rupture was measured to be about ______ meters/second.
  
• B) Once the primary or first arrival wave began to move, it began to interact in complex ways as the waves _________ (or bent around shallow features and islands), or _______ as it bounced back from shorelines. This generated secondary waves that followed the primary waves in chaotic ways. To illustrate these phenomena, follow the wave in the video as it approached the shoreline in areas of Sumatra, the Nicobar Islands, and even in Phuket, Thailand.
  
• C) Sea height data from JASON-1 satellite data show that in deep water the height of the primary or direct wave (d1 and d2 – double peak waves) was about ____ cm above the resting sea surface.Thus, the total wavelength height from peak to trough was about _____ cm.

1. Compared to other substantial tsunami events, how does the 2004 Sumatra earthquake and tsunami rank relative to magnitude and local tsunami intensity (LTI)? It appears that there are two historical events that are at least comparable. These include the 1960 quake that occurred in _____ and had a magnitude of about 9.5 and a LTI of about 4.9; as well as the ____ ____ earthquake that occurred only four years later, which had a smaller magnitude but a slightly higher LTI. This event was very similar to the 2004 Sumatra LTI.
   
2. Although tsunami wave propagation is usually in all directions, in the case of linear ruptures, the largest and most intense wave generation can be focused in a direction perpendicular to the long axis of the wave front. Thus, tsunami waves produce higher amplitude waves during open-ocean propagation. This phenomena is called tsunami _______. In the 2004 Sumatra tsunami, two prominent high amplitude vectors were generated toward the west and southwest and one was generated toward the northeast directly toward the Malay Peninsula. The westward-moving wave front likely accounted for the extreme impact that hit the island nation of ______ ________ just off the southeast coast of India.The wave front that pushed northeastward accounted for heavy damage in the Aceh region of Sumatra as well as along the Malay Peninsula.
   
3. Switching gears just a little bit... we will now explore data from the field survey conducted from January 20 to 29 in 2005, just about a month after the tsunami occurred. The International Tsunami Survey Team (ITST) included geologists and geoscientists from several countries and spent time in the province of Aceh which was one of the closest and most highly impacted areas. Their main mission was to collect data in the field which is used to ground truth the models being used to forecast tsunamis, and that are used to issue early-warning alerts so that long-term planning efforts can be more effective in limiting future death and loss. The ITST collected information about: 1.______ ______ at the beach and inland, 2. ______ _____, 3. runup elevation, 4. ____ _____, 5. erosion, 6. sediment deposition, and 7. ____________ ___________ all while they were in the area of Lampuuk?
   
4. Geoscientists determine the elevation of tsunami wave heights during field surveys by using laser range finders (or total stations, etc.) to measure and calculate the heights of water stains and debris in trees, or water lines left behind on buildings, or even, sometimes, they can use pollen marks in some cases, or even the elevation of bark stripped off trees. What they found was that west-facing coastlines in the Aceh region were struck by the largest waves, some of which were in excess of _____ meters. In contrast, the north-facing coastline had much lower waves that were about _______ meters high. Nevertheless inundation was much further inland because the area was relatively low-lying in this area.
   
5. Geologic modeling predicted that plate tectonic activity which produced the mega-thrust earthquake would result in changes in elevation of the land's surface. As a result, the international team of scientists was responsible for looking to see if there was evidence of subsidence. In many of the coastal areas, they found it in the form of upright tree trunks and roots that were __________ in seawater. These data suggested that the land had dropped by between ______ to ______ meters. On land, a Japanese scientist and his student found that other areas had subsided by 28 to 57 centimeters when they compared newly surveyed areas to historical topographic maps.
   
6. Although there was a significant amount of erosion directly as a result of the tsunami waves, evidence collected by the science team suggested that subsidence contributed to even more erosion in the months that followed. Although beaches reformed in the weeks following the tsunami, the process of ___________ retreat intensified as the beaches migrated inland by overwash processes. This process severely impacted redevelopment plans for coastal villages as roads and other infrastructure were buried by overwash processes. As shown in Figure 27 (captured by the IKONOS satellite) from the USGS website, the impact of erosion is clearly displayed in the before and after photos. By studying the after photo, it is possible to discern the direction of wave movement through the area. The linear erosional pattern shows that the shoreline moved toward the _____________ relative to the shoreline's position prior to the tsunami (what general compass direction i.e., NW, S, SW, E, etc).