Historical Earthquakes and Uplift/Subsidence of Sumatra from Coral Growth Rings - Introductory Version
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This resource was reviewed as part of the May 2009 MARGINS Mini-Lesson Workshop. Each activity received verbal feedback from two participants who had reviewed the activity and activity sheet using these guidelines. Authors revised the activities and activity sheets in response to these comments during the workshop.
This page first made public: May 29, 2009
The Sumatra region is prone to earthquakes because it lies at the boundary of two of Earth's shifting tectonic plates—the Indian Ocean crust is creeping steadily northeast and subducting beneath Sumatra. The steady horizontal movements, and pulses of faster horizontal motion that occur during earthquakes, are recorded by GPS stations on the islands. But GPS has only been around since the 1980s, so it can't tell us about land motions associated with large earthquakes that happened in Sumatra long ago. GPS also lacks precise information on vertical motions, and cannot be installed under water, so GPS measurements of coastal land movements are incomplete.
In order to figure out how often large earthquakes happen in the Sumatra region, scientists have turned to coral micro-atolls. They also use coral records to reconstruct progressive sea level changes. In this lab, students will use data from real corals collected in Sumatra to track the sea-level and earthquake record of the region over the past century.
1) relative sea-level changes in a tectonically active region
2) when a historic earthquake happened
Context for Use
There is a lengthier version here:
for use in an advanced class in oceanography or in paleoseismology/seismology. It may also be done over a longer time (1-2 weeks) for an intro oceanography class.
There is an optional discussion suggestion at the end of this mini-lesson. You can take advantage of tidal gauge data from around the world to discuss global sea-level changes that may be related to climate change, and compare these to local sea-level changes that are related to tectonic activity.
Another activity suitable for the first task is to ask students to use GeoMappApp (available as a free download here
to zoom in on Sumatra. I can provide an Excel spreadsheet to import into the program to plot the locations of different islands and of the locations of corals sampled.
Yet another activity -- find modern GPS data from Sumatra and compare it to the historical vertical data.
And one more .... under the Tectonics Observatory website (http://www.tectonics.caltech.edu/) there are several popular news articles related to the coral study and other Sumatra studies that are being used to assess the likelihood of future earthquakes in the region. This one, from Science News, is good:
Students can read some of this material and summarize article(s).
Description and Teaching Materials
1) Figures 1–4 (including a location map) are included with this lab. You will refer to and annotate the coral figures to answer the following questions.
2) Colored pencils, ruler, and calculator
Assignment handout with overview and questions (Acrobat (PDF) 884kB Apr27 11)
Figure 1 -- Location Map -- Sumatra (Acrobat (PDF) 2.4MB May28 09)
Figure 2 -- Coral Head Bai (Acrobat (PDF) 293kB May29 09)
Figure 3 -- Coral Unconformities (Acrobat (PDF) 518kB May29 09)
Figure 4 -- Two Corals (Acrobat (PDF) 540kB May28 09)
Teaching Notes and Tips
Teachers can contact me for an answer sheet, which I am happy to provide.
Also, I think the optional discussion at then end will provide a means of seeing if students grasp global vs. local records. Where else in the world could this type of earthquake measurement be done? (where do corals like this grow?)
References and Resources