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North Reef Island, Andaman S
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| Title |
North Reef Island, Andaman Sea |
| Description |
On December 26, 2004, one of the largest earthquakes in recorded history struck offshore of the island of Sumatra, Indonesia. The ocean floor heaved in some places and sank in others, creating catastrophic tsunamis that raced across the Indian Ocean. Hundreds of thousands of people died as the waves struck coastlines from Thailand to Sri Lanka to Somalia. In addition to tsunami damage, satellite images of reefs, islands, and coastlines identified signs of permanent elevation changesinking or upliftalong the fault between the Indo-Australia and Burma plates. [ http://earthobservatory.nasa.gov/NaturalHazards/natural_hazards_v2.php3?img_id=12640 ] In places such as North Reef Island, shown in this pair of images from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) [ http://asterweb.jpl.nasa.gov ] on NASA's Terra [ http://terra.nasa.gov ] satellite, the quake lifted the reefs permanently out of the water. The images use visible and infrared light detected by ASTER to make different land surfaces stand out clearly from one another: water is blue, vegetation is red, coral or bare sand appears white. In the "before" image, from December 2, 2004, the submerged reef creates a bright blue glow around the island. In the "after" image, from February 4, 2005, the white coral stands completely up out of the water. It is even tinged with red, which suggests the exposed coral had died, and algae had colonized it. In the weeks and months after the earthquake, satellite images provided broad coverage of an area where ground-based observations were initially very limited. A team of scientists led by Caltech Ph.D. geology student Aron Meltzner discovered changes in elevation along nearly 1,600 kilometers (994 miles) of the tectonic plate boundary. The images revealed that the earthquake rupture extended 100 kilometers (62 miles) farther north than estimates based on seismic and Global Positioning System (GPS) data suggested. The feature article Rise and Fall: Satellites Reveal Full Length of Tsunami-Generating Earthquake [ http://earthobservatory.nasa.gov/Study/Aceh/aceh.html ] describes how scientists used satellite images to map the length of the earthquake rupture zone. The article includes additional satellite and ground-based images of elevation changes resulting from the 2004 Aceh-Andaman earthquake. NASA images created by Jesse Allen, Earth Observatory, using data provided courtesy of the NASA/GSFC/MITI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team. [ http://asterweb.jpl.nasa.gov/ ] |
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North Reef Island, Andaman S
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| Title |
North Reef Island, Andaman Sea |
| Description |
On December 26, 2004, one of the largest earthquakes in recorded history struck offshore of the island of Sumatra, Indonesia. The ocean floor heaved in some places and sank in others, creating catastrophic tsunamis that raced across the Indian Ocean. Hundreds of thousands of people died as the waves struck coastlines from Thailand to Sri Lanka to Somalia. In addition to tsunami damage, satellite images of reefs, islands, and coastlines identified signs of permanent elevation changesinking or upliftalong the fault between the Indo-Australia and Burma plates. [ http://earthobservatory.nasa.gov/NaturalHazards/natural_hazards_v2.php3?img_id=12640 ] In places such as North Reef Island, shown in this pair of images from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) [ http://asterweb.jpl.nasa.gov ] on NASA's Terra [ http://terra.nasa.gov ] satellite, the quake lifted the reefs permanently out of the water. The images use visible and infrared light detected by ASTER to make different land surfaces stand out clearly from one another: water is blue, vegetation is red, coral or bare sand appears white. In the "before" image, from December 2, 2004, the submerged reef creates a bright blue glow around the island. In the "after" image, from February 4, 2005, the white coral stands completely up out of the water. It is even tinged with red, which suggests the exposed coral had died, and algae had colonized it. In the weeks and months after the earthquake, satellite images provided broad coverage of an area where ground-based observations were initially very limited. A team of scientists led by Caltech Ph.D. geology student Aron Meltzner discovered changes in elevation along nearly 1,600 kilometers (994 miles) of the tectonic plate boundary. The images revealed that the earthquake rupture extended 100 kilometers (62 miles) farther north than estimates based on seismic and Global Positioning System (GPS) data suggested. The feature article Rise and Fall: Satellites Reveal Full Length of Tsunami-Generating Earthquake [ http://earthobservatory.nasa.gov/Study/Aceh/aceh.html ] describes how scientists used satellite images to map the length of the earthquake rupture zone. The article includes additional satellite and ground-based images of elevation changes resulting from the 2004 Aceh-Andaman earthquake. NASA images created by Jesse Allen, Earth Observatory, using data provided courtesy of the NASA/GSFC/MITI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team. [ http://asterweb.jpl.nasa.gov/ ] |
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Uplift and Subsidence Associ
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PIA02435
Sol (our sun)
ASTER
| Title |
Uplift and Subsidence Associated with the Great Aceh-Andaman Earthquake of 2004 |
| Original Caption Released with Image |
The magnitude 9.2 Indian Ocean earthquake of December 26, 2004, produced broad regions of uplift and subsidence. In order to define the lateral extent and the downdip limit of rupture, scientists from Caltech, Pasadena, Calif., NASA's Jet Propulsion Laboratory, Pasadena, Calif., Scripps Institution of Oceanography, La Jolla, Calif., the U.S. Geological Survey, Pasadena, Calif., and the Research Center for Geotechnology, Indonesian Institute of Sciences, Bandung, Indonesia, first needed to define the pivot line separating those regions. Interpretation of satellite imagery and a tidal model were one of the key tools used to do this. These pre-Sumatra earthquake (a) and post-Sumatra earthquake (b) images of North Sentinel Island in the Indian Ocean, acquired from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument on NASA's Terra spacecraft, show emergence of the coral reef surrounding the island following the earthquake. The tide was 30 plus or minus 14 centimeters lower in the pre-earthquake image (acquired November 21, 2000) than in the post-earthquake image (acquired February 20, 2005), requiring a minimum of 30 centimeters of uplift at this locality. Observations from an Indian Coast Guard helicopter on the northwest coast of the island suggest that the actual uplift is on the order of 1 to 2 meters at this site. In figures (c) and (d), pre-earthquake and post-earthquake ASTER images of a small island off the northwest coast of Rutland Island, 38 kilometers east of North Sentinel Island, show submergence of the coral reef surrounding the island. The tide was higher in the pre-earthquake image (acquired January 1, 2004) than in the post-earthquake image (acquired February 4, 2005), requiring subsidence at this locality. The pivot line must run between North Sentinel and Rutland islands. Note that the scale for the North Sentinel Island images differs from that for the Rutland Island images. The tidal model used for this study was based on data from JPL's Topex/Poseidon satellite. The model was used to determine the relative sea surface height at each location at the time each image was acquired, a critical component used to quantify the deformation. The scientists' method of using satellite imagery to recognize changes in elevation relative to sea surface height and of using a tidal model to place quantitative bounds on coseismic uplift or subsidence is a novel approach that can be adapted to other forms of remote sensing and can be applied to other subduction zones in tropical regions. ASTER is one of five Earth-observing instruments launched December 18, 1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of Economy, Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products. The broad spectral coverage and high spectral resolution of ASTER provides scientists in numerous disciplines with, critical information for surface mapping, and monitoring of dynamic conditions and temporal change. Example applications are: monitoring glacial advances and retreats, monitoring potentially active volcanoes, identifying crop stress, determining cloud morphology and physical properties, wetlands evaluation, thermal pollution monitoring, coral reef degradation, surface temperature mapping of soils and geology, and measuring surface heat balance. The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate. |
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