Earthquake’s Affect on Earth
On March 11, 2011, a magnitude 8.9 earthquake struck offshore about 130 kilometers (80 miles) east of Sendai, the capital city of Japan’s Miyagi Prefecture, generating a tsunami that devastated the low-lying coastal city of about 1 million residents.
According to the U.S. Geological Survey, the earthquake occurred as a result of thrust faulting on or near the subduction zone interface plate boundary between the Pacific and North America plates. At the latitude of this earthquake, the Pacific plate moves approximately westwards with respect to the North America plate at a velocity of 83 millimeters (3.3 inches) per year. The Pacific plate thrusts underneath Japan at the Japan Trench, and dips to the west beneath Eurasia. The location, depth and focal mechanism of the March 11 earthquake are consistent with the event having occurred as thrust faulting associated with subduction along this plate boundary.
The U.S. Geological Survey reports that the earthquake moved the island of Japan about 8 feet. NASA geophysicist Richard Gross calculates that this shift of mass made the Earth’s rotation speed up by 1.6 microseconds (A microsecond is one-millionth of a second).
The extent of inundation from the destructive and deadly tsunami triggered by the earthquake is revealed in a before-and-after image pair from the Multi-angle Imaging SpectroRadiometer (MISR) instrument on NASA’s Terra spacecraft.
The image comparison is online at http://photojournal.jpl.nasa.gov/catalog/PIA13913 . For optimum viewing, click the link to open the full-resolution TIFF image.
The new image was acquired at 10:30 a.m. local time (01:30 UTC) on March 12, 2011. For comparison is a MISR image from about 10 years ago, on March 16, 2001, acquired under nearly identical illumination conditions. Flooding extending more than 4 kilometers (2.5 miles) inland from the eastern shoreline is visible in the post-earthquake image. The white sand beaches visible in the pre-earthquake view are now covered by water and can no longer be seen. Among the locations where severe flooding is visible is the area around Matsukawa-ura Bay, located just north and east of the image center.
From top to bottom, each image extends from just north of the Abukuma River (about 21 kilometers, or 13 miles, south of Sendai) to south of the town of Minamisoma (population 71,000, located in Japan’s Fukushima Prefecture about 70 kilometers, or 44 miles, south of Sendai). The images cover an area of 78 kilometers (48 miles) by 104 kilometers (65 miles).
These unique images enhance the presence of water in two ways. First, their near-infrared observations cause vegetated areas to appear red, which contrasts strongly with the blue shades of the water. Second, by combining nadir (vertical-viewing) imagery with observations acquired at a view angle of 26 degrees, reflected sunglint enhances the brightness of water, which is shown in shades of blue. This use of different view-angle observations causes a stereoscopic effect, where elevated clouds have a yellow tinge at their top edges and blue tinge at their bottom edges.
The topography surrounding Sendai, Japan is clearly visible in a combined radar image and topographic view generated with data from NASA’s Shuttle Radar Topography Mission (SRTM) acquired in 2000.
The city is centered in the image and lies along the coastal plain between the Ohu Mountains and the Pacific Ocean. The eastern part of the city is a low-lying plains area, while the city center is hilly (the city’s official elevation is about 43 meters, or 141 feet). Sendai’s western areas are mountainous, with its highest point being Mt. Funagata at an elevation of about 1,500 meters (4,921 feet) above sea level.
This image combines a radar image acquired in February 2000 during the SRTM mission, and color-coding by topographic height using data from the same mission. Dark green colors indicate low elevations, rising through yellow and tan, to white at the highest elevations.