Faulty Fault Zones

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Paul Lowman, a geologist at Goddard, came up with the idea for these maps twenty-five years ago. He explained he had just started working within the Geophysics branch at NASA and was searching for a few good maps showing the plate boundaries and fault zones around the world. "I began digging through the literature and all I could find were these schematic plate maps that were clearly no good at all. They were extremely generalized and often wrong in places," he said.

Part of the reason for the oversights, he explained, is the theory of plate tectonics. This is the theory that the Earth's crust (oceanic and continental) is a mosaic of large rigid plates, more or less floating on the planet's partly molten rocky mantle. Currents in the mantle constantly drive these plates, causing them to move apart, by sea-floor spreading, at mid-ocean ridges, and to collide with one another at their edges. When the plates collide, or slide past each other, earthquakes and volcanoes occur and mountains are formed.
 

   
subduction
schematic

"Many of these early plate maps were very subjective and interpretive as well," said Lowman. The geologists who put the maps together had trouble gathering data in remote areas of the world such as in Southeast Asia or the Middle East. Due to this lack of information, those who drew the maps were forced to extrapolate with poorly mapped data. However, space photography soon began to change the situation.
 

  The majority of earthquakes and volcanoes around the world occur at the intersection of plate boundaries. This diagram shows the subduction of an ocean plate underneath a continental plate. Earthquakes are caused by the two plates moving relative to each other, and volcanoes are formed when ocean crust, forced under the lighter continental crust, melts and then rises to the Earth's surface. (Image by Robert Simmon, NASA GSFC)
Tian Shan
Mountains

Upon seeing the lack of comprehensive synoptic maps, Lowman decided to make a tectonic activity map of his own. He had access to images from the NASA Landsat satellites, as well as 70mm photographs taken by Gemini, Apollo, and Skylab astronauts. Each Landsat moved in a roughly circular orbit nearly pole to pole around the Earth, and used multispectral scanners to gather imaging data of most of the land area of our planet. The data were sent down in digital form to the surface, so that researchers could make them into images and examine them. By pouring over these orbital images, Lowman and other geologists were able to pin down the location of faults and volcanoes that were not well documented. They drew in many of the features the other maps missed, and created the foundation for the first NASA global tectonic activity map, in 1979.

next Looking for Cracks in the Earth
next Putting Earthquakes in their Place

  Researchers used Landsat imagery to pinpoint faults and other geological features. This method ensured that areas that are not predicted by existing theories of plate tectonics would be accurately depicted. (Image from Geomorphology from Space)
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