Looking for Cracks in the Earth
These early maps that Lowman drew were widely used in textbooks and scientific journals. However, by 1995, the great expansion of geologic knowledge and the development of new computerized mapping techniques called for a new tectonic activity map.
Jacob Yates, another geologist at Goddard, has been involved with the digital mapping project from the start. He explained, "We wanted to create a tectonic activity map a researcher or educator could hold up in their hand on an eight and a half by eleven sheet of paper or viewable on their computer screen.
Yates said that they used the latest global topographic map compiled in digital form by the National Geophysical Data Center in Boulder, Colorado. The topographic map depicts ocean ridges, mountain ranges, and the overall terrain of the Earth in a three-dimensional relief. Yates explained they also created a second global map that differentiates between the Earths oceanic and continental crust. On this map the basaltic oceanic crust was blocked out in a light blue and the granitic crust that makes up our continents was shown in white.
Over the base map, the Goddard team digitized active faults, rifts,
subduction zones, and ocean ridges, which were then digitized. They
included the rates and directions in which the plates were moving away from
the mid-ocean ridges by sea-floor spreading, and showed regions of volcanic
activity in the last one million years.
Detail of the Goddard map, showing topography and tectonic features of the East African coast. The offset red line in the map excerpt indicates the Indian Ocean Ridge, and its rate of spread. (View large image)
"The map is really an amalgamation of a lot of research that we and other scientists from all over the world have done," Yates explained. To compile the information on the map, Lowman and his team combed over dozens of research papers and older maps prepared by scientists inside and outside of NASA. They wanted to pin down all the tectonic features over the Earth that are large enough to be depicted on a global map.
Satellite photos of the Earth were used to verify the precise location of faults and volcanoes. In some cases the Goddard team had to fill in gaps of ground-based research, by utilizing remote-sensing techniques. "Some areas such as Tibet were simply too remote. Others like Southeast Asia contained jungles, swamp, yellow fever, and just bad stuff for geologists," explained Yates. The Goddard team would use the satellite images of these hard to reach and dangerous locations to complete research on faults and other geologic features to ensure they were shown correctly.
|New crust is formed along the mid-ocean ridges. Plumes of upwelling magma push the plates apart along these ridges at a rate of 15 cm per year. Underwater volcanoesblack smokersare a common feature of the ridges. (Image by Robert Simmon, NASA GSFC)|