Faulty Fault Zones
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.
"Many of these early plate maps were very subjective and
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
|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)|
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.
|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)|
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 or download full Digital Tectonic Activity Maps)
"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)|
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.
Return to: Looking for Cracks in the Earth
Adding Up the Hazards
As an addendum to the core tectonic activity map, the Goddard team also made detailed global maps of earthquakes and active volcanoes the two hazards that accompany tectonic activity. The earthquake data were retrieved from the National Geophysical Data Center and included the epicenters of the more than 200,000 earthquakes with magnitude over 3.5 that occurred between 1963 and 1998. The volcanic data, on the other hand, were taken from the Smithsonian Global Volcanism Program and showed the location of roughly 1,200 volcanic eruptions that are known to have taken place over the past 10,000 years (Lowman et al., 1999). Older volcanoes were added from other maps and satellite photos.
The Goddard team integrated all of these data and mapped each earthquake epicenter and volcanic center on the same base map they used to show tectonic activity. Most of the earthquakes and volcanoes are along or near plate boundaries. However, many can be found in unexpected areas. "Rarely do we think of active volcanoes existing in central China," Yates pointed out.
The final map Lowman and his team pieced together displays the movement of the Earth’s plates. Space geodesy stations all over the globe make precise measurements of how far the plates move each year. The movements range from next to nothing in Africa to more than 7 centimeters a year in areas such as the Pacific Basin. The Hawaiian islands, for example, are moving toward Asia at more than 8 centimeters a year. The Goddard researchers mapped these stations readings by indicating relative velocity and direction of crustal motion.
Top: Earthquakes are one of the most destructive natural hazards. The Northridge earthquake in Southern California killed 57 people and caused 15 billion dollars of damage. (Photograph courtesy Federal Emergency Management Agency)
Above: The Goddard geologists mapped earthquakes around the world from 1963 - 1998. Thousands occurred in the United States during that time. (Download full Seismic Activity Map)
A New Tool for Tectonics
"From the start our goal has been to make all of this information available to the public," Yates explained. The researchers have held to this initial objective; they recently posted their maps on their web site (http://denali.gsfc.nasa.gov/dtam/) in a number of different formats that anyone can download or print. When overlaid on transparencies, the maps all match up point for point.
Yates said that the maps are likely to provide researchers with a much needed reference tool. On these digital maps, geologists can find features not found on any other global map of tectonic activity. In the past a scientist would have had to pore through stacks of research papers to locate the two large active faults running through the Russian Ural Mountains in the center of the Eurasian Plate or the dozen or so fractures that scar Tibet and southwestern China. With the DTAM, they should now be able to see where these features exist at a glance before making a trip to the library.
Regardless of how working scientists use these maps, both Lowman and Yates believe that the real impact of their research will be on educators and students. Already, several textbook manufacturers have shown interest in the maps. "If the maps do become a standard in the classroom, were hoping they will contribute to a paradigm shift in terms of how people view global tectonics," said Yates.
For instance, looking at the digital tectonic activity map, it isnt hard to notice that the African Plate and the Eurasian Plate are two of the slowest moving plates in the world, and should be both moving to the east. The tectonic activity at a plates boundaries should depend on the plates movement relative to the adjacent plate. Yet, the map also shows that the Mediterranean, which forms the boundary between these two plates, has one of the highest concentrations of faults, volcanoes and earthquakes in the world in spite of the slow movement (Lowman et al., 1999).
By utilizing the DTAM instead of over-simplified "plate maps," educators and students of geology will be exposed to a synoptic view of global tectonics. The Goddard team hopes that when the students become geologists they may incorporate this knowledge into their research or even improve on the current theory of plate tectonics. "Theres a lot more to geology than just plates and we hope down the road somewhere geologists will start to recognize this," said Lowman.
1. P. Lowman, J. Yates, J. O'Leary, D. Salisbury, P. Masuoka, and B. Montgomery, 1999: A Digital Tectonic Activity Map of the Earth, Journal of Geoscience Education, v. 47(5), 1999.
2. DTAM web site (http://denali.gsfc.nasa.gov/dtam/)
The Mediterranean Sea is one of the world’s most geologically active areas, even though the regional plate motion is relatively slow. (The blue, yellow, and red lines indicate different types of faults. Red dots represent volcanoes active within the past million years.) Several other areas of tectonic activity that are not well explained by conventional plate tectonics show up on the Digital Tectonic Activity Map. (View large image, or download full Digital Tectonic Activity Maps)
The Mediterranean Sea is one of the world’s most geologically active areas, even though the regional plate motion is relatively slow. (The blue, yellow, and red lines indicate different types of faults. Red dots represent volcanoes active within the past million years.) Several other areas of tectonic activity that are not well explained by conventional plate tectonics show up on the Digital Tectonic Activity Map.
Return to: A New Tool for Tectonics