Putting Earthquakes in their Place
 

In today’s information age, one can find a map for just about any occasion. There are countless maps displaying every street in North America, maps detailing the topography of every patch of land in Europe, maps outlining the types of forests in Canada, and maps showing all of India’s major mineral deposits. Maps have even been created that accurately display everything from ski resorts to scenic drives in North America.

Given the overwhelming number of maps out there, one would expect that geologists, those whose job it is to understand the Earth’s make-up, would have long ago created a complete and accurate global map showing faults, volcanoes, earthquake epicenters and mountain formations known to have occurred over the recent geological past of one million years. After all, these are the phenomena that shape our planet’s surface and are responsible for many of our worst natural disasters.

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Tectonic Activity Map

Yet, such a complete map has never been published. Most global maps of tectonic activity reflect a somewhat oversimplified view of plate tectonics. They merely show the jagged outlines of the enormous plates that make up the crust of the Earth and the faults at the boundaries of the continents. Few include active faults that lie in the middle of the plates. A number of the maps out there are even based on older, incomplete research and display ocean rifts and plate boundaries incorrectly. As a consequence, neither scientists nor students of geology have had a comprehensive, realistic, view of global tectonic activity.

This cartographic gap may soon be filled. Using modern global databases, hundreds of research reports, satellite photos, and computerized drafting methods, a group of researchers at NASA's Goddard Space Flight Center has pieced together what's considered a series of objective and comprehensive maps (actually what's known as a Geological Information System, or GIS) of the planet's tectonic activity. The map shows crustal features such as faults and volcanoes that have been active within the last one million years. This period was chosen as being long enough to be truly representative of the Earth's geologic activity, but short enough that geologic features have not been destroyed by erosion and can still be recognized. The maps show not only plate boundaries and large fault zones, but the location of major volcanic eruptions, earthquake epicenters, and movement of the Earth's crust.

The Goddard team has put all this information on the Internet for educators, researchers, and students to use. They hope the map will not only provide working scientists with an important visualization tool, but will also give future geologists the information they need to fill in the gaps of the current theories of global tectonics.

next Faulty Fault Zones

The data used in this study are available in one or more of NASA's Earth Science Data Centers.

  The schematic Global Tectonic Activity Map. It shows several types of faults, active spreading centers, and volcanoes. The geologists who prepared it achieved unprecedented completeness by using both historical data and satellite imagery. (Download full Digital Tectonic Activity Maps)

 

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.

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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)

 

Looking for Cracks in the Earth

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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 Earth’s 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.
 

  East Africa, Indian Ocean
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)

Mid-ocean
ridge

"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.

next Adding Up the Hazards
next Faulty Fault Zones

  New crust is formed along the mid-ocean ridges. Plumes of upwelling magma push the plates apart along these ridges at a rate of 1–5 cm per year. Underwater volcanoes—black smokers—are a common feature of the ridges. (Image by Robert Simmon, NASA GSFC)

 
DTAM Detail
 

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

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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.

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next Looking for Cracks in the Earth

  Earthquake Damage
Seismic Map
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

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"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, we’re 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 isn’t 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 plate’s boundaries should depend on the plate’s 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. "There’s a lot more to geology than just plates and we hope down the road somewhere geologists will start to recognize this," said Lowman.

References

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/)

next Adding Up the Hazards

  Mediterranean Sea
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)

 
Mediterranean
 

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