News Release July, 9 2001
New Mexico State University professor heads study of the Rio Grande Rift

  New Mexico State University geophysicist James Ni is directing a project
aimed at providing the most detailed description yet of the Earth's
structure beneath the Rio Grande Rift, a 700-mile-long depression
in the Earth's crust that runs through New Mexico. 
  A rift is a failure of the Earth's surface that occurs along faults.
The Rio Grande Rift is one of the Earth's major continental rifts.
Running from central Colorado to south of Juarez, Mexico, it includes the
area on both sides of the Rio Grande River, including Santa Fe, Albuquerque,
Alamogordo, Las Cruces, El Paso and Juarez.
  To geoscientists, the Rio Grande Rift is one sign that the North American plate -
that part of the Earth on which this continent sits - is breaking apart, Ni said. 
The COlorado Plateau, on the plate's western side, is moving away from 
the Great Plains.  The movement is very slow, although how slow is uncertain,
he said. 
  "Although, the Rio Grande Rift is caused by an extension of the crust, the 
underlying process is by no means clear" Ni said.  "At present, two competing 
hypotheses have been proposed, active rifting and passive rifting.  Active 
rifting is the result of a thermal upwelling of a deeper part of the mantle we 
call the asthenosphere.  Passive rifting is a response of the area near the rift 
to forces acting on the boundary of the palte.  In both processes, the 
determining factor is the structure of the Earth beneath the rift.  One 
purpose of this study is to get accurate information about those structures."      
  To get that information, along with answers to other questions, 
Ni and colleagues from four other institutions set up a line of 54
solar-powered seismometers during the fall and winter of 1999. The
seismometers ran across the rift from slightly northwest of Pecos,
Texas, to Lake Powell, Utah, a distance of about 600 miles, Ni said.
  Ni's collaborators are scott Baldridge of Los Alamos National Laboratory, 
Rick Aster and John Schlue of New Mexico Tech, Steve Semken of Dine College and 
Steve Grand of University of Texas at Austin. 
  A seismic array like the one the researcher set up records data about the Earth 
in a manner similar to the way a CAT scan records data about the human body, Ni 
explained.  " Seismometers detect ground motion and translate that motion into a 
measurement of velocity.  We aligned our seismometers with an earthquake zone called 
"Ring of Fire" that runs around the Pacific Rim from Aleutian Islands to South American. 
The sound and shear waves from that zone travel through the Earth and were picked 
up by the seismometers.  But they had different travel times to different seismometers 
and from that difference we can infer structural difference in the Earth beneath," he said. 
"It's really not that different from showing a picture of the brain in human medicine,"
he said.        	
  The line of seismometers was dismantled in May and researchers will
spend the next five years analyzing the data it recorded, Ni said.
"This is the first study designed to provide a vertical profile of the 
subsurface structure down to 400 miles," he said. 
"An understanding of the underlying structures is essential to understanding 
the rift's origin.  With new information, it is then possible to resolve the
debate over active or passive rifting in the Rio Grande Rift.  We'd also like to 
know more about the Earth's crust beneath the Great Plains, which in eastern 
New Mexico and western Texas is a source of oil and gas.  Also, while we 
know the Colorado Plateau is at a high elevation, it is not well know what 
mechanisms support that evevation," he said.  
  Part of it is basic human curiosity - how did this land become the way it 
is and what's going on beneath us?" he said. 
  While it operated, the seismic array ran through rugged country on federal, 
private, state of New Mexico and Navajo land.  Ni said getting to where the 
seismometers were planted in the ground somtimes required four-wheeled vehicles, 
but wasn't nearly the ordeal New Mexico State researchers faced four years 
ago, when they set up a similar array across the world's highest plateau 
in central Tibet.  "You didn't have to travel five days just to get there or 
work in altidudes that made you barely able to walk," he joked.