Wednesday, April 04, 2007

USGS creates 3D Map of San Andreas Fault

Geophysicists might not tell us exactly when the Big One will hit. But they will make sure we know what happened after it comes by.

Using a technique known as Airborne Laser Swatch Mapping, USGS with help from several research groups as the Scripps Institute and State Universities has been working on what is known as the B4 Project to build a 3D map of the whole San Andreas Fault (from the border with Mexico all the way to the where it reaches the Atlantic Ocean). Yes, you will be able to see all of it in Google Earth too.

Eric Hendrick from Ohio State University explained that ground measurements are taken at the same time an airplane equipped with its own GPS system (inertial navigation with Real-time Kinematic [RTK] positioning) flies over the area. The errors introduced by changes in the atmosphere affect both equipments.

The ground station should always read a fixed, known location as a county benchmark for example (photo). By removing the errors from both datasets, a precision of centimeters can be obtained from the measurements made from the airplane.

As described by this page at the University of Florida website, the plane while flying

"at 150 to 200 kilometers per hour and an altitude of 500 to 1000 meters, with a scan angle of 10 to 20 degrees and a laser repetition rate of 2000 to 5000 pulses per second, an area of several hundred meters in width and hundreds of kilometers in length can be mapped in just a few hours."
If you are trying to figure out how the laser works, read on:
"The round trip travel times of the laser pulses, from the aircraft to the ground, are measured and recorded along with the position and orientation of the aircraft at the time of transmission of each pulse. After the flight the vectors from the aircraft to the ground are combined with the aircraft position at the time of each range measurement and the three dimensional coordinates of each ground point are computed."
B4 and After

An "After Project" will come by to collect data in the same way after the quake(s) occur with the same level of detail which means billions of datapoints. All this data will be made available for the scientific community and general public for study and to try to understand what the heck happened with all that shaking.

At the end when you got your electricity, Internet and roof back you might flyover the 3D maps in Google Earth to find out where now is your backyard.

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