Lasers create 3D maps of earthquake faults
Geologists at UC Davis have a tool at their fingertips that puts everyday laser rangefinders to shame. Their technology allows them to take 100,000 range samples per second. The system is called Light Distance and Ranging, or LiDAR for short, and is being used to create hyperaccurate topography maps of post-earthquake regions.
The juiced-up rangefinder is loaded on an airplane and is then flown over a region to create a three dimensional image of the land below. It is operated by a team from the National Center for Airborne Laser Mapping.
“We learn a lot about earthquake faults by studying fresh quake ruptures,” said Ken Hudnut, a geophysicist with the United States Geological Survey (USGS). “The record of [ground] displacement is useful for assessing the hazard presented by faults.”
LiDAR has been in use for nearly a decade, but up until recently, it had only been used to document a region after an earthquake. Now, it is being used to map areas both before and after an earthquake to measure exactly what changed in the topography with down-to-the-inch resolution.
The system uses a series of tools to maintain accuracy even when flying 10,000 feet above an area. First, the ground coordinates are mapped with GPS, and then those same coordinates are programmed in the plane’s GPS to keep it on track. In addition, the LiDAR system itself has a gyroscope and accelerometer to correct for the plane’s pitch and roll.
The LiDAR system collects a huge amount of data, over 100 gigabytes over just a few acres, so researchers require tools that will allow them to efficiently visualize all of that data.
This is when UC Davis geologists use KeckCAVES to analyze the vast amounts of data. Donated by the Keck foundation, the CAVES, or Center for Active Visualization in the Earth Sciences, is a three dimensional projection room built to explore the data collected by the LiDAR system.
“There are three walls and a floor with stereoscopic displays,” said Michael Oskin, a geology professor at UC Davis. “Users wear 3D glasses and CAVES allows you to walk around inside of your data.”
The system provides a far more immersive environment for analyzing data and is far superior to looking at it on a basic computer monitor. The detailed imaging is reminiscent of the Pre-Crime department in Tom Cruise’s movie Minority Report.
According to a representative at Mechdyne, the manufacturer of the CAVES system, the four-walled projection system at UC Davis is one of the most elaborate they have set up and cost nearly a million dollars in hardware and software.
Now that LiDAR is being used to map both pre- and post-earthquake topography, there is a project underway to create accurate maps of every active fault region. This means that geologists will not have to predict where an earthquake will occur in order to get accurate pre-quake data as the data will already be on hand. LiDAR maps of the post-quake region can then be overlayed on the pre-quake data to create a difference map that will show exactly how the topography changed.
“Other methods are not as accurate,” Hudnut said. “LiDAR gives us an actual 3D representation of the pre- and post-earthquake landscape so we can look at the differences in very high detail.”
Other institutions involved in the research are Arizona State University, Centro de Investigación Científica y de Educación Superior de Ensenada in Mexico, NASA, the Jet Propulsion Laboratory and the Chinese Academy of Sciences. Funding came from the National Academy of Sciences, the USGS and the Keck Foundation.