UH geological researchers cite 10-year data in claims of NW Harris County subsiding
http://www.click2houston.com/video/26004081/index.html
According to Shuhab Khan, Jersey Village is sinking. Khan, an associate professor of geology, along with UH geology professor Kevin Burke and former UH Ph.D. student Richard Engelkemeir, recently published a study in Tectonophysics detailing nearly a decade’s worth of data measuring the elevation of a variety of locations throughout the Houston area.
The data, spanning 1995 to 2005, shows that a large portion of northwestern Harris County is subsiding, with the points in Jersey Village sinking the fastest at a rate of up to 2 inches per year, Khan said.
“Usually, we’re talking only a few millimeters a year,” he said. “This is a significant change.”
Khan names the withdrawal of groundwater as a likely culprit.
“Because GPS can pinpoint location with millimeter precision, it is an excellent tool to measure even the most subtle changes over time in the ground,” Khan said in a UH news release.
“The most likely reason for the sinking of Jersey Village is the withdrawal of water from deep beneath the surface. While groundwater withdrawal has ceased in most of the Houston area, it continues in the northwestern part of the county that has seen a rapid growth in population.”
Parts of southeast Houston, such as Pierce Junction, are rising, as well, the study says. Several salt domes are located along the coast beneath the surface, Khan said. Since salt has a lower density than most common rocks in the crust, it rises and pushes the ground upward. This may contribute to the surface movements occurring in other parts of the region, he said.
Khan and Engelkemeir have also done an extensive study of faults in southeast Texas, producing a comprehensive map in 2008 of about 300 faults in the Houston area that can move up to an inch per year.
Their work on subsidence stemmed directly from their work on faults.
“There was data acquired on the faults because they (county officials) were looking at flood control, and we used that data to better map active faults in the area. But then we started looking at them, and we found that the subsidence was also happening.”
The faults in Houston are not the kinds that trigger earthquakes, he said, but their movement can cause damage to structures and roads that straddle them.
“We call these faults aseismic. They’re continuously moving, so no energy is being stored. In seismic faults, there is no movement, so strain develops. That causes earthquakes. Here, there’s nothing stopping the movement, so we don’t have earthquakes.”
“There was data acquired on the faults because they (county officials) were looking at flood control, and we used that data to better map active faults in the area. But then we started looking at them, and we found that the subsidence was also happening.
