Geologist: Unknowns surround Irving earthquake swarm
Since Oct. 31, 2008, the USGS has located more than 120 earthquakes in North Texas that took place in four sequences.
(Photo: WFAA)
IRVING, Texas -- After weeks of worry, residents wanted answers Tuesday night from Irving City Council.
It was standing-room only as Dr. Brian Stump, an SMU geologist, revealed what little he has already learned about the earthquake "swarm" in the city.
"I do not know whether this specific swarm will die out or whether it will continue. Experience shows that the majority of earthquake swarms do not result in damaging earthquakes," Stump said. "But at this time, we cannot rule out the possibility of larger earthquakes, some possibly damaging."
Since April 17, 2014, the Irving-area has experienced 38 small earthquakes, most of which occurred in the last two months, he told local leaders.
No significant damage has been reported in any of the tremors, but the ground shaking has created concern.
Stump and his team say prior to 2008, there were no historic seismic events in North Texas and only one possible event, which was reported in 1950.
"Of course the ability to detect and locate seismic events in the region has increased as a function of time, but with the substantial population in the region for well over 100 years, any felt reports associated with small events would have been made and those events would have been identified," he said.
The first seismic activity began on October 31, 2008 near D/FW Airport. Since that day, the USGS has located more than 120 earthquakes that took place in four sequences, the most-recent of which is in Irving.
"The first was an earthquake sequence centered near D/FW Airport in 2008 and 2009 with the largest magnitude of 3.3. A second sequence from 2009 into 2010 was near Cleburne, Texas, with the largest magnitude of 2.8. A third set of events occurred near Azle, Texas, beginning in the Fall of 2013 and continuing through 2014 with the largest magnitude of 3.6," Stump said. "In all of these cases earthquakes got smaller and further apart in time following the largest events."
Some suspect injection wells from fracking might cause it, though no injection wells exist in Irving.
"In the case of two of the previous earthquake sequences - those near D/FW Airport and Cleburne - we found that there is a plausible or possible linkage between waste water disposal and the earthquakes. I will add that there are other experts who point out that even in these two cases the sequences could be natural," Dr. Stump explained.
There is no fracking in Irving either, Mayor Beth Van Duyne reminded reporters and citizens.
Injection wells were banned here in 2006.
When News 8 asked state regulators whether any human activity such as fracking or injection wells might be causing the quakes, the state said no.
"At this point in time, we have no evidence of any oil and gas activity that can be linked to earthquakes," said Craig Pearson, a seismologist with the Texas Railroad Commission, the agency that regulates the oil and gas industry.
Earthquake preparedness pamphlets from FEMA were stacked on a table Tuesday night outside the council room.
"Right now, we have no expectations of any larger activity than what we've already had, but you never know," Mayor Van Duyne said.
Dr. Stump's team from SMU deployed 22 seismic stations in the Irving area to better pinpoint where the ground is shaking.
He noted that in areas like California, where earthquake activity is high, permanent seismic stations are already in place and adequately spaced to provide more refined earthquake locations than what has been available in north Texas up to this point. In fact, before the most active day of earthquakes in Irving, Jan. 6, there were only three seismic stations within 10 miles of the quake locations and one had been deployed the day before.
Of the deployed seismic stations in Irving, 14 will be collected soon to analyze data.
"We anticipate that within the next month as additional small events occur that these data will provide the basis for a refinement of our understanding of the responsible fault. This same approach proved to be successful for the earthquake sequences that occurred near D/FW Airport, Cleburne and Azle," Stump said.
But residents wanting answers Tuesday night went home without them, as experts could not immediately conclude what's causing the ground to shake.
"Steps in this next stage of the study are the development of data on subsurface fault details, assessment of relative locations of any near-by commercial activities to the earthquakes, acquisition of data related to any identified commercial activities, and development of detailed subsurface geology and rock properties," Stump said.
After that data is gathered, researchers can begin to consider whether there is any link to a commercial activity, such as fracking.
"It is my opinion that these recent events - in the context of the increase in seismicity we've seen in our area since 2008 - are strong motivation for a comprehensive assessment of the increased seismicity rate across North Texas," Stump said. "Communities need to be able to make informed decisions about preparation as well as improve hazard assessment."
Irving is hosting a Town Hall meeting to answer more questions about the seismic activity. It happens at the Irving Arts Center on Jan. 20 at 6:30 p.m.
Stump also encouraged all North Texas residents who feel an earthquake to file a report on the USGS "Did You Feel It?" website, which you can find at this link.
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