An unpredictable science
With great uncertainty, geologists try to predict the chance of a big quake striking. By OLIVEr MOrrISON Prague, Oklahoma, in 2011, which caused around US$ 10mil ( RM42mil) in damage and sent several people to the hospital.
But scientists at the USGS have been unwilling to rule out the possibility of a magnitude- 7 quake.
One reason is that the latest earthquakes have been activating old fault lines, some of which they didn’t know existed, according to George Choy, a research geophysicist at the USGS in Colorado.
Sedgwick County’s own hazard analysis plan from 2011 points out that a 300- millionyear- old underground mountain range, the Nemaha Ridge, runs right through Sedgwick County, from approximately Oklahoma City to Omaha.
Nemaha is thought to have been the source of the largest recorded earthquake in Kansas just outside Manhattan in 1867.
And no matter the strength of the earthquake, there is reason to believe the local area is particularly vulnerable.
One reason is that earthquakes in the Midwest can be felt farther away than many coastal earthquakes, according to Halihan, the professor at Oklahoma State.
The soil in the Midwest tends to be stiffer than that on the coasts, according to Halihan. It’s like dropping a rock on concrete versus in mud – the sound waves are going to travel much further when it hits the concrete.
And most of the quakes in Kansas and Oklahoma are relatively shallow, he said, meaning they don’t have to travel as far to reach the surface and their force won’t dissipate as much.
“Usually the folks from Seattle go, ‘ What are you guys complaining about? It’s just a 4.7,’” Halihan said. “4.7’ s here are a hell of a ride.”
In 2015, the Kansas Corporation Commission limited the amount of wastewater that oil companies are allowed to dispose of deep into the earth in Harper and Sumner counties. More than a half year after these changes came into full effect, the commission reported that there is some evidence the number and severity of earthquakes originating in Kansas may have fallen in the second half of 2015.
The fall in the price of oil the past two years, could continue to mitigate the chances for more Kansas quakes. Many of the new wells that companies tried drilling farther northwest into Kansas were not that productive even before the price of oil dropped, according to Buchanan, director of the Kansas Geological Survey.
“A lot of the wells didn’t work and produce enough oil for the amount of water they were producing,” Buchanan said. “Water is heavy and it’s expensive to bring it to the surface, especially if you have to inject it back to the deep subsurface.”
But the Sierra Club has filed an intent- tosue letter, hoping to require a more ambitious reduction in the disposal of wastewater from fracking, which would include Oklahoma.
Buchanan of the Kansas Geological Survey said that while he doesn’t know anyone who would rule out a magnitude- 7 quake, he hasn’t heard anyone talking of a quake with a magnitude larger than 6, in part because the largest one recorded since the recent earthquakes started in Oklahoma so far has been a 5.6.
But he said there also are questions about the impact of smaller quakes.
Buchanan said he has been talking with the state transportation department about the potential effects of the kind of “repeated, low- level shaking” the state has already seen.
It’s not clear what repeated low- level shaking might do to water lines, roads and buildings, he said, adding: “That question is really in its infancy.” – The Wichita Eagle/ Tribune News Service LORI Lawrence said she was standing in the hallway of her home near Central and Hillside in Kansas on Jan 6 when the bedroom door started rattling.
It was, she said, the sixth earthquake she’s felt in the past two years.
Friends filled up her Facebook feed with comments about the latest quake, which was actually two back- to- back quakes, the largest of which had a magnitude of 4.8.
It was intense enough that the city of Wichita, for the first time, sent out a team to examine whether any of its infrastructure had been affected by an earthquake.
Reports had already been coming in about three water lines that had burst around the time of the quake. After a day of inspections, a few more potential cracks had turned up, including one at a wastewater treatment plant.
In the past two years, Lawrence has become one of the leading organisers for the Kansas chapter of the Sierra Club trying to document local damage from earthquakes. In November, the legal non- profit Public Justice posted on behalf of the Sierra Club, a notice of its intent to sue four of the largest fracking companies in Kansas and Oklahoma to prevent them from continuing to inject wastewater that many scientists say is probably causing the earthquakes.
But even as Lawrence and others are trying to document possible damage from low- level shaking, scientists are estimating the likelihood of a much larger earthquake in the area.
Between 2003 and 2012, there were three earthquakes in Kansas, but since then, there have been 579.
This number doesn’t include more than 900 quakes in Oklahoma in 2015 alone, or the 70 quakes in the first week of 2016.
Oklahoma’s earthquakes have been creeping farther north, until in 2013, they reached the Kansas state line.
In 2014, Kansas experienced the largest earthquake recorded originating within the state. But the two most intensely felt recent earthquakes in Wichita, in November 2015, and on Jan 6, originated in Oklahoma.
Because of the increase in the number and severity of earthquakes, the US Geological Survey ( USGS) has had to change how it maps earthquake risks and devise new ways of measuring risk locally.
The new measurements suggest a potential for an earthquake much more severe than what most structures in southern Kansas have been built to withstand.
But the new predictive models may not be anywhere near as accurate as the ones along traditional seismic plates, according to Todd Halihan, a professor of geology at Oklahoma State University.
“The predictions kind of suck,” Halihan said. “We’re somewhere between a couple of liquor bottles falling off the shelf and complete Armageddon. And that’s not particularly comforting or useful, so you should probably take some steps to prepare people for what to do that is logical in a case of uncertainty.”
The USGS makes what are called “hazard maps” that reflect how likely an area of the country is to experience a large earthquake that could cause catastrophic damage.
These maps draw on hundreds and thousands of years of historical and geological data about when earthquakes have occurred in the past and where known fault lines are.
But when the USGS scientists were making the map for 2014, they realised that the thousands of small earthquakes in Kansas and Oklahoma that were likely caused by humans were throwing off their models.
If they left in all the recent local earthquakes, south- central Kansas and Oklahoma would suddenly look like a relatively huge risk for a major earthquake.
That’s because in a typical active fault zone, such as those found in California, the number of earthquakes that have become a regular event here would be an indicator of a potentially large future earthquake.
But USGS studies have indicated that these local earthquakes probably follow a different pattern. Their likelihood increases the more wastewater is injected underground in some areas, and the earthquakes subside when the wastewater disruptions are lowered or halted.
But that wasn’t a satisfying answer for people who wanted to know the short- term likelihood and danger of earthquakes in Oklahoma and Kansas.
So in April last year, the USGS began creating separate, short- term hazard maps that estimated the chance of experiencing a catastrophic quake here. These maps put the recent upsurge of local earthquakes back into their model.
And, instead of appearing light gray or dark gray, which implies a low level of earthquake risk, south- central Kansas and a huge area of central and northern Oklahoma now appear red and orange.
There are only three places in the Lower 48 states that appear red on the USGS’ 2014 50- year hazard map.
One is the San Andreas Fault in California, which includes San Francisco, the site of the 1906 earthquake, the largest in US history outside of Alaska. The 1906 quake killed around 3,000 people and destroyed most of the city.
Another is the New Madrid Fault in far southeast Missouri, the site of the second- largest quake in US history. That quake, which occurred in 1811, was described by witnesses as a “distant thunder” that caused trees to crack and fall, rivers to overflow their banks and the sky to turn black.
The red areas of the maps are the places in which there is a 2% chance of one the most severe earthquakes occurring in the next 50 years. These are the devastating kinds of quakes that do strange things, like make the Mississippi River flow backward, as happened in 1811, according to Halihan. These earthquakes are relatively rare. Instead of modeling over 50 years, the new USGS maps for Kansas and Oklahoma cover just one year. They show a 1% or less risk of a major earthquake occurring during the year.
If this rare event happens, even the mostup- to- date buildings would experience earthquake forces as much as or more than 20 times greater than what they were built to withstand based on current building codes.
Only the most southern Kansas counties, such as Harper, are coloured red. But Sedgwick County and Wichita are close enough that they would still experience forces a number of times greater than what building codes dictate new buildings should withstand.
Many geologists have been operating on the assumption that the largest magnitude earthquake Kansas or Oklahoma might experience would be around a 5.6. That was the magnitude of the largest recent quake in
Lawrence shows a new crack on her garage floor. She claims that the foundation of her 1917 brick home in Kansas was damaged by the recent earthquakes. — TnS