North Texas Earthquake Study

Frequently Asked Questions

Following are answers – or links to sources for answers – to frequently asked questions about the SMU North Texas Earthquake Study, earthquakes and earthquake preparedness, Texas earthquakes, and induced earthquakes.

The SMU North Texas Earthquake Study

1) What is the goal of the research SMU is conducting into the recent spate of small earthquakes in the Reno-Azle area?

The primary research goal for the SMU seismology team will be to collect data from multiple locations and analyze that data to improve our understanding of the earthquake locations, size, fault plane solutions (geometry of the fault movement) and accelerations associated with the events. We do not know if we will collect enough data to point to a cause of the earthquakes.

 2) How is SMU conducting the Reno-Azle area research?

SMU has deployed several different types of earthquake monitors in the region: We first deployed five NetQuakes stations provided by the Unites States Geological Survey in the area identified as the epicenter for the quakes that occurred through January 2014. These small instruments are designed to be installed in private homes, businesses, public buildings and schools.

The raw, waveform data recorded by the Netquakes monitors is streamed to SMU over wireless and cell modem networks, where we identify and relocate earthquakes that are too small (~M<2.2) for the USGS to pick up at the National Earthquake Information Center. The USGS Data from the last 30 days of monitoring in the Reno-Azle area is available online through the USGS at http://escweb.wr.usgs.gov/cgi-bin/heliaz.pl 

Other monitors are being deployed throughout the region.  We have deployed seven continuous recording, higher performance seismic sensors to date. See how SMU teams installed one of these monitors by clicking here.

3) How long will the Reno-Azle study take to complete?

We will continue to monitor the earthquake sequence over the next six months to a year, unless activity remains high.  We have not determined a timeline for completing additional studies.  We do not consider our seismic studies complete until results have been published in peer-reviewed literature, which is the traditional, academic process that provides for thorough review of research methods and conclusions by qualified peers from within that scientific discipline. Past studies of seismicity in the Dallas-Fort Worth area have taken one to two years.

4) Can the Reno-Azle research determine if the earthquakes in that area are connected to wastewater injection wells operating nearby?

Understanding if and/or how wastewater injection wells contribute to seismicity requires not only improved identification of earthquake locations, but also high-resolution well log data and subsurface information about rock type, permeability, porosity and fault structures. Much of this data is collected by oil and gas companies as part of exploration and pre-drilling site verification, and ultimately it will take the cooperation and data sharing between the private and public sectors to make progress on this important science topic.  We cannot say at this time if we will be able to definitively, and in a scientifically verifiable way, show if the Reno-Azle sequence are induced or natural earthquakes.

5) Can the Reno-Azle research determine why North Texas as a whole is seeing in increase in felt seismicity in recent years?

No, an individual study of one active earthquake sequence, such as the Reno-Azle sequence, will not be able to address the larger question of increased seismicity throughout North Texas.   Long-term regional seismic monitoring would be helpful in order to assess the true background seismicity rate in the region and better capture small magnitude (M<3) earthquakes.

6) Who is SMU conducting its research for?

We hope to provide the residents of the Reno-Azle area with more accurate information regarding the ongoing earthquake sequence.  Financial support has been provided through Southern Methodist University with significant instrumentation and analysis support provided by the U.S. Geological Survey.

7) The residents in the Reno-Azle area have a lot of questions about these quakes.  Is there anything SMU seismologists can do to help them understand what’s going on?

This SMU website provides links to the U.S. Geological Survey Earthquake Education webpage and the Texas Earthquakes webpage supported by the University of Texas at Austin.  SMU seismologists also provide data to the Texas Railroad Commission and local municipalities upon request.  Additionally, we have purchased an Incorporated Research Institutions for Seismology (IRIS) Active Earth Monitor, which is a customizable computer-based earth science display designed for schools, libraries, etc.  The system provides an interactive way to learn about earthquakes. We are designing a Reno-Azle-specific module for this system and plan to place the system in a public area in the Reno-Azle area as soon it is delivered in March or April 2014. 

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Earthquakes and Earthquake Preparedness

8) Where can I find general information regarding earthquakes and earthquake preparedness?

The United States Geological Survey Frequently Asked Question page is an excellent source for general information about earthquakes and earthquake preparedness. http://earthquake.usgs.gov/learn/?source=sitenav

The National Earthquake Information Center also is a good source.

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Texas Earthquakes

9) People don’t think of Texas as an earthquake-prone region. Should we assume that the recent spate of earthquakes are induced by human activity, like injection wells?

Our earthquake observations in Texas recorded by monitoring equipment are limited to only the last few decades, with the best records generated in only the last 20 years.  This is a relatively short period for earthquake observations.  While we typically can extend the observations with historical records, these record only the reports of earthquakes people could actually feel – a historically sparse record. Texas does have a history of small naturally occurring earthquakes associated with the many existing faults in the subsurface. Further information about earthquakes throughout Texas can be found at http://www.ig.utexas.edu/research/seismology/TXEQ/index.html.

There are ~30,000 wastewater injection wells in the US, and the vast majority of them are located in areas where there have been no detected earthquakes. In 2011, there were eight case studies linking earthquakes to these wastewater wells in the US (Shemeta et al, 2012 National Research Council,  http://www.nap.edu/catalog.php?record_id=13355). The question is why? Understanding why a particular injection case might be associated with earthquakes while another similar well injecting under similar conditions seems not to be seismic is a critical question.

Finding the answers is complicated by the relationship of geology (such as the location of faults) to oil and gas production (extraction) or to wastewater disposal (injection), and even our growing ability to sense and locate earthquakes. It will take collaboration and shared data between scientists, industry and government to provide better information on the causes of induced seismicity.  

10) Two previous SMU studies have investigated connections between wastewater injection wells and seismicity – in the area around DFW Airport in 2009 and in the Cleburne area in 2010. Does that mean that wastewater iniection wells caused those earthquakes?

Both studies examined the temporal and spatial relationship between nearby injection wells and the earthquake sequences. For the DFW airport study, the fact that the injection well began operating shortly before the earthquakes began and that the earthquakes were close to the well, provided a plausible indication that injection was in some way related to the start of earthquakes.  In the case of the Cleburne area, although injection wells were located within a few kilometers of the earthquakes, there was not the strong timing relationship.  However, because there were no reported earthquakes prior to injection, the paper was not able to reject injection as a possible cause.  This is a weaker conclusion than in the DFW paper.

Both studies suffered from a lack of a physical explanation (a model) for exactly how fluid injection at specific sites could have resulted in the earthquake evolution over the observation period.  Neither study contained a detailed understanding of the fault geometry, subsurface geology, and subsurface stress regimes.  Neither study investigated similar natural sequences or similar injection histories with no associated earthquakes.  Without this understanding, neither study was able to suggest the future probability of larger events needed to develop the hazard associated with this fault.  Without such understanding, seismologists are limited to using relatively crude statistical methods based on the observation history in similar tectonic regions in the U.S.

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Induced Earthquakes

11) Is it accurate to describe the earthquakes that have been occurring in North Texas as “frackquakes?

No. Hydraulic fracturing or “fracking” is the process of creating fractures in subsurface rock formations by injecting fluid into cracks to create larger underground fissures, allowing more oil and gas to flow out of rock formations, from where it can be extracted.  The largest resulting seismic activity from hydraulic fracturing is typically hundreds to thousands of times smaller than the smallest earthquake that human beings can feel. In examining all reports worldwide, there have been only a few instances where hydraulic fracturing did appear to directly trigger a felt earthquake out of tens of thousands of successful operations. Such instances are very, very rare and have not, to our knowledge, happened in the North Texas area.  In the roughly 35,000 shale gas wells in the U.S., only two case studies are known (Shemeta et al, 2012 National Research Council).  The other documented hydraulic fracturing events include the M3.5 in Horn River, Canada, a M2.3 in Blackpool, UK in 2011, and the event in Basel, Switzerland in 2006.

Sometimes the waste fluids from producing oil and gas wells (those that use fracking to reach “tight gas”, as well as those that don’t) are disposed of by injection wells drilled below any fresh water aquifer.  The wastewater disposal is a separate process from the fracking operation itself and may occur away from the fracked well. Injection of wastewater can occur in oil fields unrelated to fracking.  

12) What is the relationship between induced seismicity and energy development?

Induced seismicity has been related to geothermal energy production, conventional oil and gas development (including enhanced oil recovery [EOR]), shale gas development, injection wells related to disposal of wastewater associated with energy extraction, and carbon capture and sequestration. A recent review can be found in Shemate et al, National Research Council, http://www.nap.edu/openbook.php?record_id=13355&page=59#c17

13) Where can I find additional information on induced seismicity in the United States?

The United States Geological Survey webpage on Induced Seismicity contains information, videos and links that address this question. http://earthquake.usgs.gov/research/induced/
 

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