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Remarks prepared by SMU seismologists for Jan. 15 Irving City Council meeting

Presented by Brian Stump, the Albritton Chair of Geological Sciences at SMU

January 16, 2015

I would like to thank you, the Irving City Council, for the opportunity to appear tonight and discuss the recent seismic activity in the area.  These earthquakes highlight the dynamic interplay of stresses and old faults within the earth’s crust, even here in the flatlands of North Texas, and the need to understand how and when such stresses can give rise to earthquakes.  To date, all of the North Texas earthquakes have been small, less than magnitude 4.  The fact that they have been widely felt and have continued over months has naturally raised concerns.

Report an Earthquake to the USGS
"Did You Feel It?" site.


A sample of news coverage of the Irving quakes.
Irving City Council
Watch the presentation to the Irving City Council

Jan. 6 media briefing on earthquakes.

B-Roll of Irving installation Jan. 5
     

The seismologists at SMU have been recording earthquakes in North Texas since 2008, but it is only with the close cooperation of local community governments, officials, organizations, and citizens willing to help deploy and host seismographs that such critical observations are possible.  In this most recent case for example, Jason Carriere, the Emergency Management Coordinator for the Irving Police Department and his colleagues and peers have made possible the very rapid deployment of seismographs following the M3.5 and 3.6 earthquakes only 9 days ago.

I have prepared short remarks and then we are available for questions that you might have.  My intention with these remarks is to highlight four points:

  • First, I’ll summarize the ongoing seismic activity in Irving-Dallas in the context of the rest of the seismicity that has occurred in the Fort Worth Basin since 2008;
  • Second, I’ll provide an overview of the current study of the Irving earthquake swarm and anticipated outcomes;
  • Third, I’ll list possible subsequent steps following the deployment of instruments designed to explore the cause of the activity; and
  • Finally, I’ll have some brief remarks concerning assessment of earthquake hazards and preparation going forward. 

The overview of past and ongoing research  related to possible linkages between human activities and earthquakes will not be explicitly covered tonight although you have been supplied the materials we presented to the  Texas House Subcommittee on Seismicity on 12 May 2014 and it is also available at: www.smu.edu/News/NewsIssues/EarthquakeStudy.

The Irving earthquake sequence appears to have begun on 17 April 2014 with a magnitude 2.4 event and has been followed by thirty-seven additional events as identified by the United States Geological Survey (or USGS), including the magnitude 3.5 and 3.6 earthquakes last Tuesday.  A number of these have been widely felt across the area with a total of four above magnitude 3.  Because the two largest events are of almost equal magnitude and occurred close in time to one another, we and others have called this an earthquake swarm as opposed to a single main earthquake followed by aftershocks.

It is important to put this swarm into the context of the activity that has occurred across the DFW Metroplex since Halloween night 2008.  Prior to 2008 there were no historic seismic events in the area and only one possible felt event 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.  As an aside, I would like to encourage everyone to file reports on the earthquakes they feel using the USGS “Did You Feel It” website (earthquake.usgs.gov/earthquakes/eventpage/dyfi/).  We have great technology, but reports from people who have felt earthquakes are quite useful in interpreting the location of an earthquake, its size and how seismic waves decrease in amplitude as they move away from the earthquake source.  Since October 31, 2008, the USGS has located over 120 earthquakes in our area.  The Irving earthquakes represent the fourth sequence to be studied in our local area over the last six years.   The first was an earthquake sequence centered near DFW 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.  In all of these cases earthquakes got smaller and further apart in time following the largest events.  Additional focus areas of seismicity based on USGS locations exist NE of Cleburne, near Mineral Wells and in the Venus/Midlothian area but have not been well studied.  Within the context of the increased seismicity in the area, the most recent swarm has similar characteristics to the others.

Turning to the recent Irving swarm, it is important to recognize that the USGS has primary responsibility in the US for locating earthquakes as well as providing earthquake hazard assessment.  They complete this task with a high quality network of seismic stations deployed across the United States.  In the case of the largest Irving earthquake, the existing USGS seismic stations used to first locate the event were as close as 40 miles and as far as 922 miles.  As you can imagine, using seimic waves from such distant stations typically results in intrinsic errors in location estimates that can be as large as 3-6 miles.  These errors are large enough that it can be difficult to assign an earthquake or swarm  to a particular fault, which is critical to understanding the process.  As a result, the deployment of additional seismic stations closer to initial earthquake location estimates provides the basis for refining these locations in order to attribute them to a fault.  In areas such as California where earthquake activity is high, permanent seismic stations are already installed with spacing adequate to provide these types of refined earthquake locations.  We in North Texas do not have such a network. 

Before Tuesday, January 6,  there were only three seismic stations within about 10 miles of the events, one of which was deployed on Monday afternoon, January 5.  In order to improve our mapping of the fault causing these earthquakes, over the last week we have worked with the City of Irving and others to deploy additional seismometers designed to provide high precision locations.  Today we have a total of 22 instruments fielded,  although 14 of them are designed to record for only 10 days and will be recovered by the end of the week.  Data from a number of these instruments is being shared with the USGS in order to enhance their real-time analysis of any subsequent earthquakes.  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 DFW airport, Cleburne and Azle.  The timing of this work is dependent on how much longer subsequent earthquakes occur in the coming weeks.  Once the fault location is refined, the data provdes a basis for improving the location estimates of the earthquakes that occurred before the local stations were deployed.  Thanks to the support of City of Irving, this deployment subsequent to the largest events last Tuesday has been the most rapid of any of the sequences in the area and will provide one of the best data sets for assessing the swarm.

Irving EarthquakesThe third thing I want to discuss are the next steps in a study like this one.  Once the locations have been completed, only then can we assess possible causes.  We will consider a wide-range of possibilities, including whether the earthquakes are strictly natural or possibly associated with human activities.  In either case, the waves released from the earthquake are associated with pre-existing stored energy along natural faults.  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 identfied commercial activities, and development of detailed subsurface geology and rock properties.  If there are near-by commercial activities related to the injection or recovery of fluids, it might be that the impact of the associated fluids on near-by faults will be important to explore and thus require additional supporting data.  In the case of two of the previous earthquake sequences, those near DFW 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. 

Finally, I want to touch briefly on the seismic activity and its possible hazard to our communities.  It is important for you to understand that this area is beyond our specific expertise and an important area for continued cooperation with the USGS.  All of the events since 2008 have been small and, although startling to all of us when we feel them - they have not been large enough to cause significant damage.  The fact that the events appear to be shallow, 2-5 miles deep, means they are close to the surface where we live and thus well felt.  The previous sequences have decayed away following the largest event with magnitudes similar to those experienced last Tuesday.  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.  But at this time we cannot rule out the possibiltiy of larger earthquakes, some possibly damaging.  I believe these statements are consistent with guidance provided by the USGS.  Recent earthquakes in West Texas, East Texas and South Texas have been large enough that they might cause some damage if they occurred in our area, and thus motivates the assessment of current seismicity in our local area and meetings like this one tonight.  The USGS is an excellent resource for both hazard assessment and preparedness and therefore I encourage the local governments to work with these experts.

I close with thanks again for the leadership of the City of Irving, the support of the City of Dallas, the cooperation of the USGS, instrumentation from IRIS, and help provided by a number of individuals in the area over the last ten days.  These events have led to cooperation and collaboration with a number of groups, governments and organizations.  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.  Communities need to be able to make informed decisions about preparation as well as improve hazard assessment.  Such a comprehensive study will need to involve contributions from a diverse collection of individuals within government, industry and academia with expertise across a broad spectrum.



January 7 statement from SMU Seismology Team

DALLAS (SMU) – SMU’s seismology team will deploy 22 more seismographs in the Irving area over the next few days to better understand the series of earthquakes that United States Geological Survey (USGS) data indicates are occurring on or near the site of the old Texas Stadium.

Fifteen monitors are being deployed today, Jan. 7.  Two more being provided by the USGS are expected to arrive and be deployed Thursday, and another five provided by Incorporated Research Institutions for Seismology (IRIS) are scheduled for deployment Friday.

The SMU scientists stress that learning more about this recent series of earthquakes will be an incremental process.

“In the near term, our first step is to put out seismographs to confirm and refine the location of the quakes and define the faults in the area,” said Heather DeShon, associate professor of physics at SMU. “Only after we get that data will we be in a position to investigate the potential cause of the earthquakes.”

The current earthquakes are the fourth sequence of felt earthquakes recorded in the Fort Worth Basin since 2008.  The previous earthquakes sequences occurred near DFW Airport, Cleburne, and the Reno-Azle area.  SMU studies of the DFW and Cleburne quakes cited wastewater injection wells as a plausible cause of the seismicity in those areas. Information on those previous SMU studies is available at http://www.smu.edu/News/NewsIssues/EarthquakeStudy. The report on the earthquakes in the Azle-Reno area has not yet been released.

“It’s premature to speculate on the cause of this current series of seismic events,” said Brian Stump, SMU’s Albritton Chair of Geological Sciences. “We’re just getting started. We want to support the local community in understanding these earthquakes, and the team appreciates the cooperation of the City of Irving, the United States Geological Survey and IRIS in helping us get the best information possible.”


January 6 statement from SMU Seismologist Brian Stump

SMU’s seismology team is committed to helping North Texans understand more about the increasing number of earthquakes felt in our region over the last few years, most recently near the City of Irving. 

A 2.4-magnitude earthquake recorded at 8:29 p.m. Jan. 1, 2015, and estimated to be near the old Texas Stadium site was the 17th earthquake felt in the area since early September.

An SMU team installed one portable seismometer in a building on the northeast side of the City of Irving Monday, Jan. 5, aiming to supplement data being collected from more distant sites by the United States Geological Survey to identify the location of the quakes.  The location of the Irving seismometer is not being made public to preserve the integrity of the data it collects.

This latest installation provides a third source of data SMU can tap in helping to determine the location of the Irving-area earthquakes.  The seismology team also can retrieve data from a University-controlled portable seismometer previously installed at a site south of DFW airport, as well as the seismometer permanently installed in the basement of Heroy Hall on the SMU campus. 

SMU’s interest in these Irving-area earthquakes is at this point focused on helping to identify their exact location. 

The University’s seismology team is not currently engaged in a larger study of the cause of the Irving quakes, but I will brief the Irving City Council Jan. 15 on what data might be expected from the Irving installation, as well as on the results of past research into earthquakes in the Fort Worth Basin. Information on those previous SMU studies is available at http://www.smu.edu/News/NewsIssues/EarthquakeStudy.

There has been a significant increase in earthquakes in the Fort Worth basin since October 2008. It’s important to all of us to learn as much as we can about them.

Related Links:

About the Seismology Team

  Earthquake Study Team Brian Stump, SMU Claude C. Albritton Chair in Geological Sciences, whose previous research includes studies of earthquakes that began in the DFW airport area in 2008 and in the Cleburne area in 2009.
  Earthquake Study Team Heather DeShon, SMU associate professor of geophysics, led the Reno-Azle research team, and a report is pending.
  Earthquake Study Team Chris Hayward, senior scientist and director of the Geophysics Research Program.
  Earthquake Study Team Matt Hornbach, Associate Professor of Geophysics
  Earthquake Study Team Beatrice Magnani, Associate Professor of Geophysics
  Earthquake Study Team Remi Oldham, SMU geophysics graduate student and member of the monitor installation team.
  Earthquake Study Team Mason MacPhail, SMU geophysics graduate student and member of the monitor installation team.
  Earthquake Study Team Chris Cain, SMU seismo-acoustic technician.
  Kevin Kwong Kevin Kwong, SMU geophysics graduate student.