University of Texas at Austin

Texas Seismicity Studies

Synopsis: Seismicity analysis of Texas Permian Basin/Panhandle and building of local seismic velocity model and magnitude calibration for Texas

Project Status: active

Funding Source: 100% TexNet

Research Leaders: Jake Walter, Cliff Frohlich, Alexandros Savvaidis

Project Start: 3Q2015

Project Interface: Project closely interfaces with Ft. Worth Basin Earthquake Characterization, Faults and Geomodels, Basin-Scale Assessment of Fault Reactivation and Seismicity Potential, and Seismic Hazard and Risk Assessment - Shaking Intensity

Seismology research is an important component of TexNet and CISR and it complements and supports the other research elements. Detailed spatial and temporal earthquake observations provide rich datasets to investigate the physics of faulting – essential to all of the other components of the integrated research plan. The ability of the TexNet to locate and characterize earthquakes relies on developing robust velocity and magnitude calibration data for Texas. 

Expected research outcomes:

  • Methods for improved EQ location and depth
  • Maps of improved EQ locations
  • Seismic velocity model for TexNet earthquake locations
  • Detailed EQ characterizations for fault characterization and geomechanics modeling
  • EQ compilations for comparison with fluid injection data
  • Input for shake maps
  • EQ data to improve Vs30 maps in Texas

A primary activity of routine TexNet operations will be to accurately locate earthquakes at regional scales, with spatial (location) uncertainties of a few km or less when using permanent stations and uncertainties of 100’s of m when rapid-response stations are deployed. TexNet-CISR seismology research efforts will focus on developing and implementing cutting-edge methods to determine earthquake locations more accurately than possible with routine methods. While phase arrivals can sometimes be automatically picked accurately, ambiguous phase arrivals require careful re-analysis. Precise locations are achieved with these data and a locally-tailored seismic velocity model. Sometimes relocating aftershocks, or clusters of earthquakes, reveals new information about regional geology that has significance for seismic hazard analysis. For example, planar aftershock clouds may delineate previously unknown subsurface faults. Detailed spatial maps and temporal plots of seismic activity provide a baseline for all other aspects of TexNet-CISR research. These data will help constrain improved crustal seismic velocity models that will be distributed to the broader community through peer-reviewed publications and the CISR website.

The relationship between seismicity and injection (and/or extraction) exhibits varying behavior in the regions that we have already studied using Transportable Array data (e.g., Barnett of Texas, Haynesville of East Texas, and Bakken of North Dakota). Furthermore, out of the thousands of UIC Class II injection wells in Texas only a few are associated with nearby earthquakes. Thus, we will comprehensively study seismicity of the Permian Basin and Panhandle of Texas from mid-2008-2011, when the Transportable Array was installed there, and understand those findings in the context of injection/production well properties and local geology. Concurrently, we will begin to build a seismic velocity model and magnitude calibration for all of Texas. The importance of these elements, which are essential to the success of TexNet-CISR, is highlighted by news that agencies in some states may be considering regulatory rules that call for ceasing injection based on earthquake proximity and magnitude from an operating well. However, neither of these parameters can be accurate without a local seismic velocity model and magnitude scale calibrated to local crustal geology, calibrated for the different regions of Texas. This project will provide this model, which would be used by TexNet operations.

The Snyder-Cogdell oil field near Snyder, TX Texas has experienced several earthquakes ranging from magnitude ~2 to 4.4, most of which have occurred since 2006, including a M 2.7 as recently as April of 2016. The EarthScope USArray, a set of temporary stations deployed between 2009 and 2011 detected some of these earthquakes and provided much improved epicentral locations (Gan and Frohlich, 2012). However, the ~70 km USArray spacing was insufficient for estimating accurate focal depths of those earthquakes. We propose to deploy 9 portable stations with ~2 km spacing directly over the known seismicity and oil recovery area for an initial period of 6 months beginning in July 2016. We are currently cultivating a collaborative relationship with the field operator and believe the experiment will yield insight into the ongoing seismicity as well as reservoir mechanics.