Onset Time of Possibly-Induced Seismicity in the Delaware Basin, West Texas
Abstract
The Delaware Basin, a sedimentary sub-basin located within the West Texas portion of the Permian basin, is undergoing increasing seismicity rates. By 2017, the number of earthquakes in the Delaware Basin had exceeded the number of events in the Fort Worth Basin, and the larger events are focused near the city of Pecos in Reeves County.
To document when earthquake rates changed in Reeves County, we analyze continuous seismic data recorded by the Lajitas Array (TXAR) for the years 2000 to 2017. TXAR is a 10-station International Monitoring System 3 km aperture array consisting of 9 short-period vertical sites and 1 central broadband system that includes a 3-component short-period instrument, a posthole broadband instrument, and a 100 m borehole broadband instrument. The array noise levels are low, it has been in continual operation since 1993 and it is located 240 km south of Pecos. We developed a computer algorithm to identify P and S arrivals at the TXAR array. To locate Reeves County earthquakes, the algorithm evaluates phase arrival-time differences at the various TXAR stations to determine back azimuth values, and utilizes S-P arrival time differences to determine distance to the source. Reeves County earthquakes have back azimuths between 350° - 360° or 0° - 15°, and auto-detected S-P of 10 to 30 seconds. To assess seismic activity in Reeves County and surrounding regions, at broadband station TX31 we manually picked more than 8000 P and S times for events identified by the computer algorithm. Manual picking of P and S provides more accurate S-P times and removes spurious event detections. Locating manually-picked events for 2000-2018 reveals that Reeves County earthquakes began in 2009 with the number of events increasing into 2017; altogether we identified and located more than 5000 Reeves County earthquakes having local magnitudes of 0.8 and greater. Since the Delaware basin has been a region of high hydrocarbon production, we compare earthquake rates to oil and gas production data for the area, which saw a sizeable increase in the year 2009 based on yearly Texas Railroad Commission data. Future work will focus on expanding manual verification to the full Delaware Basin dataset and collecting more granular data on oil and gas operations in order to better understand cause and aid in mitigation strategies.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S23A0505R
- Keywords:
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- 4475 Scaling: spatial and temporal;
- NONLINEAR GEOPHYSICSDE: 7215 Earthquake source observations;
- SEISMOLOGYDE: 7223 Earthquake interaction;
- forecasting;
- and prediction;
- SEISMOLOGYDE: 8164 Stresses: crust and lithosphere;
- TECTONOPHYSICS