The Midland – Odessa earthquakes: An integrated study characterizing a series of recent earthquakes in west Texas

Abstract:

There has been a notable increase in seismicity near the cities of Midland and Odessa in west Texas. The epicentral region is within the Midland Basin and has been the center of extensive hydrocarbon production for decades, including the development of unconventional formations in recent years. Seismic activity has increased significantly, with the six known M3.0+ events all occurring in 2020. The epicenters are located in close proximity to populated urban areas, critical infrastructure and oil & gas operations. All of the M 3.0+ events were reported in Odessa and Midland. We investigate the locations and focal mechanisms of the events by integrating various methods to constrain the parameters for the largest events using the waveforms from TexNet seismic stations. We use a combination of first motion polarity and full waveform analysis to constrain the depth and focal plane mechanisms for these events. We use deep learning techniques to detect uncatalogued earthquakes, including aftershocks of the larger events and use them to further constrain the hypocentral patterns. In addition, the stress drops and consequently fault dimensions are estimated using an empirical Green’s function (EGF) approach. The velocity model is simultaneously optimized by using a combination of arrival times and sonic log data from nearby wells. Preliminary results indicate that the waveforms are consistent with a strike slip faulting mechanism and depths between 5-6.5 km. These results are used along with spatial and temporal correlation with nearby oil & gas operations to investigate whether these are natural or induced events. The analysis highlights the importance of a well constrained velocity model and station coverage in determining the parameters for smaller magnitude events. We also show how recent deployment of three seismic stations by TexNet in the vicinity of the events may help in reducing the uncertainty. Considering the proximity of these events to major urban centers and the potential risk they pose, increasing the number of public seismic stations in the area would facilitate tracking of the evolving seismicity.