Seismicity in the Delaware basin is suggested to be associated with oilfield operations. To better characterize the seismogenic structures revealed by the induced seismicity, in this study we determined source mechanisms for the Delaware basin of Texas and leveraged the obtained source mechanisms to perform stress inversion for evaluating the region’s stress state. Based on the seismogenic patterns and seismicity distribution, we identified seven distinctive seismogenic zones. Within each zone, earthquakes form several parallel-trending linear clusters. Most notably, there is an observable change in the seismicity trend on either side of the basin-bisecting Grisham fault zone. In addition, the extent of hypocentral depths vary drastically across the fault zone, with events located below the basin–basement interface north of the fault zone and more shallowly to the south. We also see spatial variations of source mechanism patterns and the direction of the maximum horizontal stress across the Delaware basin. A vast majority of seismic moment release can be attributed to the basement-rooted tectonic faults in the Culberson–Mentone seismogenic zone. A statistic deficit present in the magnitude–frequency distribution suggests that earthquakes with M_w 3.8–4.7 are needed to fulfill this scaling law. It indicates a strong possibility for future occurrence of earthquakes within this magnitude range.

Analysis of earthquake locations and centroid moment tensors (CMTs) is critical in assessing seismogenic structures and connecting earthquakes to anthropogenic activities. The objective of this study was to gain insights into the seismotectonics of the Eagle Ford Shale play (EF), southern Texas, through relative relocation of earthquakes, assessment of CMT solutions, and investigation of the background stress field. Using Texas Seismological Network (TexNet) data from 2017 through 2019, we were able to relocate 326 earthquakes and obtain CMT solutions for 37 ML ≥2:0 earthquakes. These earthquakes are located in the sedimentary basin and uppermost crust, with depths ranging from 2 to 10 km. The earthquake groups in the northeastern EF are linearly distributed along the Karnes fault zone, whereas the southern and western groups are spatially scattered around mapped or unmapped faults. CMTsolutions identified 32 normal fault earthquakes and five strike-slip earthquakes. The orientation of the fault plane of most normal fault earthquakes is southwest-northeast, whereas the possible fault plane of the strike-slip fault is from north-northwest to south-southeast, which is roughly perpendicular to the normal faults. Normal and strike-slip faults in the EF are of high dip angles, with the dip angles of the most faults ranging from 60° to 80°. Stress inversion results show that the major orientation of maximum horizontal stress (SHmax) is southwest-northeast, with minor local stress-field rotations. We further estimated earthquake energy release in the EF region using moment magnitude from the CMT solutions, and the cumulative earthquake energy release curve reveals three notable increases in cumulative seismic moment, which occurred in January-July 2018 and January-March 2019, and May-August 2019. Whether these energy releases were caused by anthropogenic activities is a matter for further investigation.