Complex Seismotectonic Characteristics in the Midland Basin of Texas: Constrained by Seismicity and Earthquake Source Mechanisms

Abstract

Earthquake activities in areas across the Midland basin and the Central Basin Platform of West Texas have significantly increased since mid-2019 because of continuing industrial activities involving wastewater injection. The induced seismicity has allowed us to discover previously unknown seismogenic structures. This article presents a study focusing on seismotectonic characteristics of the Midland basin. For this purpose, we first delineated seismicity to identify seismogenic structures. In addition, we performed waveform moment tensor inversion to determine earthquake source mechanisms; subsequently, we inverted for the regional stress field using the obtained source mechanisms. As a result, we have obtained 150 focal mechanisms (from 2017 to November 2023). Based on the seismicity distribution and source mechanism patterns, we have identified 15 distinctive seismogenic zones. A vast majority of seismicity are located in the crystalline basement. Most of the 15 seismicity zones contain seismogenic structures commonly presenting linear geometry but with various orientation. Although the inverted focal mechanisms are a mix of strike-slip and normal faulting, the inverted stress field contains the least compression axes (S3) commonly oriented in 330° azimuth across the 15 identified seismogenic zones. A combination of all seismogenic features has demonstrated that the Midland basin contains fault architectures resulting from the latest extensional tectonic activities, creating a series of basement-rooted strike-slip and normal faults. The two types of basement-rooted faults coexist in our study area, where a presumed basement-rooted rift system transects the Midland basin. They are reactivated by the current fluid injection.