Injection-Induced Earthquakes on Complex Fault Zones of the Raton Basin Illuminated by Machine-Learning Phase Picker and Dense Nodal Array

Abstract

Seismicity in the Raton Basin over the past two decades suggests reactivation of basement faults due to waste-water injection. In the summer of 2018, 96 short period three-component nodal instruments were installed in a highly active region of the basin for a month. A machine-learning based phase picker (PhaseNet) was adopted and identified millions of picks, which were associated into events using an automated algorithm-REAL (Rapid Earthquake Association and Location). After hypocenter relocation with hypoDD, the earthquake catalog contains 9,259 M-L-2.2 to 3 earthquakes focused at depths of 4-6 km. Magnitude of completeness (Mc) varies from -1 at nighttime to -0.5 in daytime, likely reflecting noise variation modulated by wind. The clustered hypocenters with variable depths and focal mechanisms suggest a complex network of basement faults. Frequency-magnitude statistics and the spatiotemporal evolution of seismicity are comparable to tectonic systems.