The Raton Basin is known as an area of injection induced seismicity for the past two decades, but the reactivated fault zone structures and spatiotemporal response of seismicity to evolving injection have been poorly constrained in the past due to scarce public monitoring. Application of a machine-learning phase picker to four years of continuous data from a local array enables the detection and location of ~38,000 earthquakes. The events between 2016-2020 are ~2.5-6 km below sea level and range from ML<-1 to 4.2. Most earthquakes occur within previously identified ~N-S zones of seismicity, however our new catalog illuminates these zones are composed of many short faults with variable orientations. The two most active zones, the Vermejo Park and Tercio, are potentially linked by small intermediate faults. In total, we find ~60 short (<3 km) basement faults with strikes from WNW to slightly east of N. Faulting mechanisms are predominantly normal but some variability, including reverse dip-slip and oblique-slip, is observed. The Trinidad fault zone that hosted the 2011 Mw 5.3 earthquake is quiescent during 2016-2020, likely in response to decreased wastewater injection after 2012 and the shut-in of two nearby wells in 2015. Unlike some induced seismicity regions with higher injection rates, Raton Basin frequency-magnitude and spatiotemporal statistics are not distinguishable from tectonic seismicity. The similarity suggests that induced earthquakes in the Raton Basin are dominantly releasing tectonic stress.

Volcanic arcs consist of many distinct vents that are ultimately fueled by the common process of melting in the subduction zone mantle wedge. Seismic imaging of crustal scale magmatic systems can provide insight into how melt is organized in the deep crust and eventually focused beneath distinct vents as it ascends and evolves. Here we investigate the crustal-scale structure beneath a section of the Cascades arc spanning four major stratovolcanoes: Mt. Hood, Mt. St. Helens, Mt. Adams, and Mt. Rainier, based on ambient noise interferometry measurements from 234 seismographs. Simultaneous inversion of Rayleigh and Love wave dispersion better constrain the isotropic shear velocity (Vs) and identify the unusual occurrence of radially anisotropic structures. Isotropic Vs shows two sub-parallel low-Vs zones at ~15-30 km depth with one connecting Mt. Rainier to Mt. Adams, and another connecting Mt. St. Helens to Mt. Hood, which are interpreted as deep crustal magma reservoirs containing up to ~2.5-6% melt, assuming near-equilibrium melt geometry. Negative radial anisotropy is prevalent in this part of the Cascadia margin, but is interrupted by positive radial anisotropy extending vertically beneath Mt. Adams and Mt. Rainier at ~10-30 km depth and weaker positive anisotropy beneath Mt. St. Helens with a west dipping. The positive anisotropy regions are adjacent to rather than co-located with the isotropic low-Vs anomalies. Ascending melt that stalled and mostly crystallized in sills with possible compositional difference from the country rock may explain the near-average Vs and positive radial anisotropy adjacent to the active deep crustal magma reservoirs.