The 180-km-long Meers-Willow fault system in the Southern Oklahoma Aulacogen: A potential U.S. mid-continent seismic hazard

Abstract

We integrate new high-resolution aeromagnetic data with seismic reflection data, well logs, satellite remote sensing, and field observations to provide a regional view of buried and exposed structures in the Southern Oklahoma Aulacogen and to assess their potential for future seismicity. Trends ranging from NW−SE to ∼E−W, peaking at 330° ± 4.5° and 280° ± 3°, dominate the magnetic lineaments of the Southern Oklahoma Aulacogen, reflecting basement contacts, dikes, and faults, including a previously unmapped ∼100-km-long basement fault, which is herein referred to as the Willow fault. The fault disrupts, truncates, and vertically offsets basement-related seismic reflectors and overlying Paleozoic strata up through the Permian reflectors. Surface deformation along the trend includes fault-parallel monoclinal folds, pervasive fractures, and fracture-hosted mud dikes in Permian evaporite units. These structures indicate a Permian or post-Permian reactivation of the fault. Along-strike, the Willow fault connects to the NW-trending, seismically active Meers Fault to comprise the ∼180-km-long Meers-Willow fault system, which potentially represents a major seismic hazard along the Southern Oklahoma Aulacogen. Fault slip potential analyses of the mapped potential fault traces show that seismic hazards are elevated where faults have steeper dips. Given some uncertainty in the regional stress state, we also show that hazards along the NW−SE to E−W trending faults vary considerably within the uncertainty range. We propose that the Meers-Willow fault system originated as a Cambrian aulacogen-scale, basement-rooted fault that was later reactivated as a left-lateral strike-slip fault (with ∼40 km displacement) during the late Paleozoic Ancestral Rocky Mountain orogeny, highlighting that lateral offset accommodated a major component of deformation during the orogen.

Magnetotelluric Imaging of the Lithospheric Structure of the Southern Oklahoma Aulacogen: Evidence for Long‐Term Weakening Caused by Rifting

“…A second phase, dominated by sinistral strike‐slip movement, continued until sometime into the Permian (Brewer et al., 1983; Chase et al., 2022; Granath, 1989; Turko & Mitra, 2021). Overall, transpressional tectonics was the primary mechanism for SOA ARM deformation which resulted in ∼12–15 km of vertical uplift, ∼15 ± 5 km of crustal shortening, and sinistral strike slip deformation ranging from <1 km to as much as 40 km (Chase et al., 2022; Granath, 1989; Keller & Stephenson, 2007; McConnell, 1989; Perry, 1989; Turko & Mitra, 2021). Continued sedimentary deposition would occur in the newly created basins yielding the 12–15 km deep Anadarko and 2–4 km deep Holis‐Hardeman basins to the north and south of the SOA, respectively.…”

“…Some intermediate igneous rocks occur in the subsurface, with these units often intercalated with the rhyolitic units (Hanson et al., 2013). No calderas or volcanic centers have been reported, and feeder dikes are inferred to have produced most of the volcanism (McConnell & Gilbert, 1990), which can be defined in aeromagnetic data (Chase et al., 2022). Volcanism lasted from 539 to 529 Mya, was largely bimodal with limited breaks between phases, and most of the magmatism occurred in a ∼2 My timeframe from 532 to 530 Mya (Hogan & Gilbert, 1998; Wall et al., 2021).…”

“…The first phase and thrust faulting ceased by the Atokan (∼311–308 Ma). A second phase, dominated by sinistral strike‐slip movement, continued until sometime into the Permian (Brewer et al., 1983; Chase et al., 2022; Granath, 1989; Turko & Mitra, 2021). Overall, transpressional tectonics was the primary mechanism for SOA ARM deformation which resulted in ∼12–15 km of vertical uplift, ∼15 ± 5 km of crustal shortening, and sinistral strike slip deformation ranging from <1 km to as much as 40 km (Chase et al., 2022; Granath, 1989; Keller & Stephenson, 2007; McConnell, 1989; Perry, 1989; Turko & Mitra, 2021).…”

“…Study of the SOA provides the opportunity to understand (a) how Cambrian rifting modified the lithosphere, (b) if this modification is still preserved, and (c) how this modification may have influenced the evolution of the SOA during the ARM orogeny. Relative to the much of the regional basement the SOA is buried at shallow depths (100s of meters to <1 km) which has allowed it to be subjected to a wide variety of geochemical, geophysical, and structural studies (e.g., Brewer et al., 1983; Chase et al., 2022; Hanson et al., 2013). However, geophysical imaging of sufficient resolution at depths greater than the mid‐crust is lacking.…”

“…Proterozoic basin is fromBrewer et al (1983) andPratt et al (1992). Sense of strike-slip movement during Ancestral Rocky Mountain deformation is fromChase et al (2022). Note that the boundary between the Granite-Rhyolite and Mazatzal province is speculative and should not be taken as a definitive marker.…”