Aeromagnetic Data Reveal Potential Seismogenic Basement Faults in the Induced Seismicity Setting of Oklahoma

Abstract

New aeromagnetic survey data collected over north central Oklahoma image possible seismogenic faults in the crystalline basement. Linear earthquake sequences associated with induced seismicity suggest the reactivation of ancient basement faults, but few of these sequences are aligned with mapped faults. The new data show many earthquake sequences aligned with linear magnetic gradients or offsets between anomalies, while mapped faults, which mainly describe sedimentary cover, show limited correspondence with either. This strongly suggests significant structural differences between the crystalline basement and sedimentary cover. Furthermore, while the earthquakes are occurring on reactivated ancient faults, most of these faults have likely been inactive for millions of years. The magnetic data exhibit many gradient lineaments that are optimally oriented for fault slip, and the earthquake data suggest additional optimally oriented faults. Together these data suggest the presence of potentially numerous seismogenic faults throughout the region, which may contribute to high levels of induced seismicity.

Detailed 3D Seismic Velocity Structure of the Prague, Oklahoma Fault Zone and the Implications for Induced Seismicity

“…The 3D velocity models show near‐vertical, low‐velocity zones (Figures 3b and 3d) with low Vp/Vs (Figure 3f) occurring between 2.5 and 8 km depth, coincident with the coseismic rupture of the mainshock and spatial extent of the aftershocks. In addition, the vertical variations of the velocity and Vp/Vs structures (e.g., "Layer 2" vs. "Layer 3" in Figure 3c) suggest that small‐scale complexities do exist within the fault zone, as previously recognized by Shah and Crain (2018). It should be noted that our model has a spatial resolution of ∼2.5 km, which prevents the identification of minor fault structures, such as the EW‐trending fault branch outlined by the aftershocks of the Mw 4.8 aftershock on 8 November 2011 (Cochran et al., 2020; McMahon et al., 2017).…”

“…WFZ is the most significant mapped fault system near the Prague area, but the distribution of earthquakes (Figures 1 and 2) suggests that the unmapped NE‐oriented MPF, instead of the WFZ, is the primary host of the 2011 Prague sequence (Keranen et al., 2013; McMahon et al., 2017). Aeromagnetic Data reveals a correlation between low magnetic anomalies and MPF with strong heterogeneities within the fault zone (Shah & Crain, 2018). Yet, there has been no high‐resolution tomographic studies to date at local scale to constrain the detailed morphology of MPF and its relationship with the Prague sequence.…”

Rift Basins and Intraplate Earthquakes: New High‐Resolution Aeromagnetic Data Provide Insights Into Buried Structures of the Charleston, South Carolina Seismic Zone

“…Such differences may arise because (a) older faults in the crystalline basement might not have propagated into the younger unconsolidated sediments, especially if slip on those faults is no longer favored in the current stress regime, (b) faults in the sedimentary rocks might not have counterparts in the crystalline basement, but slip on them may have generated offsets in the overlying unconsolidated sediments, and (c) some basement faults might have little vertical offset and so were not imaged by the aeromagnetic data. Scenarios analogous to (a) and (b) have been observed elsewhere, such as is Oklahoma, where faults imaged via aeromagnetic and earthquake data were correlated with each other but different from those based on data imaging the upper 2–3 km of Paleozoic sedimentary rock (Schoenball et al., 2018; Shah & Crain, 2018). We note that seismicity in Oklahoma has not, to date, been directly correlated with surface ruptures.…”

“…The location and characterization of faults of interest typically require analyses of multiple types of data sets (e.g., Pratt et al., 2022; Thompson Jobe et al., 2020). To understand subsurface structures and their geologic context, methods that image depths where earthquakes occur such as aeromagnetic surveys and deep seismic reflection profiling (e.g., Blakely et al., 2002; Shah & Crain, 2018) are needed. Not all faults imaged using these methods are active in the modern stress regime, however.…”

Evidence for Post‐Assembly Modification of Western Laurentia by Back‐Arc Extension

“…The increased risk in these areas, such as the SCD, could arise due to relatively increased structural complexity linked to a higher abundance of brittle fault structures, compared with magmatic belts or high‐grade metamorphic terranes in the upper crystalline basement. Basement structures that may control fault structures that host induced earthquakes are often expressed as linear features on magnetic maps (Shah & Crain, 2018); thus, potential‐field anomaly fabrics such as the SA are of particular relevance for the development of induced seismicity risk models.…”