Seismic illumination of small-offset seismogenic faults, Anadarko Basin, Oklahoma

Interpretation:1-50 (forthcoming)

Abstract

In the past decade across the Central and Eastern U.S., there has been a substantial increase in the seismicity rate, which scientists broadly attribute to wastewater disposal and, to a lesser extent, hydraulic fracturing. Active clusters of seismicity illuminate linear fault segments within the crystalline basement that were unknown until seismicity began. Such surprises are due to the limited availability of 3D surface seismic surveys and the difficulty of imaging relatively shallow earthquake events from sparse seismic monitoring arrays. The Sooner Trend Anadarko Basin Canadian Kingfisher Counties play of Central Oklahoma provides an opportunity to map such basement faults. Modern high-quality surface seismic data acquired to map the Meramec and Woodford unconventional resource plays enable us to image the basement faults and intrusions. Furthermore, because of increased earthquake risk from anthropogenic activities in the past decade, state regulatory agencies have deployed a relatively dense array of seismic monitoring stations, which allows us to integrate earthquake data into subsurface fault analysis. We have mapped structural deformation using a suite of seismic attributes, including multispectral coherence, volumetric curvature, and aberrancy, in a 3D seismic reflection data set covering 625 sq mi of the STACK area of the Anadarko Basin, Oklahoma. To unravel the relationship between the structures and seismicity, we use relocated locally recorded earthquakes and compute the focal mechanism solution for the relocated events. Our results reveal previously unmapped fault segments with dominant north–south, northwest, and northeast trends, most of which extend into the shallower sedimentary Hunton and Woodford Formations. Because of the small offset, we find that aberrancy and the curvature attribute best illuminate the basement-rooted faults in the study area. Fault segments with significant offset are better illuminated by band-limited multispectral coherence. We argue that the inherited structure of these faults makes them easily illuminable by flexure-related seismic attributes, especially within the sedimentary cover. The integration of the illuminated faults with relocated earthquakes and focal mechanism solutions shows that some of the illuminated faults that have hosted intrasedimentary and/or basement seismicity are reactivated strike-slip faults. We hypothesize that careful attribute mapping of faults and flexures, coupled with an understanding of the local stress and geomechanical properties, calibrated with recent seismic activity in the area, can help mitigate seismic hazards in tectonic settings where small-offset faults predominate.

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