ELECTRICAL RESISTIVITY TOMOGRAPHY SURVEYS OF THE PAWNEE BILL MANSION CREEP, BLUE HAWK PEAK, OKLAHOMA

Recent seismicity in Central Oklahoma has had a substantial impact not only on the local petroleum industry through increased regulation of injection and disposal well volumes but also on local communities. The Pawnee Bill Mansion is a historical landmark that rests on the edge of Blue Hawk Peak, Pawnee County, Oklahoma and has sustained significant structural damage over the past 20 years. Local earthquakes such as the September 3, 2016 Mw5.8 Pawnee earthquake has accelerated the damage and creep of the mansion down the 15° slope. As a result, the west-facing wall and patio have accommodated ~8cm of separation while the northeast corner of the mansion has also begun to display surface fractures in the rock and cement façade. In order to understand the damage to the cultural landmark and its preservation we characterized the local subsurface with electrical resistivity tomography. Our surveys spanning across different seasons and precipitation levels reveal an electrically heterogeneous subsurface with a 3m-thick layer of 100-600 Ωm underlying the mansion. Beneath the upper resistive layer lies a thick substratum of 15-55 Ωm with localized zones of low resistivity (5-10 Ωm). The bottom of the profile displays a discontinuous layer with similar moderately high resistivity (100-600 Ωm). The upper and lower layers of high resistivity are interpreted to be limestone bedrock that outcrops on site, while the low resistivity zones are thought to be areas of high clay and moisture content representing possible localized dissolution zones within the bedrock.