HIGH-RESOLUTION SEISMIC REFLECTION INVESTIGATION OF A SUBSIDENCE FEATURE ON U.S. HIGHWAY 50 NEAR HUTCHINSON, KANSAS
Richard D. Miller and Jianghai Xia Kansas Geological Survey, 1930 Constant Avenue, Lawrence, Kansas
High-resolution seismic reflections were used to map the upper 150 m of the ground surface around and below an actively subsiding sinkhole currently affecting the stability of U.S. 50 highway in Reno County, Kansas. Primary objectives of this study were to delineate the subsurface expression of this growing salt dissolution induced sinkhole and appraise its threat to highway stability and the characteristically heavy commercial traffic load. The high signal-to-noise ratio and resolution of these seismic reflection data allowed detection, delineation, and evaluation of rock failure and associated episodes of material collapse into voids left after periodic and localized leaching of the 125 m deep, 40 m thick Permian Hutchinson Salt member. Mechanisms and gross chronology of structural failures as interpretable from stacked seismic sections suggest initial subsidence and associated bed offset occurred as accumulated stress was rapidly released and was constrained to a tensional dome defined by reverse fault planes. As the downward movement (settling, relaxation) of sediments slowed with little or no incremental build up of stress, gradual subsidence continued in the subsurface, advancing as an ever-expanding bowl, geometrically defined by normal fault planes.
Several episodes of subsidence are evident in most dissolution related features (current and paleo) imaged on these two 1 km long seismic profiles. The rate of destabilization and failure as well as the load bearing potential of the rock layers above zones of dissolution strongly influenced both the original subsidence geometries and dimensions as well as the subsequent reactivation of subsidence along the profiles. Current surface subsidence at the intersection of U.S. 50 and Victory Road is probably related to the reactivation of natural salt dissolution processes that produced the seismically imaged, 300 m wide subsidence feature interpreted to have been active during Tertiary and/or Quarter-nary. Alternately, recent failure of Permian rock layers above the salt bridging (roof rock) void or rubble areas that remained after the majority of the Tertiary to Quaternary subsidence had slowed or stopped could explain the most recent sinkhole development.
If salt dissolution has begun again at this site-anthropogenic or natural-it is not possible with these data alone to definitively identify a fluid source or pathway. However, with the superimposition of this modern sinkhole and the mid-Tertiary to early Quaternary subsidence feature, and considering the nearest disposal well with a history of fluid containment problems is more than 2 km away, the sinkhole is likely natural in origin. Unfortunately, considering the long history of oil field disposal well-induced dissolution in this area and the proximity of this particular site to the natural dissolution front, neither catalyst can be completely ruled out.
This study evaluated the effectiveness of using high-resolution vibroseis on the shoulder of
U.S. 50 when traffic was slowed but not stopped. Previous data collected in this area was acquired 1.5 kilometers south along a quiet, east/west county road using a small recording channel seismograph and an invasive, low energy, impulsive source survey. Equivalent dominant frequencies were recorded on both surveys, but recent efforts resulted in significantly greater energy penetration and a signal-to-noise ratio that resulted in usable data regardless of cultural noise levels. The bed resolution, coherency of bedding within subsidence features, and overall signal-to-noise ratio were greatly improved using minivibroseis survey techniques.