Evaluating hazards at salt cavern sites using multichannel analysis of surface waves

S resulting in sinkholes within dissolution mine fields in and around the city of Hutchinson, Kansas, USA (Figure 1) has been reported for more than 90 years. Salt dissolution and the resulting unpredictable upward migration of the dissolution voids can be observed both in proximity to well bores (dissolution mining, brine disposal, and oil wells; seismic shot holes, etc.) and in areas known to experience natural dissolution with no apparent anthropogenic influences. One potential outcome of the upward migration of these long-inactive dissolution voids in the city of Hutchinson is significant structural damage to facilities, infrastructure, or traffic areas. Monitoring the condition of a void’s roof is key to determining and managing this risk. Drilling is expensive for this investigative application in part because of the number of potential targets. At a depth of approximately 120 m, most surface geophysical methods have neither the sensitivity nor resolution necessary to detect these voids, much less interrogate the roof. From the shear modulus (stress/strain relationship), rock failure can be loosely predicted from the stress/strain curve. Because shear velocity is proportional to the shear modulus, increases in rock stress translate to increases in shear velocity. Therefore, the likelihood of failure of a void’s roof increases as the measured shear-wave velocity increases in the roof rock. Measuring shear velocity noninvasively in this urban setting and at these depths would be extremely challenging using any active seismic method. Considering the objectives and JULIAN IVANOV, Kansas Geological Survey BIRGIT LEITNER, Fugro, Austria GmbH, formerly University of Leoben WILLIAM SHEFCHIK, Burns and McDonnell Engineering Company J. TYLER SHWENK and SHELBY L. PETERIE, Kansas Geological Survey