APPLICATIONS OF TROMINO® PASSIVE AND ACTIVE SEISMIC TECHNIQUES TO HYDROGEOLOGICAL QUESTIONS ACROSS IOWA

The Iowa Geological Survey (IGS) has begun using the passive and active seismic measurement capabilities of Tromino^® tromographs to complement a variety of groundwater resource projects and to also address new research questions. The passive seismic measurement technique is the horizontal-to-vertical spectral ratio (HVSR) microtremor analysis, which is utilized to determine depth-to-bedrock at the measurement point. To evaluate shallow subsurface sediments, the instrument is used as a geophone for seismic refraction and multichannel analysis of surface waves (MASW) techniques to evaluate the sediments of the shallow subsurface.

Three case studies are presented, the first being delineation of a buried bedrock valley aquifer in eastern Iowa through the collection of over 350 points for H/V analysis. The second case is the application of the HVSR, seismic refraction, and MASW capabilities to discern between different alluvial sediment layers and the bedrock surface in the Iowa River alluvial aquifer system. The third and final case presented is an exploratory study of the H/V technique to identify a karst cavity in the subsurface at Coldwater Cave in northeastern Iowa.