25 February 2019

This E-Lecture "Bedrock and fracture zone delineation using different near-surface seismic sources" discusses a seismic survey conducted using four different small-scale and inexpensive seismic sources to delineate bedrock surface and a fracture zone intersected by a well at c. 50 m depth. The seismic sources analyzed are a 5-kg sledgehammer, a metal I-beam struck laterally, an accelerated weight drop and a prototype EM based seismic source with two hammers striking successively at an adjustable impact rate. From the recording perspective, a high-fold (star-type) acquisition spread was designed combining a three-component microelectro-mechanical system (MEMS) seismic landstreamer and wireless seismic recorders. The performance of every source used is analyzed and reflection seismic sections, along with 3D tomography results shown. The results indicate well delineated undulating bedrock topography, both on tomography and seismic sections for all sources. Weak reflectivity is observed where the fracture zone is expected. Most of the sources used show similar potential for fracture zone and near-surface imaging and star-type seismic array used enables 3D overview of the shallow subsurface and potential for pseudo 3D reflection seismic processing.

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