The Microvibe, a broad band, light-weight and cost effective seismic source for near surface imaging

For shallow environmental and engineering surveys in generally unconsolidated sediment to depths of a few meters to several hundred metres high resolution seismic reflection surveys require heavy and expensive vibration sources such as a Minivib(TM). It weights 9 tons and costs approximately $400K. Best practice for optimized characterization of shallow surficial properties multi-component acquisition is required and this necessitates multiple passes and recording with the Minivibe - landstreamer system with the source being set in various horizontal and vertical directions. To provide a cheaper and lighter seismic source we have developed the Microvibe (180 kg and ~$30k) uses a suite of lighter electromagnetic transducers that can provide multicomponent seismic signal in a single pass. The Microvibe consists of forty tactile transducers, twenty per direction, on a solid concrete block mounted on a steel skid plate. This vibrator can provide various types of sweeps from 20 Hz up to 800 Hz with a power up to 2000 watts, for each direction, providing ~25% of the power provided by an IVI Minvib. To compensate for the reduced power level, we increase the time length of the sweep. The Microvibe provides higher frequency ranges than any known land seismic source available on the market. The Microvibe is coupled with an in-house built landstreamer array designed for use along paved or gravel roads. The landstreamer is built with 3 kg metal sleds connected using straps or low stretch ropes. The receiver spacing can vary from 0.75 m to 3 m. Receiver set-up is customized depending on the near-surface velocities and the targeted depths of observation. Each sled is equipped with a 3-component (3-C) geophone unit constructed in-house with 30 Hz omni-directional geophone elements oriented in three orthogonal directions: one vertical and two horizontal, in-line (parallel to the survey direction) and cross-line (perpendicular to the acquisition direction). The Microvibe - landstreamer combination allows data acquisition with shaking in vertical and horizontal directions in one pass to capture P-wave and S-wave seismic reflection sections. In order to demonstrate the value of this new geophysical tool, examples will be presented from a ground water example in the Vars - Winchester esker of southeastern Ontario. The system is also very efficient for evaluating the soft soil response for earthquakes and for locating neo-tectonic faults or buried tunnels.