Seismic imaging using an e-vib — A case study analyzing the signal properties of a seismic vibrator driven by electric linear synchronous motors

Abstract

Seismic imaging characteristics of a prototype electrically driven, linear synchronous motor (LSM) based, vertical-force seismic vibrator (“e-vib”) were evaluated at a site in the Netherlands. The system weighs 1.65 t and excites seismic signals with a peak force of 6.7 kN. Data were recorded along two collocated geophone based-nodal and landstreamer MEMS-based (micro-electromechanical sensors) 2D seismic profiles. To obtain a broad bandwidth dataset, the e-vib operated with a 1-200 Hz linear sweep. Shot gathers of the merged nodal-landstreamer dataset show good quality seismic data of a broadband nature. The processed merged dataset demonstrates high-resolution reflections of the stratigraphic members from approximately 200 m to 2 km, with visible reflections as deep as 2.5 to 2.9 km. As a reference, we also processed a legacy 3D microspread dataset acquired at the same site with a magnitude stronger (14.1 t, 67.5 kN) hydraulic vibrator. Comparison of our nodal-landstreamer seismic section versus 2D slices extracted from the processed microspread volume suggests similar signal penetration depth and same key marker horizons seen in both. Analysis of the reaction mass and base-plate accelerometer signals recorded with the e-vib source operating both on grass and asphalt surfaces shows that the e-vib has low total harmonic distortion. The results obtained indicate that, although relatively small, the e-vib is capable of generating high-quality, broadband seismic data.

Broadband seismic source data acquisition and processing to delineate iron oxide deposits in the Blötberget mine‐central Sweden

“…Additionally, tested methods for raw vibrogram compression involved base plate and reaction mass signals cross‐correlation and ground‐force deconvolution (Ghose, 2002) with cross‐correlation with the theoretical sweep providing the best results (e.g. Boucard and Ollivrin, 2010; Brodic et al ., 2021a). The theoretical sweep provided better continuity of the first breaks and the expected mineralization reflection.…”

“…2b). When an electrical current is induced in the coil, linear forces are generated, acting along a line over the full stroke, which results in lower harmonic distortion, thus allowing a wider range of low frequencies to be produced (Li et al ., 2019; Noorlandt et al ., 2015; Brodic et al ., 2021a, 2021b). The forces generated are transferred into the subsurface via a ground‐coupled base plate while the suppression mechanism reduces the resonance produced by the mass of the carrier vehicle and improves ground coupling.…”

“…The source weighs approximately 1650 kg, operates at a constant drive level with a peak force of 7 kN and requires 14 kW of power to operate. The absence of hydraulics, combined with the frictionless guidance system of the LSMs behind the E‐Vib overcome some of the intrinsic limitations of the hydraulic vibrators (Sallas, 2010; Bagaini et al ., 2014; Brodic et al ., 2021a). To support this, in studies conducted by Sallas (2010) it was found that more than two third of the power produced by a hydraulic vibrator engine is transferred as heat, thus not usable.…”

“…(2015) and Brodic et al . (2021a). To be better suited for hardrock surveys and within a larger research and innovation project, the source was upgraded and ruggedized to withstand different ground coupling and weather conditions (Fig.…”

“…The source provides a flat amplitude response capable of a 2–200‐Hz bandwidth at a peak force of approximately 7 kN. Earlier tests with the source were done at a sedimentary rock setting and inside mining tunnels (Brodic et al ., 2021a, 2021b; Donoso et al ., 2021), while in this study we validated the source on the surface at a hardrock site, more specifically, an iron oxide deposit located near Blötberget in central Sweden (Fig. 1).…”