Towards low-impact sources for near-surface characterization

Conventional seismic sources, such as airguns, dynamite and hammers/thumpers, produce high-amplitude signals that are unsuitable for use in areas with structural sensitivity or within Marine Protected Areas (MPAs) due to their environmental impact. As a remedy, low-impact sources emitting long, deterministic, noise-like signatures offer a promising alternative. These signals not only reduce peak amplitudes but also provide technical advantages such as spectral shaping, amplitude control, repeatability, and the ability to multiplex sources. In this study, we explore the use of such deterministic noise-like signatures through a series of proof-of-concept trials using commercially available low-impact sources. We are targeting near-surface seismic characterization, focusing on the shallow structural and geotechnical properties. We tested electric vibrators and underwater transducers across three environments, i.e., land, lake, and offshore, to evaluate their performance and environmental impact. The land trial demonstrated that pseudo-random binary sequences emitted by an electric vibrator could generate clear surface-wave dispersion curves with significantly lower particle velocities than traditional hammer sources. In the lake trial, an underwater transducer produced seismic signals with amplitudes up to 35 dB lower than a small airgun (5 cubic inches), while still delivering comparable signal-to-noise ratio data quality. The offshore trial showed that the same transducer could acquire ultra-high resolution data, like 2D seismic data, across a broad frequency range (200-1000 Hz) in MPAs where impulsive sources are restricted. We also present a fast-track processing workflow that enables effective signal recovery and imaging using these continuous sources. These findings confirm that low-impact, deterministic sources are a viable and environmentally responsible alternative for near-surface seismic investigations, particularly in sensitive or regulated areas.