Origin and Periodic Behavior of Short Duration Signals Recorded by Seismometers at Vestnesa Ridge, an Active Seepage Site on the West-Svalbard Continental Margin

Abstract

Short duration events (SDEs) are reported worldwide from ocean-bottom seismometers (OBSs). Due to their high frequency (4–30 Hz) and short duration, they are commonly attributed to aseismic sources, such as fluid migration related processes from cold seeps, biological signals, or noise. We present the results of a passive seismic experiment that deployed an OBS network for 10-month (October 2015–July 2016) at an active seepage site on Vestnesa Ridge, West Svalbard continental margin. We characterize SDEs and their temporal occurrence using the conventional short-time-average over long-time-average approach. Signal periodograms show that SDEs have periodic patterns related to solar and lunar cycles. A monthly correlation between SDE occurrences and modelled tides for the area indicates that tides have a partial control on SDEs recorded over 10 months. The numbers of SDEs increase close to the tidal minima and maxima, although a correlation with tidal highs appears more robust. Large bursts of SDEs are separated by interim quiet cycles. In contrast, the periodicity analysis of tremors shows a different pattern, likely caused by the effect of tidally controlled underwater currents on the instrumentation. We suggest that SDEs at Vestnesa Ridge may be related to the dynamics of the methane seepage system which is characterized by a complex interaction between migration of deep sourced fluids, gas hydrate formation and seafloor gas advection through cracks. Our observation from this investigated area offshore west-Svalbard, is in line with the documentation of SDEs from other continental margins, where micro-seismicity and gas release into the water column are seemingly connected.

Sedimentary deformation relating to episodic seepage in the last 1.2 million years: a multi-scale seismic study from the Vestnesa Ridge, eastern Fram Strait

“…Two large (ca. 500 m in diameter) pockmarks (i.e., Lunde and Lomvi), have been used to study paleo-methane seepage and methane transport mechanisms (Smith et al, 2014;Panieri et al, 2017;Dessandier et al, 2019;Yao et al, 2019;Hong et al, 2021;Sauer et al, 2021;Domel et al, 2022). Previous studies suggest that the regional stress regime is the main external factor controlling the long-term pattern of gas seepage here (Plaza-Faverola and Keiding, 2019).…”

“…The inactivity of pockmarks in the west, however, does not rule out the possibility that seepage is occurring as micro-seepage or intermittently. Recent studies suggest that seepage periodicity at the Vestnesa Ridge may be related to pressure changes induced by sea-level changes or other external mechanisms able to generate seismicity (Domel et al, 2022); other studies suggest that external pressure is generated by sediment compaction, gravity sliding, and glacial isostatic adjustment (controlled by varying ice sheet thicknesses) (Himmler et al, 2019;Vachon et al, 2022).…”

Stress Constraints From Shear‐Wave Analysis in Shallow Sediments at an Actively Seeping Pockmark on the W‐Svalbard Margin

“…Ideally, hydrocarbon gases in the presence of water should form hydrates in the GHSZ. However, if the gas supply and pressure is above a certain point, seepage occurs even if gas hydrate stability conditions are met (Domel et al., 2022; Ramachandran et al., 2022). Gas hydrates have been recovered through drilling (Himmler et al., 2019), as well as sampling of near seafloor sediments (Panieri et al., 2017) from Lunde Pockmark.…”