Beschreibung: Hydrocarbon gases are actively seeping from pockmarks in the eastern part of the Vestnesa Ridge, western-Svalbard Margin. One of these is Lunde pockmark which is characterized by a seismic chimney below. Such seismic anomalies are widely believed to represent fluid migration pathways. However, their detailed structure and the physical properties of such structures is poorly understood and might be highly variable. Tomographic seismic velocity analysis can resolve the inner structure of the chimney beneath the Lunde pockmark. The aim is to understand the distribution of gas hydrate, free gas and carbonates within the gas chimney. Here, we present first results of our detailed 3D seismic travel time tomography using newly acquired high-resolution ocean bottom seismometer data guided by high-resolution 3D multi-channel seismic data. These models were generated with the Jive3D software. Our initial results show the variability of the seismic velocity structure beneath the Lunde pockmark. Our analysis, combined with earlier datasets and results shows that fluid pathways through the gas hydrate stability zone are anything but simple and highlights the importance of understanding the evolution of methane seepage pathways through time.

Beschreibung: 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.