First results on velocity analyses of multichannel seismic data acquired with the icebreaker RV Araon across the southern Beaufort Sea, offshore Yukon

Abstract

Abstract:One thousand two hundred twenty kilometres of multichannel seismic data were acquired in the Beaufort Sea in 2013 and 2014 to interpret shallow sedimentary structures associated with the upper Cenozoic Iperk and Shallow Bay depositional sequences. Seismic velocity analyses suggest a remarkably consistent regional velocity-depth trend on the slope within the upper 4 s two-way traveltime. A separate velocity trend was not defined beneath the shelf in this region, where data are influenced by the occurrence of permafrost. Deviations from this trend were noted at unconformities including an upper erosional unconformity.The seismic data in the Mackenzie Trough region suggest a different velocity-depth trend within the upper section and the region is marked by a large erosional unconformity, likely the base of the Shallow Bay sequence. Velocity analyses suggest the removal of up to 425 m of overburden; however, this is an overestimate of erosion as differential compaction from the glacial history has not yet been taken into account. In deeper water (>750 m) a bottom-simulating reflector is present, characterized by the occurrence of free gas and a low-velocity zone.Analyses of three fluid-expulsion features on the slope indicate that the Pokak fluid-expulsion feature and the Triple-Mound fluid-expulsion feature are linked to underlying anticline structures. A flat-topped fluidexpulsion feature at the flank of an equivalent anticline was also examined, but the occurrence of shallow gas creates a blank zone beneath this structure. Pronounced changes in the velocity-depth function at these fluid-expulsion features are linked to occurrence of free gas, and/or fluidized mud extrusions. Résumé :En 2013 et 2014, des données sismiques multicanal ont été acquises sur 1220 km dans la mer de Beaufort afin d'interpréter les structures sédimentaires à faible profondeur associées aux séquences sédimentaires d'Iperk et de Shallow Bay du Cénozoïque supérieur. Des analyses de la vitesse sismique indiquent une tendance vitesse-profondeur remarquablement constante à l'échelle régionale sous le talus pour les quatre premières secondes de temps de trajet double. Dans cette région, nous n'avons pas défini une tendance vitesse-profondeur distincte pour le secteur sous-jacent à la plate-forme continentale, un endroit où les données sont influencées par la présence de pergélisol. Des écarts par rapport à la tendance ont été relevés au niveau de discordances, notamment d'une discordance d'érosion supérieure.Dans la région de la cuvette de Mackenzie, les données sismiques révèlent une tendance vitesseprofondeur différente dans la partie supérieure de la coupe et la région est marquée par la présence d'une importante discordance d'érosion, qui correspond vraisemblablement à la base de la séquence de Shallow Bay. Les analyses de la vitesse laissent croire à la suppression de terrains de couverture sur une épaisseur pouvant atteindre 425 m. Cependant, il s'agit là d'une surestimation de l'importance de l'érosion, étant donné que la compac...

Evidence for gas hydrate occurrences in the Canadian Arctic Beaufort Sea within permafrost-associated shelf and deep-water marine environments

“…Newly acquired 2D MCS data across the shelf-edge region with the icebreaker ARAON in 2013 and 2014 (Jin et al, 2015;Jin and Dallimore, 2016) provide further evidence for the existence of a reflection from the BGHSZ ( Figure 6). Data processing and imaging is, however, challenged by the presence of strong seafloor-multiples that could not be completely removed as described by Riedel et al (2016). Yet, the 2D MCS data generally confirm observations made across the 3D seismic data volumes.…”

“…(Figure 8) was imaged, manifesting very similar character as the BSR off Alaska (compare to Figure 6a in Phrampus et al 2014). Seismic velocity analyses conducted along this seismic line (Riedel et al, 2016) show a clear decrease in the rms-velocity beneath this reflection, indicating the presence of free gas. Both, this and the Alaska-BSR, display gas-brightening of stratigraphic horizons underneath the BSR which cross-cut the phase boundary (CDPs 1500 -1800, Figure 8).…”

Mega‐scale glacial lineations formed by ice shelf grounding in the Canadian Beaufort Sea during multiple glaciations

“…The KOPRI 2D MCS survey used an airgun array of 1200 in 3 volume and a streamer with 120 channels with maximum offset of 1600 m (Riedel et al, 2016). Seismic data were processed (after crooked-line 2D geometry definition) using a sequence including removal of DC offset, muting of direct arrivals and refractions, minimum phase band-pass filtering, surface-consistent deconvolution, stacking-velocity definition using the semblance technique, staking (full-offset range) and post-stack Kirchhoff time migration using a 2D variable velocity field.…”

“…Seismic data were processed (after crooked-line 2D geometry definition) using a sequence including removal of DC offset, muting of direct arrivals and refractions, minimum phase band-pass filtering, surface-consistent deconvolution, stacking-velocity definition using the semblance technique, staking (full-offset range) and post-stack Kirchhoff time migration using a 2D variable velocity field. Details of the processing and interpretation of these 2D MCS data are given in Riedel et al (2016). The MCS data have been used previously to define interval velocities (Riedel et al, 2016) and we use these velocity-depth functions to convert observations on the 2D and 3D data made in two-way travel time to depth (metres below seafloor, mbsf).…”

“…Details of the processing and interpretation of these 2D MCS data are given in Riedel et al (2016). The MCS data have been used previously to define interval velocities (Riedel et al, 2016) and we use these velocity-depth functions to convert observations on the 2D and 3D data made in two-way travel time to depth (metres below seafloor, mbsf). The uncertainty in this conversion depends on water-depth and burial depth below seafloor and is practically a measure of robustness of the P-wave velocity-depth functions defined from the MCS data.…”