Role of gas hydrates in slope failure on frontal ridge of northern Cascadia margin

Several slope failures are observed near the deformation front on the frontal ridges of the northern Cascadia accretionary margin off Vancouver Island. The cause for these events is not clear, although several lines of evidence indicate a possible connection between the occurrence of gas hydrate and submarine landslide features. The presence of gas hydrate is indicated by a prominent bottom-simulating reflector (BSR), at a depth of ∼265–275 m beneath the seafloor (mbsf), as interpreted from vertical-incidence and wide-angle seismic data beneath the ridge crests of the frontal ridges. For one slide, informally called Slipstream Slide, the velocity structure inferred from tomography analyses shows anomalous high velocities values of about 2.0 km s−1 at shallow depths of 100 mbsf. The estimated depth of the glide plane (100 ± 10 m) closely matches the depth of these shallow high velocities. In contrast, at a frontal ridge slide just to the northwest (informally called Orca Slide), the glide plane occurs at the same depth as the current BSR. Our new results indicate that the glide plane of the Slipstream slope failure is associated with the contrast between sediments strengthened by gas hydrate and overlying sediments where little or no hydrate is present. In contrast, the glide plane of Orca Slide is between sediment strengthened by hydrate underlain by sediments beneath the gas hydrate stability zone, possibly containing free gas. Additionally, a set of margin perpendicular normal faults are imaged from seafloor down to BSR depth at both frontal ridges. As inferred from the multibeam bathymetry, the estimated volume of the material lost during the slope failure at Slipstream Slide is about 0.33 km3, and ∼0.24 km3 of this volume is present as debris material on the ocean basin floor. The 20 per cent difference is likely due to more widely distributed fine sediments not easily detectable as bathymetric anomalies. These volume estimates on the Cascadia margin are approaching the mass failure volume for other slides that have generated large tsunamis—for example 1–3 km3 for a 1998 Papua New Guinea slide

Dual-vergence structure from multiple migration of widely spaced OBSs

Highlights • Dual-vergence structure is observed for the first time on the northern Cascadia margin. • Around central Vancouver Island, vergence switches from seaward in the south to landward in the north. • First OBS migration study imaging the top of the igneous oceanic crust using only a small airgun source (120 in.3). • OBS migration indicates that an OBS, in water depths up to 2.5 km, can image up to 5 km on either side of its seafloor position. Abstract The detailed structure of the northern Cascadia basin and frontal ridge region was obtained using data from several widely spaced ocean bottom seismometers (OBSs). Mirror imaging was used in which the downgoing multiples (mirror signal) are migrated as they provide information about a much larger area than imaging with primary signal alone. Specifically, Kirchhoff time migration was applied to hydrophone and vertical geophone data. Our results indicate remarkable structures that were not observed on the northern Cascadia margin in previous single-channel or multi-channel seismic (MCS) data. Results show that, in these water depths (2.0–2.5 km), an OBS can image up to 5 km on either side of its position on the seafloor and hence an OBS spacing of 5 km is sufficient to provide a two-fold migration stack. Results also show the top of the igneous oceanic crust at 5–6 km beneath the seafloor using only a small airgun source (120 in.3). Specifically, OBS migration results clearly show the continuity of reflectors which enabled the identification of frontal thrusts and a main thrust fault. These faults indicate, for the first time on this margin, the presence of a dual-vergence structure. These kinds of structures have so far been observed in < 0.5% of modern convergent margins and could be related to horizontal compression associated with subduction and low basal shear stress resulting from over-pressure. Reanalysis of previous MCS data from this region augmented the OBS migration results and further suggests that the vergence switches from seaward to landward around central Vancouver Island. Furthermore, fault geometry analyses indicate that the total amount of shortening accommodated due to faulting and folding is about 3 km, which suggest that thrusting would have started at least ∼ 65 ky ago

A remarkable case of rhabdomyolysis associated with ingestion of energy drink ‘neon volt’

Rhabdomyolysis is defined as a syndrome characterized by muscle necrosis and the release of intracellular muscle constituents into the circulation. We present a case of a 35-year-old male who exercised for 2 h after ingesting energy drink and subsequently presented with rhabdomyolysis. After excluding common and uncommon causes of rhabdomyolysis, we reached the conclusion that the likely cause was the ingestion of energy drink ‘NEON VOLT’ in a setting of mild dehydration. Increasing physical activity and intense exercise is becoming a trend in many countries, due to its many health-related benefits such as prevention of obesity. This renewed focus toward optimal fitness has spawned many supplements that aid in improvement of the performance, muscle growth, and recovery. Energy drinks predominantly contain caffeine that is often combined with other supplements to form what manufacturers have termed an ‘energy blend’. Studies have shown that excessive caffeine intake from energy drinks can cause arrhythmias, hypertension, dehydration, sleeplessness, nervousness, and in rare instances, rhabdomyolysis. As per Drug Abuse Warning Network report, there is a sharp increase in the number of emergency department visits involving energy drinks from 1,128 visits in 2005 to 16,053 and 13,114 visits in 2008 and 2009, respectively. Due to emergence of energy drink abuse as a national health problem, Food and Drug Administration has launched a dietary supplement adverse event reporting system for surveillance of any adverse events linked to these agents