S U M M A R YContinental rupture models emphasize the role of faults in extensional strain accommodation; extension by dyke intrusion is commonly overlooked. A major rifting episode that began in 2005 September in the Afar depression of Ethiopia provides an opportunity to examine strain accommodation in a zone of incipient plate rupture. Earthquakes recorded on a temporary seismic array (2005 October to 2006 April), direct observation of fault patterns and geodetic data document ongoing strain and continued dyke intrusion along the ∼60-km long Dabbahu rift segment defined in earlier remote sensing studies. Epicentral locations lie along a ∼3 km wide, ∼50 km long swath that curves into the SE flank of Dabbahu volcano; a second strand continues to the north toward Gab'ho volcano. Considering the ∼8 m of opening in the September crisis, we interpret the depth distribution of microseismicity as the dyke intrusion zone; the dykes rise from ∼10 km to the near-surface along the ∼60-km long length of the tectono-magmatic segment. Focal mechanisms indicate slip along NNW-striking normal faults, perpendicular to the Arabia-Nubia plate opening vector. The seismicity, InSAR, continuous GPS and structural patterns all suggest that magma injection from lower or subcrustal magma reservoirs continued at least 3 months after the main episode. Persistent earthquake swarms at two sites on Dabbahu volcano coincide with areas of deformation identified in the InSAR data:(1) an elliptical, northwestward-dipping zone of seismicity and subsidence interpreted as a magma conduit, and (2) a more diffuse, 8-km radius zone of shallow seismicity (<2 km) above a shadow zone, interpreted as a magma chamber between 2.5 and 6 km subsurface. InSAR and continuous GPS data show uplift above a shallow source in zone (2) and uplift above the largely aseismic Gab'ho volcano. The patterns of seismicity provide a 3-D perspective of magma feeding systems maintaining the along-axis segmentation of this incipient seafloor spreading segment.

Microseismic monitoring of hydraulic fractures is an important tool for imaging fracture networks and optimizing the reservoir engineering of the stimulation. The range of magnitudes of the recorded microseisms depends at the lower limit on the array sensitivity; while the upper limit varies significantly from site to site. In this paper the variation in the microseismic magnitude range is examined and compared with the injection and site characteristics. Although there are numerous potential factors effecting the seismic deformation, the energy of the pumping and state of stress appear to be the two dominant factors. However, interaction with pre-existing faults also results in increased deformation. Ultimately, this can potentially be used to design the stimulation to maximize the deformation. Characterization of the seismogenic potential is also important for seismic hazard assessment, as well as the design of passive monitoring. Introduction Over the last few years, microseismic imaging of hydraulic fracture stimulations 1 has become a widespread diagnostic technology. Microseismicity is used to image fracture geometry dynamics and optimize stimulations in a wide variety of settings. The resulting images are useful in both simple and complex fracture networks and able to detect fracture complexity resulting from injections in naturally fractured reservoirs. Particularly in North America, microseismic imaging has become a standard in development of both conventional and unconventional resource plays. Generally, the temporal locations of microseisms detected in an offset observation well are used to monitor the growth of the hydraulic fracture geometry. In most cases the hydraulic fracture is being created by tensile failure of the rock resulting from injection of fluids at pressures exceeding the minimum principal stress level, although the deformation mechanism associated with the recorded microseisms appears to be shear dominated deformations. Microseisms typically contain significant shear wave energy suggesting substantial shear deformation in the source of the microseismic energy, although fracture opening could occur simultaneous with the shear deformation and play a role in the permeability enhancement. One model to explain the shearing is stress changes or pore pressure increases associated with the primary hydraulic fracture 2, leading to induced shear failure. However, dog legs, offsets or other complexities along the hydraulic fracture could also result in localized shear deformations along a conventional tensile fracture. Intersections of a hydraulic fracture with oblique angle pre-existing fractures could also lead to localized shear deformation. Microseism signal analysis can be used to investigate aspects of the source characteristics of the shear deformation, although this may or may not provide insight into the stimulation objective of creating a permeable fracture possibly containing a fluid conductive proppant pack. An important microseism source attribute is the source strength or magnitude 3. Source strength is best quantified by seismic moment (product of shear modulus, shear displacement and area) which can be expressed with a moment magnitude scale, analogous to the well known Richter Magnitude scale. Investigating source strength has proven valuable in determining the effective detection range, by simply plotting magnitude versus distance between the microseisms and seismometers. However, the spatial extent of the seismic deformation has been postulated to image the extent and density of a stimulated fracture network in the Barnett Shale, and appears to provide a useful attribute that correlates with gas production in a case study examining several wells 4.

Marine mammals can play important ecological roles in aquatic ecosystems, and their presence can be key to community structure and function. Consequently, marine mammals are often considered indicators of ecosystem health and flagship species. Yet, historical population declines caused by exploitation, and additional current threats, such as climate change, fisheries bycatch, pollution and maritime development, continue to impact many marine mammal species, and at least 25% are classified as threatened (Critically Endangered, Endangered or Vulnerable) on the IUCN Red List. Conversely, some species have experienced population increases/recoveries in recent decades, reflecting management interventions, and are heralded as conservation successes. To continue these successes and reverse the downward trajectories of at-risk species, it is necessary to evaluate the threats faced by marine mammals and the conservation mechanisms available to address them. Additionally, there is a need to identify evidence-based priorities of both research and conservation needs across a range of settings and taxa. To that effect we: (1) outline the key threats to marine mammals and their impacts, identify the associated knowledge gaps and recommend actions needed; (2) discuss the merits and downfalls of established and emerging conservation mechanisms; (3) outline the application of research and monitoring techniques; and (4) highlight particular taxa/populations that are in urgent need of focus.

The development of the striatum dopamine (DA) system through human adolescence, a time of increased sensation seeking and vulnerability to the emergence of psychopathology, has been difficult to study due to pediatric restrictions on direct in vivo assessments of DA. Here, we applied neuroimaging in a longitudinal sample of n = 146 participants aged 12-30. R2′, an MR measure of tissue iron which co-localizes with DA vesicles and is necessary for DA synthesis, was assessed across the sample. In the 18-30 year-olds (n = 79) we also performed PET using [11C]dihydrotetrabenazine (DTBZ), a measure of presynaptic vesicular DA storage, and [11C]raclopride (RAC), an indicator of D2/D3 receptor availability. We observed decreases in D2/D3 receptor availability with age, while presynaptic vesicular DA storage (as measured by DTBZ), which was significantly associated with R2′ (standardized coefficient = 0.29, 95% CI = [0.11, 0.48]), was developmentally stable by age 18. Our results provide new evidence for maturational specialization of the striatal DA system through adolescence.