ABSTRACT Two contrasting views of the Oak Ridge fault in the Ventura basin have emerged: a thick-skinned view based on onshore subsurface oil-well data and a thin-skinned view based on interpretation of seismic profiles and dipmeter data from the Santa Barbara Channel. The offshore Oak Ridge structure is interpreted as an active axial surface above the ramp of a blind, south-vergent thrust; growth triangles in the kink band south of this surface contain parallel, north-dipping strata in which the kink band tapers toward the surface. In contrast, dips of growth strata onshore near the coast at Montalvo steepen with depth, evidence of progressive limb rotation and a steeply-dipping, large-displacement Oak Ridge fault. The onshore Oak Ridge fault is northward-vergent. West of Oak Ridge, the post-Saugus displacement is transferred via the ductile Rincon Formation to folding of the Ventura-Rincon anticline, also a north-vergent structure onshore and offshore. An onshore seismic line along a cross section documented by electric logs shows a narrow panel of north dips that could be the onshore termination of an offshore kink band mapped in the Santa Barbara Channel. North dips at greater depth in this seismic line do not correspond to well data and are artifacts of processing. Farther east, north dips are possible only if the kink band turns to the northeast, parallel to the Montalvo fault. The onshore-offshore controversy will only be resolved by comparing seismic profiles in the Santa Barbara Channel with subsurface well profiles in the same transect using well-log correlations as well as dipmeter data.

Abstract Scientific knowledge of transient and difficult-to-access airborne volcanic emissions comes primarily from remote sensing observations, and a few in situ data from sporadic heroic or inadvertent airborne encounters. In the past, patchy knowledge of the composition and behaviour of such plumes from explosive volcanic eruptions, and associated drifting ash and gas clouds, have centrally contributed to unwanted and dangerous aircraft encounters that have put crews at risk and, in some cases, greatly damaged aircraft. Thus, improved knowledge of boundary conditions and plume composition, as inputs to both mass retrieval and predictive models for cloud trajectories , would be of benefit. In this paper, we describe how small robotic unmanned aerial vehicles (sUAVs) can address a variety of measurements that are typically beyond the reach of, and sometimes too dangerous for, manned aircraft. The direct measurements and sampling that can be achieved by sUAVs address serious gaps in knowledge of volcanic processes, and provide important validation data for estimations of volcanogenic ash and gas concentrations gleaned using remote sensing techniques. These data, in turn, constrain key proximal and distal boundary conditions for aerosol and gas transport models on which are based a number of decisions and evaluations by hazard responders and regulatory agencies. We briefly describe a case study from our ongoing field study at Turrialba Volcano in Costa Rica, where we are conducting an international campaign of systematic airborne in situ measurements of volcanogenic SO 2 and other gases, as well as aerosols, with sUAVs and aerostats (e.g. tethered balloons and kites), in conjunction with data acquisitions by the Advanced Spaceborne Thermal Emission and Reflection (ASTER) radiometer onboard the NASA Terra Earth orbital platform. To our knowledge, this is the first such systematic in situ UAV- and aerostat-based observation programme for SO 2 and particulates in a volcanic plume for correlation with orbital data. We preliminarily report good agreement between our UAV/aerostat and ASTER SO 2 retrievals within a 5 km radius of the volcano summit, at altitudes of up to 12 500 ft ( c. 3850 m) above sea level (asl) for concentrations within the range of 5–20 ppmv (ppm by volume). Additional work continues.

ABSTRACT The Santa Barbara Channel basin, located in southern California, is undergoing significant shortening. We use contour and axial surface maps of several horizons and balance regional cross sections through the eastern and western Santa Barbara Channel, as well as structural profiles and surface restoration techniques, to analyze how the subsurface structures in this basin accommodate the deformation. Reflection seismic profiles show that some of the mapped structures are active (e.g. the Oak Ridge, the Blue Bottle, the Pitas Point, the Dos Cuadras, the Carpinteria and the Santa Rosa trends) and accommodate a large part of the shortening, whereas others are completely inactive (e.g. the Western Deep trend). Restoration of seismic profiles shows that structures in the basin grow by kink-band migration. In cross sections, we interpret that to the east, there are mainly two levels of faulting. The Oak Ridge trend develops above the deeper one, whereas the Dos Cuadras, the Pitas Point, the Carpinteria and the Blue Bottle trends develop on the shallow one. To the west, we interpret the existence of three levels of faulting. A mid-crustal detachment is the deepest one, the Blue Bottle and the Western Deep trends are developed above the shallowest one. The Santa Rosa trend is growing above an intermediate one. The axial surface and contour maps suggest that the Blue Bottle and Pitas Point trends end progressively to the west, accommodating an average of 2 to 4 km of shortening. The Oak Ridge trend terminates at a tear fault south of the Santa Barbara city. This fold accommodates about 11 km of slip. We show, using map view restoration, that slip involved in this trend is transferred to the west through a mid-crustal bedding parallel detachment fault. The Dos Cuadras trend extends beyond the mapped area both to the east, where it becomes the Ventura anticline, and to the west. We determine that the Dos Cuadras and Carpinteria trends accommodate about 11 km of shortening. The Santa Rosa trend is a new mapped trend in the southwestern area of the basin.