Morphology of the Ebro fan valleys from SeaMARC and sea beam profiles

The northern continental slope off the Ebro Delta has a badland topography indicating major slope erosion and mass movement of material that deposits sediment into a ponded lobe. The southern slope has a low degree of mass movement activity and slope valleys feed channel levee-complexes on a steep continental rise. The last active fan valley is V-shaped with little meandering and its thalweg merges downstream with the Valencia Valley. The older and larger inactive channel-levee complex is smoother, U-shaped, and meanders more than the active fan valley.     

Chromospheric and coronal Alfvénic oscillations in non-vertical magnetic fields

We generalize previous studies of Alfvénic oscillations in the solar atmosphere to geometries in which the background magnetic field is not parallel to the gravitational acceleration. A uniform but inclined field produces only subtle changes in the mathematics, and virtually no changes to the coronal energy flux, over previous vertical field studies. We show that simple, two-layer models agree remarkably well with more sophisticated, multi-layer calculations. In addition, we derive several useful and accurate analytic results with which we highlight many features and parameter dependences. We also study a model with a spreading field geometry. For low magnetic fields (- 10 G) the corona still appears WKB to the oscillations and we do not find any significant deviations from the uniform field calculations. This is not the case for higher magnetic fields in active regions (- 3000 G) where we confirm previous results which suggest an order of magnitude increase in the coronal flux. Again, we derive useful analytic approximations.Now at: Mathematics Department, Monash University, Clayton, Victoria, Australia.     

Hazard-consistent response spectra in the Region of Murcia (Southeast Spain): comparison to earthquake-resistant provisions

Hazard-consistent ground-motion characterisations of three representative sites located in the Region of Murcia (southeast Spain) are presented. This is the area where the last three damaging events in Spain occurred and there is a significant amount of data for comparing them with seismic hazard estimates and earthquake-resistant provisions. Results of a probabilistic seismic hazard analysis are used to derive uniform hazard spectra (UHS) for the 475-year return period, on rock and soil conditions. Hazard deaggregation shows that the largest hazard contributions are due to small, local events for short-period target motions and to moderate, more distant events for long-period target motions. For each target motion and site considered, the associated specific response spectra (SRS) are obtained. It is shown that the combination of two SRS, for short- and long-period ground motions respectively, provides a good approximation to the UHS at each site. The UHS are compared to design response spectra contained in current Spanish and European seismic codes for the 475-year return period. For the three sites analysed, only the Eurocode 8 (EC8) type 2 spectrum captures the basic shape of the UHS (and not the EC8 type 1, as could be expected a priori). An alternative response spectrum, anchored at short- and long-period accelerations, is tested, providing a close match to the UHS spectra at the three sites. Results underline the important contribution of the frequent, low-to-moderate earthquakes that characterize the seismicity of this area to seismic hazard (at the 475-year return period).     

A composed index of critical accessibility (CICA) to healthcare services in a traditional African City

While empirical works that analyse rural–urban differentials in accessibility to health services are common in the developing countries, systematic studies focusing on intra-urban variations in accessibility to overall healthcare resources remain scant. Yet, many urban dwellers especially in the Sub-Saharan Africa have to travel long distances within the urban space to access basic health services. This study employs composed index of critical accessibility (CICA) to analyse differentials in access to health resources in Ibadan, a traditional African City. Data on healthcare centre location, ownership, doctors’ population were collected through field survey while spatial data on the administrative units and populated places were obtained from archival sources. Also, data on road networks was collected. Results show that the distribution of health facilities across local administrative units varies. In terms health facilities, Ibadan South West has 26 (36 %) of the total number while Ibadan South east has only 7 (9.8 %). The Doctor-Population Ratio also exhibits similar variations as Ibadan North has 20.5 as against 2.2, 1.9 and 0.3 for Ibadan SW, Ibadan NW and Ibadan NE respectively. The CICA analysis shows that 228,938 inhabitants are in high risk of negative accessibility while 49,234 are faced with condition of low risk of negative accessibility, which implies that a significant proportion of the population still finds it difficult to access basic health services as and when needed. The variations in the distribution of this deprived population are also noteworthy as the largest proportion of this group was localized in Ibadan NW. This has grave implication for the health and wellbeing of the population and raises once again the question of spatial equity in the delivery of urban public service. Curiously, these differences in the level of accessibility cut across administrative boundaries which brings to the fore the role of jurisdictional partitioning in ensuring equity in the delivery of urban public services. This opens a vista of research opportunity into the role jurisdictional partitioning in service provision in the urban centres.     

A strontium isotope evolution model for cenozoic magma genesis,Estern Great Basin,U.S.A.

Cenozoic volcanism in the Great Basin is characterized by an outward migration of volcanic centers with time from a centrally located core region, a gradational decrease in the initial Sr⁸⁷/Sr⁸⁶ ratio with decreasing age and increasing distance from the core, and a progressive change from calc-alkalic core rocks to more alkalic basin margin rocks. Generally each volcanic center erupted copious silicic ignimbrites followed by small amounts of basalt and andesite. The Sr⁸²/Sr⁸⁶ ratio for old core rocks is about 0.709 and the ratio for young basin margin rocks is about 0.705. Spatially and temporally related silicic and mafic suites have essentially the same Sr⁸⁷/Sr⁸⁶ ratios. The locus of older volcanism of the core region was the intersection of a north-south trending axis of crustal extension and high heat flow with the northeast trending relic thermal ridge of the Mesozoic metamorphic hinterland of the Sevier Orogenic Belt. Derivation of the Great Basin magmas directly from mantle with modification by crustal contamination seems unlikely. Initial melting of lower crustal rocks probably occurred as a response to decrease in confining pressure related to crustal extension. Volcanism was probably also a consequence of the regional increase in the geothermal gradient that is now responsible for the high heat flow of the Basin and Range Province. High Sr isotopic ratios of the older core volcanic rocks suggests that conditions suitable for the production of silicic magmas by partial fusion of the crust reached higher levels within the crust during initial volcanism than during production of later magmas with lower isotopic ratios and more alkaline chemistry. As the Great Basin became increasingly attenuated, progressively lower portions of the crust along basin margins were exposed to conditions suitable for magma genesis. The core region became exhausted in low temperature melting components, and volcanism ceased in the core before nearby areas had completed the silicic-mafic eruption cycle leading to their own exhaustion of crustal magma sources.     

Interpretation of gravimetric and magnetic anomalies in the Cameros Basin (North Spain): combination of deep and shallow sources

Outstanding potential field anomalies (gravimetric and magnetic) in the Cameros Basin (N Spain) follow a WNW-ESE trend, parallel to the geological structures resulting from Mesozoic extension and Tertiary basin inversion. The positive Bouguer gravity anomaly (15 mGal) is interpreted as the result of a strong contrast between the density of Tertiary rocks of the foreland basin and the Paleozoic and Mesozoic rocks, combined with crustal thickening in the Iberian Chain with respect to the Ebro Basin. The dipolar magnetic anomaly, slightly shifted to the south with respect to the relative maximum of the Bouguer anomaly, can be interpreted as related to volcanic rocks within the basement, which are linked to Triassic rifting as witnessed by outcrops of basalts along the basin margins. An exhaustive analysis of rock properties (density, magnetic susceptibility and remanence) and basin geometry from other sources (seismic reflection profiles) allow to constrain variations in crustal thickness and the location of large-scale basement faults.     

WSO-UV progress and expectations

The World Space Observatory Ultraviolet (WSO-UV) is the space mission that will grant access to the ultraviolet (UV) range in the post Hubble epoch. WSO-UV is equipped with instrumentation for imaging and spectroscopy and it is fully devoted to UV astronomy. In this article, we outline the WSO-UV mission model and present the current status of the project.     

Tectonic indentation in the central Alboran Sea (westernmost Mediterranean)

The Alboran Sea constitutes a Neogene–Quaternary basin of the Betic–Rif Cordillera, which has been deformed since the Late Miocene during the collision between the Eurasian and African plates in the westernmost Mediterranean. NNE–SSW sinistral and WNW–ESE dextral conjugate fault sets forming a 75° angle surround a rigid basement spur of the African plate, and are the origin of most of the shallow seismicity of the central Alboran Sea. Northward, the faults decrease their transcurrent slip, becoming normal close to the tip point, while NNW–SSE normal and sparse ENE–WSW reverse to transcurrent faults are developed. The uplifting of the Alboran Ridge ENE–WSW antiform above a detachment level was favoured by the crustal layering. Despite the recent anticlockwise rotation of the Eurasian–African convergence trend in the westernmost Mediterranean, these recent deformations—consistent with indenter tectonics characterised by a N164°E trend of maximum compression—entail the highest seismic hazard of the Alboran Sea.