Real Observatorio de la Armada

Santa María la Real de Nieva, Spain

Real Observatorio de la Armada

Santa María la Real de Nieva, Spain
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Koulali A.,British Petroleum | Ouazar D.,British Petroleum | Tahayt A.,Institute National Of Geophysique | King R.W.,Massachusetts Institute of Technology | And 6 more authors.
Earth and Planetary Science Letters | Year: 2011

We use velocities from 65 continuous stations and 31 survey-mode GPS sites as well as kinematic modeling to investigate present day deformation along the Africa-Iberia plate boundary zone in the western Mediterranean region. The GPS velocity field shows southwestward motion of the central part of the Rif Mountains in northern Morocco with respect to Africa varying between 3.5 and 4.0. mm/yr, consistent with prior published results. Stations in the southwestern part of the Betic Mountains of southern Spain move west-southwest with respect to Eurasia (~ 2-3. mm/yr). The western component of Betics motion is consistent with partial transfer of Nubia-Eurasia plate motion into the southern Betics. The southward component of Betics motion with respect to Iberia is kinematically consistent with south to southwest motion of the Rif Mountains with respect to Africa. We use block modeling, constrained by mapped surface faults and seismicity to estimate the geometry and rates of strain accumulation on plate boundary structures. Our preferred plate boundary geometry includes one block between Iberia and Africa including the SW Betics, Alboran Sea, and central Rif. This geometry provides a good fit to the observed motions, suggesting a wide transpressive boundary in the westernmost Mediterranean, with deformation mainly accommodated by the Gloria-Azores fault system to the West and the Rif-Tell lineament to the East. Block boundaries encompass aspects of earlier interpretations suggesting three main deformation styles: (i) extension along the NE-SW trending Trans-Alboran shear zone, (ii) dextral strike-slip in the Betics corresponding to a well defined E-W seismic lineament, and (iii) right lateral strike-slip motion extending West to the Azores and right-lateral motion with compression extending East along the Algerian Tell. We interpret differential motion in the Rif-Alboran-Betic system to be driven both by surface processes related the Africa-Eurasia oblique convergence and sub-crustal dynamic processes associated with the long history of subduction of the Neotethys ocean lithosphere. The dextral slip identified in the Betic Mountains in Southern Spain may be related to the offshore fault that produced the Great 1755 Lisbon Earthquake, and as such may represent a significant seismic hazard for the West Mediterranean region. © 2011 Elsevier B.V.

Diaz J.,CSIC - Institute of Earth Sciences Jaume Almera | Gallart J.,CSIC - Institute of Earth Sciences Jaume Almera | Villasenor A.,CSIC - Institute of Earth Sciences Jaume Almera | Mancilla F.,University of Granada | And 5 more authors.
Geophysical Research Letters | Year: 2010

Controversial evolutionary models have been proposed for the Gibraltar Arc system, a complex interaction zone between the Eurasia and African plates. Here we derive new mantle anisotropic constraints from SKS splitting measurements on a dense network of about 90 broad-band stations deployed over South Iberia and North Morocco. The inferred fast polarization directions (FPD) clearly show a spectacular rotation along the arc following the curvature of the Rif-Betic chain, while stations located at the South and South-East edges show distinct patterns. These results support geodynamical processes invoking a fast retreating slab rather than convective-removal and delamination models. The FPD variations along the Gibraltar arc can be explained by fossil anisotropy acquired during the Western Mediterranean Eocene subduction, while changes to the South and South-East of the Rif-Betic chain could be the imprint of a flow episode around an Alboran high velocity slab during its Miocene fragmentation from the Algerian slab. © 2010 by the American Geophysical Union.

De Lis Mancilla F.,University of Granada | Stich D.,University of Granada | Morales J.,University of Granada | Julia J.,Federal University of Rio Grande do Norte | And 7 more authors.
Journal of Geophysical Research: Solid Earth | Year: 2012

During the TopoIberia experiment, a total of 26 seismic broadband stations were recording in northern Morocco, providing for the first time extended regional coverage for investigating structure and seismotectonics of the southern branch of the Betic-Rif arc, its foreland, and the Atlas domain. Here, we analyze P-to-S converted waves in teleseismic receiver functions to infer gross crustal properties as thickness and Vp/Vs ratio. Strong lateral variations of the crustal thickness are observed throughout the region. Crustal thicknesses vary between 22 and 44 km and display a simple geographic pattern that divides the study area into three domains: entire northwestern Morocco underlain by a thickened crust with crustal thicknesses between 35 and 44 km; northeastern Morocco affected by significant crustal thinning, with crustal thicknesses ranging from 22 to 30 km, with the shallowest Moho along the Mediterranean coast; and an extended domain of 27-34 km thick crust, farther south which includes the Atlas domain and its foreland regions. Vp/Vs ratios show normal values of ∼1.75 for most stations except for the Atlas domain, where several stations give low V p/Vs ratios of around 1.71. The very sharp transition from thick crust in northwestern Morocco to thin crust in northeastern Morocco is attributed to regional geodynamics, possibly the realm of present-day subcrustal dynamics in the final stage of western Mediterranean subduction. Crustal thicknesses just slightly above 30 km in the southern domain are intriguing, showing that high topography in this region is not isostatically compensated at crustal level. Copyright © 2012 by the American Geophysical Union.

Lara M.,Real Observatorio de la Armada | San-Juan J.F.,University of La Rioja | Folcik Z.J.,Massachusetts Institute of Technology | Cefola P.,State University of New York at Buffalo
Journal of the Astronautical Sciences | Year: 2011

On time scales of interest for mission planning of GNSS satellites, the qualitative motion of the semimajor axis and the node evolves primarily from resonances with the Earth's gravitational field. The relevant dynamics of GPS orbits, which are in deep 2 to 1 resonance, is modeled with an integrable intermediary that depends only on one angle, the stroboscopic mean node, plus a two degrees of freedom perturbation that is factored by the eccentricity. Results are compared with long-term runs of the GTDS DSST showing very good agreement.

Lara M.,Real Observatorio de la Armada | Fukushima T.,Japan National Astronomical Observatory | Ferrer S.,University of Murcia
Monthly Notices of the Royal Astronomical Society | Year: 2011

Available observations of the shape of Ceres show it as a rotationally symmetric oblate spheroid. However, deviations from axisymmetry even at the level of observational accuracy may show significant effects on its rotational dynamics. These presumed deviations can be accounted for in a purely analytical way by means of perturbation theory. In our approach, the spherical rotor is taken as the unperturbed part of the motion instead of the more common torque-free motion or uniaxial body approaches. This alternative allows us to compute an analytical solution for the rotation of Ceres under the gravitational pull of the Sun by proceeding with a successive elimination of the different angles, which only involves quadratures of straightforward computation. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Lara M.,Real Observatorio de la Armada
Acta Astronautica | Year: 2011

The behavior of low altitude near-circular lunar orbits is a key design issue for some missions related to the physical exploration of the Moon. Because of its masconian character, the gravity field of the Moon requires higher order truncations to give a realistic description of the long-term behavior of low-lunar orbits. We show that the required understanding of the dynamical behavior in the vicinity of the Moon can be reached through the combination of analytical techniques and periodic orbits computation. A model that consists of a high degree, zonal truncation of the Selenopotential superimposed to the Earth mass-point attraction is used to explore the existence and orbital characteristics of long-lifetime orbits close to the Moon at any inclination. The averaging provides a global view on the frozen orbit's geometry and local descriptions of the averaged flow. But it also makes available the short-period terms of the transformation from mean to osculating elements. A refinement of the osculating elements by means of differential corrections allows to compute lunar repeat ground-trace orbits in high fidelity potentials without restricting to zonal models. © 2011 Elsevier Ltd. All rights reserved.

Lara M.,Real Observatorio de la Armada | Palacian J.F.,Public University of Navarra | Yanguas P.,Public University of Navarra | Corral C.,GMV Aerospace and Defence S.A.
Acta Astronautica | Year: 2010

In the framework of the elliptic restricted three-body problem we develop an analytical theory for spacecraft motion close to Mercury. Besides the perturbations due to the gravity of the Sun and Mercury and the eccentricity of Mercury's orbit around the Sun, i.e., the elliptic restricted three-body problem, the theory includes the effects of the oblateness and the possible latitudinal asymmetry of Mercury, and is valid for any eccentricity of the spacecraft's orbit. The initial Hamiltonian defines a non-autonomous but periodic dynamical system of two degrees of freedom. The mean motion of the spacecraft and the time are averaged using two successive Lie-Deprit transformations. The resulting Hamiltonian defines a one degree of freedom system and depends upon three essential parameters. When the latitudinal asymmetry coefficient vanishes the flow of this system is entirely analyzed through the discussion of the occurrence of its (relative) equilibria and bifurcations in accordance with the parameters the problem depends upon. Frozen orbits of the initial system together with their stability are obtained related to the relative equilibria. If the latitudinal asymmetry of Mercury is taken into account, the equatorial symmetry of the problem is broken and introduces important changes in the dynamics. A variety of tests show a very good agreement between averaged and non-averaged models, and the reliability of the theory is further checked by performing long-term integrations in ephemeris. © 2009 Elsevier Ltd. All rights reserved.

Ferrer S.,University of Murcia | Lara M.,Real Observatorio de la Armada
Astronomical Journal | Year: 2010

For rigid bodies close to a sphere, we propose an analytical solution that is free from elliptic integrals and functions, and can be fundamental for application to perturbed problems. After reordering the Hamiltonian as a perturbed spherical rotor, the Lie-series solution is generated up to an arbitrary order. Using the inertia parameters of different solar system bodies, the comparison of the approximate series solution with the exact analytical one shows that the precision reached with relatively low orders is at the same level of the observational accuracy for the Earth and Mars. Thus, for instance, the periodic errors of the mathematical solution are confined to the microarcsecond level with a simple second-order truncation for the Earth. On the contrary, higher orders are required for the mathematical solution to reach a precision at the expected level of accuracy of proposed new theories for the rotational dynamics of the Moon. © 2010. The American Astronomical Society.

Ferrer S.,University of Murcia | Lara M.,Real Observatorio de la Armada
Advances in the Astronautical Sciences | Year: 2011

The roto-translational dynamics of an axial-symmetric rigid body is discussed in a central gravitational field. The six-degree of freedom Hamiltonian problem is formulated as a perturbation of the Kepler motion and torque-free rotation in which we limit to the MacCullagh term. A chain of canonical transformations is used to reduce the problem. First, the elimination of the nodes reduces the problem to a system of four degrees of freedom. Then, the elimination of the parallax simplifies the resulting Hamiltonian, which is shaped as a radial intermediary plus a remainder. Some features of this integrable intermediary are pointed out. The normalized first order system in closed form is also given, thus completing the solution. Finally the full reduction of the radial intermediary is constructed using the Hamilton-Jacobi equation.

Lara M.,Real Observatorio de la Armada
Advances in the Astronautical Sciences | Year: 2010

The averaged equations of a high degree Selenopotential are used to find lunar frozen orbits at altitudes below 100 km. Despite the formal expressions to handle are very large their efficient evaluation makes feasible the fast generation of frozen orbits' inclination-eccentricity diagrams. Simple inspection of these diagrams shows that circular frozen orbits only occur close to the known inclinations of 27, 50, 76 and 86 deg. In addition, the averaged equations provide an estimation of the period that is good enough for mapping frozen orbits into their partner periodic orbits of the non-averaged problem.

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