Royal Institute and Observatory of the Spanish Navy

About: Royal Institute and Observatory of the Spanish Navy is a facility organization based out in San Fernando, Spain. It is known for research contribution in the topics: Gamma-ray burst & Magnetic anomaly. The organization has 50 authors who have published 106 publications receiving 2565 citations. The organization is also known as: Instituto y Observatorio de Marina de San Fernando.

The Hénon and Heiles Problem in Three Dimensions.: II. Relative Equilibria and Bifurcations in the Reduced System

Abstract: The second part of a research on the Henon and Heiles system in three dimensions is presented. We focus on motions around the origin, where the system may be treated as a case of three perturbed isotropic harmonic oscillators. It is the only Hamiltonian of the family of axially symmetric cubic potentials in 1–1–1 resonance, which needs at least order four in the normalization to reach the features of the system. The fourth order normalized system is analyzed, considering orbits at any inclination. We study and classify the relative equilibria of the system finding pitchfork, centre-saddle and cusp bifurcations in the reduced orbit space.

The 2013 Ibiza Calibration Campaign of Jason-2 and SARAL Altimeters

Abstract: This study presents the results of the 2013 Ibiza (Western Mediterranean) calibration campaign of Jason-2 and SARAL altimeters. It took place from 14 to 16 September 2013 and comprised two phases: the calibration of the GNSS (Global Navigation Satellite System) buoys to estimate the antenna height of each of them and the absolute calibration to estimate the altimeter bias (i.e., the difference of sea level measured by radar altimetry and GNSS). The first one was achieved in the Ibiza harbor at a close vicinity of the Ibiza tide gauge and the second one was performed at ∼ 40 km at the northwest of Ibiza Island at a crossover point of Jason-2 and SARAL nominal groundtracks. Five buoys were used to delineate the crossover region and their measurements interpolated at the exact location of each overflight. The overflights occurred two consecutive days: 15 and 16 September 2013 for Jason-2 and SARAL, respectively. The GNSS data were processed using precise point positioning technique. The biases found are of (−0.1 ± 0.9) and (−3.1 ± 1.5) cm for Jason-2 and SARAL, respectively.

Non-linear filter, using the wavelet transform, applied to seismological records

Abstract: As any process in Nature, seismic recordsare affected by noise that the analystwould want to eliminate. One of the mostcommon techniques used to minimise thisnoise effect is the application of linearfilters, which reduce the bandwidth of thesignal. This method is based on the FourierTransform, and therefore any perturbationon the coefficients affects the entirerecord.We have developed a non-linear filter basedon the multiresolution analysis of theDiscrete Time Wavelet Transform (DTWT). Themain idea is to use the time-frequencylocalisation properties of the waveletdecomposition. Each coefficient isassociated to a window on thetime-frequency plane, so any perturbationwould only affect the time and frequencyrange of the correspondent window.The procedure we propose has three stages:periodic noise elimination, spikesreduction and, finally, the non-linearfiltering. The non-linear filter acts bythresholding the wavelet coefficients. Thethresholding estimator will depend on thesignal-noise ratio (SNR) in each of thefrequency bands associated to the waveletdecomposition.We have compared the proposed method to thecoherent structures method (Mallat, 1998)and to two 4th order linear filterbanks (Butterworth and Elliptic filters),applying all of them to a syntheticdatabase, and a real earthquake databaserecorded by the Short Period ROA Network.The proposed method improves the SNR in the87% of the tested events, being therelative rms error less than three, and themaximum amplitude relative error less than10% in the 90% of the synthetic database.

A magnetic anomaly study offshore the Canary Archipelago

Abstract: A scalar magnetic anomaly map of the regions offshore the Canary Archipelago is presented here. This map is based on measurements taken inside the Exclusive Economic Zone Project framework. This paper contains a description of the data set, whose accuracy and internal consistency are analysed. The magnetic anomalies are described and the main structural trends are highlighted. This analysis has served to detect two possible fractures with a NW—SE component: one separates Fuerteventura from Gran Canaria Island, and the other apparently runs through Fuerteventura. The latter finding agrees with a 1.7 km depth offset, between its northern and southern halves, detected by the algorithm based on the Euler Deconvolution. A similar approach has been performed, estimating the depth to the top of the most significant anomalies. This result shows that the most noteworthy magnetic anomaly source of the archipelago, which lies between Tenerife and Gran Canaria Island, seems to be located at an average depth of 4 km below sealevel. A spectral analysis was performed to estimate the depth extent of the deepest anomalies. It argues the presence of sub-crustal magnetic sources (underplating) in the archipelago. A standard Euler Deconvolution analysis was executed to analyse the spatial distribution of these mantle-like sources. Our results seem to support the existence of magmatic underplating under Gran Canaria, Tenerife, and Fuerteventura, and suggest this possibility for La Palma.

Gravity modeling of the Muertos Trough and tectonic implications (north-eastern Caribbean)

Abstract: The Muertos Trough in the northeast Caribbean has been interpreted as a subduction zone from seismicity, leading to infer a possible reversal subduction polarity. However, the distribution of the seismicity is very diffuse and makes definition of the plate geometry difficult. In addition, the compressive deformational features observed in the upper crust and sandbox kinematic modeling do not necessarily suggest a subduction process. We tested the hypothesized subduction of the Caribbean plate's interior beneath the eastern Greater Antilles island arc using gravity modeling. Gravity models simulating a subduction process yield a regional mass deficit beneath the island arc independently of the geometry and depth of the subducted slab used in the models. This mass deficit results from sinking of the less dense Caribbean slab beneath the lithospheric mantle replacing denser mantle materials and suggests that there is not a subducted Caribbean plateau beneath the island arc. The geologically more realistic gravity model which would explain the N-S shortening observed in the upper crust requires an overthrusted Caribbean slab extending at least 60 km northward from the deformation front, a progressive increase in the thrusting angle from 8� to 30� reaching a maximum depth of 22 km beneath the insular slope. This new tectonic model for the Muertos Margin, defined as a retroarc thrusting, will help to assess the seismic and tsunami hazard in the region. The use of gravity modeling has provided targets for future wide-angle seismic surveys in the Muertos Margin.