Mechanism of 2003, 2007 and 2009 earthquakes (S. Vicente Cape) and implications for the 1755 Lisbon earthquake

The San Vicente Cape region (SW Iberia) is of great seismological interest due to its tectonic complexity and for the occurrence of the 1755 Lisbon mega-earthquake. A structure capable of generating such large earthquake has not been convincingly found but authors agree with the possible occurrence in the future of a similar earthquake offshore of San Vicente Cape.We have studied the mechanism of three earthquakes in this area: 29 July 2003 (Mw = 5.3), 12 February 2007 (Mw = 6.1) and 17 December 2009 (Mw = 5.5) which throw light on the dynamics of the region. These earthquakes are the largest occurred in the last 40 years at the western of San Vicente Cape. From inversion of body waves and kinematic slip distribution, we have obtained that the three shocks have similar characteristics (dimensions, maximum slip, stress drop, source time function, focal depth and rupture velocity), but we can observe differences on geometry of the rupture that reflect the great seismotectonics complexity of the zone. The 2003 and 2007 focal mechanisms are similar, corresponding to thrusting motion but the 2009 earthquake has dip-slip motion on a vertical plane. The ruptures planes for the three shocks, deduced from the slip distribution, show ruptures on NE-SW planes, with the released energy propagating to NE direction, compatible with the regional horizontal compression in the NW-SE direction produced by the convergence between the Eurasian and African plates. This direction of faulting may be applied to the generation of the 1755 Lisbon earthquake, in terms of a complex rupture along NE-SW trending thrust faults at the Gorringe Bank, the Horseshoe Scarp and the Marques de Pombal Fault, with rupture propagating in NE direction toward the coast of Portugal and which may explain the large damage at Lisbon city

Seismic source in the Iberian-African plate boundary

The plate boundary between Iberia and Africa has been studied using data on seismicity and focal mechanisms. The region has been divided into three areas: A; the Gulf of Cadiz; B, the Betics, Alboran Sea and northern Morocco; and C, Algeria. Seismicity shows a complex behavior, large shallow earthquakes (h < 30 km) occur in areas A and C and moderate shocks in area B; intermediate-depth activity (30 < h < 150 km) is located in the depth earthquakes (h » 650 km) are located to the south of Granada. Moment rate, slip velocity and b values have been estimated for shallow shocks, and show similar characteristics for the Gulf of Cadiz and Algeria, and quite different ones for the central region. Focal mechanisms of 80 selected shallow earthquakes (8 ‡ mb ‡ 4) show thrust faulting in the Gulf of Cadiz and Algeria with horizontal NNW-SSE compression, and normal faulting in the Alboran Sea with E-W extension. Focal mechanisms of 26 intermediate-depth earthquakes in the Alboran Sea display vertical motions, with a predominant plane trending E-W. Solutions for very deep shocks correspond to vertical dip-slip along N-S trends. Frohlich diagrams and seismic moment tensors show different behavior in the Gulf of Cadiz, Betic-Alboran Sea and northern Morocco, and northern Algeria for shallow events. The stress pattern of intermediate-depth and very deep earthquakes has different directions: vertical extension in the NW-SE direction for intermediate depth earthquakes, and tension and pressure axes dipping about 45 ° for very deep earthquakes. Regional stress pattern may result from the collision between the African plate and Iberia, with extension and subduction of lithospheric material in the Alboran Sea at intermediate depth. The very deep seismicity may be correlated with older subduction processes

Correlations and the Cross Section of Exclusive (e,e′pe,e'p) Reactions for 16^{16}O

The reduced cross section for exclusive ($e,e'p$) reactions has been studied in DWIA for the example of the nucleus $^{16}$O using a spectral function containing effects of correlations. The spectral function is evaluated directly for the finite nucleus starting from a realistic nucleon-nucleon interaction within the framework of the Green's function approach. The emphasis is focused on the correlations induced by excitation modes at low energies described within a model-space of shell-model configurations including states up to the $sdg$ shell. Cross sections for the $p$-wave quasi-hole transitions at low missing energies are presented and compared with the most recent experimental data. In the case of the so-called perpendicular kinematics the reduced cross section derived in DWIA shows an enhancement at high missing momenta as compared to the PWIA result. Furthermore the cross sections for the $s$- and $d$-wave quasi-hole transitions are presented and compared to available data at low missing momenta. Also in these cases, which cannot be described in a model without correlations, a good agreement with the experiment is obtained.Comment: 12 pages, LaTeX, 4 figures include

Nuclear transparencies in relativistic A(e,e'p) models

Relativistic and unfactorized calculations for the nuclear transparency extracted from exclusive A(e,e'p) reactions for 0.3 \leq Q^2 \leq 10 (GeV/c)^2 are presented for the target nuclei C, Si, Fe and Pb. For Q^2 \geq 0.6 (GeV/c)^2, the transparency results are computed within the framework of the recently developed relativistic multiple-scattering Glauber approximation (RMSGA). The target-mass and Q^2 dependence of the RMSGA predictions are compared with relativistic distorted-wave impulse approximation (RDWIA) calculations. Despite the very different model assumptions underlying the treatment of the final-state interactions in the RMSGA and RDWIA frameworks, they predict comparable nuclear transparencies for kinematic regimes where both models are applicable.Comment: 15 pages, 4 figure

Intermediate depth and deep earthquakes: complexity of the Ibero-Magrhebian region

The Ibero-Magrhebian region is located at the plate boundary between Eurasia and Africa and it is a tectonically complex region. A sign of the complexity, is the occurrence of intermediate depth earthquakes (40<h<150 km), located in south Spain, between Granada- Malaga and at the west part of Alboran Sea, together with the occurrence of very deep earthquakes (h≈650 km) near Dúrcal (Granada). Intermediate depth shocks are mostly confined within a relatively narrow region (50 km width) located East of Gibraltar, extending NNE-SSW from the Malaga (Spain) area to a region offshore the Moroccan coast. We have studied focal mechanisms of these earthquakes from inversion of body wave. The stress pattern in the Ibero-Maghrebian region obtained from solutions of selected shallow, intermediate depth and deep shocks show the complexity of the region. The seismotectonic scheme show horizontal compression in NNW-SSE direction in the Gulf of Cádiz. In northern Africa, the stress pattern changes and it corresponds to strike-slip motion, with extends from west of the Gibraltar Strait until the western Algeria, where in the Oran region the horizontal compression N-S reapers, with a clear domain of the thrusting faults in Algeria. In the Alboran Sea there is horizontal extension in E-W direction for shallow events. The intermediate depth shock located at the western part of the Alboran Sea show a change on the stress pattern: to the west of 4.5oW, focal mechanisms show vertical tension axis, while to the east, they show vertical pressure axis. These stress orientations are not present in deep earthquakes, where the pressure axes dip 45o to the east. The intermediate and deep earthquakes may be related to some kind of subduction or delamination processes, more recent for the intermediate depth shocks and older for the very deep activity

Relativistic descriptions of quasielastic charged-current neutrino-nucleus scattering: application to scaling and superscaling ideas

The analysis of the recent experimental data on charged-current neutrino-nucleus scattering cross sections measured at MiniBooNE requires fully relativistic theoretical descriptions also accounting for the role of final state interactions. In this work we evaluate inclusive quasielastic differential neutrino cross sections within the framework of the relativistic impulse approximation. Results based on the relativistic mean field potential are compared with the ones corresponding to the relativistic Green function approach. An analysis of scaling and superscaling properties provided by both models is also presented.Comment: 11 pages, 8 figures, version accepted for publication in Physical Review

Final-State Interactions in the Superscaling Analysis of Neutral-Current Quasielastic Neutrino Scattering

Effects of strong final-state interactions in the superscaling properties of neutral-current quasielastic neutrino cross sections are investigated using the Relativistic Impulse Approximation as guidance. First- and second-kind scaling are analyzed for neutrino beam energies ranging from 1 to 2 GeV for the cases of 12C, 16O and 40Ca. Different detection angles of the outgoing nucleon are considered in order to sample various nucleon energy regimes. Scaling of the second kind is shown to be very robust. Validity of first-kind scaling is found to be linked to the kinematics of the process. Superscaling still prevails even in the presence of very strong final-state interactions, provided that some kinematical restrains are kept, and the conditions under which superscaling can be applied to predict neutral-current quasielastic neutrino scattering are determined.Comment: 39 pages, 16 figures, accepted for publication in Phys. Rev.

Enhanced time response of 1-in. LaBr3(Ce) crystals by leading edge and constant fraction techniques

We have characterized in depth the time response of three detectors equipped with cylindrical LaBr$_{3}$ (Ce) crystals with dimensions of 1-in. in height and 1-in. in diameter, and having nominal Ce doping concentration of 5%, 8% and 10%. Measurements were performed at $^{60}$Co and $^{22}$Na {\gamma}-ray energies against a fast BaF$_{2}$ reference detector. The time resolution was optimized by the choice of the photomultiplier bias voltage and the fine tuning of the parameters of the constant fraction discriminator, namely the zero-crossing and the external delay. We report here on the optimal time resolution of the three crystals. It is observed that timing properties are influenced by the amount of Ce doping and the crystal homogeneity. For the crystal with 8% of Ce doping the use of the ORTEC 935 CFD at very shorts delays in addition to the Hamamatsu R9779 PMT has made it possible to improve the LaBr$_{3}$(Ce) time resolution from the best literature value at 60Co photon energies to below 100 ps.Comment: Article submitted to Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipmen