The western Mediterranean subduction system - Insight from full-waveform inversion

We present a new 3D model of anisotropic S- and P-velocity from the surface to 1,300 km depth beneath the western Mediterranean region. The construction of our model is based on the combination of spectral-element simulations of anisotropic, visco-elastic wave propagation with adjoint techniques. Spectral-element simulations provide highly accurate synthetic seismograms for nearly arbitrarily heterogeneous media, thereby reducing artefacts related to simpli- fications of the forward model. Adjoint techniques allow us to compute sensitivity kernels efficiently, which is essential for iterative gradient-based optimisation. Our model of the western Mediterranean is embedded in a larger Eurasian model. While we model and invert waves at periods from 30 to 200 s within Eurasia, we use a broader band from 12 to 200 s for the smaller western Mediterranean submodel. This multi-scale strategy allows us to simultaneously invert for crustal and mantle structure. Benefits of this approach include the absence of crustal corrections, and more reliably imaged anisotropy. The majority of seismic data used in our full-waveform inversion were recorded by IberArray and other temporary networks, as well as permanent regional networks, thus providing excellent coverage of the Iberian Peninsula, northernmost Africa, and the western Mediterranean basin. For the inversion we use those parts of the seismograms where observed and synthetic waveforms are sufficiently similar to allow for the meaningful measurement of time- and frequency-dependent phase differences. In our final model we quantify resolution with the help of second-order adjoints that can be used to com- pute direction- and position-dependent resolution lengths, as well as inter-parameter tradeoffs. The model reveals a complex system of high-velocity anomalies that may be interpreted as signatures of subducted Tethyan slabs. While subducting slabs beneath the eastern Mediterranean region may penetrate into the lower mantle, western Mediterranean slabs appear to stagnate around 660 km depth.Peer Reviewe

Deep learning phase picking of large-N experiments

The popularisation of the use of large-N arrays of seismometers has resulted in a significant increase of the size of the datasets recorded during these experiments. Therefore, new challenges have arisen on how to process all these data efficiently, and in an automated fashion. This is particularly true in the case of induced seismicity monitoring, where often a large number of number of events are recorded at high frequency sampling rates. Several methods of automatic picking have been developed during recent years, from triggering algorithms (e.g. STA/LTA) to higher order statistics or waveform similarity. Latest development in computational power and the popularization of GPUs have made possible to apply machine learning methods to several problems, from arrival picking and phase detection to earthquake location. We have developed a deep neural network to detect the arrivals of seismic body waves, using an architecture based on convolutional layers. This type of models are widely used in computer vision applications, which is the most similar case to the phase picking by an operator. Trained with the data of the Southern California Seismic Network, this network is able to differentiate P and S waves from background noise with a precision higher than 98%. We have applied this neural network to other large-N experiments in other regions (Europe and Asia) and found that the network localizes the events with a precision comparable or superior to an human operator, even in the case of low signal-noise ratio and superposition of earthquakes.This research has been funded by MICINN Project CGL2017-88864-

Rayleigh wave ellipticity measurements in the Iberian Peninsula and Morocco

We combine Rayleigh wave ellipticity, or H/V (horizontal to vertical) amplitude ratios, measurements obtained using teleseismic earthquake recordings and ambient noise cross correlations to provide improved constraints on the crustal models across the Iberian Peninsula and Morocco. To obtain the H/V ratios, we use more than 250 shallow (h<40 km) teleseismic events with magnitudes Mw>6.0 recorded at more than 450 seismic stations. We also use all the multicomponent ambient noise cross correlations computed for each station pair for the time period 2010 to 2012. Periods between 20 and 100 seconds are investigated. We observe a good agreement between the uppermost geological features of the crust and the obtained Rayleigh H/V ratios, with low values in major mountain ranges and high ratios in sedimentary basins. Combination of Rayleigh H/V ratio measurements from both earthquakes and ambient noise data with phase velocities and other types of seismic data will help to better constrain the Earth’s structure at different crustal levels

Dynamic analysis of runout correction in milling

Tool runout and its effects is an important area of research within modelling, simulation, and control of milling forces. Tool runout causes tool cutting edges to experience uneven forces during milling. This fact also affects tool life and deteriorates workpiece surface quality. In this article a procedure, in order to diminish the effects of tool runout, is presented. The procedure is based on chip thickness modification by means of the fast correction of the tool feed rate. Dynamic feed rate modification is provided by superposing our own design of a fast feed system driven by a piezoelectric actuator to the conventional feed drive of the CNC machine tool. Previously, a model of the dynamic behaviour of the system was developed to analyze the influence of fast feed rate modification on cutting forces. The model incorporates the piezoelectric actuator response as well as the structural dynamics of the tool and the designed Fast Feed Drive System (FFDS). Simulated and experimental results presented in this paper show the effectiveness and benefits of this new tool runout correction procedure

Cross-correlation imaging of ambient noise sources

We develop and apply a novel technique to image ambient seismic noise sources. It is based on measurements of cross-correlation asymmetry defined as the logarithmic energy ratio of the causal and anticausal branches of the cross-correlation function. A possible application of this technique is to account for the distribution of noise sources, a problem which currently poses obstacles to noise-based surface wave dispersion analysis and waveform inversion. The particular asymmetry measurement used is independent of absolute noise correlation amplitudes. It is shown how it can be forward-modelled and related to the noise source power-spectral density using adjoint methods. Simplified sensitivity kernels allow us to rapidly image variations in the power-spectral density of noise sources. This imaging method correctly accounts for viscoelastic attenuation and is to first order insensitive to unmodelled Earth structure. Furthermore, it operates directly on noise correlation data sets. No additional processing is required, which makes the method fast and computationally inexpensive.We apply the method to three vertical-component cross-correlation data sets of different spatial and temporal scales. Processing is deliberately minimal so as to keep observations consistent with the imaging concept. In accord with previous studies, we image seasonally changing sources of the Earth's hum in the Atlantic, Pacific and the Southern Ocean. The sources of noise in the microseismic band recorded at stations in Switzerland are predominantly located in the Atlantic and show a clear dependence on both season and frequency. Our developments are intended as a step towards full 3-D inversions for the sources of ambient noise in various frequency bands, which may ultimately lead to improvements of noise-based structural imaging.This research was supported by the Swiss National Supercomputing Center (CSCS) in the form of the GeoScale and CH1 projects, by the Swiss National Science Foundation (SNF) under grant 200021 149143 and by the Netherlands Organisation for Scientific Research (VIDI grant 864.11.008). Iber-Array data are a contribution of the Team Consolider-Ingenio 2010 TOPO-IBERIA (CSD2006-00041).Peer reviewe

Improving the location of induced earthquakes associated with an underground gas storage in the Gulf of Valencia (Spain)

On September 2013, increased seismic activity was recorded near the CASTOR offshore underground gas storage (UGS), in the Gulf of Valencia (Spain). According to the reports by the Spanish Instituto Geográfico Nacional (IGN), more than 550 events occurred during two months, the strongest having a magnitude of Mw = 4.2 which took place two weeks after the gas injection stopped. The low magnitude of the events (with only 17 earthquakes having mbLg greater than 3), the lack of nearby stations, and the inhomogeneous station distribution made the location problem a great challenge. Here we present improved locations for a subset of 161 well recorded events from the earthquake sequence using a probabilistic nonlinear earthquake location method. A new 3-D shear-wave velocity model is also estimated in this work from surface-wave ambient noise tomography. To further improve the locations, waveform cross-correlations are computed at each station for every event pair and new locations are obtained from an inverted set of adjusted travel time picks. The resulting hypocentral solutions show a tighter clustering with respect to the initial locations and they are distributed in a NW-SE direction. Most of the earthquakes are located near the injection well at depths of about 6 km. Our results indicate that the observed seismicity is closely associated with the injection activities at the CASTOR underground gas storage and may have resulted from the reactivation of pre-existing unmapped faults, located a few kilometers below the reservoir. © 2016 Elsevier B.V.This research was partially funded by project MISTERIOS (CGL2013-48601-C2-1-R).Peer reviewe

Evaluación de la calidad en organizaciones deportivas : adaptación del modelo SERVQUAL

The SERVQUAL model (Parasunaman, Zeithaml and Berry, 1993) has proven to be a useful procedure for evaluating quality. Nevertheless, several studies have criticized the model's methodological layout. This question is relevant because of organizations' growing interest in quality management. Furthermore, given that the model has proven to be useful, it seems necessary to demonstrate whether methodological criticism is confirmed or, on the contrary is only an effect of the analysis procedures. This study presents an adaptation of the model to the realm of sports organisations. Our results support the hypothesis that the different adaptations were not devised with methodological guarantees. The results also support the existence of a stable and parsimonious factorial structure containing acceptable adjustment indexes

Seismicity and active tectonics in the Alboran Sea, Western Mediterranean: Constraints from an offshore-onshore seismological network and swath bathymetry data

Seismicity and tectonic structure of the Alboran Sea were derived from a large amphibious seismological network deployed in the offshore basins and onshore in Spain and Morocco, an area where the convergence between the African and Eurasian plates causes distributed deformation. Crustal structure derived from local earthquake data suggests that the Alboran Sea is underlain by thinned continental crust with a mean thickness of about 20 km. During the 5 months of offshore network operation, a total of 229 local earthquakes were located within the Alboran Sea and neighboring areas. Earthquakes were generally crustal events, and in the offshore domain, most of them occurred at crustal levels of 2 to 15 km depth. Earthquakes in the Alboran Sea are poorly related to large-scale tectonic features and form a 20 to 40 km wide NNE-SSW trending belt of seismicity between Adra (Spain) and Al Hoceima (Morocco), supporting the case for a major left-lateral shear zone across the Alboran Sea. Such a shear zone is in accord with high-resolution bathymetric data and seismic reflection imaging, indicating a number of small active fault zones, some of which offset the seafloor, rather than supporting a well-defined discrete plate boundary fault. Moreover, a number of large faults known to be active as evidenced from bathymetry, seismic reflection, and paleoseismic data such as the Yusuf and Carboneras faults were seismically inactive. Earthquakes below the Western Alboran Basin occurred at 70 to 110 km depth and hence reflected intermediate depth seismicity related to subducted lithosphere

Estimación muestral en la percepción de los servicios deportivos a través de la teoría de la generalizabilidad

La presente investigación utiliza la Teoría de la Generalizabilidad (TG) aplicada al ámbito de la gestión deportiva con el objetivo de conocer el tamaño muestral adecuado para la evaluación de la calidad percibida. Para ello, se utilizó una estructura compuesta por las facetas ítems (I) y participantes (P), con un diseño totalmente cruzado. Dentro del Modelo Lineal General (GLM), con estas dos facetas, se realizó un análisis de la varianza y se estimó la precisión de generalización. La herramienta empleada fue un cuestionario compuesto por 25 ítems y los participantes, un total de 330, pertenecían a una instalación deportiva de la ciudad de Málaga. Los resultados muestran que el número de participantes utilizado obtuvo un registro fiable (ξρ²(δ) = 0.98), y permitió estimar el nivel de precisión en la generalización para el tamaño muestral empleado (coeficiente de generalizabilidad, ξρ²(Δ) = 0.96), suponiendo de esta manera un importante avance en cuanto a la eficiencia en futuras evaluaciones de servicios deportivos.The present study uses the Generalizability Theory (GT) apply into the sport management area aiming to know the accurate sample size to evaluate the perceived quality. For this purpose, a compound structure was used for the participants (P) and items (I) aspects, with a fully crossed design. Applying general linear model (GLM), with both aspects, a variance analysis was realised and it estimated the generalization's precision. The instrument was a survey composed for 25 items and the sample, in total 330, comes from a fitness centre in the city of Malaga. The obtain results shows a number of participants using a reliable register (ξρ²(δ) = 0.98), and it estimates the precision level in the generalization to the sample size used (generalizability coefficient, ξρ²(Δ) = 0.96), assuming in this side an important progress in relation to the efficiency in upcoming evaluations in sports services

Aplicación de la TG en el deporte para el estudio de la fiabilidad, validez y estimación de la muestra.

La Teoría de la Generalizabilidad (TG) es una teoría de los errores multifaceta que asume que cualquier situación de medida posee infinitas fuentes de variación. En este sentido esta teoría puede aplicarse en el ámbito de la observación con la intención de conocer lainfluencia de estas fuentes de error sobre la medida. De todas las posibilidades, en este trabajo se presentan, a modo de ejemplo, tres aplicaciones de la TG en las primeras fases de una investigación en el ámbito observacional: 1) para el estudio de la validez, 2) para la estimación de la muestra; y, 3) para el estudio de la fiabilidad. Actualmente existen aplicaciones informáticas (GT, EduG o, recientemente, SAGT) que facilitan la implementación de este tipo de análisis que permiten al investigador contar con recursos procedimentales para que las decisiones que tiene que tomar en el proceso de investigación puedan estar justificadas antes de ser implementadas como la muestra necesaria para poder generalizar con precisión o disponer de una herramienta de observación válida y fiable para afrontar el arduo proceso de codificación y registro de las conductas acontecidas en los contextos naturales donde se aplican