Mislocation vectors for the Tripoli seismic array, Greece, and structural effect implications from backazimuth and slowness residual analysis

Η αποτελεσματικότητα της Σεισμικής Διάταξης Τριπόλεως (TRISAR) στον προσδιορισμό των εστιακών παραμέτρων των σεισμών περιορίζεται από το μικρό ανάπτυγμα και αριθμό αισθητήρων αυτής. Η λεπτομερής ανάλυση των σφαλμάτων στον αυτόματο προσδιορισμό επκέντρων δημιουργεί υπόνοιες για επιδράσεις της δομής του φλοιού και της τοπικής γεωλογίας. Για τη διερεύνηση της δυνατότητας αυτόματης διόρθωσης των αποτελεσμάτων του ανύσματος βραδύτητας, υπολογίστηκαν τα ανύσματα διόρθωσης για ένα εκτεταμένο δείγμα δεδομένων. Οι θεωρητικές τιμές προσδιορίστηκαν βάσει των σεισμικών καταλόγων του Εθνικού Αστεροσκοπείου Αθηνών και του Διεθνούς Σεισμολογικού Κέντρου (ISC). Τα ανύσματα διόρθωσης, που προέκυψαν, έχουν σημαντικό μήκος, σύμφωνο με τα μεγάλα σφάλματα που παρατηρούνται για το αζιμούθιο και τη βραδύτητα. Οι μικρότερες τιμές διαπιστώνονται ΒΑ της διάταξης, για επικεντρικές αποστάσεις μικρότερες των 200 km. Όπως είναι αναμενόμενο, οι διορθώσεις αφορούν κυρίως στο αζιμούθιο και δεν είναι αρκετές ώστε να επηρεάσουν την τελική λύση, δεδομένου ότι τα μεγαλύτερα σφάλματα του αυτόματου αλγόριθμου αφορούν στον προσδιορισμό της επικεντρικής απόστασης. Ωστόσο, καθίσταται σαφής η δυνατότητα αυτόματης διόρθωσης του ανύσματος βραδύτητας, αναμένεται δε μία βελτιωμένη γεωμετρία της σεισμικής διάταξης να δώσει πολύ καλύτερα αποτελέσματα, κυρίως λόγω της μειωμένης διασποράς, που θα επιτυγχάνειTripoli Seismic Array, Greece, performance in terms of event location is restricted by its very small aperture and limited number of sensors. Detailed investigation of errors in automatic location results suggests structural and local geology effects. In order to investigate the possibility to correct for systematic errors automatically, mis location vectors were calculated for an extended data-set. Theoretical values were calculated based on earthquake catalogues compiled by the National Observatory of Athens and the ISC. Resulting mis location vectors are characterized by significant vector length, consistent with the large observed backazimuth and slowness residuals, the smaller values being met in the area NE of the array and for epicentral distance values less than 200 km. As expected, resulting corrections mostly concern backazimuth values and are not able to sufficiently affect the final epicentre solution, as the largest automatic algorithm errors are observed in epicentral distance determination. However, the possibility to automatically correct for systematic deviations is verified, and future research with an extended array configuration is expected to provide clearer results, due to significantly lower scatter

Inner-shelf circulation and sediment dynamics on a series of shoreface-connected ridges offshore of Fire Island, NY

Locations along the inner-continental shelf offshore of Fire Island, NY, are characterized by a series of shoreface-connected ridges (SFCRs). These sand ridges have approximate dimensions of 10 km in length, 3 km spacing, and up to similar to 8 m ridge to trough relief and are oriented obliquely at approximately 30 degrees clockwise from the coastline. Stability analysis from previous studies explains how sand ridges such as these could be formed and maintained by storm-driven flows directed alongshore with a key maintenance mechanism of offshore deflected flows over ridge crests and onshore in the troughs. We examine these processes both with a limited set of idealized numerical simulations and analysis of observational data. Model results confirm that alongshore flows over the SFCRs exhibit offshore veering of currents over the ridge crests and onshore-directed flows in the troughs, and demonstrate the opposite circulation pattern for a reverse wind. To further investigate these maintenance processes, oceanographic instruments were deployed at seven sites on the SFCRs offshore of Fire Island to measure water levels, ocean currents, waves, suspended sediment concentrations, and bottom stresses from January to April 2012. Data analysis reveals that during storms with winds from the northeast, the processes of offshore deflection of currents over ridge crests and onshore in the troughs were observed, and during storm events with winds from the southwest, a reverse flow pattern over the ridges occurred. Computations of suspended sediment fluxes identify periods that are consistent with SFCR maintenance mechanisms. Alongshore winds from the northeast drove fluxes offshore on the ridge crest and onshore in the trough that would tend to promote ridge maintenance. However, alongshore winds from the southwest drove opposite circulations. The wind fields are related to different storm types that occur in the region (low-pressure systems, cold fronts, and warm fronts). From the limited data set, we identify that low-pressure systems drive sediment fluxes that tend to promote stability and maintain the SFCRs while cold front type storms appear to drive circulations that are in the opposite sense and may not be a supporting mechanism for ridge maintenance

Combined Ground Deformation Study Of Broader Area Of Patras Gulf (W. Greece) Using PSI-WAP, DGPS And Seismicity Analyses

Long-term ground deformation monitoring using the Persistent Scatterer Interferometry Wide Area Product (PSI-WAP) technique for the period 1992-2003, combined with Differential GPS measurements and seismicity analysis has provided useful information about the tectonic motions of the tectonically complex area of Patras Gulf (Western Greece), and lead to new insights on the geotectonic regime of this region. Descending ERS radar images were used to compile the PSI-WAP product that has been calibrated using the absolute velocity field of available GPS stations in the area. It has been found that the deformation of the southern part of Patras Gulf near the coastline has been characterized by considerable subsidence (>-5mm/yr), where unconsolidated sediments usually prevail, compared to the northern part of the gulf. Significant subsidence has also been identified in areas along the down-throw side of possible faults, as well as areas where extensive ground water pumping has occurred for irrigation. These results correlate well with local GPS and seismicity data

Aerodynamics of aero-engine installation

This paper describes current progress in the development of methods to assess aero-engine airframe installation effects. The aerodynamic characteristics of isolated intakes, a typical transonic transport aircraft as well as a combination of a through-flow nacelle and aircraft configuration have been evaluated. The validation task for an isolated engine nacelle is carried out with concern for the accuracy in the assessment of intake performance descriptors such as mass flow capture ratio and drag rise Mach number. The necessary mesh and modelling requirements to simulate the nacelle aerodynamics are determined. Furthermore, the validation of the numerical model for the aircraft is performed as an extension of work that has been carried out under previous drag prediction research programmes. The validation of the aircraft model has been extended to include the geometry with through flow nacelles. Finally, the assessment of the mutual impact of the through flow nacelle and aircraft aerodynamics was performed. The drag and lift coefficient breakdown has been presented in order to identify the component sources of the drag associated with the engine installation. The paper concludes with an assessment of installation drag for through-flow nacelles and the determination of aerodynamic interference between the nacelle and the aircraft

CLON: overlay networks and gossip protocols for cloud environments

Although epidemic or gossip-based multicast is a robust and scalable approach to reliable data dissemination, its inherent redundancy results in high resource consumption on both links and nodes. This problem is aggravated in settings that have costlier or resource constrained links as happens in Cloud Computing infrastructures composed by several interconnected data centers across the globe. The goal of this work is therefore to improve the efficiency of gossip-based reliable multicast by reducing the load imposed on those constrained links. In detail, the proposed clon protocol combines an overlay that gives preference to local links and a dissemination strategy that takes into account locality. Extensive experimental evaluation using a very large number of simulated nodes shows that this results in a reduction of traffic in constrained links by an order of magnitude, while at the same time preserving the resilience properties that make gossip-based protocols so attractive.HP Labs Innovation Research Award, project DC2MS (IRA/CW118736