Stazioni accelerometriche con Reftek-130/modem GSM: note tecniche sui softwares in ambiente Linux per la Rete Accelerometrica dell'Italia Settentrionale

L'INGV, Sezione di Milano, ha recentemente ultimato la fase di test su alcuni nuovi softwares progettati e sviluppati in ambiente Linux, per lo scarico dei dati sismici di stazioni accelerometriche connesse al centro di acquisizione dati tramite modem GSM. L'acquisitore utilizzato dalla Sezione è il Reftek-130 (www.reftek.com), a 24 bit, il sensore è l'Episensor (www.kinemetrics.com), mentre il modem è il Wavecom (www.wavecom.com). Per poter eseguire le chiamate telefoniche con le stazioni remote e lo scarico dei relativi dati, sono stati progettati e realizzati softwares in ambiente Linux, con la duplice finalità di avere un completo controllo su tutte le operazioni richieste da tale sistema e di totale integrazione con il sistema di acquisizione dati già operativo all'INGV-MI per la rete velocimetrica. In particolare è stato scelto di utilizzare una programmazione di tipo “script” con le shell bash (www.gnu.org/software/bash/) che utilizzano quasi integralmente comandi di sistema e due programmi esterni open-source licenziati con GPL: m i n i c o m (http://linux.softpedia.com/get/Communications/Telephony/minicom-753.shtml) e wvdial (www.linuxcommand.org/man_pages/wvdial1.html), in modo tale che siano esportabili su altre architetture di macchine con piccole modifiche di configurazione e che fosse possibile l'automatizzazione per diverse stazioni installate. Il computer utilizzato per la gestione della Rete ha un sistema operativo Linux Suse 10.0 (www.novell.com/it-it/linux/suse/), sul quale è stata installata una porta multiseriale per poter eseguire contemporaneamente fino a 9 chiamate. Per la gestione delle configurazioni delle stazioni sismiche e del loro corretto funzionamento, l'INGV-MI utilizza i softwares creati dalla stessa Reftek, ma con alcune modifiche per essere integrati nei sistemi Linux delle reti sismiche dell'Ente. In questo lavoro saranno anche accennate brevemente tali modifiche ai softwares per poter dare un quadro completo su come è gestita la rete accelerometrica dell'INGV-MI; l'autore darà per acquisita, da parte del lettore, la conoscenza degli acquisitori Reftek-130, dei sensori Episensor, delle problematiche di base di una rete sismometrica oltre ai sistemi Linux in genere. Le stazioni Reftek prevedono la possibilità di scaricare i dati contenuti nella propria RAM su dischi locali, su una porta internet o su una porta seriale, anche in combinazione contemporanea. L'INGV-MI utilizza un'acquisizione dati in continuo su supporto locale, ed un collegamento modem GSM sulla porta seriale per scaricare soltanto i dati remoti di particolare interesse tramite protocollo FTP

Studio sulla polarità dei sensori MARK L4-3D

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Metodologie per l'installazione e la gestione delle stazioni sismiche Mars88 Modem Control

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Site Classification Assessment for Estimating Empirical Attenuation Relationships for Central-Northern Italy Earthquakes

The aim of this article is to investigate the ground motion attenuation of the most industrialized and populated regions of Italy, evaluating the capability of different approaches to estimate site dependent models. The 5.2 magnitude earthquake on November 24, 2004 shocked the areas of Northern Italy producing damage of about 215 million euros. The data set, including 243 earthquakes of local magnitude up to 5.2, has been collected in the period December 2002–October 2005 by 30 threecomponent seismic stations managed by Istituto Nazionale di Geofisica e Vulcanologia, Sezione of Milano (INGV-MI). Empirical attenuation relationships have been estimated for horizontal peak ground velocity (PGHV), acceleration (PGHA), displacement (PGHD), and for response spectral acceleration (SA) for periods between 0.1 and 1.5 s. To estimate suitable attenuation models, in particular for sites characterized by thick sedimentary geological formations, a soil discrimination based on EU8 code can lead to wrong evaluations. On the contrary, a classification based on H/V spectral ratios of seismic ambient noise (NHV) allows the models to fit better real and predicted data and to reduce the uncertainties of the process. For each receiver, NHV have been strengthened by additional H/V spectral ratio of earthquake data (EHV), calculated considering different portions of the analysed signals. In order to validate the PGHA attenuation relationship for greater magnitudes, accelerometric records, relative to Central-Northern Italy strong motions occurring in the last 30 years, have been collected and superimposed to our attenuation curves

Interpretation of microtremor 2D array data using Rayleigh and Love waves: the case study of Bevagna (central Italy)

In the last decades, geophysicists and seismologists have focused their attention on the inversion of empirical surface-waves’ dispersion curves from microtremor measurements for estimating the Swaves velocity structure at a site. This procedure allows a fast and convenient investigation without strong active sources, which are difficult to deploy especially in urban areas. In this study we report on a 2D seismic noise array experiment carried out at Bevagna (Central Italy) near the station BVG of the Italian Accelerometric Network (RAN). The site was investigated within the DPC-INGV S4 Project (2007-2009). The Rayleigh- and Love- waves dispersion characteristics were estimated using different methods. The inversion of the dispersion curves was then performed independently, obtaining two estimations for the S-waves velocity profiles. The results of cross-hole logging near the seismic station are used for a comparison. The shear waves velocity profiles estimated by microtremor analyses range up to 150m depth. The two independent procedures provide consistent shear waves velocity profiles for the shallow part of the model (20-30 m in depth) in agreement with the results of the cross-hole logging. Some problems arise between 30 and 40 m in depth in the profile estimated by surface waves. In this range cross-hole logging evidences an inversion of S-waves velocity. Although the cross-hole logging stops at 40 m of depth, we are confident about the results provided by the Rayleigh-waves analysis below 40-50 m. This case study suggests that greater efforts should be devoted to exploit the potential of a coupled analysis of Rayleigh and Love waves from microtremor array measurements

Microtremor measurements interpretations at the BVG station of the Italian accelerometric network

In the last decades, researchers focused their attention on using inverse analysis of empirical surface‐waves dispersion curves from microtremor measurements since it allows to keep the cost of investigation relatively low and to avoid the use of active sources that might be prohibitive in urban areas. In this study we reports the results and interpretations of the passive measurements carried out at a test site in Bevagna (Italy) near the BVG station of the Italian Accelerometric Network (RAN) within the framework of the DPC‐INGV S4 Project (2007‐2009). Using two independent approaches, Rayleigh and Love wave dispersion characteristics were reproduced through two different inversion methods. At this site a cross‐hole test made nearby the seismic station offers the opportunity to compare the subsoil velocity profiles derived by seismic noise array data with independent geophysical information. The results obtained from the separated Love waves and Rayleigh wave inversions analyses showed that the two procedure provide consistent shear wave velocity profiles for the shallow part of the model in good agreement with the results of the nearby cross‐hole test. This case history shows the capabilities of surface wave analyses from passive source to adequately retrieve the S‐wave subsoil structure and suggests that more efforts should be devoted in exploiting the potential of coupled analysis of Rayleigh and Love waves from microtremor array measurements for site characterization