POTERE RISOLUTIVO DEI DATI NELLE INVERSIONI PER SORGENTI SISMICHE ESTESE

1995/1996IX Ciclo1968Versione digitalizzata della tesi di dottorato cartacea

Accounting for rupture directivity in ShakeMap

The rapid and accurate information about the ground shaking following an earthquake is necessary for emergency response planning. A prompt strategy is contouring the real data recorded at the stations. However only few regions, i.e. Japan and Taiwan, have an instrumental coverage as good as needed to produce shaking maps relying almost entirely on real data. ShakeMap has been conceived in order to “fill” the data gap and producing stable contouring using the ground motion predictive equations (GMPEs) and site effect. Thus for regions where the data coverage is sparse, the interpolation plays a crucial role and the choice of the GMPE can affect strongly the goodness of the ground shaking estimation. However the GMPEs derive from an empirical regression describing the averaged behavior of the ground shaking and tend to mask, when present, specific trends due to multidimensional effects like the asymmetry of the rupture process (directivity effect). Thus, ShakeMaps for large events may not reproduce faithfully the ground motion in the near source if determined without the introduction of rupture related parameters. One way to improve the ShakeMap prediction is to modify the ground motion modeling in order to better explain the ground motion variability. To this purpose, the empirical model can be refined with information about the rupture process (Spagnuolo PhD2010), in this case using the directivity term defined by Spudich and Chiou (Earthquake Spectra 2008). The aim of this work is to quantify the effectiveness of refined GMPEs in improving the performance of ShakeMap. We quantify the agreement of this new GMPE with the real recorded data, and make inference about the reliability of this new ShakeMap. The test is focused on the study of the ShakeMap degradation when the number of the observations is reduced, and on the quantification of the improvements due to the directivity term. In order to conduct properly the test, we investigate two well- recorded events from Japan: the 2008 Iwate-Miyagi (M7) and the 2000 Tottori (M6.6) events. This work is part of the DPC-INGV S3 project (2007-09), as described in the companion abstract Ameri et al. (ESC2010)

Acquiring, archiving, analyzing and exchanging seismic data in real time at the Seismological Research Center of the OGS in Italy

The Centro di Ricerche Sismologiche (CRS, Seismological Research Center) of the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS, Italian National Institute for Oceanography and Experimental Geophysics) in Udine (Italy) after the strong earthquake (magnitude M=6.4) occurred in 1976 in the Italian Friuli-Venezia Giulia region, started to operate the North-east Italy (NI) seismic network: it currently consists of 11 very sensitive broad band and 23 more simple short period seismic stations, all telemetered to and acquired in real time at the OGS-CRS data center in Udine. Real time data exchange agreements in place with other Italian, Slovenian, Austrian and Swiss seismological institutes lead to a total number of 89 seismic stations acquired in real time, which makes the OGS the reference institute for seismic monitoring of Northeastern Italy. Since 2002 OGS-CRS is using the Antelope software suite as the main tool for collecting, analyzing, archiving and exchanging seismic data in the framework of the EU Interreg IIIA project “Trans-national seismological networks in the South-Eastern Alps”. SeisComP is also used as a real time data exchange server tool. At OGS-CRS we then adapted existing programs and created new ones like: a customized web-accessible server to manually relocate earthquakes, a script for automatic moment tensor determination, scripts for web publishing of earthquake parametric data, waveforms, state of health parameters and shaking maps, noise characterization by means of automatic spectra analysis, plus scripts for email/SMS/fax alerting. A new OGS-CRS real time web site has also been recently designed and made operative in the framework of the DPC-INGV S3 Project

Acquiring, archiving, analyzing and exchanging seismic data in real time at the Seismological Research Center of the OG S in Italy: an updated view

The Centro di Ricerche Sismologiche (CRS, Seismological Research Center) of the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS, Italian National Institute for Oceanography and Experimental Geophysics) in Udine (Italy) after the strong earthquake (magnitude M=6.4) occurred in 1976 in the Italian Friuli-Venezia Giulia region, started to operate the North-east Italy (NI) seismic network: it currently consists of 11 very sensitive broad band and 22 more simple short period seismic stations, all telemetered to and acquired in real time at the OGS-CRS data center in Udine. Real time data exchange agreements in place with other Italian, Slovenian, Austrian and Swiss seismological institutes lead to a total number of 90 seismic stations acquired in real time, which makes the OGS the reference institute for seismic monitoring of Northeastern Italy. Since 2002 OGS-CRS is using the Antelope software suite as the main tool for collecting, analyzing, archiving and exchanging seismic data in the framework of the EU Interreg IIIA project “ Trans-national seismological networks in the South-Eastern Alps”. SeisComP is also used as a real time data exchange server tool. At OGS-CRS we then adapted existing programs and created new ones like: a customized web-accessible server to manually relocate earthquakes, a script for automatic moment tensor determination, scripts for web publishing of earthquake parametric data, waveforms, state of health parameters and shaking maps, noise characterization by means of automatic spectra analysis, plus scripts for mail/SMS/fax alerting. A new OGS-CRS real time web site has also been recently designed and made operative in the framework of the Italian P C-INGV S3 P roject

Improving the seismic monitoring of North-eastern Italy: the state of the art of the North-eastern Italy (NI) Seismic Network run by OGS

The Centro di Ricerche Sismologiche (CRS, Seismological Research Center) of the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS, Italian National Institute for Oceanography and Experimental Geophysics) in Udine (Italy) after the strong earthquake of magnitude Mw=6.4 occurred in 1976 in the Italian Friuli-Venezia Giulia region, started to operate the North-eastern Italy (NI) Seismic Network: it currently consists of 12 very sensitive broad band and 21 simpler short period seismic stations, all telemetered to and acquired in real time at the OGS-CRS data center in Udine. Real time data exchange agreements in place with other Italian, Slovenian, Austrian and Swiss seismological institutes lead to a total number of 93 seismic stations acquired in real time, which makes the OGS the reference institute for seismic monitoring of North-eastern Italy. Since 2002 OGS-CRS is using the Antelope software suite on a SUN SPARC cluster as the main tool for collecting, analyzing, archiving and exchanging seismic data, initially in the framework of the EU Interreg IIIA project “Trans-national seismological networks in the South-Eastern Alps”. SeisComP is also used as a real time data exchange server tool. In order to improve the seismological monitoring of the North-eastern Italy area, at OGS-CRS we tuned existing programs and created ad hoc ones like: a customized web server named PickServer to manually relocate earthquakes, a script for automatic moment tensor determination, scripts for web publishing of earthquake parametric data, waveforms, state of health parameters and shaking maps, noise characterization by means of automatic spectra analysis, and last but not least scripts for email/SMS/fax alerting. A new OGS-CRS real time seismological website (http://rts.crs.inogs.it/) has also been operative since more than one year in the framework of the Italian DPC-INGV S3 Project: the website shows classic earthquake locations parametric data plus shakemap and moment tensor information; recently also daily PSD quality check of seismic stations plots have been added. At OGS-CRS we also spent a considerable amount of efforts in improving the long-period performances of broadband seismic stations, either by carrying out full re-installations and/or applying thermal insulations to the seismometers: the example of the new PRED broad band seismic station installation in the cave tunnel of Cave del Predil using a Quanterra Q330HR high resolution digitizer and a Sterckeisen STS-2 broadband seismometer will be illustrated. Efforts have been put also in strengthening the reliability of data links, exploring the use of redundant satellite/radio/GPRS links

Testing the improvement of ShakeMaps using f inite-f ault models and synthetic seismograms

ShakeMap package uses empirical ground motion prediction equations (GM PEs) to estimate the ground motion where recorded data are not available. Recorded and estimated values are then interpolated in order to produce a shaking map associated to the considered event. Anyway GMPEs account only for average characteristics of source and wave propagation processes. Within the framework of the DPC-INGV S3 project (2007-09), we evaluate whether the inclusion of directivity effects in GMPEs (companion paper Spagnuolo et al., 2010) or the use of synthetic seismograms from finite-fault rupture models may improve the ShakeMap evaluation. An advantage of using simulated motions from kinematic rupture models is that source effects, as rupture directivity, are directly included in the synthetics. This is particularly interesting in Italy where the regional GMPEs, based on a few number of near-source records for moderate-to-large earthquakes, are not reliable for estimating ground motion in the vicinity of the source. In this work we investigated how and if the synthetic seismograms generated with finite-fault models can be used in place of (or in addition to) GMPEs within the ShakeMap methodology. We assumed a description of the rupture model with gradually increasing details, from a simple point source to a kinematic rupture history obtained from inversion of strong-motion data. According to the available information synthetic seismograms are calculated with methods that account for the different degree of approximation in source properties. We chose the M w 6.9 2008 Iwate-M iyagi (Japan) earthquake as a case study. This earthquake has been recorded by a very large number of stations and the corresponding ShakeMap relies almost totally on the recorded ground motions. Starting from this ideal case, we removed a number of stations in order to evaluate the deviations from the reference map and the sensitivity of the map to the number of stations used. The removed data are then substituted with synthetic values calculated assuming different source approximations, and the resulting maps are compared to the original ones (containing observed data only). The use of synthetic seismograms computed for finite-fault rupture models produces, in general, an improvement of the calculated ShakeMaps, especially when synthetics are used to integrate real data. When real data are not available and ShakeMap is estimated using GMPEs only, the improvement adding simulated values depends on the considered strong-motion parameters

Programma del gruppo di lavoro Open Science della Consulta dei Presidenti degli EPR

Programma di lavoro del gruppo Openscience della CoPER (già ConPER

Prossimi Passi

Documento conclusivo e programmatico del Primo convegno nazionale del gruppo di lavoro Openscience della Consulta dei presidenti degli enti pubblici di ricerca. https://agenda.infn.it/e/ConvegnoOpenscienceCoPER202

Fault-plane solutions from moment-tensor inversion and preliminary Coulomb stress analysis for the Emilia Plain

We investigate the seismicity occurred in the Po area, in the period July 2011-June 1012, by means of moment tensor and we use our set of revised focal mechanisms - computed for M> 3.7 earthquakes - to evaluate Coulomb elastic stress changes in order to detect potential intermediate-distance faults interaction, and the main features of this complex structural system

DataSheet1_Sensitivity of the second seismic moments resolution to determine the fault parameters of moderate earthquakes.pdf

Second-degree seismic moments provide a simple description of the spatiotemporal extent of the earthquake source. Finite source attributes such as rupture length, width, duration, velocity, and propagation direction can be estimated by computing second-degree seismic moments without the need for a predefined rupture model. This is achieved by analyzing the properties of apparent source time functions (ASTFs) obtained from seismic signals recorded at different stations after eliminating instrument responses and path effects. In this study, to define the limits of its application in the analysis of small earthquakes and to evaluate the sensitivity and reliability of the results to uncertainties due to observations and prior knowledge, we modeled a synthetic seismic source and examined how potential uncertainties in hypocentral depth, velocity model, focal mechanism, source duration, and number of recording stations can affect the inversion results. An accurate ASTF is essential to obtain robust results and our findings show that the mean values of the key source parameters, i.e., fracture size, source duration, and rupture velocity, are generally well reproduced in all sensitivity tests, with some exceptions, within the standard deviation. We also demonstrate that large uncertainties in the hypocentral depth and inaccurate velocity models introduce a significant bias, especially in rupture size and average centroid velocity, indicating the strong influence of ray path calculation in the inversion process. These resolution limits must therefore be taken into account when interpreting the results obtained with this technique.</p