Received28April2010 Receivedinrevisedform5November2010 Accepted10March2011 Editedby:G. Helffrich. Keywords: Probability-basedMagnitudeof Completeness SeismometricNetworks EarthquakeDatabases North-EasternItaly SeismicAttenuation Weinvestigatedetectionprobabilitiesandrecordingcompletenessof theseismicnetworkinnorth- easternItaly, operatedbytheOGS(IstitutoNazionalediOceanografiaeGeofisicaSperimentale)during the years 1977–2007, using the Probability-basedMagnitude of Completeness (PMC) methodby SchorlemmerandWoessner(2008). Completenessof thedatasetisvaryinginspaceandtimeduetotheevolutionof networkgeome- try, instrumentalcharacteristics, andmonitoringandprocessingstrategiesovertime:thisisacommon featurefor all theregional andnational instrumental cataloguesthat shouldbeproperlyaccounted forinseismicityrateevaluations. Forthefirsttime, wequantifywiththenewPMCmethoddetection probabilitiesofaregionalnetworkoperatingsincethelate70s, alsoincludingpaperrecords. PMCisbasedonempiricaldataandrequirestheearthquakecatalogcontainingphasepicks,thestation locationsandon-/off-times,andtheattenuationrelationusedtocomputelocalmagnitudes.Inthe30-year period, weidentifiedfourtimewindows, roughlycorrespondingtothemainchangesintheacquisition system. Wereconstructedon-/off-timesbymergingtheavailableinformationoninstrumentswiththe analysisofinter-picktimesateachstation. Werevisedtherelationshipbetweendurationandlocal magnitudesasthecalibrationof duration magnitudedemonstratedtobenothomogeneousamongthedifferentacquisitionsystems. Moreover, weintroducedsomeconstraintsontheapplicationofthePMCmethodtoimproveitsperformancefor networkswithsparsedataandshowtheroleofmissingeventsandoftemporarynetworksonregional completenessmaps. TheresultsdemonstratethattheOGSnetworkisdetectingearthquakescompletelydowntomagnitude 1.5foralargepartoftheFriuli-Venezia-Giuliaregionsincetheearlieststagesofitsfunctionality;the OGSinstrumentalcatalogisthereforethemostpreciseandcompletedatasetavailableforthisarea. Our analysisshowsthatthechangefromanalogtodigital systemsdoesnotnecessarilycorrespondtoan improvementindetectioncapabilities. Thecomputedtimeseriesof completenessmapsareavailable andshouldbeconsideredforanyseismicitystudyinvolvingdatafromtheOGSnetwork.
Probabilistic completeness assessment of the past 30 years of seismic monitoring in northeastern Italy
Gentili S;Sugan M;Peruzza L;
2011-01-01
Abstract
Received28April2010 Receivedinrevisedform5November2010 Accepted10March2011 Editedby:G. Helffrich. Keywords: Probability-basedMagnitudeof Completeness SeismometricNetworks EarthquakeDatabases North-EasternItaly SeismicAttenuation Weinvestigatedetectionprobabilitiesandrecordingcompletenessof theseismicnetworkinnorth- easternItaly, operatedbytheOGS(IstitutoNazionalediOceanografiaeGeofisicaSperimentale)during the years 1977–2007, using the Probability-basedMagnitude of Completeness (PMC) methodby SchorlemmerandWoessner(2008). Completenessof thedatasetisvaryinginspaceandtimeduetotheevolutionof networkgeome- try, instrumentalcharacteristics, andmonitoringandprocessingstrategiesovertime:thisisacommon featurefor all theregional andnational instrumental cataloguesthat shouldbeproperlyaccounted forinseismicityrateevaluations. Forthefirsttime, wequantifywiththenewPMCmethoddetection probabilitiesofaregionalnetworkoperatingsincethelate70s, alsoincludingpaperrecords. PMCisbasedonempiricaldataandrequirestheearthquakecatalogcontainingphasepicks,thestation locationsandon-/off-times,andtheattenuationrelationusedtocomputelocalmagnitudes.Inthe30-year period, weidentifiedfourtimewindows, roughlycorrespondingtothemainchangesintheacquisition system. Wereconstructedon-/off-timesbymergingtheavailableinformationoninstrumentswiththe analysisofinter-picktimesateachstation. Werevisedtherelationshipbetweendurationandlocal magnitudesasthecalibrationof duration magnitudedemonstratedtobenothomogeneousamongthedifferentacquisitionsystems. Moreover, weintroducedsomeconstraintsontheapplicationofthePMCmethodtoimproveitsperformancefor networkswithsparsedataandshowtheroleofmissingeventsandoftemporarynetworksonregional completenessmaps. TheresultsdemonstratethattheOGSnetworkisdetectingearthquakescompletelydowntomagnitude 1.5foralargepartoftheFriuli-Venezia-Giuliaregionsincetheearlieststagesofitsfunctionality;the OGSinstrumentalcatalogisthereforethemostpreciseandcompletedatasetavailableforthisarea. Our analysisshowsthatthechangefromanalogtodigital systemsdoesnotnecessarilycorrespondtoan improvementindetectioncapabilities. Thecomputedtimeseriesof completenessmapsareavailable andshouldbeconsideredforanyseismicitystudyinvolvingdatafromtheOGSnetwork.| File | Dimensione | Formato | |
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