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1、SeismicActivityinTucundubaReservoir,SenadorS´a-CE,Brazil,1997-1998.GeorgeSandFran¸ca1,JoaquimMendesFerreiraandMarioKoechiTakeyaDepartamentodeF´ısicaTe´oricaeExperimental,UniversidadeFederaldoRioGrandedoNorte,Natal-RN,59072-970,BrazilAbstractTheTucundubaDamisabout290km
2、WestofFortaleza,Cear´astate.Theseismicmonitoringofthearea,withalocalnetwork,hasbeganonJune11,1997,soonaftertheoccurrenceoftheeventwithmagnitude3.2mbonJune09,1997.Themonitoringwasdonewithonetheanalogicalstation(usedformagnitudedurationmeasurementandstatisticalcontrolac
3、tivity)andsevendigitalstations.Thedigi-talstations,withthreecomponentseach,wereoperatedfromJunetoNovember1997.Inthiswork,thedatacollectedduringdigitalmon-itoringwasanalyzedtodeterminehypocentersandfocalmechanism.Todeterminehypocenters,theHYPO71programwasused,withhalf-
4、spacemodel,whoseparameterswere5.95km/s,forP-wavevelocities,and1.69fortheratiobetweenPandS-wavevelocity.Theactivezonewasnearly1kmlength,withdepthbetween4.5and5.2km.With16eventsrecordedinthesamesixstations,wedeterminedthedirectionofthefaultplane(NE-SW).Thefaultmechanism
5、isstrike-slipwithasmallnormalcomponent.Thedipestimatewas65◦SEwithFPFITand80◦SEwithFOCMEC.Preliminaryestimatesofmaximumhori-zontalcompressivestress,usingP-axisdirection,wereinaccordancewithFerreiraetal.(1998).Thesmalldifferenceisprobablyduetoinfluenceofthesedimentarybasi
6、nintheregionalstress.TheactiveareaisinaccordancewithseismicitydescribedbyAssump¸c˜ao(1998),i.e.,thecombinationregionalstress,localflexuraleffectfromthicksedimentaryloads,andapresumablyweakercrustfromMesozoicthin-ning.Keywords:Seismicity,focalmechanismarXiv:physics/04051
7、45v1[physics.geo-ph]27May20041george@dfte.ufrn.br11IntroductionTheNorthwestofCear´aisanareaofseismicactivityknownsincetheXIXcentury(Ferreira&Assump¸c˜ao,1983;Berrocaletal.,1984;Ferreiraetal.,1998).OnJune09,1997(districtofSerrota,SenadorS´a-CE),aneventwithmagnitudemb=3
8、.2(IntensityIII-IVMM)happened,scaringthelocalpopulation.ThegrowthoftheseismicactivityinSerrota,speciallyintheTucundubaReserv
