简介：HeavilypopulatedbyBeijingandTianjincities,BohaibasinisaseismicallyactiveCenozoicbasinsufferingfromhugelostbydevastatingearthquakes,suchasTangshanearthquake.Theattenuation(QPandQS)ofthesurficialQuaternarysedimenthasnotbeenstudiedatnaturalseismicfrequency(1-10Hz),whichiscrucialtoearthquakehazardsstudy.Boreholeseismicrecordsofmicroearthquakeprovideusagoodwaytostudythevelocityandattenuationofthesurficialstructure(0-500m).Wefoundthattherearetwopulseswellseparatedwithsimplewaveformsonboreholeseismicrecordsfromthe2006MW4.9Wen'anearthquakesequence.Thenweperformedwaveformmodelingwithgeneralizedraytheory(GRT)toconfirmthatthetwopulsesaredirectwaveandsurfacereflectedwave,andfoundthattheaveragevPandvSofthetop300minthisregionareabout1.8km/sand0.42km/s,leadingtohighvP/vSratioof4.3.Wealsomodeledsurfacere-flectedwavewithpropagatingmatrixmethodtoconstrainQSandthenearsurfacevelocitystructure.OurmodelingindicatesthatQSisatleast30,orprobablyupto100,muchlargerthanthetypicallyassumedextremelylowQ(～10),butconsistentwithQSmodelinginMississippiembayment.Also,thevelocitygradientjustbeneaththefreesurface(0-50m)isverylargeandvelocityincreasesgraduallyatlargerdepth.Ourmodelingdemonstratestheimportanceofboreholeseismicrecordsinresolvingshallowvelocityandattenuationstructure,andhencemayhelpinearthquakehazardsimulation.

简介：Thedensebroadbandseismicnetworkprovidesmorehigh-qualitywaveformthatishelpfultoimproveconstraintfocaldepthofshallowearthquake.Manyshallowearthquakesoccurringinsedimentwereregardedasinducedevents.InSichuanbasin,gasindustryandsaltminingaredependentonfluidinjectiontechniquethattriggersmicroseismicity.WeadoptedwaveforminversionmethodwithregionalrecordstoobtainfocalmechanismofanMs4.8earthquakeatChangning.TheresultsuggestedthattheChangningearthquakeoccurredataESEthrustfault,anditsfocaldepthwasabout3km.ThedepthphasesincludingteleseismicpPphaseandregionalsPLphaseshowsthatthefocaldepthisabout2km.Thestrong,shortperiodsurfacewavesuggeststhatthiseventisaveryshallowearthquake.TheamplituderatiobetweenRayleighwaveanddirectSwavewasalsousedtoestimatethesourcedepthofthemainshock.Thefocaldepth(2–4km)isfarlessthanthedepthofthesedimentarylayerthickness(6–8km)inepicentralregion.Itisclosetothedepthoffluidinjectionofsaltmining,whichmayimplythatthiseventwastriggeredbytheindustrialactivity.