Abstract
We investigate crustal seismic attenuation by the coda quality parameter (Qc) in the Gargano area (Southern Italy), using a recently released dataset composed of 191 small earthquakes (1.0 ≤ ML ≤ 2.8) recorded by the local OTRIONS and the Italian INGV seismic networks, over three years of seismic monitoring. Following the single back-scattering theoretical assumption, Qc was computed using different frequencies (in the range of 2–16 Hz) and different lapse times (from 10 to 40 s). The trend of Qc vs. frequency is the same as that observed in the adjacent Umbria-Marche region. Qc at 1 Hz varies between 11 and 63, indicating that the area is characterized by active tectonics, despite the absence of high-magnitude earthquakes in recent decades. The 3D mapping procedure, based on sensitivity kernels, revealed that the Gargano Promontory is characterized by very low and homogeneous Qc at low frequencies, and by high and heterogeneous Qc at high frequencies. The lateral variations of Qc at 12 Hz follow the trend of the Moho in this region and are in good agreement with other geophysical observations.
Highlights
Coda waves recorded from small local earthquakes are interpreted as body waves of backscattering from heterogeneities that are distributed randomly but uniformly in the Earth’s crust and upper mantle
We investigate crustal seismic attenuation by the coda quality parameter (Qc) in the Gargano area (Southern Italy), using a recently released dataset composed of 191 small earthquakes (1.0 ≤ ML ≤ 2.8) recorded by the local OTRIONS and the Italian INGV seismic networks, over three years of seismic monitoring
The trend of Qc vs. frequency is the same as that observed in the adjacent Umbria-Marche region
Summary
Coda waves recorded from small local earthquakes are interpreted as body waves of backscattering from heterogeneities that are distributed randomly but uniformly in the Earth’s crust and upper mantle. In the early 1970s, Aki and Chouet [1] and Sato [2] developed a singlescattering model in the Born approximation, where the primary wave encounters a scatterer (inhomogeneity) only once, producing a secondary wave reaching the receiver with no other impact This model parametrizes the seismic attenuation using a single parameter, Qc, called Q-coda, which is calculated once the decay rate of the coda envelope is measured from data. CCoonnssiiddeerriinnggtthheesseerreecceennttrreessuullttss[[2266]],,rreellaatteeddttootthheessttrroonnggllaatteerraallaannddvveerrttiiccaallccrruussttaall hheetteerrooggeenneeitiytyoofftthheeGGPP,,iinntthhiissppaappeerrwweeppeerrffoorrmmeeddaanneewwaannddmmoorreerroobbuussttssttuuddyyooff QQc iinnoorrddeerrttooaaddddrreessss ssoommee ssttiillll ooppeenn qquueessttiioonnss::tthheeffiirrssttiisstthheerreeaassoonnffoorr tthhee pprreesseennccee ooff lloowweerr ccrruussttaallsseeisimsmiciictiytyininthethNeENseEctosercotfotrheofGtPh, ewiGthPt,hwe aitbhsetnhcee oafbsshenalcleowoefr ssheiaslmloiwcietyr; sGbmomWtifacaebetrhoPnpaaisontisemd,pppatmremhaiepprsfbcnonileiiitortiacennahcdnsenitdocggetsiifsyohinnpritrb;oonsagsdeebtytpfmsccsrhatheitpehQsoscenitlrteeopfahototsdml.theeneaywitaeoWcceohrbrrohinewneiteptinnchshltrephebsdihqdenflnaeairusapnsgeitsureastleveesynaiwkddtsidtisctheohpriiedeseceutveeothailwcisonrepwttntcafyafeirelutissstsuevwthkoeeeltshiaeitdnedemmtrtrostndiyhdnhoicafacateaieengieGtstrvtleahncpsapiPoisuniatosrrfte[ylelemeuf1taltvtvvo5hdtQkiewoii]wiceeoooer.cfrsyiurnuuoTtGinsrhsenpssehiaePanhpinoeeltrtssahmeshtgnmt3hltrheeiel[iDinqom1ieccGc[gupw5rr2iutaou]Patrob3.typeeksse]mea[vtpTe,et2i.riiswoneuoh3ostTrfhg[sem]ueht2,eqrcehsQ7iida3trunsceh,uDp3oiafae1tsh1Snkoyitt]nWyuatteer.oeainssTntonmtn[edh[hhs2fudd2teeoe3i2hQa7scg]f.d2,te,8trG3cariDoao,oa1utSPwrtmatnp]Wasemnoaheasn[sda2edsfnyatus3tud3pttoea]hhfioDdpcb,tosfeeiftyrtiortomenaohsnGQbrnimgatenahelmPospaeone,utfardpupwfeasgt23ifildehQnnaebeDDdtyeddsdgycs. daarteaasiest eisxteennldaergdetdo athnedNcoEn, sthisatnskosf teoaarthchqaunagkeesinwthitehOmTagnnetiwtuodreksgreaonmgientgryb. eAtwll teheend1eatanidls ft2gMrtkdchu.ehee8eeinoogesn,rprcmantaeaGiterceinoredortPledvtssein,raned[tuys.trgh1h.sT,ad5eiteAth3]nheSD3erhsgle-lia,awvpdam6tivemrhaapedeaptvearasnbleoefegdedarnjadeeeonetts1nctmdtaat2eQopirintolefHhsesunaereQzatnfrmoinot,essimrgerioemteeftanitowosxvrherpgtdsioodettretirydrnanhckfupdotgekbcicrheveataGtduytreshnhnrePledtyeebde,o.eledfidusopWtraocshni[sotwic1eetannwt5tnsgwNsi]aemutntihaEihollgdetla,eephavsitdtSrnthhe3hio-naio2twejbnhneg-wekcanik[esf2tmveshuin7aoetont]wrdnpo.ewaceoMeattmapitr.rooefkotTcenonuhrhthrusce,rhameaoiadopnnnvtpederigetoredrbhereisbn,evrsfeia3eeoensnscDendrtetorttfdtunhiifrhQmmrecseoeoqutcaaumOnulfgtgtrioeTeereewsmnssdsetdnceonopyiiteofggnsirtwmbiQrohwta[aivtnec2vopinin7fridhtidot]nkogyye.sr ae3v2id-kemncedethpatht ,thine tshtrroeengfreesqt uaettnecnyubaatinodnsccoennttrearsetds aarte3w, 6elalncdor1r2elHatze,drewspitehctthiveeglye.oWtecetwonililc ssheottwinhgoowf thoue rGpPr.esent images provide evidence that the strongest attenuation contrasts are well correlated with the geotectonic setting of the GP
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