Preliminary macroseismic survey of the 2016 Amatrice seismic sequence ANNALS OF GEOPHYSICS, 59, Fast Track 5, 2016; DOI: 10.4401/ag-7172 1 Preliminary macroseismic survey of the 2016 Amatrice seismic sequence MARIANO ANGELO ZANINI*, LORENZO HOFER, FLORA FALESCHINI, PAOLO ZAMPIERI, NICOLA FABRIS, CARLO PELLEGRINO University of Padova, Dept. of Civil, Environmental and Ar- chitectural Engineering, Padova, Italy *marianoangelo.zanini@dicea.unipd.it Abstract After the recent destructive L’Aquila 2009 and Emilia-Romagna 2012 earthquakes, a sudden MW 6.0 seis- mic event hit Central Italy on August 24, 2016. A low population density characterizes the area but, due to its nighttime occurrence, about 300 victims were registered. This work presents the first preliminary re- sults of a macroseismic survey conducted by teams of the University of Padova. Macroseismic intensities were assessed according to the European Macroseismic Scale (EMS98) for 180 sites. I. INTRODUCTION n August 24, 2016, at 3:36 local time (1:36 UTC), most of the inhabitants of central Italy were woken up by a MW 6.0 earthquake that occurred at the boundaries of Lazio, Umbria, Marche and Abruzzo regions. The epicenter was located by the Istituto Nazionale di Geofisica e Vul- canologia (INGV) seismic network [ISIDe 2016] at 42.70°N and 13.24°E, between the Municipalities of Accumoli and Amatrice, in the Lazio region. The Central Apennines sec- tor is highly prone to seismic hazard: in re- cent years other devastating events occurred with epicenters located in a range of 30 km far from the actual one, like the April 6, 2009 (MW 6.29) L’Aquila event and the 1997 Um- bria seismic sequence, characterized by a MW 5.97 mainshock. According to the Parametric Catalogue of Italian Earthquakes (CPTI15) [Rovida et al. 2016], historical information reveals that the seismic activity in the Monti Sibillini area is frequent and in the past cen- turies was characterized by highly destruc- tive events: from the eighteen century a mean annual rate of about 0.25 events with magnitude MW higher than 4.0 was ob- served. The first evidences of damage in- duced by earthquake occurrences in the area of Accumoli were related to the effects of the July 1627 Monti della Laga event (MW 5.3, IO 7-8 MCS) [Monachesi and Castelli 1992]. It was followed by the severe October 7, 1639 (MW 6.21, IO 8-9 MCS) [Castelli 2013] Ama- trice earthquake, that seemed very similar to the actual seismic scenario. The Accumoli area suffered extensive damages also after the most destructive January 14, 1703 (MW 6.92, IO 10 MCS), and was re-struck by the May 12, 1730 Valnerina event (MW 6.04, IO 7 MCS) [Guidoboni et al. 2007]. After about 150 years these territories were hit again by the November 7, 1883 Monti della Laga earthquake (MW 5.10, IO 7 MCS) and in the twentieth century by other significant events with IO MCS 7-8 in 1916, 1950 [Tertulliani et al. 2006] and 1979. In the days following the August 24 event, teams of the University of Padova organized a field survey of the dam- aged areas with the aim to develop an ex- haustive macroseismic assessment of the O ANNALS OF GEOPHYSICS, 59, Fast Track 5, 2016; DOI: 10.4401/ag-7172 2 earthquake scenario, according to the Euro- pean Macroseismic Scale (EMS98) [Grünthal 1998]. The survey was continuously updated until September 6, 2016 to better define the damage effects induced by the mainshock event. II. SURVEY METHODOLOGY The teams surveyed 180 sites, assessing the intensity level on the basis of the structural damage suffered by the residential building stock and classifying it according to the Eu- ropean Macroseismic Scale (EMS98) [Grün- thal 1998]. Industrial buildings were not tak- en into account due to their lack of repre- sentativeness for intensity assessment pur- poses in the region. Short interviews on the perception of the effects experienced by the inhabitants integrated damage data. A vul- nerability class was identified for each ana- lyzed building, and failures were classified according to the EMS98 damage grades. The most common residential building types in the area are: one-or-two-story old masonry buildings in stone and low quality mortar, with lack of connections (vulnerability class A and B); recently retrofitted masonry build- ings (mostly renovated after the 1997 Umbria sequence, to which a vulnerability class D was assigned); and two-story seismically de- signed reinforced concrete frame structures (vulnerability class C). Historical buildings like churches, castles and towers were con- sidered for the intensity assessment purpos- es only in sites where the building stock was undamaged or slightly affected. III. INTENSITY ASSESSMENT Differently from the 2012 Emilia-Romagna seismic sequence, characterized by relevant aftershocks comparable to the May 20 mainshock, only one event was characterized by a magnitude MW greater than 5.0, about one hour after the 1:36 UTC MW 6.0 mainshock: for this reason, the intensity map can be reasonably viewed as the effects of the main event. Intensity values were defined on the basis of the damage grades detected on the different vulnerability classes observed in the analyzed villages. In some centers, dif- ficulties in the intensity assessment were ex- perienced mainly due to differences between damage levels observed in old centers and on recent reinforced concrete buildings: hence, teams surveyed such sites more times, to reduce subjectivity judgment. Figure 1 il- lustrates the intensity IEMS distribution over the struck territories and Table 1 lists IEMS values for each site surveyed. Major intensi- ties were observed in Amatrice and Pescara del Tronto, which were mainly justified by a diffused level 5 of damage to several mason- ry buildings (Figure 2). Damages compatible with a IEMS 8 were detected in villages in an area within a radius of about 12 km far from the instrumental epicenter: in these cases, most of the vulnerability class B residential masonry buildings suffered level 3 of dam- age. Some particular situations of very slight damage were observed close to the instru- mental epicenter zone in the villages of Vez- zano, Colle d’Arquata and Spelonga, proba- bly due to beneficial site effects. The IEMS 6 area instead extended asymmetrically northwards, about 30 km from the instru- mental epicenter, whereas southwards ef- fects seemed significantly attenuated. Some difficulties were encountered in the intensity evaluation of damage in the southeastern towns of the Abruzzo region, since many buildings were still presenting damage caused by the 2009 L’Aquila sequence, and the relatively slight level of ground shaking induced in these areas by the MW 6.0 mainshock, if compared to the epicentral zones. Another challenging issue was related to the assessment in the Umbria towns, since most of them were seismically retrofitted af- ter 1997 sequence: here the critical issue ANNALS OF GEOPHYSICS, 59, Fast Track 5, 2016; DOI: 10.4401/ag-7172 3 Figure 1: Macroseismic intensities observed after the August 2016 seismic sequence (damage up to September 6, 2016). ANNALS OF GEOPHYSICS, 59, Fast Track 5, 2016; DOI: 10.4401/ag-7172 4 Table 1: Localities surveyed after the August 2016 seismic sequence. D(*) Municipality Locality IEMS D(*) Municipality Locality IEMS AP Arquata del T. Pescara del T. 10-11 RI Amatrice Nommisci 6-7 RI Amatrice Saletta 10 PG Norcia Savelli 6-7 RI Amatrice Amatrice 9-10 PG Norcia Valcadara 6-7 RI Accumoli Illica 9 AP Arquata del T. Trisungo 6-7 RI Amatrice San Lorenzo Fl. 9 RI Accumoli Roccasalli 6 AP Arquata del T. Arquata del T. 9 RI Amatrice Pasciano 6 RI Accumoli Accumoli 8-9 RI Amatrice San Giorgio 6 RI Accumoli Fonte del Campo 8-9 RI Amatrice Santa Giusta 6 RI Accumoli Villanova 8-9 PG Norcia Agriano 6 RI Amatrice Casale 8-9 PG Norcia Campi 6 RI Amatrice Preta 8-9 AP Acquasanta T. Acquasanta T. 6 AP Arquata del T. Capodacqua 8-9 AP Arquata del T. Colle 6 AP Arquata del T. Tufo 8-9 AP Arquata del T. Faete 6 RI Accumoli Grisciano 8 AP Arquata del T. Spelonga 6 RI Accumoli San Giovanni 8 AP Arquata del T. Vezzano 6 RI Accumoli Tino 8 AP Montegallo Montegallo 6 RI Amatrice Casteltrione 8 FM Montefortino Montefortino 6 RI Amatrice Cornelle di Sotto 8 MC Tolentino Tolentino 6 RI Amatrice Cossito 8 MC Visso Visso 6 RI Amatrice Mosicchio 8 RI Accumoli Terracino 5-6 RI Amatrice Petrana 8 RI Amatrice Cornillo Nuovo 5-6 RI Amatrice Retrosi 8 RI Amatrice Forcelle 5-6 RI Amatrice Sommati 8 RI Amatrice Varoni 5-6 PG Norcia Castelluccio 8 PG Cascia Cascia 5-6 AP Arquata del T. Piedilama 8 PG Cascia Castel S. Maria 5-6 AP Arquata del T. Pretare 8 PG Cascia Civita 5-6 RI Accumoli Macchia 7-8 PG Norcia Ospedaletto 5-6 RI Amatrice Bagnolo 7-8 PG Norcia Pescia 5-6 RI Amatrice Capricchia 7-8 PG Norcia Piè la rocca 5-6 RI Amatrice Collepagliuca 7-8 PG Preci Preci 5-6 RI Amatrice Colli 7-8 AP Montegallo Bisignano 5-6 RI Amatrice Cornillo Vecchio 7-8 AP Montegallo Castro 5-6 RI Amatrice Moletano 7-8 AP Montegallo Uscerno 5-6 RI Amatrice Scai 7-8 FM Amandola Amandola 5-6 RI Amatrice Torrita 7-8 FM Montefortino Cerretana 5-6 PG Norcia San Pellegrino 7-8 MC Castelsantangelo Castelsantangelo 5-6 RI Amatrice Collegentilesco 7 MC Sarnano Sarnano 5-6 RI Amatrice Colleposta 7 MC Ussita Ussita 5-6 RI Amatrice Configno 7 AQ Campotosto Poggio Cancelli 5-6 RI Amatrice Patarico 7 AQ Montereale Aringo 5-6 RI Amatrice Poggio Vitellino 7 RI Borbona Borbona 5 RI Amatrice Roccapassa 7 RI Cittareale Cittareale 5 RI Amatrice San Benedetto 7 RI Cittareale Santa Croce 5 RI Amatrice Voceto 7 RI Posta Bacugno 5 PG Cascia Avendita 7 RI Posta Fontarello 5 PG Norcia Fontevena 7 RI Posta Posta 5 PG Norcia Frascano 7 PG Norcia Aliena 5 PG Norcia Norcia 7 PG Norcia Fogliano 5 PG Norcia Nottoria 7 PG Norcia Maltignano 5 AQ Montereale Santa Lucia 7 PG Norcia Puro 5 RI Accumoli Collespada 6-7 PG Norcia Sant’Andrea 5 RI Amatrice Collemoresco 6-7 PG Preci Collescille 5 RI Amatrice Domo 6-7 PG Preci Piedivalle 5 ANNALS OF GEOPHYSICS, 59, Fast Track 5, 2016; DOI: 10.4401/ag-7172 5 D(*) Municipality Locality IEMS D(*) Municipality Locality IEMS PG Preci Saccovescio 5 AQ Capitignano Capitignano 5 AP Ascoli Piceno Castel Trosino 5 AQ Capitignano Collenoveri 5 AP Ascoli Piceno Mozzano 5 AQ Capitignano Pago 5 AP Acquasanta T. Arli 5 AQ Capitignano Paterno 5 AP Acquasanta T. Centrale 5 AQ Capitignano Sivignano 5 AP Acquasanta T. Corneto 5 AQ Montereale Casale Bottone 5 AP Acquasanta T. Novele 5 AQ Montereale Castiglione 5 AP Acquasanta T. Paggese 5 AQ Montereale Cesaproba 5 AP Acquasanta T. Ponte d’Arli 5 AQ Montereale Cesariano 5 AP Acquasanta T. Quintodecimo 5 AQ Montereale Lonaro 5 AP Acquasanta T. San Martino 5 AQ Montereale Marana 5 AP Acquasanta T. Santa Maria 5 AQ Montereale Montereale 5 AP Montegallo Forca 5 AQ Montereale Piedicolle 5 AP Montemonaco Montemonaco 5 AQ Montereale San Vito 5 AP Montemonaco Pignotti 5 AQ Montereale Santa Vittoria 5 AP Montemonaco Rocca 5 AQ Montereale Verrico 5 AP Montemonaco San Giorgio Isola 5 AQ Montereale Ville 5 AP Roccafluvione Roccafluvione 5 TE Cortino Cortino 5 MC Caldarola Caldarola 5 TE Crognaleto Alvi 5 MC Camerino Camerino 5 TE Crognaleto Cesacastina 5 MC Camerino San Luca 5 TE Crognaleto Crognaleto 5 MC Camerino San Marcello 5 TE Crognaleto Nerito 5 MC Castelsantangelo Gualdo 5 TE Crognaleto Poggio U. 5 MC Gualdo Gualdo 5 TE Crognaleto San Giorgio 5 MC Muccia Muccia 5 TE Crognaleto Tottea 5 MC Pieve Torina Apennino 5 TE Valle Castellana Ceraso 5 MC Pieve Torina Capriglia 5 TE Valle Castellana Cerquito 5 MC Pieve Torina Pieve Torina 5 TE Valle Castellana Morrice 5 MC Pievebovigliana Pievebovigliana 5 TE Valle Castellana Pascellata 5 MC Ripe S. Ginesio Ripe S. Ginesio 5 TE Valle Castellana Pietralta 5 MC San Ginesio San Ginesio 5 TE Valle Castellana San Vito 5 MC Ussita Calcara 5 TE Valle Castellana Valle Castellana 5 MC Ussita Cuore di Sorbo 5 AP Ascoli Piceno Ascoli Piceno 4-5 MC Ussita Frontignano 5 AP Ascoli Piceno Casette 4-5 MC Visso Borgo S. Antonio 5 AP Venarotta Venarotta 4-5 AQ Campotosto Campotosto 5 MC Belforte Belforte 4-5 AQ Campotosto Ortolano 5 MC Muccia Maddalena 4-5 (*) Districts: Rieti (RI), Perugia (PG), Ascoli Piceno (AP), Fermo (FM), Macerata (MC), Aquila (AQ), Teramo (TE). was to define the most reliable EMS98 vul- nerability class, for properly derive the IEMS degree. A review of the local strengthening techniques suggested to adopt, in such cases, a vulnerability class D for masonry struc- tures. Unreinforced buildings, if present, were also considered in these localities to check the reliability of the assigned intensity value. IV. CONCLUSIONS Results of a macroseismic survey performed in the area struck by the August 24, 2016 Amatrice sequence were presented. A total number of 180 sites were surveyed and for each of them a IEMS value was defined. Ac- cording to the results shown in this work, it can be concluded that site effects ANNALS OF GEOPHYSICS, 59, Fast Track 5, 2016; DOI: 10.4401/ag-7172 6 Figure 2: Diffused collapses in Amatrice (left) and aerial view of Pescara del Tronto (right, retrieved on www.meteoweb.eu). significantly influenced the 2016 Central Ita- ly sequence. Additionally, a key aspect of this work related the evaluation of the effects induced by the analyzed earthquake to pre- damaged and seismically retrofitted residen- tial buildings, for a proper derivation of the a IEMS value. 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