Seismically Induced Ground Effects of the 1805, 1930 and 1980 Earthquakes in the Southern
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Seismically induced ground effects of the 1805, 1930 and 1980 earthquakes in the Southern Apennines, Italy S. PORFIDO (*), E. ESPOSITO (*), L. GUERRIERI(**), E. VITTORI (**), G. TRANFAGLIA (**) & R. PECE (***) (*) CNR-IAMC, Calata Porta di Massa, Interno Porto – 80133 Naples, Italy. E-mail: [email protected] (**) Italian Agency for Environment Protection and for Technical Services (APAT), Rome, Italy. (***) Department of Earth Sciences, Federico II University, Naples, Italy.
ABSTRACT Seismically induced environmental effects (in particular, surface faults, ground cracks, slope failures, liquefaction, soil compaction, hydrological changes, tsunamis) are assumed to provide fundamental information on the earthquake size and its intensity field, crucial for a more efficient seismic hazard assessment. Accordingly, this study is aimed at substantiating this assumption by showing that the knowledge about ground effects acquired in recent earthquakes, when combined with that illustrated in historical documents, allows to build an improved picture of historic seismic events, with respect to that usually provided by the solely damage-based macroseismic scales. In this perspective, the environmental effects are analysed and catalogued of three of the most ruinous earthquakes in Southern Italy of the last two centuries: the July 26,1805, Molise event (XI MCS, M 6.8), the July 23, 1930, Irpinia event (X MCS, M 6.7), and the November 23, 1980 Campania-Basilicata event (X MSK, Ms 6.9). The distribution of the earthquake environmental effects, in particular their distance from the known or supposed causative fault, has been investigated to obtain a more detailed and comprehensive picture of the macroseismic field, a key parameter in seismic hazard assessment and seismic zonation.
KEY WORDS: historical seismicity, intensity, ground effects, earthquakes, Southern Apennines.
RIASSUNTO Effetti sul terreno indotti dai terremoti del 1805, 1930 e 1980 nell’Appennino Meridionale. Per una corretta analisi della valutazione dell’hazard sismico di una regione è di fondamentale importanza il riconoscimento, l’analisi ed il censimento degli effetti sismoindotti. Ciò rappresenta un metodo innovativo per la definizione della vulnerabilità del territorio: infatti tenendo conto, degli effetti indotti sull’ambiente dai terremoti storici, come di quelli indotti dai terremoti più recenti, si può ipotizzare una pianificazione degli interventi in prospettiva futura. Strutture tettoniche superficiali, attivate in occasione di terremoti con moderata-elevata energia (M>5), possono provocare modificazioni più o meno permanenti nel paesaggio. I più comuni effetti geomorfologici indotti da un evento sismico sono: la fagliazione superficiale (rotture primarie e secondarie), i fenomeni di liquefazione (vulcanelli di sabbia, iniezioni, espandimenti laterali, deformazioni plastiche in sedimenti soffici saturi), i fenomeni franosi (crolli in roccia, ribaltamenti, scorrimenti, colate, sackungen), le variazioni idrologiche, per lo più temporanee (mutamenti di portata di fiumi, pozzi e sorgenti, intorbidimenti, cambi delle proprietà chimico-fisiche) e gli tsunami. È stato intrapreso uno studio sistematico degli effetti indotti sull’ambiente fisico innescati da alcuni tra i più forti terremoti che hanno colpito l’Appennino meridionale negli ultimi due secoli: il terremoto del 26 luglio 1805 (Molise I= XI MCS, M=6.8), il terremoto del 23 luglio 1930 (Irpinia I=X MCS, M=6.7) ed il terremoto del 23 novembre 1980 (Campania-Basilicata I=X MSK, M=6.9). Per la ricerca degli effetti indotti dagli eventi sismici è stato adottato un approccio multidisciplinare, che ha visto il coinvolgimento di specifiche competenze geologiche, sismologiche e storiche. Per il terremoto più antico in esame, avvenuto nel 1805, si è operato attraverso la raccolta e l’analisi critica della bibliografia e del patrimonio documentario esistente, e contestualmente il recupero di nuove fonti, possibilmente originali e coeve all’evento sismico. La ricerca è stata effettuata soprattutto presso gli Archivi di Stato di Napoli, Benevento, Isernia e Campobasso, nonché presso archivi privati e parrocchiali del Molise. Per gli eventi sismici del XX secolo (1930 e 1980), ci si è basati soprattutto su una vasta bibliografia a carattere tecnico-scientifico (oltre un centinaio di pubblicazioni-relazioni tecniche), non trascurando le fonti giornalistiche ed iconografiche, il tutto integrato con l’analisi delle foto aeree, con nuovi rilevamenti sul terreno, e mediante il contributo delle testimonianze dirette (ESPOSITO et alii, 1987, 1998, 2000; BLUMETTI et alii, 2002; PORFIDO et alii, 2002 e relative bibliografie). Sono stati riconosciuti e censiti un elevato numero di fenomeni sismoindotti: dai fenomeni di fagliazione superficiale, fenomeni di fratturazione, fenomeni franosi e variazioni idrologiche, ai fenomeni di liquefazione. È stato possibile analizzarne la distribuzione degli stessi rispetto alle intensità assegnate e rispetto alla distanza dalla faglia riconosciuta o direttamente sul terreno, come nel caso del terremoto del 1980, o il cui andamento è stato ricostruito attraverso le descrizioni dedotte dalle fonti storiche, come nel caso dei terremoti del 1805 e del 1930. Sono state individuate relazioni tra intensità, numero di effetti e distanze dall’epicentro, valide per l’Appennino Meridionale e confrontate con quelle individuate da KEEFER (1984) e RODRIGUEZ et alii (1999) per i maggiori terremoti avvenuti nel mondo. Infine, la ricostruzione dei terremoti storici attraverso il riconoscimento e la definizione degli effetti sismoindotti è stata un valido contributo per la verifica e la calibrazione della nuova scala macrosismica (MICHETTI et alii, 2004) proposta in ambito INQUA, che si basa essenzialmente sulla valutazione degli effetti nell’ambiente fisico completando, di fatto, l’archivio informativo raccolto attraverso le scale macrosismiche tradizionali.
TERMINI CHIAVE: effetti geologici sismoindotti, intensità, sismicità storica, terremoto del 1805, terremoto del 1930, terremoto del 1980, Appennino meridionale.
INTRODUCTION Earthquakes of moderate to high magnitude (M > 5) commonly produce temporary and permanent environmental effects. The effects can be primary (surface faulting and distributed deformation at the surface) and secondary effects. The latter include sand blows, dykes, sills, lateral spreads and soft-sediment deformation, slope failures (rock falls, topples, slides, flows), sackungen, hydrological anomalies (chemical or physical changes in springs and wells, flow changes of rivers and springs, turbidity) and tsunamis. Noteworthy case studies, with a variety of often impressive primary and secondary effects, include the following earthquakes: 1957 Gobi-Altai (M=7.9), 1960 Chile (M=8.4), 1964 Alaska (M=8.6), 1964 Niigata (M=7.5), 1975 Haicheng (M=7.3), 1989 Loma Prieta (M=7.1), 1992 Landers (M=7.6), 1994 Northridge event (Mw=6.7), 1995 Kobe (Mw=6.9), 1999 Izmit (M=7.4) and Chichi 1999 (M=7.3) (USGS, 1994; AZUMA et alii, 1995; SASSA et alii, 1996; MICHETTI et alii, 2004 and references therein; OTA et alii, 2005). Some of these seismic events produced surface ruptures up to several hundreds of kilometres in length with 10 m and more of offset, liquefaction and lateral spreading and landslides, effects that have significantly and permanently modified the landscape. In contrast, coseismic environmental effects are often disregarded for smaller events, due to their paucity and lack of significant practical impact. For the same reasons, they are overlooked for the lower degrees of the macroseismic fields of the major events. In this paper, the environmental effects of three of the most ruinous earthquakes in Southern Italy of the last two centuries are analysed and catalogued (fig. 1): the July 26, 1805, Molise event (X MCS, M 6.8), the July 23, 1930, Irpinia event (X MCS, M 6.7) and the November 23, 1980 Campania- Basilicata event (X MSK, Ms 6.9). In this perspective, this is a contribution to document the basic assumption of the new Earthquake Environmental Effects (EEE) scale developed under the umbrella of the International Union for Quaternary Research (INQUA) (MICHETTI et alii, 2004), that coseismic environmental effects provide invaluable information on the earthquake size and its intensity field, complementing, de facto, the traditional damage-based macroseismic scales.
Fig. 1 - Epicentres of studied earthquakes in this paper (yellow stars), cited in the text (white stars) and other seismic events (M>5.5) (CPTI04). – Mappa degli epicentri di eventi sismici con M>5.5 (CPTI04). In giallo sono riportati gli epicentri dei terremoti studiati in questo lavoro, in bianco gli epicentri dei terremoti citati nel testo. Fig. 2 - Distribution of geological effects reported for the 1805 Molise earthquake (after PORFIDO et alii, 2002). – Distribuzione degli effetti geologici indotti dal terremoto Molisano del 1805 (PORFIDO et alii, 2002).
BACKGROUND AND METHODOLOGY The recognition, cataloguing and analysis of seismically induced environmental effects is of fundamental importance for seismic hazard assessment. Environmental effects are an unexplored source of information bearing on the size of earthquakes and seismic risk. Historical documents contain a wealth of information on ground effects, which complement knowledge provided by recent earthquakes. This approach is commonly applied for large earthquakes (M>6), but not to moderate quakes (M≤5-6), even though these events may produce a variety of ground effects. An example of a moderate earthquake with numerous ground effects is the Mw=5.3 event in the Dead Sea (Israel) on February 11, 2004. This earthquake produced cracks, compaction, landslides, collapse of gully and channel banks, liquefaction, tsunamis up to 1 m high, a rough sea, hydrological and chemical changes, dust (SALOMON, 2004 and references therein). A series of earthquakes struck the Umbria-Marche regions of Central Italy in September and October 1997: the two largest events had Mw 6.0 and 5.7. Primary and secondary effects were observed, including surface faulting, landslides (mostly rock falls and rotational slides), ground fractures in Quaternary colluvial and fluvio-lacustrine deposits and in rock, compaction and hydrological changes (CELLO et alii, 1998; ESPOSITO et alii, 1999b, 2000b; VITTORI et alii, 2000). On September 9, 1998, a Mw=5.6 earthquake struck the west side of the Southern Apennines. A fault in bedrock 200 m long developed a free-face up to 1-2 cm high in what was thought to be an aseismic area (MICHETTI et alii, 2000b). Numerous secondary effects were observed, including ground fractures in a road, landslides (mostly rockfalls in limestone), changes in water flow and turbid water in the aqueduct and in some springs (MICHETTI et alii, 2000b). The most recent significant earthquake in Italy is the 2004 Salò event in the Lake Garda region at Northern Italy, within the active fold and thrust belt of the Southern Alps. It had a Ml=5.2 and a focal depth of 8 km, according to INGV (http://www.ingv.it/terremoti/bresciano2004/mecc- focale.html). It produced ground effects in the area of Salò and along the Chiese River valley (Val Sabbia). Rockfalls up to about 100 m3 occurred at four sites, other landslides up to ca. 1000 m3 at three sites, fractures on the ground and on paved roads at five sites, fractures along the lake shore at two sites, and temporary turbidity of the water in an aqueduct and a stream. In prticular, liquefaction and localized lateral spreading and settlemet, with fissures up to 30 cm wide parallel to te shoreline, were observed in the Salò harbour. These effects were similar to those reported during a comparable event in 1901 (ESPOSITO et alii, 2005b; MICHETTI et alii, 2005a,b). This paper analyses the characteristics and spatial distribution of ground effects of three devastating earthquakes with comparable magnitudes that affected broad adjoining and partly overlapping areas in the Southern Apennines during the last two centuries. For these events, studied with modern criteria, there is a large availability of descriptions of coseismic ground effects, well-established MCS intensities, and possibility to infer EEE intensities either from primary and secondary effects. The ground effects of the 1805, 1930 and 1980 earthquakes were identified and catalogued, using a multidisciplinary approach involving geology, seismology, historical and archive data. The 1805 event was studied by critically evaluating contemporary documents (IADONE, 1805; POLI, 1805; FORTINI, 1806; PEPE, 1806; CAPOZZI, 1834). A document search was carried out in the State Archives of Naples, Benevento, Isernia and Campobasso, and in some private and parish archives in the Molise Region (ESPOSITO et alii, 1987, 1991, 1999a). The study of the 1930 and 1980 earthquakes was based on examination and interpretation of more than 100 publications, technical reports, examination of aerial photographs, field surveys and a collection of eyewitness accounts (ESPOSITO et alii, 1998a, b; BLUMETTI et alii, 2002; PORFIDO et alii, 2002 and references therein). A large number of ground seismic effects were catalogued, including ground cracks, landslides, ground settlements, liquefaction features and hydrological anomalies. Their distribution was analyzed with respect to the distance from the fault trace and observed local macroseismic intensities. This analysis has permitted relationships to be developed among intensity, number and dimension of effects and epicentral distances, which are valid for the Southern Apennines (ESPOSITO et alii, 1998a; PORFIDO et alii, 2002) and are comparable to those obtained for major earthquakes worldwide by KEEFER (1984) and RODRIGUEZ et alii (1999).
TABLE 1 Landslides of the 1805 Molise earthquake. LEGEND: Sef (slump-earthflow); RF (rockfall); Ef (earth flow); Und (Undefined). In brackets the number of land-slides on site. – Fenomeni franosi indotti dal terremoto Molisano del 1805. LEGENDA: Sef (slump-earth flow); RF (rockfall); Ef (earth flow); Und (indefinito). Tra parentesi è indicato il numero di frane nel sito.
N° Sites Latitude Longitude Fault IMCS Type of distance landslide (km) Fig. 3 - Isoseismal map of the 1930 Irpinia earthquake (after SPADEA et alii, 1985). – Campo macrosismico del terremoto Irpino del 1930 (SPADEA et alii, 1985).
THE MOLISE EARTHQUAKE OF 1805 On July 26, 1805, a ruinous earthquake hit the Molise Region and part of Campania. It damaged over 200 localities, with its maximum recorded intensity at Frosolone (I=XI MCS), and claimed more than 5,000 lives. The estimated magnitude is 6.7-6.8 (ESPOSITO et alii, 1987; WORKING GROUP CPTI04, 2004). The Bojano basin, between the provinces of Isernia and Campobasso, was the most damaged area. Most ground effects were within the area delineated by the isoseismal VIII MCS. One hundred seismically induced environmental effects are known for the 1805 earthquake mostly in the near-field area (fig. 2), although some were reported as far as 70 km from the epicentre (ESPOSITO et alii, 1987; MICHETTI et alii, 2000a; PORFIDO et alii, 2002). According to the contemporary sources, vertical ground displacements of about 1.5 m occurred at Guardiaregia and Morcone, likely due to movements along a Holocene normal fault about 30 km long on the northeastern slopes of the Matese Massif (N-Matese fault system). A detailed description of the fault rupture was given by a priest (CAPOZZI, 1834), standing on the front door of an inn: «flames from the ground ... were seen near the inn, where horrible chasms opened over a length of about one third of a mile, some of which had the ground overthrown at a height exceeding six palmi (Neapolitan palmo = 26.45 cm), and of which the width was over three palmi and comparable the depth. These fractures now can be seen from far away, because the grass along the crevasses is desiccated as it had been on fire. In one such crevasse I observed a pear tree, that, in that moment (of the earthquake), lost all its unripe fruits, threw many branches to the ground and, of the ones left, many are now desiccated. In the same place the soil was completely disturbed, as it had excavated by innumerable moles. Here a spring increased its flow rate, leaving a slight smell of sulphur. A new spring gushed out from the ground...». A geophysical survey in the same area confirmed the presence of a near surface, north-northwest trending, normal fault (GEMINA, 1963) located at the south-eastern end of the Bojano and Sepino fault system (GUERRIERI et alii, 1999). The earthquake triggered at least 26 slides (tab. 1): mainly rock falls, topples, slumps, earth flows and slumpearth flows. Among the largest of them were the earth flow of San Giorgio la Molara (Benevento), which affected the course of the Tammaro River, the earth flow of Acquaviva di Isernia, the rotational slide at San Bartolomeo in Galdo (Benevento), and a rotational slide-flow at Calitri (Avellino) (PEPE, 1806; ESPOSITO et alii, 1987, ESPOSITO et alii, 1998b). The earthquake also caused hydrological changes. In 29 localities, mainly around Bojano (Biferno springs) and the Matese Massif, 48 hydrological anomalies were reported, mainly changes in discharge of springs. Flow increases were observed in at least 16 springs, mainly south-southwest of the Matese Mountains. New springs appeared at S. Salvatore Telesino (Caserta), Morcone (Benevento), the Matese Mountains, and Bojano (Campobasso). The new spring at Bojano was active for about two months after the earthquake (ESPOSITO et alii, 1987; ESPOSITO et alii, 2001). Only one case of liquefaction was reported at Cantalupo (tab. 2). Furthermore, small tsunami waves were noted in the gulfs of Naples and Gaeta (CAPUTO & FAITA, 1984; TINTI &MARAMAI, 1996). THE 1930 IRPINIA EARTHQUAKE The earthquake of July 23, 1930, affected a large area in the Campania, Basilicata and Puglia regions. TABLE 3 Ground effects of the 1930 Irpinia earthquake. LEGEND: Tsr (tectonic surface rupture); C (compaction); Sef (slumpearth flow); Fr (Fractures). – Effetti al suolo indotti dal terremoto Irpino del 1930. LEGENDA: Tsr (rottura di superficie tettonica); C (compattazione); Sef (slump-earth flow); Fr (fratture). N° Sites Latitude Longitude Fault IMCS Type of distance ground (km) effects Fig. 4 - Ancient Aquilonia (Avellino). Rotational slump-earth flow induced by the 1930 earthquake on the Nord side of S. Pietro. (Courtesy of Museo Etnografico of Aquilonia). – Aquilonia Vecchia (Avellino). Scorrimento rotazionale-colata indotto dal terremoto del 1930 nella parte settentrionale del rione S. Pietro (Cortesia del Museo Etnografico di Aquilonia). About 1425 people were killed, more than 10,000 were injured and 100,000 were left homeless (SPADEA et alii, 1985; DIPARTIMENTO DI PROTEZIONE CIVILE-SERVIZIO SISMICO NAZIONALE, 2002). Magnitude estimates range from 6.2 to 6.72 (MARGOTTINI et alii, 1993; CPTI04, 2004). The maximum intensity (X MCS, fig. 3) was at Villanova del Battista, Aquilonia, and Scampitella in the upper Irpinia (Avellino district; SPADEA et alii, 1985). Contemporary technical and scientific reports (ALFANO, 1931; MAJO, 1931; ODDONE, 1931, 1932) provide rich documentation of primary and secondary effects. Northwest-trending surface ruptures at Flumeri, Villanova del Battista and Ariano Irpino (PORFIDO et alii, 2001; ESPOSITO et alii, 2004) were interpreted by ODDONE (1931; 1932) to be fault reactivations. The rupture extended over distances of at least 30 km and had up to 40 cm of offset. Oddone (1932) described the ruptures and their effects: «at S. Sossio.... the road on the southern side is cut by a frightening fault, a true crevasse that evilly crosses Flumeri heading toward between Villanova and Ariano. It follows a path of many kilometres, and we had already noted it during our first trip from Ariano to Villanova. In the countryside the farms along its trace were all razed to the ground. Somebody states that two were the faults, nearly parallel...». Ground fissures up to several hundred meters long were seen in the Irpinia area close to the fronts of the mountains Formicoso and Serralonga and in the villages of Aquilonia, Bisaccia, Lacedonia, Melfi, Monteverde, S. Sossio Baronia, Zungoli (Avellino) and Rocchetta S. Antonio (Foggia). At least, 26 landslides were triggered by the earthquake (tab. 3). Large landslides struck Aquilonia (Avellino) and San Giorgio la Molara (Benevento). The former was a reactivation of a slump-earth flow, along the north side of the Rione San Pietro, that forced the abandonment of the entire village (fig. 4) (ESPOSITO et alii, TABLE 4 Hydrological effects of the 1930 Irpinia earthquake. – Effetti idrologici indotti dal terremoto Irpino del 1930. N° Sites Latitude Longitude Fault distance (km) IMCS
The latter was a 1 km wide and 3 km slump within the Argille Varicolori formation, on the left bank of the Tammaro River, that dammed a short section of the river (VARI, 1931). A slide occurred at the same location at least twice before, during the 1688 and 1805 earthquakes, and was reactivated also during the 1962 and 1980 earthquakes (PORFIDO et alii, 1991; ESPOSITO et alii, 1998a; 2000a; PRESTININZI & ROMEO, 2000). Other noteworthy landslides occurred at Ariano Irpino, Vallata, Montecalvo Irpino, Lacedonia, Rocchetta S. Antonio and Acerenza. Ground settlements were observed in the historical centre of Bisaccia, due to compaction of late Cenozoic clastic sediments (GENIO CIVILE DI AVELLINO, 1930; ODDONE, 1931; D’ELIA, 1992). Hydrological changes were observed throughout the area affected by the earthquake, mainly in the far field near the main aquifers (tab. 2). Thirty nine documented anomalies included flow-rate changes of springs and wells, turbid water, drying up of springs, appearance of new springs, and variations in the chemistry of waters (ESPOSITO et alii, 2001; 2004). Changes in discharge were observed at Vallata, Aquilonia, Caposele and Telese (tab. 4). Fig. 5 shows a hydrological anomaly in the Sanità spring at Caposele. An increase in flow rate of 150 l/s (about 3%) was noted few hours after the earthquake (CELENTANI UNGARO, 1931). An anomalous emission of CO2 and H2S was noted in the small lake of Mefite (Rocca San Felice) in the Ansanto Valley. A change in the gas emission activity was observed also near Naples in the Campi Flegrei, in particular at the Solfatara (Pozzuoli), and in the Nero’s Ovens at Bacoli (ALFANO, 1931; MAJO, 1931a). THE 1980 CAMPANIA-BASILICATA EARTHQUAKE The November 23, 1980, earthquake affected 800 localities over a large area of the Southern Apennines, killing 3,000 people. The highest intensity was IX-X MSK (fig. 6), in several towns in the Campania and Basilicata regions, including Castelnuovo di Conza, Pescopagano, Laviano and S. Angelo dei Lombardi (POSTPISCHL et alii, 1985). The rupture process was complex, with three main events at 0,20 and 40 seconds. Several normal faults were reactivated over a distance of at least 40-45 km. Coseismic east-dipping ruptures with a maximum downthrow of nearly 1.1 m were mapped at M. Marzano-M. Ogna, S. Gregorio Magno and Bella, Muro Lucano (CINQUE et alii, 1981; WESTAWAY, 1993; PANTOSTI et alii, 1993; PANTOSTI & VALENSISE, 1993; BLUMETTI et alii, 2002). Reinterpretation of the field data also indicates the reactivation of a southwest dipping fault over a distance of ca. 8 km at Castelgrande, Bella and Muro Lucano (fig. 7). Such rupture likely produced the 40 seconds event (BLUMETTI et alii, 2002). Many either isolated and grouped secondary ground fractures were also observed, mainly inside the isoseismal Fig. 5 - The 1930 Irpinia earthquake. Hydrological anomaly recorded at the Sanità spring, Caposele. – Terremoto Irpino del 1930. Anomalie idrologiche registrate nella sorgente Sanità a Caposele. zone VIII MSK. These fractures ranged in length from a few centimetres to several kilometres (CANTALAMESSA et alii, 1981; CARMIGNANI et alii, 1981). The review of more than 100 technical and scientific publications has allowed to locate and classify 200 landslides over a total area of 22,000 km2. About 47,2% of the landslides were rock falls/topples, 20,1% rotational slides, 20,1% slump-earthflows, 3.5% rapid earth flows, 9,1% left undefined (tab. 5) (ESPOSITO et alii, 1998; PORFIDO et alii, 2002). The frequency of slope failures was particularly high in the Ofanto and Sele River valleys. In the former, weakly-to-well cemented conglomerates and sandstones commonly overlie fine-grained soft deposits. The geologic setting of the Sele Valley is characterized by steep limestone fault scarps, with the hanging-wall made of basin Flysch-type deposits with a complex rheology, often masked by a veneer of slope deposits of highly variable thickness. The largest rock falls occurred mostly in the epicentral area, at Acerno, Calabritto, Capaccio, Castelgrande, Colliano, Laviano, Muro Lucano, Senerchia and Valva. Their volumes ranged from 1,000 to 10,000 m3. The distribution of rotational slides was strongly influenced by pre-existing instabilities. The largest one (23 million m3) was a slump-earth flow that affected the historical centre of Calitri (Avellino) and its recent urban expansion (SAMUELLI-FERRETTI & SIRO, 1983; HUTCHINSON & DEL PRETE, 1985; COTECCHIA, 1986; MARTINO & SCARASCIA MUGNOZZA, 2005). Even larger were the mudflows at Buoninventre (30 million m3), near Caposele (COTECCHIA, 1986; ESPOSITO et alii, 1998) and Serra d’Acquara, Senerchia (28 million m3). At Costa Monticello, eyewitnesses described the coseismic reactivation of a sackung, with the formation of a trench in limestone across the mountain slope (fig. 8) (BLUMETTI et alii, 2002). Liquefaction (21 cases) was recorded at Buccino, Calitri, Lago Laceno, Lioni, Montecalvo Irpino, Muro Lucano, Senerchia, Pontecagnano, Ruvo del Monte, San Giorgio la Molara, San Marzano del Sarno, Scafati, Sturno, San Michele di Serino, Volturara Irpina (CARULLI et alii, 1981; DA RIOT et alii, 1983; GALLI, 2000). The earthquake also produced significant changes of the flow rates of rivers, springs and wells (tab. 6); anomalies were reported at seven of 30 springs in the upper Sele Valley and the Matese Massif (COTECCHIA & NUZZO, 1986; ESPOSITO et alii, 2001). Flow of the Caposele spring increased of 3000 l/s. A general increase in discharge was observed for a period of 6 to 12 months after the earthquake
Fig. 6 - Distribution of geological effects reported for the 1980 Campania-Basilicata earthquake (after BLUMETTI et alii, 2002). – Distribuzione degli effetti geologici indotti dal terremoto Campano-Lucano del 1980 (BLUMETTI et alii, 2002). (Acqua Fetente near Montecorvino Pugliano, Caposele and Cassano springs) (COTECCHIA et alii, 1986; ESPOSITO et alii, 1999 b). DISCUSSION AND CONCLUSIONS The Southern Italy earthquakes occurred in 1805, 1930 and 1980 share similar magnitudes and complex rupture mechanisms. In all cases, several fault segments reactivated over a time period of a few seconds to minutes. The distribution of seismically induced surface phenomena can help defining the location and total extent of the fault ruptures. For example, this is the case of the 1930 earthquake, for which the actual precise location of the causative fault segments is lost hidden by erosion. Here, the distribution of the secondary effects well constrains the location of the coseismic ruptures, as reported but not mapped by ODDONE (1931, 1932). The observed or estimated fault rupture lengths and displacements for the three seisms analyzed here (respectively, 40-45 km and 1-1.50 m) scale well with the worldwide database (WELLS & COPPERSMITH, 1994) and the preliminary regression analysis with intensity given in MICHETTI et alii (2004). For all the considered earthquakes, the distribution of landslides generally follows that of the isoseismals: most landslides are scattered within the area encircled by the intensity VIII isoseismal, and their density declines rapidly away from it. Most (88.5%) of the landslides triggered by the 1805 earthquake occurred less than 30 km from the causative fault, and the remainder within 80 km of it. During the 1930 event, there were no landslides at more than 50 km from the fault. Most (84.7%) of the slides occurred less than 30 km from the fault. Half of the landslides triggered by the 1980 earthquake were at less than 10 km from the causative faults, and about 80% were within 30 km (fig. 9). The distribution of hydrologic anomalies displays an almost linear decay away from the causative faults, with 90% of the effects within 40 km for the 1805 event and 130 km for the 1980 event. In contrast, most of the anomalies produced by the 1930 earthquake were 30 to 120 km from the fault (tabs. 2, 4, 6) (ESPOSITO et alii, 2001; PORFIDO et alii, 2002) (fig. 10).
Fig. 7 - Isoseismals of the 1980 Irpinia-Basilicata earthquake (after POSTPISCHL et alii, 1985). – Campo macrosismico del terremoto Campano-Lucano del 1980 (POSTPISCHL et alii, 1985). TABLE 5 Landslides of the 1980 Campania-Basilicata earthquake. LEGEND: Sef (Slump earthflow); RF (Rockfall); Ef (Earth flow); Und (Undefined). In brackets the number of land-slides on site. – Fenomeni franosi indotti dal terremoto Campano-Lucano del 1980. LEGENDA: Sef (slump-earth flow); RF (rockfall); Ef (earth flow); Und (indefinito). Tra parentesi è indicato il numero di frane nel sito. N° Sites Latitude Longitude Fault IMSK Type of distance landslide (km)
The results of this study demonstrate that moderate to large earthquakes in the Southern Apennines can trigger landslides at distances larger than 100 km, in areas with macroseismic intensities I=V MCS/MSK. The area distribution of the slope failures mirrors, in general, the pattern of the isoseismals, displaying a higher concentration in the areas of higher intensity, and a typical decay with distance from the epicentre and the causative fault. Most of the landslides were restricted to the areas enclosed by the intensity VIII isoseismals (c.a. 4000 Km2) (ESPOSITO et alii, 1998), in good agreement (PORFIDO et alii, 2002) with the area-magnitude relation proposed by RODRIGUEZ et alii (1999) and the maximum distance of landslides from faults vs. magnitude proposed by KEEFER (1984). Liquefaction has occurred at distances of up to 55 km from the epicentre within intensity zone VI MCS/MSK. The distribution of hydrologic anomalies is more variable. Anomalies in discharge can occur more than 200 km away from the epicentre, due to the high sensitivity of aquifers to stress changes and seismic shaking (ESPOSITO et alii, 2001; PORFIDO et alii, 2002). Similar studies are underway for other earthquakes in the Southern Apennines, starting from magnitude 5.5, the approximate threshold for producing environmental effects. The aim is to have available a comprehensive database of geological phenomena induced by moderate to strong earthquakes in Italy. Such data are basic to enhance the intensity assessment, by allowing a more exhaustive comparison of historic and recent quakes, which is one of the aims of the new EEE scale (MICHETTI et alii, 2004). This is crucial for better constrained seismic hazard assessment, and consequently, for improving the efficiency of emergency intervention and urban and infrastructural planning. ACKNOWLEDGEMENTS The authors are grateful to J.J. Clague (Simon Fraser University - Burnaby, British Columbia, Canada) and G. Scarascia Mugnozza (Università La Sapienza - Roma, Italy) for their constructive reviews, that have significantly improved the initial version of the paper. TABLE 6 Hydrological effects of the 1980 Campania-Basilicata earthquake. – Effetti idrologici indotti dal terremoto Campano-Lucano del 1980. N° Sites Latitude Longitude Fault IMSK distance (km)
Fig. 8 - The 1980 Campania-Basilicata earthquake effects. Top: at Costa Monticello fault scarp. Bottom: sackung scarp produced by earthquake near Bella (after BLUMETTI et alii, 2002). – Terremoto Campano-Lucano del 1980: scarpata di faglia presso Costa Monticello (in alto), traccia del sackung nei pressi di Bella, in basso (BLUMETTI et alii, 2002).
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