Hydrological anomalies connected to earthquakes in southern Apennines () E. Esposito, R. Pece, S. Porfido, G. Tranfaglia

To cite this version:

E. Esposito, R. Pece, S. Porfido, G. Tranfaglia. Hydrological anomalies connected to earthquakes in southern Apennines (Italy). Natural Hazards and Earth System Sciences, Copernicus Publ. / European Geosciences Union, 2001, 1 (3), pp.137-144. ￿hal-00301593￿

HAL Id: hal-00301593 https://hal.archives-ouvertes.fr/hal-00301593 Submitted on 1 Jan 2001

HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Natural Hazards and Earth System Sciences (2001) 1: 137–144 c European Geophysical Society 2001 Natural Hazards and Earth System Sciences

Hydrological anomalies connected to earthquakes in southern Apennines (Italy)

E. Esposito1, R. Pece2, S. Porfido1, and G. Tranfaglia3 1Consiglio Nazionale delle Ricerche, Geomare sud, Via Vespucci 9, 80142 Napoli, Italy 2Dipartimento di Scienze della Terra, Universita` di Napoli Federico II, Largo S. Marcellino, 10, 80138 Napoli, Italy 3Servizio Idrografico e Mareografico Nazionale, Compartimento di Napoli, Via Marchese Campodisola 21, 80133 Napoli, Italy Received: 14 May 2001 – Revised: 27 September 2001 – Accepted: 17 October 2001

Abstract. The study of hydrological variations in the wa- trical conductivity, dissolved oxygen are measured. We en- tersheds of seismic areas can be useful in order to acquire visage to increase the number of monitoring sites and con- a new knowledge of the mechanisms by which earthquakes trolled parameters. can produce hydrological anomalies. Italy has the availabil- ity of many long historical series both of hydrological param- eters and of seismological data, and is an ideal laboratory to 1 Introduction verify the validity of theoretical models proposed by various authors. Information on hydrological variations associated with seis- In this work we analyse the hydrological anomalies asso- mic events (anomalies, such as increase or decrease of ciated with some of the big earthquakes that occurred in the spring and river flows, the rising or lowering of the water last century in the southern Apennines: 1930, 1980 and 1984. level in wells) concomitant and/or preceding seismic events For these earthquakes we analysed hydrometric and pluvio- has been widely known for at least 2000 years. In the metric data looking for significant anomalies in springs, wa- last decades some hydrological anomalies have been used ter wells and mountain streams. The influence of rainfalls as earthquake precursors (Savaresky and Rikitake, 1972; on the normal flows of rivers, springs and wells has been as- Scholtz et al., 1973; Rikitake, 1974, 1975; Whitehead et al., certained. Also, the earthquake of 1805, for which a lot of 1985; Chengmin, 1985; Mogi, 1987; Kissin and Grinevsky, hydrological perturbations have been reported, is considered 1990; Igarashi et al., 1992). One of the best examples is in order to point out effects imputable to this earthquake that the Haicheng earthquake in 1975, when a lot of hydrological can be similar to the effects of the other big earthquakes. anomalies occurred before the earthquake and the city was The considered seismic events exhibit different modes then evacuated (Molnar et al., 1976). of energy release, different focal mechanisms and different Also in Italy, a possible correlation between earthquakes propagation of effects on the invested areas. Furthermore, and piezometric anomalies has been recognised (Albarello even if their epicentres were not localised in contiguous seis- et al., 1991; Albarello and Martinelli, 1994; Onorati and mogenetic areas, it seems that the hydrological effects im- Tranfaglia, 1994; Onorati et al., 1994; Pece et al., 1999; Es- putable to them took place in the same areas. Such phe- posito et al., 1998a, 1999). Many other documents of the nomena have been compared with macroseismic fields and XVIII and XIX centuries report information regarding vari- transformed in parameters, in order to derive empirical rela- ations of water levels and spring flows in occurrence with tionships between the dimensions of the event and the char- earthquakes. acteristics of the hydrological variations. Only in the last two decades have the hydrological vari- The results of this work point to a close dependence among ations been related to the characteristics of seismic sources. hydrological anomalies, regional structures and fault mech- Various interpretative models (Gold and Soter, 1985; Brede- anisms, and indicate that many clear anomalies have been hoeft et al., 1987; King and Muir-Wood, 1993; Muir-Wood forerunners of earthquakes. In 1993, the Bureau of and King, 1994; Briggs, 1994; Curry et al., 1994; Rojs- the Hydrographic National Service started the continuous taczer and Wolf, 1994) indicate how the fluctuations of the monitoring of hydrologic parameters by a network of auto- water level in wells and the variations in the flow of springs matic stations and transmission in real time; presently 7 ac- and/or mountain rivers can be used as earthquake precursors quifers are under control in which also pH, T , salinity, elec- and, moreover, to characterise the mechanisms of the seismic source, because they are significantly influenced by the de- Correspondence to: R. Pece ([email protected]) formation field associated with the earthquake. In particular, 138 E. Esposito et al.: Hydrological anomalies connected to earthquakes in southern Apennines (Italy)

ity and temporarily enhanced groundwater flow rates. In 1993, the Naples Bureau of Hydrographic National Service started the continuous monitoring of hydrologic parameters by a network of automatic stations in real time transmission. This network (Tranfaglia, 1994; Onorati and Tranfaglia, 1996) consists of 82 stations, 7 repeaters and the acquisition Centre in Naples, controlling a total of 175 sensors (26 ultra- sonic hydrometers on bridges, 63 rain gauges, 23 thermome- ters, 13 hygrometers, 5 barometers, 4 anemometers, 6 water level gauges). All the data from the sensors are transmitted at the Monitoring Centre in Naples where they are contin- uously controlled, visualised and stored (Fig. 1). We hope that this monitoring can furnish clearly the evidence that hy- drological anomalies are forerunners of earthquakes in the Fig. 1. Sketch map of southern Italy illustrating the Monitoring controlled areas. Center in Naples and the mentioned hydrological sites. Also, the four epicenters of the studied earthquakes are indicated.

2 Earthquakes in southern Apennines

King and Muir-Wood (1993) recently proposed a model of The areas considered in this work constitute nearly all of the the deformation associated with the dislocation phenomena southern part of the Apennine Chain from the Molise Re- in complex systems of faults with different mechanisms and gion to the Lucania () Region. The seismicity in orientations. According to this model, the coseismic disloca- this section of the Apennine Chain is characterised by severe tion during strong earthquakes produces a notable deforma- seismic events with intensities greater than IX MCS. In this tion of the superficial crust (surface layers) which influences work we analyse the hydrological anomalies associated with directly the superficial acquifers. Therefore, the hydrological some of the strong earthquakes that occurred in the last cen- regime and the spatial variation of anomalies are correlated turies in southern Apennines: to the spatial variation of the volumetric deformation pro- duced by the phenomena of the coseismic dislocation in a – 1984 (Southern Abruzzo, 7–11 May) wide area. – 1980 (-Basilicata, 23 November) Furthermore, some authors tried to classify the possible “shapes” of the hydrological anomalies and to find some – 1930 (Irpinia, 23 July), relationships among magnitude, precursor time and dis- – 1805 (Molise, 26 July). tance from epicentre of the hydrological anomalies. Kissin and Grinevsky (1990) examined carefully many hydrologi- For the most recent earthquakes (1980 and 1984), we anal- cal anomalies reported in various parts of the Earth. Also, ysed hydrometric and pluviometric data from 1972–1992 Chengmin (1985) examined many anomalous variation pre- looking for significant anomalies in springs, water wells and cursors of 60 earthquakes with M > 6.0 in China. They mountain streams. The influence of rainfalls on the normal found essentially that: (1) most of these anomalies took place flows of rivers, springs and wells has been statistically veri- at distance less than 50 km from the epicentres; (2) their fied. With regards to the older earthquakes (1805 and 1930), number decreases rapidly at a growing distance from the epi- we considered the historical sources contemporaneous to the centre; (3) the type or the “shape” of the anomaly depends on seismic event and we could classify types and entities of hy- the fault type, topography, magnitude and distance from the drological phenomena strictly imputable to the earthquake. epicentre, the time before and/or after the earthquake. Kissin The considered seismic events show different modes of en- and Grinevsky (1990) classified some typical shapes of hy- ergy release, different focal mechanisms and different prop- drological anomalies: 57% of the anomalies consist of a gen- agation of effects on the invested areas. Furthermore, even eralized depression of groundwater levels, 24% and 12% are if their epicentres were localised in seismogenetic, and not stepwise increases and decreases, respectively, of groundwa- the contiguous areas, it seems that the hydrological effects ter levels, and 7% are complex variations. The groundwater imputable to them took place in the same areas. level variations can be 0.5 cm–16 m, but 76% are comprised Such phenomena have been compared at first with macro- between 1 cm and 1 m. seismic field and subsequently transformed in parameters, in Also many hydrological variations were reported by Ro- order to derive empirical relationships between the dimen- jstaczer and Wolf (1994) for the Loma Prieta earthquake sions of the event and the characteristics of the hydrological in 1989: groundwater levels in the highland parts of the variations. drainage basins were lowered for a long time, while most of The first results of this work point to a close dependence the streamflow increased within 15 min after the earthquake, among hydrological anomalies, regional structures and fault indicating that the earthquake increased the rock permeabil- mechanisms.

E. Esposito et al.: Hydrological anomalies connected to earthquakes in southern Apennines (Italy) 139

25 23 July 1930 earthquake 23 July 1930 earthquake Daily rainfall at S. Domenico 250 Monthly rainfall at Caposele 5500 20 Flow rate of Sanità spring in Caposele 23/07/30 Streamflow level of Tasso river at Scanno 5300 20 18 16/07/30 200 5100 ) c e ) s

16 / m s c r

4900 e ) l ( e ) m

15 (lit v

m e m 14 te ( m

150 4700 a ( ll a 25 Jul ll a f inf mflow l a

12 in

a 4500 a e r tr ily r

10 s ring flow r a p D 100 4300 s 10 ily a onthly D M 4100 8 5 23 Jul 50 3900 Fortnightly 6 18 Jul 3700 0 4

l l l l l l l l 0 3500 u u u u u u u u un un un un un un un un J J J J J J J J J J J J J J J J Aug Aug Aug Aug Aug Aug Aug 03 07 11 15 19 23 27 31 01 05 09 13 17 21 25 28 04 08 12 16 20 24 28 01/01/30 16/01/30 01/02/30 16/02/30 01/03/30 16/03/30 01/04/30 16/04/30 01/05/30 16/05/30 01/06/30 16/06/30 01/07/30 16/07/30 23/07/30 01/08/30 16/08/30 01/09/30 16/09/30 01/10/30 16/10/30 01/11/30 16/11/30 01/12/30 16/12/30 01/01/31

Fig. 2. Hydrological anomaly correlated to the 23 July 1930 earth- Fig. 3. Hydrological anomaly correlated to the 23 July 1930 earth- quake, consisting of a sharp decrease a few days before the seismic quake, consisting of an increase in the flow rate of Sanita` Spring at event followed by a strong increase of the streamflow level of the Caposele of about 150 l/s. Tasso River measured at Scanno.

in more than 16 springs, mostly SSW of the Matese Moun- 3 Discussion tains. Contemporaneously, 4 new springs appeared at S. Sal- vatore Telesino (Caserta district), Morcone (Benevento dis- 3.1 The Molise earthquake of July 1805 trict), Matese Mountains and Boiano (Campobasso district). The new spring in Boiano was active for about 2 months after The 26 July 1805 earthquake happened inside the Molise the seismic event. seismogenetic zone (Alessio et al., 1993), where various strong earthquakes (greater than X MCS) took place, like 3.2 The earthquake of July 1930 those in 346, 848 and December 1456. At present, the seis- micity is constituted by low magnitude swarms, like the se- The 23 July 1930 earthquake, erroneously defined as “the quence at Isernia in January 1986, with M = 4.0 and that Vulture earthquake”, destroyed almost entirely many villages max of Sannio-Matese in March 1997 with Mmax = 4.6 (Alessio in Eastern Irpinia, causing severe damages also in the Ben- et al., 1990). evento, Foggia and Potenza provinces. The victims were This strong earthquake was felt in all of southern Italy and more than 1400 and the wounded were about 10 000. The damaged more than 200 cities and villages in the Molise and main shock happened at 00:08 GMT with the greatest inten- regions. The macroseismic epicentre is localised sity of X MCS and a magnitude Ms = 6.7, followed by many in the Molise zone, between Isernia and Campobasso; the aftershocks, some of which with intensity of VII MCS. Nu- highest intensity of XI MCS was at Frosolone (Isernia dis- merous and impressive phenomena on the physical environ- trict). The effects of this earthquake before, during and af- ment were observed in the villages of Andretta, Aquilonia, ter the main shock are particularly interesting. We collected Ariano Irpino, Bisaccia, Calitri, Flumeri, Melfi, , San the descriptions of a lot of phenomena possibly linked to Giorgio la Molara, Vallata, and Zun- the seismic event; in fact, starting from the XVII century, goli. the interest of naturalists to analyse and interpret the seismic To reconstruct the effects on the environment caused by phenomenon, and also the attention on the effects of earth- this strong earthquake, we started to: (1) research methodi- quakes, increased; as a consequence, both the number of cally all the documents relative to it; (2) to analyse critically reports and the accuracy in the descriptions of strange phe- the administrative and technical reports in the Record Offices nomena grew considerably. The many historical sources al- and in Civil Engineer Offices of Avellino and cities low one to understand and point out types and entities of the and in the Municipal Technical Offices of the towns around phenomena directly imputable to this earthquake. Fractures, the epicentre. Furthermore, all the information from local landslides, liquefaction, hydrological variations in springs, and national newspapers have been collected. rivers and wells are distributed in the area of VII MCS. The The critical examination of the seismological knowledge details in the descriptions of the earthquake’s effects allow at that time completed this investigation in order to better un- one to distinguish a temporal succession of such effects: in derstand the collected information. The comparison between particular, in the phase preceding the earthquake, variations the bibliographic sources and the unpublished reports al- of hydrological parameters, flow rate and chemical compo- lowed us to draft the map of the coseismic geological effects: sition in some localities in Molise have been reported; be- landslide phenomena, hydrological anomalies, soil fractures sides the hydrologic variations (anomalies), other numerous and surficial tectonic breaks. coseismic effects have been observed: ground effects, as This investigation revealed that the greatest number of the fractures and landslides (Esposito et al., 1987, 1995, 1998b; seismic effects were found in the isoseismic area of VIII Michetti et al., 2000). Flow increases have been observed MCS (Esposito et al., 2000; Porfido et al., 2001). Two hy-

140 E. Esposito et al.: Hydrological anomalies connected to earthquakes in southern Apennines (Italy) drological anomalies are shown in Figs. 2 and 3 for the Tasso 250,0 60 Fortnightly Rainfall (mm) at Pontecagnano 30/11/80 River and one spring at Caposele. Flow rate of Acqua Fetente Spring at Montecorvino Pugliano 50 200,0 23 November 1980 earthquake

In Fig. 2 the hydrological anomaly correlated to the 1930 ) c e s )

40 r/ m earthquake consists of a sharp decrease in the streamflow e (lit

150,0 ll (m te a a inf a few days before the seismic event, even if high rainfalls a 30 preceded this decrease. Also, the increase after the seismic 100,0 17/11/80 20 Fortnightly r

event seems to be an anomalous hydrological behaviour of Fortnightly flow r 50,0 the springs that contribute to the Tasso River. 10 In Fig. 3 an increase of 150 l/s in the flow rate of Sanita` Spring at Caposele was noted in the measurements carried 0,0 0 out a few hours after the seismic event with respect to the 15/07/80 15/08/80 15/09/80 06/10/80 20/10/80 03/11/80 17/11/80 12/12/80 29/12/80 12/01/81 26/01/81 09/02/81 23/02/81 09/03/81 23/03/81 06/04/81 27/04/81 11/05/81 25/05/81 08/06/81 29/06/81 13/07/81 03/08/81 21/08/81 08/09/81 27/09/81 10/10/81 25/10/81 21/11/81 15/12/81 measurements carried out on 16 July 1930, a week before Fig. 4. Hydrological anomaly correlated to the 23 November 1980 the earthquake. earthquake, consisting of a great increase in the flow rate of Acqua Fetente Spring at Montecorvino Pugliano from 14.7 to 50.8 l/s. This 3.3 The earthquake of November 1980 variation lasted for more than one year. The 23 November 1980 earthquake happened inside a seis- 18 75 mically active band extending from southern Abruzzo to Lu- 23 November 1980 earthquake 16 70 cania (Basilicata). This Campanian-Lucanian seismogenetic Daily rainfall at Barrea (mm) 14 65 zone is characterised by a complex seismotectonic structure, Streamflow level of Zittola river at Montenero ) m

12 c ) l (

m 60 e v

buried under the thick alloctonous terrains that constitute the e 10 ll (m a 55 inf

Apennine Chain. a mflow l

8 a e ily r tr a 50 s On the basis of geological, structural and geophysical ev- D

6 ily a

24 Nov D 45 idences, the seismogenetic band has been subdivided into 4 more seismogenetic zones (Scandone et al., 1990; Alessio 2 40 23 Nov et al., 1993, 1995) characterised by a frequent seismicity, 0 35

both historical as the earthquakes in 1561, 1694, 1851, 1857, Nov Nov Nov Nov Nov Nov Nov Nov Nov Nov Nov

18 19 20 21 22 23 24 25 26 27 28 1930 with I ≥ IX MCS and recent, main shock-aftershock type, as the earthquakes in 1980, 1990, 1991 with I ≥ VIII Fig. 5. Hydrological anomaly correlated to the 23 November 1980 and 5 ≤ M ≤ 6.9. earthquake, consisting of an increase in the streamflow rate of Zit- About 800 villages were damaged in Campania and Lu- tola River measured at Montenero, not imputable to rainfalls. cania. The Imax was X MSK. This great intensity and the nature of the geological structures caused very numerous effects. Surface fractures were observed in all the areas starting from 24 November, lasting for about 24–48 h. In from the epicentre until to the VIII isoseismal line. About some cases, the positive anomaly lasted until 27 November. 200 landslide phenomena were observed in an area more A detailed study of the spring flows at Caposele and Cas- than 20 000 km2 wide around the epicentre (Esposito et al., sano Irpino, located near the epicentre, have been carried out, 1998b). by considering the monthly averages in 10 years (Pece et al., The study of the hydrological effects has been carried out 1999). The year 1980 appears to be hydrologically anoma- on: lous. Figures 4 to 9 show some hydrological anomalies. – measurements of water levels in 9 wells with 3 days pe- In Fig. 4 the anomaly consists of the great increase in the riodicity; flow rate of a thermal spring (Acqua Fetente) between 17 and 30 November (earthquake was on 23 November) and this in- – spring flows measured each day; crease lasted many months. All this behaviour is anomalous – streamflow levels measured each day; and the rainfalls could not produce such a sudden and great increase. It is sufficient to observe what is the contribution – continuous registration of water level in rivers. of each rainfall event on hydrograph of the flow rate. We suppose that the pre- and co-seismic stresses modified the We also considered many other similar, but less continu- groundwater circulation. ous measurements carried out during 1975–1985 (periodicity In Fig. 5 there is another type of anomaly. Measurements varied from weekly to monthly) on minor springs and rivers. are carried out on the mountain stream by a river gauge and Seven of the about 30 greatest springs exhibited a clear the continuous record shows that a decrease is followed by anomaly. Most of them are in the high Sele River and on an increase recorded at 12:00 MLT each day. It is not possi- Matese Mountains. ble that this increase is due to some rainfall (no rainfalls are Before the earthquake, the trends of hydrometric levels present in 23 and 24 November). The response of water level were normal or decreasing, but showed a general increase to rainfalls in this site is almost contemporaneous, because

E. Esposito et al.: Hydrological anomalies connected to earthquakes in southern Apennines (Italy) 141

45,0 160 Monthly rainfalls (dashed) and flow rates at Caposele and 23 November 1980 earthquake 8000 Cassano Irpino springs in 1975-1985 500 40,0 150

450 ele )

Daily rainfall (mm) at Montemarano 7000 s m

m 35,0 400 (

Calore Irpino at Montella ) apo 140 6000 o C n cm 350 ( a

r 30,0

el 5000 ) at

130 v 300 m le tema 25,0 m w 4000 250 on o

120 l M f all ( all 20,0 3000 200 f eam r all at t 110 150 rain f s

n 15,0 Flow rate (liters/sec) 2000 ai hly r 100 t

100 aily D

10,0 1000 on aily 23 Nov 25 Nov 50 Nov M

D 24 5,0 90 0 0 83 76 0 7 4 0 3 6 2 5 8 5 8 7 84 8 77 8 79

8 7 ch ch 8 7

0,0 80 t 8 7

y r r y v r c t t c p b 79 l l a a a a ug 75 o c c p ug 82 e e u u un 81 un ov ov ov ov ov ov ov ov ov ov ov ov Jan Jan J J J M De A N M M O O De A A M S F N N N N N N N N N N N N 29 28 27 26 25 24 23 22 21 20 19 18

Fig. 6. Hydrological anomaly correlated to the 23 November 1980 Fig. 8. Monthly rainfalls (dashed) and flow rates at Caposele and earthquake. In this case the streamflow level of Calore Irpino mea- Cassano Irpino Springs in 1975–1985 showing the lag between rain- sured daily at Montella decreased the day after the earthquake. falls and subsequent increase in flow rate.

3000 23 November 1980 earthquake 140 50 23 November 1980 earthquake 7500 130 45 2800 7000 120 40 ) ) c e

2600 m s

110 6500 /

35 s (m r

Daily rainf all at Cassano Irp ino e le

100 e (lit s 2400 30

Daily rainfall at Caposele te po 6000 a 90 a

Flow rate of Bagno spring C 2200 t 25 Flow rate of Sanità spring in Caposele a

80 ll

a 5500 Flow rat e of Pollent ina spring 20 inf ring flow r

2000 70 a p s

ily r 15

Nov 5000 ily 23 60 a a D

1800 D 10 50 25 Nov

Daily rainfall (mm) 4500 1600 40 5 23 Nov

Daily flow rate (liters/sec) rate flow Daily 30 24 Nov 1400 10 N o v 0 4000 Dec Dec Dec Dec Dec Dec Dec Dec Dec Dec Dec 23 Nov 20 Nov Nov Nov Nov Nov Nov Nov Nov Nov Nov

1200 01 04 07 10 13 16 19 22 25 28 31 10 Nov 10 01 04 07 10 13 16 19 22 25 28 1000 0 v v v v v v v v c c c c c c c c o o o o o o o o e e e e e e e e N N N N N N N N D D D D D D D D Fig. 9. Hydrological anomaly correlated to the 23 November 1980 01 05 09 12 17 21 25 29 03 07 11 15 19 23 27 31 earthquake consisting of a small decrease in the spring flow rate the day after the earthquake, followed by a very great increase. Fig. 7. Hydrological anomalies correlated to the 23 November 1980 earthquake consisting of the strong increase in the flow rate of Pol- lentina and Bagno Springs. flow rates is consistent: some months, with Caposele preced- ing Cassano Irpino. This evidence has been already reported the catchment area of rainfall is small (see 27 November). by many authors (Celico, 1981; Cotecchia and Salvemini,

So the increase between 23 and 24 November appears to be 1981). imputable only to the seismic event. In Fig. 9 the hydrological anomaly at Caposele consists In Fig. 6 the anomaly seems to be the opposite of that of a small decrease in the spring flow rate the day after the shown in Fig. 5. In fact, there is a decrease from 23 to earthquake, followed by a very great increase. 24 November: the increase took place on 25–26 November. Also in this case, no rainfalls occurred in those days. The 3.4 The earthquake of May 1984 decrease at this site can be explained by taking into account that near Caposele Spring, the same behaviour is exhibited The seismic sequence, which started in May 1984, consists of (Fig. 9). two main shocks, on 7 May and on 11 May with I = VII MSK Figure 7 shows the hydrological anomalies consisting of in Southern Abruzzo, mainly in the National Park seismoge- the strong increase in flow rate of Pollentina and Bagno netic zone (Alessio et al., 1993). The hypocentral depths are Springs, very near each other at Cassano Irpino. It seems between 5 and 15 km. The seismic sequence terminated in that this increase started about ten days before the seismic October with a duration of about 5 months. event. A further sharp increase took place soon after the In order to evaluate the hydrological effects produced by earthquake. We retain that these increases cannot be im- the seismic sequence, we analysed the data registered in 15 putable to the rainfalls that preceded the seismic event. In hydrometrical stations and the variations of levels of two fact, Fig. 8 shows the trends of monthly cumulated flow rates lakes (Barrea and Scanno), all localised in the epicentral area of these two springs compared to the rainfalls in the decade and monitored by the National Hydrologic Departments in 1975–1985. This figure also reports the flow rate of the Ca- Napoli and Pescara. posele Spring. The lag among rainfalls and increases in the Hydrological variations have been registered in 12 hydro-

142 E. Esposito et al.: Hydrological anomalies connected to earthquakes in southern Apennines (Italy)

350 7 and 11 May 1984 earthquakes monthly rainfall (mm) at Picinisco 14 ure 11 shows “a detail” of Fig. 10. The two sites are very streamflow rate of Sangro river at Barrea 300 12 near each other. It shows how during April 1984 the sharp 1984-05

) increase of 7 May cannot be imputed to the very small rain- c e

250 10 s

1984-04 3/ )

m falls on 6 May. Data are daily. ( mm te ( a r l 200 8 a f ow in l a f r

150 6 eam r t s onthly M 4 Conclusions 100 4 onthly M

50 2 In the southern Apennines we found that some earth- 0 0 quakes produced forerunner signals in various areas where

1983-01 1983-03 1983-05 1983-07 1983-09 1983-11 1984-01 1984-03 1984-05 1984-07 1984-09 1984-11 1985-01 1985-03 1985-05 1985-07 1985-09 1985-11 geochemical and hydrological parameters were controlled. These results seem to indicate that the hydrological phenom- Fig. 10. Hydrological anomaly correlated to the May 1984 earth- ena are associated with the changes in the stress field, during quake consisting of an increase in the streamflow rate of Sangro and after an earthquake. River at Barrea, not imputable to the rainfalls. Data are monthly. We analysed the relations of primary tectonic effects with the local geomorphic and structural setting. We also applied,

30 7 and 11 May 1984 earthquakes 130 for some categories of secondary effects, a statistical test to daily rainfall in May at Avezzano 120 infer the presence of trends, and a regression analysis based 25 streamflow level of Fucino at Pratofranco 110 on the least-squares method was performed. ) m c

) 20 100 l ( m e

v In particular, a simple bivariate scatter plot of two vari- 90 e ll (m a 15 7

inf ables has been computed, specifically: macroseismic in- a

80 l mflow a e ily r tr a s tensities versus epicentral or fault distances of hydrological D 10 70 ily a 6 8 60 D anomalies. Figure 12 shows, for each of the 4 considered 5 50 earthquakes, the trend macroseismic intensity-distance from

0 40 the epicenter of the hydrological anomalies we have found 12345678910111213141516171819202122232425262728293031 (30 for 1805 earthquake, 65 for 1930 earthquake, 35 for 1980 Fig. 11. Hydrological anomaly correlated to the May 1984 earth- earthquake and 21 for 1984 earthquake). Very similar trends quake consisting of an increase in the streamflow rate of Fucino have been found for these earthquakes with a better fit for the River at Pratofranco, not imputable to the rainfalls. Data are daily. two most recent earthquakes (1980 and 1984). Hydrological phenomena occurred throughout the macro- seismic field, and were the most numerous among the in- metric sections. Among them, 3 hydrometric stations WSW duced effects. They include flow increase both in springs in the epicentral area, and another station located west of the and wells, turbid water and drying up of springs, and even continuation toward north of the Val di Sangro fault did not creation of new springs. Some variations in the chemical pa- show notable hydrological anomalies in the days before the rameters of the waters were observed at different locations, event of 7 May, while during all this month, flow rates were both inside and outside the epicentral areas. comparable with the average values calculated for the pe- The data relative to the hydrological variations’ distribu- riod 1979–1989, even if the rainfalls from January to May tion versus the distance from the epicenter (Fig. 12) show the 1984 have been slightly higher than the average (Onorati and that the high concentration of phenomena (75%) lie between Tranfaglia, 1994). 25–80 km, whereas 19% were inside the epicentral area (0– Nevertheless, gas outpouring and the muddying of water 25 km); only 6% of these phenomena occurred at greater have been noticed in the evening of 5 May, in the springs at distances (about 100 km); this distribution is very similar to Posta Fibreno, localized about 2 km before the hydrometric those reported by Kissin and Grinevsky (1990). sections (Fibreno at Broccostella). A dramatic increase in the springs’ flow implies the de- Also in the hydrometric section of the Sangro River at formation of a major tectonic block. A comparable phe- Ateleta, the hydrological anomaly was pointed out only in nomenon occurred at the Sanita` Spring near Caposele during the value of the average streamflow level in May 1984. Con- the 23 November 1980 earthquake. sequently, for these earthquakes, we have a total of 14 sites A remarkable aspect of these anomalies is that they were where hydrological effects have been noticed, taking into ac- observed at distances of several hundred kilometres from the count that in 3 sites (the Rapido and Gari Rivers at Cassino, earthquake epicentral area. the Gari River at S. Angelo in Theodice), the positive hydro- Figure 12 shows that much more data on hydrological logical anomalies preceded the earthquake of 7 May. changes are available for the 1980 earthquake compared to Figures 10 and 11 show the anomalous behaviour in two the 1805 earthquake. Even taking into account the better ac- studied sites. In Fig. 10 we show an hydrological anomaly curacy of the research conducted after the 1980 event, this consisting of a strong increase in the streamflow rate of the suggests that the impact of the Irpinia earthquake on the hy- Sangro River at Barrea, not imputable to the rainfalls. Fig- drogeological structure of the southern Apennines was more E. Esposito et al.: Hydrological anomalies connected to earthquakes in southern Apennines (Italy) 143

(a) 26 July 1805 earthquake (b) 23 July 1930 earthquake 12,0 9,5

9,0 y = -0,03x + 8,54 10,0 2 8,5 R = 0,38

8,0 8,0 y = -0,03x + 8,21 R2 = 0,44 7,5 6,0 7,0

6,5 4,0

6,0 Macroseismic intensity (MCS) Macroseismic intensity (MCS) 2,0 5,5

5,0 0,0 0 102030405060708090100 050100150200 Hydrological anomaly distance from the macroseismic epicenter (km) Hydrological anomaly distance from the macroseimic epicenter (km)

(c) 23 November 1980 earthquake (d) 7 May 1984 earthquake 10,0 8,0 y = -0,02x + 7,86 9,0 R2 = 0,67 y = -0,02x + 7,20 8,0 R2 = 0,57 7,0 7,0

6,0

6,0 5,0 Macroseismic intensity (MSK) Macroseismic intensity (MSK) 4,0

3,0 5,0 0 20 40 60 80 100 120 140 160 180 200 0 1020304050607080 Hydrological anomaly distance from the macroseismic epicenter (km) Hydrological anomaly distance from the macroseismic epicenter (km)

Fig. 12. The figure shows for each earthquake the distance from epicenter and intensity (MCS or MSK) of the sites where hydrological anomalies have been observed. A clear negative linear regression is visible. For the 1930 (M = 6.5) and 1980 (M = 6.8) earthquakes the two trends are parallel.

important, in terms of both the total number of recorded at the Hydrographic National Service in Campania can fur- anomalies and for their epicentral and fault distance. nish a valid occasion to increase the number of parameters to Today, there are no valid earthquake precursors, but many monitor water tables and springs. effects are invoked as good forerunners: geophysical changes We envisage that the proposed improvement of this net- (vp/vs, telluric currents, electromagnetic effects), geochem- work can reveal many and contemporaneous anomalies in ical changes (chemical composition, pH, water temperature, the trends of the monitored parameters; the examination of gases like Rn, CO2) and hydrological changes (piezometric trends and anomalies are fundamental in order to produce a levels, spring and stream flow). valid model of the interaction between stress fields and hy- In this work we show hydrological anomalies for the con- drological behaviour in the monitored areas; this model can sidered Italian earthquakes similar in “form and type” to be considered reliable in order to verify the occurrence of those reported by previous authors in other regions of the pre-seismic anomalies. Earth. They are examples of the many anomalies we have chosen for the considered earthquakes (see Fig. 12) and show how hydrological anomalies are made. Probably the simulta- References neous observation of all of these effects can constitute a sure forecasting. Many efforts and money are necessary for this Albarello, D. and Martinelli, G.: Piezometric levels as possible geo- purpose. dynamic indicators: analysis of data from a regional deep waters Taking into account that earthquakes are not always pre- monitoring network in northern Italy, Geoph. Res. Lett., 21, 18, ceded by all of the above mentioned precursory phenomena, 1955–1958, 1994. and that today’s technology can provide probes for many Albarello, D., Ferrari, G., Martinelli, G., and Mucciarelli, M.: Well level variation as a possible seismic precursor: a statistical as- geochemical and geophysical parameters at an affordable sessment from Italian historical data, Tectonophysics, 193, 385– cost, we maintain that a regional monitoring network can be 395, 1991. installed in order to continuously control as many parameters Alessio, G., Godano, C., and Gorini, A.: A low magnitude seismic as possible. sequence near Isernia (Molise, central Italy) on January 1986, The presence of an already installed hydrological network PAGEOPH, 134, 2, 243–260, 1990. 144 E. Esposito et al.: Hydrological anomalies connected to earthquakes in southern Apennines (Italy)

Alessio, G., Esposito, E., Gorini, A., Luongo, G., and Porfido S.: fects and Seismic Hazard Assessment in Italy: examples from the Identification of seismogenic areas in the southern Apennines, Matese and Irpinia areas, southern Apennines, In: Active Fault Italy, Annali di Geofisica, 36, 1, 227–235, 1993. Research for the New Millennium, Proc. Hokudan Symposium Alessio, G., Esposito, E., Gorini, A., and Porfido, S.: Detailed study and School on Active Faulting, 279–284, 2000. of the Potentino seismic zone of the southern Apennines, Italy, Mogi, K.: Comparison of precursory phenomena before the 1975 Tectonophysics, 250, 113–134, 1995. Haicheng (China) earthquake and the 1978 Izu-Oshima-Kinkai Bredehoeft J. D., Riley F. S., and Roeloffs E. A.: Earthquakes and (Japan) earthquake: the possible effect of stress history on pre- Groundwater. Earthquakes and Volcanoes, 19, 4, 142–146, 1987. cursory phenomena, Tectonophysics, 138, 33–43, 1987. Briggs, R. O.: Effects of the earthquakes on surface waters in Molnar, P., Hanks, T., Nur, A., Raleigh, B., Wu, F., Savage, J., Waddell Valley. In: The Loma Prieta (California) Earthquake of Scholz, C., Craig, H., Turner, R., and Bennet, G.: Prediction 17 October 1989 – Hydrologic disturbances, USGS Prof. Paper of the Haicheng earthquake, “The Haicheng Earthquake Study 1551–E, 21–30, 1994. Delegation” Report, 1976. Celico, P.: Relazioni tra idrodinamica sotterranea e terremoti in Muir-Wood, R. and King, G. C. P.: The impact of earthquakes on Irpinia (Campania), Rendiconti Societa` Geologica Italiana, 4, fluids in the crust, Annali di Geofisica, XXXVII, 6, 1453–1460, 103–108, 1981. 1994. Chengmin, W.: Ground-water studies for earthquake prediction in Onorati, G. and Tranfaglia, G.: L’anomalia idrologica che ha prece- China, Pageoph, 122, 215–217, 1985. duto i terremoti del maggio 1984 nel Parco Nazionale d’Abruzzo, Cotecchia, V. and Salvemini A.: Correlazione fra eventi sismici e Acc. Naz. Lincei. Convegno su “Terremoti in Italia: previsione e variazioni di portata alle sorgenti di Caposele e Cassano Irpino, prevenzione dei danni”, 1994. con particolare riferimento al sisma del 23 novembre 1980, Ge- Onorati, G. and Tranfaglia, G.: La rete di telemisura del bacino ologia Applicata e Idrogeologia, XVI, 167–191, 1981. idrografico del fiume Sele: esperienze di monitoraggio delle Curry, R. R., Emery B. A., and Kidwell T. G.: Sources and Mag- piene – Atti Conv. Int. “revenzione delle catastrofi idrogeo- nitudes of increased streamflow in the Santa Cruz Mountains for logiche: il contributo della ricerca scientifica”, Alba, November, the 1990 water year after the earthquake, In: The Loma Prieta 1996. (California) Earthquake of 17 October 1989 – Hydrologic distur- Onorati, G., Pece, R., Tranfaglia, G., and Zollo, A.: Sismicita` e bances, USGS Prof. Pap. 1551-E, 31–50, 1994. regime delle falde acquifere nell’Appennino meridionale, Atti Esposito, E., Luongo, G., Maturano, A., and Porfido, S.: Il Ter- 13◦ Conv. Naz. GNGTS, Roma, 895–906, 1994. remoto di S. Anna del 26 luglio 1805, Mem. Soc.Geol. It., 37, Pece, R., Tranfaglia, G., and Avino, R.: Geochemical monitor- 171–191, 1987. ing integrated in a real time hydrological network, Il Nuovo Ci- Esposito, E., Laurelli, L., and Porfido, S.: Damage pattern in his- mento, 22 C, 483–490, 1999. torical centres: Isernia an example in Southern Italy, Annali di Porfido, S., Esposito, E., Iaccarino, G., Pece, R., Tranfaglia, G., Geofisica, 38, 663–677, 1995. Esposito, G., and Alaia, F.: Ground effects during the 23 July Esposito, E., Porfido, S., Tranfaglia, G., and Avino, R.: Effetti idro- 1930 Irpinia earthquake (southern Italy), Geophys. Res. Abst., 3, logici associati con i terremoti dell’Appennino meridionale, Atti 2001 – 26th General Assembly, Nice, France, 2001. 16◦ Conv. GNGTS, Trieste, 1998a. Rikitake, T. (Ed): Focal processes and prediction of earthquakes – Esposito, E., Gargiulo, A., Iaccarino, G., and Porfido, S.: Tectonophysics, 23, 217–318, 1974. Distribuzione dei fenomeni franosi riattivati dai terremoti Rikitake, T.: Earthquake Precursors – Bulletin of the Seismological dell’Appennino meridionale. Censimento delle frane del terre- Society of America, 65, 5, 1133–1162, 1975. moto del 1980, Proc. Conv. Int. Prevention of Hydrogeological Rojstaczer, S. and Wolf, S.: Hydrologic changes associated with the Hazards: the role of scientific research 1, CNR-IRPI, Alba, 409– earthquake in The San Lorenzo and Pescadero drainage basins, 429, 1998b. In: The Loma Prieta (California) earthquake of 17 October 1989 Esposito, E., Pece, R., Porfido, S., Tranfaglia, G., and Onorati, G.: – Hydrologic disturbances, USGS Prof. Paper 1551-E, 51–64, Effetti dei terremoti dell’Appennino meridionale sulle acque su- 1994. perficiali, Atti Acc. Naz. Lincei, 154, 91–96, 1999. Savaresky, E. F. and Rikitake T. (Eds): Forerunners of strong earth- Esposito, E., Porfido, S., Iaccarino, G., and Tranfaglia, G.: Ter- quakes – Tectonophysics, 14, 3/4, 177–343, 1972. remoti e centri storici dell’Irpinia: gli effetti del terremoto del Scandone, P., Patacca, E., Meletti, E., Bellatalla, C., Perilli, N., and 1930, Proc. GeoBen 2000, CNR-GNDCI, 2133, 477–484, 2000. Santini, U.: Struttura geologica, evoluzione cinematica e schema Gold, T. and Soter, S.: Fluid ascent through the solid lithosphere and sismotettonico della penisola italiana, Atti Convegno GNDT- its relation to earthquakes, Pageoph., 122, 2/4, 492–530, 1985. CNR, 1, 119–136, 1990. Igarashi, G., Wakita, H., and Sato, T.: Precursory and coseismic Scholtz, C. H., Sykes, L. R., and Aggarwal, Y. P.: Earthquake pre- anomalies in well water levels observed for the 2 February 1992, diction: A physical basis, Science, 181, 803–810, 1973. Tokyo Bay earthquake, Geoph. Res. Lett., 19, 15, 1583–1586, Thomas, D.: Geochemical precursors to seismic activity – Pageoph, 1992. 126, 2/4, 241–266, 1988. King, G. C. P. and Muir-Wood, R.: Hydrological Signatures of Tranfaglia, G.: Realizzazione di una rete idrometeorologica in tele- Earthquake Strain, Jour. Geoph. Res., 98 (B12), 22 035–22 068, trasmissione nei Bacini del Liri-Garigliano e del Volturno – Atti 1993. del Convegno “Atmospheric Physics and Dynamics in the Analy- Kissin, I. G. and Grinevsky, A. O.: Main features of Hydrogeo- sis and Prognosis of Precipitation Fields”, Rome, 15–16 Novem- dynamic earthquake precursors, Tectonophysics, 178, 277–286, ber 1994. 1990. Whitehead, R. L., Harper, R. W., and Sisco, H. G.: Hydrologic Michetti, A. M., Blumetti, A. M., Esposito, E., Ferreli, L., Guerrieri, changes associated with the 28 October 1983, Idaho earthquake, L., Porfido, S., Serva, L., and Vittori, E.: Earthquake Ground Ef- Pageoph, 122, 280–293, 1985.