**4. The earthquake of November 1980**

The 23 November 1980 earthquake happened inside a seismically active band extending from southern Abruzzo to Lucania (Basilicata). This Irpinia-Lucania seismogenetic zone is characterised by a complex seismotectonic structure, buried under the thick alloctonous terrains that constitute the Apennine Chain.

On the basis of geological, structural and geophysical evidences, the seismogenetic band has been subdivided in more seismogenetic zones characterised by a frequent seismicity, both historical as the earthquakes in 1561, 1694, 1851, 1857, 1930 with IIX MCS and recent, main shock-aftershock type, as the earthquakes in 1980, 1990, 1991 with IVIII and 5M6.9.

About 800 villages were damaged in Campania and Lucania. 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 area from the epicentre till to the VIII isoseismal line. About 200 landslide phenomena were observed in an area more than 20.000 Km2 wide around the epicentre.

The study of the hydrological effects has been carried out on measurements of water levels, spring flows measured each day, streamflow levels measured each day, continuous registration of water level in rivers (Esposito et al., 2001)

We considered also many other similar, but less continuous, measurements carried out during 1975-1985 (periodicity varied from weekly to monthly) on springs and rivers which exhibited a clear anomaly. Most of them are in the high Sele river and on Matese mountains (figures 5a-f).

Before the earthquake the trends of hydrometric levels were normal or decreasing, but show a general increase starting from 24 November, lasting for about 24-48 hours. In some cases the positive anomaly lasted till to 27 November.

A detailed study of the spring ow at Caposele and Cassano Irpino, located near the epicentre, have been carried out, by considering the monthly averages in 10 years (Pece et al., 1999). The year 1980 appears to be hydrologically anomalous.

In Fig. 5a the anomaly consists of the great increase in the flow rate of a thermal spring (Acqua Fetente) between 17 and 30 November (earthquake was on 23 November) and this increase lasted many months. All this behaviour is anomalous and the rainfalls could not produce such a sudden and great increase. It is sufficient to observe what is the contribution of each rainfall event on hydrograph of the flow rate. We suppose that the pre- and coseismic stresses modified the groundwater circulation.

In Fig. 5b there is another type of anomaly. Measurements are carried out on the mountain stream by a river gauge and the continuous record shows that a decrease is followed by an

lasted about six hours. For the 18 November 1755 Cape Anne historic earthquake in New England (USA) with an epicentral intensity MM=VIII, Thorson (2001) reported hydrological responses up to 275 km from the epicentre**,** consisting in coseismic, abrupt, long-term changes in the flow rate and chemistry of water wells from five towns in Connecticut. The anomalies were evaluated to determine whether there were patterns of hydrologic change related to epicentral or fault distance. Figure 4 shows that: (a) most of the phenomena lie between 30-120 km from the epicentre, whereas the maximum distance was 200 km; (b) most hydrological changes occurred within 30-110 km from the fault rupture segment. The maximum distance of such variations from the fault rupture was 155 km. Note that few hydrological anomalies occurred near the fault or near the epicentre (<30 km).

The 23 November 1980 earthquake happened inside a seismically active band extending from southern Abruzzo to Lucania (Basilicata). This Irpinia-Lucania seismogenetic zone is characterised by a complex seismotectonic structure, buried under the thick alloctonous

On the basis of geological, structural and geophysical evidences, the seismogenetic band has been subdivided in more seismogenetic zones characterised by a frequent seismicity, both historical as the earthquakes in 1561, 1694, 1851, 1857, 1930 with IIX MCS and recent, main shock-aftershock type, as the earthquakes in 1980, 1990, 1991 with IVIII and 5M6.9. About 800 villages were damaged in Campania and Lucania. 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 area from the epicentre till to the VIII isoseismal line. About 200 landslide phenomena were observed in an area more than 20.000 Km2 wide

The study of the hydrological effects has been carried out on measurements of water levels, spring flows measured each day, streamflow levels measured each day, continuous

We considered also many other similar, but less continuous, measurements carried out during 1975-1985 (periodicity varied from weekly to monthly) on springs and rivers which exhibited a clear anomaly. Most of them are in the high Sele river and on Matese mountains

Before the earthquake the trends of hydrometric levels were normal or decreasing, but show a general increase starting from 24 November, lasting for about 24-48 hours. In some cases

A detailed study of the spring ow at Caposele and Cassano Irpino, located near the epicentre, have been carried out, by considering the monthly averages in 10 years (Pece et

In Fig. 5a the anomaly consists of the great increase in the flow rate of a thermal spring (Acqua Fetente) between 17 and 30 November (earthquake was on 23 November) and this increase lasted many months. All this behaviour is anomalous and the rainfalls could not produce such a sudden and great increase. It is sufficient to observe what is the contribution of each rainfall event on hydrograph of the flow rate. We suppose that the pre- and co-

In Fig. 5b there is another type of anomaly. Measurements are carried out on the mountain stream by a river gauge and the continuous record shows that a decrease is followed by an

**4. The earthquake of November 1980** 

terrains that constitute the Apennine Chain.

registration of water level in rivers (Esposito et al., 2001)

al., 1999). The year 1980 appears to be hydrologically anomalous.

the positive anomaly lasted till to 27 November.

seismic stresses modified the groundwater circulation.

around the epicentre.

(figures 5a-f).

increase recorded at 12:00 MLT each day. It is not possible that this increase is due to some rainfall (no rainfalls are present in 23 and 24 November). The response of water level to rainfalls in this site is almost contemporaneous, because the catchment area of rainfall is small (see 27 November). So the increase between 23 and 24 November appears to be imputable only to the seismic event.

Fig. 5. Acqua Fetente spring (a); Zittola river at Montenero (b); Streamflow level of Calore Irpino at Montella (c); Cassano Irpino springs: Pollentina (d) and Bagno (e); Sanità spring at Caposele (f).

In Fig. 5c the anomaly seems to be the opposite of that shown in Fig. 5b. In fact, there is a decrease from 23 to 24 November: the increase took place on 25–26 November. Also in this case, no rainfalls occurred in those days. The decrease at this site can be explained by taking into account that near Caposele Spring the same behaviour is exhibited.

Figures 5d and 5e show the hydrological anomalies consisting of the strong increase in flow rate of Pollentina and Bagno Springs, very near each other at Cassano Irpino. It seems that this increase started about ten days before the seismic event. A further sharp increase took place soon after the earthquake.

We retain that these increases cannot be imputable to the rainfalls that preceded the seismic event. In fact, Fig. 6 shows the trends of monthly cumulated flow rates of these two springs compared to the rainfalls in the decade 1975–1985. This figure also reports the flow rate of the Caposele Spring. The lag among rainfalls and increases in the flow rates is consistent: some months, with Caposele preceding Cassano Irpino.

Fig. 6. (see text)

306 Earthquake Research and Analysis – Seismology, Seismotectonic and Earthquake Geology

Fig. 5d. November 23rd, 1980 earthquake

**Nov-24 Nov-23**

**Daily rainfall (mm)**

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at Caposele (f).

**Daily rainfall at Caposele (mm)**

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Fig. 5. Acqua Fetente spring (a); Zittola river at Montenero (b); Streamflow level of Calore Irpino at Montella (c); Cassano Irpino springs: Pollentina (d) and Bagno (e); Sanità spring

In Fig. 5c the anomaly seems to be the opposite of that shown in Fig. 5b. In fact, there is a decrease from 23 to 24 November: the increase took place on 25–26 November. Also in this

Dec-03

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**Spring flow rate (liters/sec)**

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**Daily rainfall at Caposele Flow rate of Sanità spring in Caposele**

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Fig.5f. November 23rd, 1980 earthquake

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**Flow rate (liters/sec)**

Daily rainfall (mm)

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**Fig.5e. November 23rd, 1980 earthquake**

**Nov-25**

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**Daily rainfall at Cassano Irpino Flow rate of Bagno spring**

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**Daily rainfall at Cassano Irpino Flow rate of Pollentina spring**

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**Dec-31**

Flow rate (liters/sec)
