Mt. Vesuvius: a macroseismic study of the earthquake of 9 October 1999

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Abstract

A macroseismic study of the earthquake of 9 October 1999, which took place at Vesuvius’ crater, was carried out. The event was not only the most energetic since the last eruption in 1944 but also one of the most energetic of those occurring in the Vesuvian area as shown by an analysis of historical seismicity. This paper contains the results obtained from an analysis of questionnaires sent out to all the schools in the Vesuvian and Neapolitan areas and the surrounding towns in the provinces of Caserta and Salerno. Over 10 000 questionnaires were administered, covering 92 sites, 18 of which were within the city of Naples. The percentage of positive reports concerning single effects was taken into account (the percentage response to Question 1 was called felt index). Thus maps of earthquake intensity and felt index were drawn up, whose isoseisms show maximum values near the volcano and radially decreasing values. The surveyed intensity plane is remarkably dense. As far as 30 km from the epicenter, the distance between two radially consecutive sites of the surveyed plane is, on average, lower than 500 m. The maximum degree turned out to be V for sites whose mean distance RV from the epicenter was 7.0±2.3 km, maximum intensity being found for the towns of Boscotrecase, Cercola and S. Sebastiano, characterized by some of the sixth degree characteristics. Typical parameters such as epicentral intensity (I0), attenuation coefficients (s), and absorption factor (b) were determined. Their values range between 6.0 and 6.4 (I0), 3.9 and 4.1 (s, Blake’s formula) and 0.1 for b, while magnitude (M) values range between 3.6 and 4.1. Furthermore, Q quality factor was determined by assuming direct proportionality between energy and felt index (A), peak frequency f=2–3 Hz and a wave velocity β=3.3 km/s. The values obtained are Q=60–90 and, subtracting geometrical spreading, Qa=100–150. Marked attenuation areas were found in the epicentral zone E and NE of the volcano and in the Phlegraean Fields associated with the source mechanism, scattering and the high temperature of a magmatic body. Historical eruptions were taken into account, which enabled us to gain an insight into seismicity associated with them. Also, effects expected for seismic events in the Vesuvian area were estimated, their magnitude ranging from 3 to 4.5.

Introduction

The seismic event of 9 October 1999, the most energetic since the 1944 eruption and one of the most energetic of those occurring in the Vesuvian area, once again drew public attention to Vesuvius since it was also felt outside the Vesuvian area and affected the city of Naples and its surroundings. As is well-known, explaining seismic source mechanisms in volcanic areas may be ambiguous owing to the complex processes involved (fracturation, fluid expansion) as well as the action of the medium, across which seismic waves spread (alternation of high acoustic impedance layers; rapid, frequent side variations in the medium’s physical characteristics). Under such conditions, interpretation is a crucial factor in forecasting eruptions and providing for public safety.

In this paper we present the results of an analysis of the macroseismic questionnaires sent out to schools in the Vesuvian and Neapolitan areas as well as surrounding towns in the provinces of Caserta and Salerno; the questionnaires were designed to mark the limits of the felt area and analyze energy spreading. Such a study makes it possible to obtain empirical formulas for magnitude intensity and seismic energy attenuation laws in quake-stricken areas. These are crucial factors in assessing seismic hazard in the Vesuvian towns and the neighboring city of Naples from seismic sources in the Vesuvian area.

Section snippets

Geological outline

An isolated symmetrical cone-shaped massif, Vesuvius stands in the Campanian Plain graben reaching a height of 1281 m. It consists of an older stratovolcano, Mount Somma, and a recent cone, Vesuvius, which has been quiescent since 1944. It is uncertain when Vesuvius began its eruptive activity. The oldest products from a 1220 m deep drilling date back about 300 000 years but the oldest outcropping ones are not older than 25 000 years. The earliest eruptive history of Vesuvius has been

Historical and present seismic activity

The oldest seismic events in the Vesuvian area that may be dated occurred in the first century A.D. when, a few days before the death of the emperor Tiberius, in 37 A.D., an earthquake brought down the lighthouse on Capri. On 5 February 62 A.D. an earthquake hit the whole Campania region causing considerable damage to Pompeii and Herculaneum and relatively minor damage to Naples and Nuceria. It was the most severe earthquake ever recorded in the Vesuvian area, M=6.1 according to Boschi et al.

The earthquake of 9 October 1999

The earthquake was felt over a very wide area within about 25 km from the crater, causing fear and anxiety among the people. Following the event, questionnaires were sent to all middle schools in the Vesuvian area, Naples and surrounding towns in the provinces of Caserta and Salerno in order to define the extent to which the earthquake had been felt. The questionnaires consisted of 18 yes/no questions (Branno et al., 1984). The students appeared to take considerable interest in the survey. The

Evaluating intensity and magnitude

The effects caused by an earthquake are measured in quantitative terms by using intensity scales (MCS, MM, MSK 64–78). Intensity degrees, up to VI, are actually the same for all scales. Higher degrees involving damage to buildings and effects on things vary as a result of different discriminating criteria, thus differing even by a degree. Macroseismic questionnaires are used for lower degrees (Karnik et al., 1976, Husebey et al., 1978, Postipishl et al., 1982, Branno et al., 1984, Marturano et

Quality factor (Q) and anomalies in the macroseismic field

The energy spreading from a seismic source decreases as distance from the hypocenter increases. In a purely homogeneous, elastic Earth, geometric spreading controls the amplitude of a seismic pulse. In actual fact, propagating waves attenuate with distance because of various energy loss mechanisms collectively described as due to anelastic processes (intrinsic attenuation). Such a decrease is quantified by parameter Q (e.g. Aki and Richards, 1980, Lay and Wallace, 1995):1/Q=ΔE/2πEwhere ΔE/E is

Conclusions

The earthquake of 9 October 1999 was the strongest recorded in the Vesuvian area since 1944, the year in which Vesuvius’ latest eruption took place, bringing to an end a cycle that had begun with the 1631 eruption. The present study is the first to provide a reliable, extended macroseismic field. It is thus possible to assess the importance of the historical information there is on Vesuvius’ seismicity, and gain many useful insights into the level of energy released in the area and the

Acknowledgments

We are grateful to Prof. B.D. Marsh and two anonymous reviewers for their helpful suggestions. We would like to thank Prof. R. Scandone and particularly Prof. G. Luongo for helpful comments and discussion.

References (62)

  • Aster, R.C., Meyer, R.P., De Natale, G., Zollo, A., Martini, M., Del Pezzo, E., Scarpa, R., Iannaccone, G., 1992....
  • W.H. Bakun et al.

    Estimating earthquake location and magnitude from seismic intensity data

    Bull. Seismol. Soc. Am.

    (1997)
  • F. Bianco et al.

    Attenuation of short period seismic waves at Mt. Vesuvius, Italy

    Geophys. J. Int.

    (1999)
  • A. Blake

    On the estimation of focal depth from macroseismic data

    Bull. Seismol. Soc. Am.

    (1941)
  • V. Bonasia et al.

    Eruptive history, seismic activity and ground deformations at Mt. Vesuvius, Italy

    Ann. Geofis.

    (1985)
  • Boschi, E., Guidoboni, E., Ferrari, G., Valensise, G., Gasparini, P., 1997. Catalogo dei Forti Terremoti in Italia dal...
  • A. Branno et al.

    The October 4th 1983 Magnitude 4 earthquake in Phlegraean Fields: macroseismic survey

    Bull. Vulcanol.

    (1984)
  • P. Capuano et al.

    A detailed analysis of some local earthquakes at Somma-Vesuvius

    Ann. Geofis.

    (1999)
  • Cassano, E., La Torre, P., 1987. Geophysics. In: Santacroce, R. (Ed.), 1987. Somma Vesuvius. Quad. Ric. Sci. 114,...
  • U. Chandra et al.

    Attenuation of intensities in Iran

    Bull. Seismol. Soc. Am.

    (1979)
  • U. Chandra

    Attenuation of intensities in the United States

    Bull. Seismol. Soc. Am.

    (1979)
  • E. Cubellis et al.

    The roots of Mt.Vesuvius from Gravity Anomalies

    Mineral. Petrol.

    (2001)
  • C. Dal Maso et al.

    Pompei, il racconto dell’eruzione

    Scienze

    (1999)
  • E. Del Pezzo et al.

    Qc of three component seismograms of volcanic microearthquakes at Campi Flegrei volcanic area (Southern Italy)

    Pageoph

    (1985)
  • Figliuolo, B., Marturano, A., 1998. The eruption of Vesuvius from 7th to the 12th centuries. Proc. 20th INHIGEO...
  • Gasperini, P., Ferrari, G., 1997. Stima dei parametri sintetici: nuove elaborazioni. In: Boschi, E., Guidoboni, E.,...
  • I.N. Gupta et al.

    Spatial attenuation of intensities for central US. earthquake

    Bull. Seismol. Soc. Am.

    (1976)
  • B. Gutemberg et al.

    Earthquake magnitude, intensity, energy, and acceleration

    Bull. Seismol. Soc. Am.

    (1942)
  • B. Gutemberg et al.

    Earthquake magnitude, intensity energy and acceleration

    Bull. Seismol. Soc. Am.

    (1956)
  • B.F. Howell et al.

    Attenuation of Modified Mercalli intensity with distance from epicenter

    Bull. Seismol. Soc. Am.

    (1975)
  • Husebey, E.S., Ringdal, F., Sandvin, O.A., Cristofferson, A., 1978. Statistical test theory in the analysis of...
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