A common source for the destructive earthquakes in the volcanic island of Ischia (Southern Italy): insights from historical and recent seismicity

Stefano Carlino,Vincenzo De Novellis,Anna Tramelli,Vincenzo Convertito,Nicola Alessandro Pino

doi:10.1007/s11069-021-04675-z

Abstract

The island of Ischia, located in the Gulf of Naples, represents an unusual case of resurgent caldera where small-to-moderate magnitude volcano-tectonic earthquakes generate large damage and catastrophic effects, as in the case of 4 March 1881 (Imax-VIII-IXMCS) and 28 July 1883 (Imax X-XI MCS) historical earthquakes, and of the recent 21 August 2017 MW = 3.9, event. All these earthquakes struck the northern area of the island. With about 65,000 inhabitants, Ischia is a popular touristic destination for thermals baths, hosting more than 3,000,000 visitors per year, thus representing a high seismic risk area. Assessing its seismic potential appears a fundamental goal and, to this end, the estimate of the magnitude of significant historical events and the characterization of their source are crucial. We report here a reassessment of historical data of damage of 1881 and 1883 earthquakes to evaluate the main source parameters of these events (obtained with the BOXER and EXISM software) and quantitatively compare, for the first time, the results with the source characteristics, obtained from instrumental data, of the recent 2017 earthquake. The results allowed us to assess the location, as well as the possible dimension and the related maximum magnitude, of the seismogenic structure responsible for such damaging earthquakes. Our results also provide an additional framework to define the mechanisms leading to earthquakes associated with the dynamics of calderas.

Highlights

The seismicity of active volcanic areas is generally characterized by low magnitude earthquakes (McNutt and Roman 2015)
The results suggest the presence of a unique seismogenic structure, which can be periodically reactivated during the present quiescent phase of the volcano, providing new elements to assess the processes that could generate earthquakes in subsiding calderas
In order to proceed with the simulations for the 1881 and 1883 earthquakes, we first assessed the magnitude of these events, which have been used together with the other parameters, as input data of BOXER

Summary

Introduction

The seismicity of active volcanic areas is generally characterized by low magnitude earthquakes (McNutt and Roman 2015). A well-known case is the active volcanic island of Ischia (located in the Gulf of Naples), where recent and historical earthquakes have caused heavy damage and thousands of fatalities (Cubellis and Luongo 1998; Carlino et al 2010) (Table 4, Appendix) (Fig. 1). These events appear to be associated with a phase of subsidence of the central part of the island (Trasatti et al 2020). The resurgence was accompanied by volcanic activity outside the block (last eruption in 1302) and produced the exhumation of a high-temperature hydrothermal system, with geothermal gradients > 150 °C km−1 (Vezzoli 1988; Sbrana et al 2009; Sbrana and Toccaceli 2011; Carlino 2018)

Results

Discussion

Conclusion