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

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.

The Seismicity of Ischia Island, Italy: An Integrated Earthquake Catalogue From 8th Century BC to 2019 and Its Statistical Properties

“…The values of moment magnitude M w obtained for the destructive earthquakes of 1881 and 1883 (epicentral intensity I 0 IX and XI, respectively) are now 4.4 and 5.2, significantly higher than the ones reported in CPTI15 (4.1 and 4.3, respectively). Overall, our results are consistent with the seismogenic volumes proposed for Ischia in the literature (Carlino et al, 2006(Carlino et al, , 2010Castaldo et al, 2017;Cubellis and Luongo, 2018;Selva et al, 2019;Trasatti et al, 2019;Cubellis et al, 2020;Carlino et al, 2021). • The extension of the instrumental catalogue as far back as 1991 confirms the very low rate seismicity in recent times.…”

“…This is crucial to produce reliable and homogeneous information through time. Note that, at the present state, there is a large variability of the parameters in the literature even for the most studied events: for example, the magnitude estimations for the largest known event (1883) range in literature from 4.3 to 5.2 (CPTI15, Rovida et al, 2019Rovida et al, , 2020Cubellis and Luongo, 1998;Cubellis et al, 2020;Carlino et al, 2021).…”

“…Seismicity is mainly concentrated on the E-W structures that limit to the north the resurgent block of Mt. Epomeo (Carlino et al, 2006;Cubellis and Luongo, 2018;Trasatti et al, 2019;Cubellis et al, 2020;Carlino et al, 2021;Nappi et al, 2021;and references therein). Local seismicity may be connected to a relevant seismic hazard (Cubellis et al, 2004;Selva et al, 2019) and, in a multi-hazard view, it can be seen as one of the possible events in a multi-hazard chain that may include other phenomena like landslides or tsunami (e.g., Violante et al, 2003;Della Seta et al, 2012;Paparo and Tinti, 2017;Selva et al, 2019).…”

Campi Flegrei, Vesuvius and Ischia Seismicity in the Context of the Neapolitan Volcanic Area

“…Several destructive earthquakes have been located in the northern part of the island with shallow hypocentre and estimated magnitude between 3.6 and 5.2: in 1,228 (700 casualties), 1796 (7 casualties), 1828 (30 casualties), 1881 (126 casualties), 1883 (2,333 casualties), and 2017 (2 casualties) Luongo, 1998, 2018;D'Auria et al, 2018;De Novellis et al, 2018;Cubellis et al, 2020;Selva et al, 2021;Carlino et al, 2021).…”

The Volcano-Tectonics of the Northern Sector of Ischia Island Caldera (Southern Italy): Resurgence, Subsidence and Earthquakes

“…The most devastating event was in 1883, which caused more than 2,300 victims and the whole destruction of the town of Casamicciola Terme (Carlino et al, 2010;Carlino et al, 2021). In spite of their inferred relatively low magnitude (Table 1), the high damaging level of these events has been mainly ascribed to the FIGURE 1 | Volcanological phases of Ischia volcanic field (Sbrana et al, 2018, modified).…”