The Seismicity of Ischia Island

Abstract

Ischia is a volcanic island, west of the caldera of Campi Flegrei, southern Italy. Since the deployment of a modern seismic network in 1970, until the 21 August 2017 earthquake, the seismicity of Ischia has been characterized by low-magnitude (Md ≤ 2:3) earthquakes located in the northern part of the island, mostly beneath the town of Casamicciola Terme at very shallow depths (∼500 m). Some of these events seem to have occurred on the same seismogenetic structure in the northern part of the island. This area coincides with that where the devastating events of 1881 and 1883 occurred and where the small-magnitude seismicity recorded between 1927 and 1936 was located. The August 2017 seismic sequence affected the same area. The current network configuration is able to locate shallow events with Md ≥ 1:0 and to detect smaller earthquakes or other types of natural and artificial events (e.g., blast fishing, geothermal well explosions; see The Seismic Network section). Here, we present the catalog of earthquakes recorded on Ischia between 1999 and February 2018 and compare the August 2017 seismic sequence with the background seismicity. Furthermore, we identified a sequence of events possibly linked to the explosion of a geothermal well on the island.