A photographic collection of the coseismic geological effects induced by the 21 August 2017, M=4, Casamicciola earthquake (Ischia island, Italy)

Abstract

On 21 August 2017, a shallow earthquake of Md 4.0 struck the Casamicciola Terme village in the north of Ischia volcanic island (Italy). The earthquake has the typical characteristics of volcano­tectonic events recorded at active volcanoes and occurred along the E­W normal system fault bounding the northern slope of Mt. Epomeo. The epicentral area has been repeatedly damaged in the last three centuries (1796, 1828, 1881, 1883) [Alessio et al., 1996; Carlino et al., 2011; Cubellis and Luongo, 1998]. In this work, we present a collection of pictures showing the geological effects produced on either the natural or the built environment by the Casamicciola earthquake. Most of the coseismic geologic effects were observed along the E­W piedmont belt of Mt. Epomeo, which extends for about 2 km between the village of Fango (Lacco Ameno) to the west and Bagni Square to the East (Fig. 1). Mapped effects define a belt which closely follows the trace of the Casamicciola E­W trending normal fault system, bounding the northern slope of Mt. Epomeo, previously known as a Latest Pleistocene to Holocene normal fault [Nappi et al., 2018]. The Emergeo Working Group conducted a field work, collecting data that were managed following the procedures codified after the earthquake sequences of Emilia 2012 and Amatrice­Visso­Norcia 2016­2017 [Emergeo Working Group, 2012, 2016; Pucci et al., 2017; Civico et al., 2018; Villani et al., 2018]. Photographic collections of the coseismic geological effects induced by these earthquake were also published [Emergeo Working Group, 2012; Emergeo Working Group, 2017 a, b]. Field measurements were greatly aided by the use of mobile devices equipped with a specific software employing GPS, compass and orientation sensors (Rocklogger© mobile app, www.rockgecko.com), which allowed for quick and accurate structural data collection and real­time sharing. The whole data set was stored and managed in a georeferenced database on an Environmental Systems Research Institute ArcGIS platform. Further data were acquired using remotely piloted aircraft systems (RPAS) equipped with a Sony Alpha 6000 camera and a Flir SC655 thermal camera. We collected more than 100 observations of several different coseismic effects across the epicentral area and its sourroundings. These include fractures, ruptures, and a few minor gravitational phenomena like collapses and small landslides in volcanoclastic deposits. Moreover we observed widespread effects related to shaking, such as the collapse of drywalls made of green tuff and lava and known locally as “parracine”. The photographic dataset consist of 72 pictures of coseismic geological effects along a E­W direction. The pictures are grouped in three areas of observation. Each picture reports a series of information such as type of effect, site of observation, and geographical coordinates (decimal degrees). The reference system/datum used is WGS84. In Figure 1 we show the map of the pictures sites along with the location of the mainshock of the seismic event.