High precision leveling survey following the Md 4.0 Casamicciola earthquake of August 21, 2017 (Ischia, Southern Italy): field data and preliminary interpretation

Abstract

The aim of this paper is the presentation of the results obtained from the high precision leveling survey carried out from November 6 to 11, 2017, in the area hit by the Md 4.0 Casamicciola earthquake of August 21, 2017, and critical discussion of these results in the light of the possible seismic source models. The measurements have been carried out on benchmarks of the northwestern sector of the altimetric network of the Ischia island, in the epicentral area. The heights of each benchmark have been obtained considering the historical reference benchmark n.1 located at Ischia Porto, and have been compensated over the whole stretch of the measured network; such heights have also been compared with those derived from the previous leveling campaign that was performed along the entire network in June 2010. The results obtained from the specific investigated leveling lines, which are considered representative of the kinematics of the northwestern area of the island, show conspicuous anomalies of ground deformation in the epicentral area of the August 21, 2017 earthquake.In particular, a significant ground subsidence of about 3.5 centimeters has been found between the benchmarks n. 92 and n. 98A along the "Borbonica Line", quite anomalous compared to the previous measurements. Such subsidence located between the Piazza Maio (Casamicciola) and Fango (Lacco Ameno) localities, results spatially correlated with the deformation detected by the InSAR data analysis and coincides with the greatest macroseismic damages and with the coseismic surface fracture systems E-W oriented. Future leveling campaign in the area would be very crucial in order to follow and define the rate of postseismic motion of the seismogenetic source, also contributing with independent and valuable data to the seismic hazard knowledge of the Ischia island.

Improving the Accuracy of Digital Terrain Models Using Drone-Based LiDAR for the Morpho-Structural Analysis of Active Calderas: The Case of Ischia Island, Italy

“…Epomeo has accommodated a maximum vertical displacement of ca. 1 km [30][31][32][33]45,48,52,53]. In the foothill area of Casamicciola Terme, a structure, part of the E-ENE fault system, separates Mt.…”

“…In the instrumental era, a stage of subsidence has been dated by geometric leveling data collected in 1913, 1987, 2003, 2010 [52,63] and references therein], and 2018 [52], topographic measurements by continuous Global Positioning Systems (GPS; [64,65]), and Interferometric Synthetic Aperture Radar (InSAR) imagery. This subsidence stage is reported to be at a rate of up to 10 mm/yr, primarily affecting the south-central region of the island.…”

The 2017, MD = 4.0, Casamicciola Earthquake: ESI-07 Scale Evaluation and Implications for the Source Model

“…The high precision leveling from 1987, 2003, 2010, and 2018 campaigns, together with the measurements from continuous Global Positioning System (cGPS), tiltmetric monitoring networks, as well as Interferometric Synthetic Aperture Radar (InSAR) imagery have shown the existence in the past decades, since 1913, of a phase of general subsidence, of as much as 10 mm/yr across the south-central part of the island [50][51][52], including a local NW ground subsidence, observed also after the 21 August 2017, Casamicciola earthquake [18].…”

“…The Casamicciola earthquake is in fact the first damaging seismic event occurred in Ischia island which has been relatively well documented by seismological, geodetic, geophysical and geological data, can propose different source models for the earthquake [1][2][3][4][17][18][19][20][21].…”

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

“…On the evening of the 21st August 2017, a M w 3.9 earthquake struck the island of Ischia, causing 2 casualties, many injuries, and extensive damage in the village of Casamicciola, on the northern coast of the island (Azzaro et al, 2017). The earthquake was very shallow (depth <1 km), with a source striking E-W in the northern sector of Ischia revealed by ground deformation and surface fracturing (e.g., Gruppo di Lavoro INGV, 2017;Braun et al, 2018;De Novellis et al, 2018;Nappi et al, 2018Nappi et al, , 2019Calderoni et al, 2019;Ricco et al, 2019). Different solutions of the source geometry have been proposed from the joint interpretations of seismic and geodetic data, or field geological data alone, differing in the dip-angle and the fault plane geometry at depth, and its generation mechanism (Braun et al, 2018;De Novellis et al, 2018;Devoti et al, 2018;Calderoni et al, 2019;Cubellis et al, 2020).…”