Directional amplification and ground motion polarization in Casamicciola area (Ischia volcanic island) after the 21 August 2017 Md 4.0 earthquake

Abstract

In this paper, we investigated ground motion directional amplification and horizontal polarization using ambient noise measurements performed in the northern sector of Ischia Island which suffered damage (VIII EMS) during the 21 August 2017, Md 4.0 earthquake. Over 70 temporary seismic stations were installed by the INGV EMERSITO task force, whose aim is to monitor site effects after damaging earthquakes in Italy. To investigate ground motion directional amplification effects, we have applied three different techniques, testing their performance: the HVSR calculation by rotating the two horizontal components, the covariance matrix analysis, and time–frequency domain polarization analysis. These techniques resulted in coherent outcomes, highlighting the occurrence of directional amplification and polarization effects in two main sectors of the investigated area. Our results suggest an interesting pattern for ground motion polarization, that is mainly controlled by recent fault activity and hydrothermal fluid circulation characterizing the northern sector of the Ischia Island.

Directional Amplification at Rock Sites in Fault Damage Zones

“…The performance in the use of these three techniques to constrain directional amplification was recently tested on Ischia Island by [51], through over 70 ambient noise measurements. They confirmed coherent outcomes.…”

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

“…In the foothill area of Casamicciola Terme, a structure, part of the E-ENE fault system, separates Mt. Epomeo from the coastal area and forms the Casamicciola Holocene Graben (CHG) (Figure 2) [25,54].…”

“…It was characterized by a shallow hypocentral depth of around 1.2 km, with an E-trending normal fault plane as the seismogenic source [24,34,60]. The main factors contributing to the extensive destruction were as follows: (1) the shallow nature of the seismogenic source, (2) complications resulting from site-specific amplification due to geological variations in the epicentral area, and (3) the poor construction quality of the edifices during that period [24,54,61,62].…”

Técnicas de sísmica pasiva HVSR aplicadas a la geotecnia. Aplicación al estudio de Movimientos en Masa en la Planificación Territorial e Infraestructura Civil en Ecuador

“…La amplificación direccional de un sitio se produce a lo largo de un azimut determinado o específico de la zona en el plano horizontal. A lo largo del azimut amplificado, en el dominio del tiempo, esta amplificación direccional corresponde al movimiento del suelo polarizado linealmente (Pischiutta et al, 2012(Pischiutta et al, y 2022. La amplificación direccional tiene lugar sobre las dos componentes horizontales del movimiento del suelo, las cuales no presentan la misma amplitud, ya que el movimiento es focalizado (mayor) a lo largo de un azimut específico conocido también como "resonancia direccional del sitio" (Bonamassa y Vidale, 1991).…”

“…En estos casos, la estructura geológica del subsuelo juega un papel fundamental en lugar de estar relacionada con la fuente o trayectoria del frente de ondas o ruido ambiental, habiendo sido observado esto tanto en terremotos como en microtemblores (Pischiutta et al, 2022). Esta amplificación direccional ha sido investigada en varios ambientes geológicos tales como: deslizamientos gravitacionales (en roca o suelos), deslizamientos genéricos (Del Gaudio y Wasowski, 2007;Burjaneck et al, 2010;, zonas de falla (Pischiutta et al, 2012) y en ambientes volcánicos (Panzera et al, 2020).…”