The European Union's Copernicus Sentinel-1 satellites, together with the COSMO-SkyMed constellation, provided important data related to the 2017 Ischia earthquake.
On 21 August 2017, the island of Ischia in the Campania region of southern Italy was struck by an Md 4.0 (Mw 3.9) quake on the magnitude scale.
Two people lost their lives, thousands were displaced, many evacuated and extensive damage occurred to the Casamicciola Terme town and its surroundings, along the northern structural rim of Mount Epomeo, followed by a seismic sequence of almost 20 earthquakes with significantly lower magnitude.
The 2017 Ischia earthquake represents the largest seismic event ever observed with modern techniques over the island. The Institute for Electromagnetic Sensing of the Environment (IREA) of the National Research Council of Italy (CNR), activated by the Department of Civil Protection (DPC) as Centre of Competence in radar data processing, analysed and measured the Earth surface displacements induced by the earthquake using Sentinel-1 and COSMO-SkyMed data.
Founded in 2001 as a result of the reorganisation process of CNR, the institute research activities are focused on remote sensing, diagnostics, and monitoring of natural and environmental risks.
By exploiting radar data acquired by the Sentinel-1 satellites of the Copernicus programme, as well as by those of the Italian COSMO-SkyMed (CSK) constellation-owned by the Italian Space Agency (ASI) and the Italian Ministry of Defence-a team of researchers at CNR-IREA measured the earthquake-induced ground displacements through the Differential SAR Interferometry (DInSAR) technique.
This technique uses radar images acquired before and after an event to measure the ground displacement along the sensor Line of Sight (LOS), which occurred in the interval between the two acquisitions with centimetric accuracy. Moreover, thanks to the satellite's ascending and descending passes, it is possible to compute the vertical component of the deformation field. In particular, it detected a subsidence up to 4 centimetres in a region close to the Casamicciola Terme town, the area most affected by damage.
The fault, associated with the event, was located at a small depth in the northern sector of the island, at the base of Mount Epomeo. Its identification was made possible thanks to a multidisciplinary approach that allowed the integration of seismological and GPS data (global positioning system) by the National Institute of Geophysics and Volcanology (INGV) - Vesuvius Observatory networks with satellite radar data processed by the CNR-IREA.
The joint inversion of the DInSAR and continued GPS co-seismic measurements allowed experts to estimate the fault plane parameters and to retrieve the associated slip distribution. They found a main patch of slip (with values up to 14 cm) located at the centre of the fault plane at a depth of about 800 m, which is rather shallow and provides a possible explanation, together with local amplification effects, to the damage caused by this relatively low magnitude earthquake.
This result provides a picture of the seismogenic mechanism of the earthquake, dominated by a normal fault mechanism where the hanging block (located in the northern part of Mount Epomeo) moves downward. Furthermore, it confirms that the seismicity of the northern side of the island is associated with a local seismogenic structure that is stressed, and periodically reactivated, by the loading of Mt. Epomeo along its maximum elevation sector.
Riccardo Lanari, CNR-IREA Director, stated, "This dramatic episode represents a key example in the natural disaster scenario because the satellite-based mapping of the co-seismic surface displacements were essential for the comprehension of the occurred event."
About the Sentinels
The Sentinels are a fleet of dedicated EU-owned satellites, designed to deliver the wealth of data and imagery that are central to Europe's Copernicus environmental programme.
In partnership with EU Member States, the European Commission leads and coordinates this programme, to improve the management of the environment, safeguarding lives every day. ESA is in charge of the space component, responsible for developing the family of Copernicus Sentinel satellites and ensuring the flow of data for the Copernicus services, while the operations of the Sentinels have been entrusted to ESA and EUMETSAT.