Ischia island: strain field by GPS and Levelling data.

Vienna-Austria

Geophysical Research Abstracts
Vol. 13, EGU2011-13941-3, 2011
EGU General Assembly 2011
© Author(s) 2011
Ischia island: strain field by GPS and Levelling data.
Francesco Obrizzo and the INGV (CNT-OV) Geodesy Team
Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Napoli, Italy
In this paper, we discuss the results obtained by means high precision levelling and GPS surveys performed at
Ischia island in June 2010.
The levelling survey has been carried out on the whole network of the island. The compensated heights for each
benchmark (bm), referred to bm 1 located at Ischia harbour, were compared to those obtained in the previous
levelling survey performed during 2003.
The GPS network operating on Ischia Island consists of 21 3D vertices homogeneously distributed on the island.
Six different GPS surveys of the whole network were carried out since 1997, in order to investigate the subsidence
phenomena. The comparison among the 1997, 1998, 1999, 2001, 2003 and 2010 surveys results show that some
GPS points present significant horizontal displacements confirming slow but continuous deformations in the
Southern and North West sectors of the island.
The results show significant ground subsidence of various amplitude affecting different areas of the island. In addition,
a further comparison with the measurements performed in 1987 confirms the existence of such differential
movements characterised by subsidence velocity constant over time. Finally, we found a good agreement between
levelling and GPS velocities, calculated in time span 1997-2010.
Therefore, the integration of GPS and levelling data allowed to define the strain field on the island over the past 20
years.