The coseismic ground deformations of the 1997 Umbria-Marche earthquakes: a lesson for the development of new GPS networks

M Anzidei M Anzidei,E Serpelloni E Serpelloni,P Baldi P Baldi

doi:10.4401/ag-3029

M Anzidei M Anzidei, E Serpelloni E Serpelloni + Show 1 more

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https://doi.org/10.4401/ag-3029

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Abstract

After the occurrence of the two main shocks Mw=5.7 (00.33 GMT) and Mw=6.0 (09:40 GMT) on September 26, 1997, which caused severe damages and ground cracks in a wide area of the Umbria Marche region, the Istituto Nazionale di Geofisica in cooperation with the Istituto Geografico Militare Italiano set out to detect the coseismic ground deformation and reoccupied the available geodetic monuments placed across the epicentral area, belonging to the first order Italian GPS network IGM95 and to the Tyrgeonet network. The comparison between the pre and post-earthquakes coordinate set, the latter obtained from the surveys performed in the early days of October 1997 in the Umbria Marche earthquake area, showed maximum displacements values at the closest stations to the epicentres, up to 14.0±1.8 and 24.0±3.0 cm in the horizontal and vertical components, respectively. The availability of the IGM95 stations allowed geodetic data to be translated into relevant geophysical results. For the first time in Italy, the evaluation of post-earthquake coordinates at 13 vertices provided the estimation of a significant deformation field associated with a seismic sequence. Unfortunately, the same actions could not be applied to the October 14, 1997, Mw=5.6 Sellano earthquake, whose epicentre was located a few tens of km south of the previous ones, due to a lack of available geodetic vertices of Tyrgeonet and IGM95 networks in the surroundings of the epicentral zone. This fact, which prevented the estimation of coseismic deformation and seismic source modelling for this earthquake, clarified the need to set up tailor made GPS networks devoted to geophysical applications, able to capture a possible coseismic signal, but also interseismic and post-seismic signals, at the surface of the Earths crust at the scale of the expected magnitudes and fault length. Here we show and discuss the development of the Discrete GPS and Continuous GPS (CGPS) networks in the Italian region started since the early 1990s, which greatly increased after the 1997 Umbria Marche earthquakes, and the insights gained from this action which can be also integrated as Global Observing Strategy to monitor our Environment from Earth and Space.

Highlights

The Italian peninsula is among the most active seismic areas of the Mediterranean basin andM
The inhomogeneous coverage of the IGM95 and Tyrgeonet networks, the quality or type of the benchmarks, the on average short time-window of available observations and the lack of Continuous GPS (CGPS) stations in the earthquake region, prevented us benefitting from optimal geodetic constraints for the geophysical modelling of the causative faults of the Umbria Marche earthquakes, especially in the surroundings of the epicentre of October, 14, 1997, near Sellano, where there was a lack of available GPS benchmarks
Besides the large development of the IGM95 network mainly devoted to topographic applications, three major new GPS networks, CAgeoNet, REtreating TRench Extension and Accretion Tectonics (RETREAT) and Capo Vaticano, together with the INGV Rete INtegrata GPS (RING) CGPS network, are briefly described as follows. These new GPS networks, designed after the experience gained during the 1997 Umbria-Marche seismic crisis, are located across some of the most seismic areas of Italy and they have been repeatedly measured during recent years

Summary

Introduction

Serpelloni strumental seismicity depicts the high crustal fragmentation of the area and provides a picture of the plate boundary mosaic with tectonic units developed during the subduction and collision of the Alpine and Apennine belts (Dercourt et al, 1993; Malinverno and Ryan, 1986; Patacca et al.,1990; Chiarabba et al, 2005). From seismic tomography it appears that the initially continuous Apennines subduction has been segmented into different arcs, due to the nature of the lithospheric subducting material (Piromallo and Morelli, 2003).

The Umbria Marche seismic sequence of September-October 1997

A lesson for the development of new GPS networks

The new GPS networks

The new CGPS networks