Publication Date:
2021-04-07
Description:
In 1989 a joint work was developed in co-operation with the University"Sapienza"of Rome and Servizio Geologico d'Italia (SGI) (today ISPRA). A
gravity research started in the Aquila area aimed to realize a gravity
network for high precise gravity measurements to detect gravity changes
due to mass redistribution in the underground inferred by the geodynamic
activity.
The gravity network has been designed so as to incorporate 17 stations,
settled in 1989 and periodically reoccupied in 1990, 1992, 1995, 2005
and 2011. The local gravity network coincides with some benchmarkes of
the local leveling networks (L126, L197, L124 and L9) [Giuliani & Mattone,
2010] in order to remove the effect of the vertical ground movements and
taking into account the spatial distribution of seismic events. High
precision gravity combined with levelling benchmarks offers increasing
potentialities for the study of time variations of the earth gravity field and
crustal deformations related with geodynamic or tectonic processes.
Presently, the network consists of 17 relative stations which are not
destroyed during the earthquake. Gravity readings were made using two
LaCoste & Romberg D model gravimeters (D-60 and D-138) at the same
time. Presently, and similar to previous studies the new gravity data set
has been referred to the Absolute gravity station established in 1977 at
the Osservatorio Astronomico di Monte Porzio Catone [Cannizzo et al.,
1978].
The gravity readings, for both gravimeters, are corrected for tidal effects,
atmospheric loading and instrument drift. Later, as regard the gravity
survey, the corrected and weighted gravity differences between each pair
of stations are organized on joined loops and then adjusted according to
the least square method; finally the gravity value at any station is
computed relative to the local reference station (Fonte Cerreto-Assergi (4)
station) and linked to the absolute gravity station.
During the time period covered by this study, six precise relative gravity
surveys were also carried out at all stations of the network. Long-term
spatial distribution of gravity changes performed before and repeated after
earthquake is represented. Gravity changes have been observed on the
whole area, before and after the earthquake period.
The gravity distribution shows different patterns in the eastern, central
and western part of the seismic area. The gravity variation field is
smoother in the central part of L'Aquila city and it shows a gravity
decrease from the stations located in the northen part of the city.
Qualitative gravity results are not totally in agreement with vertical
changes measured by local leveling networks. It is possible to suppose
that the observed gravity changes should indicate a mass variation in the
underground, not in the shallow part but in depth.
Moreover, the results obtained from high precision gravity measurements
show that, the most significant long-term observed gravity changes on
Aquila area, were recorded not in the area corrisponding to the
seismogenic belt but in a largest zone. However gravity changes were
observed in the same magnitude before and after the earthquake.
Description:
Published
Description:
Torino 19-23 settembre 2011
Description:
2T. Sorgente Sismica
Description:
4T. Sismologia, geofisica e geologia per l'ingegneria sismica
Description:
6T. Variazioni delle caratteristiche crostali e precursori
Description:
1SR. TERREMOTI - Servizi e ricerca per la Società
Keywords:
gravity network
;
L'Aquila
;
earthquake april 2009
;
gravity changes
;
gravity variations
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
Conference paper
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