Reflection and refraction seismics in areas of complex geology. An example in the Northern Apennines

Abstract

An experimental survey, employing refraction wide-angle reflection seismic techniques (DSS: deep seismic soundings) was carried out in the Northern Apennines (North Italy).The main objective of the experiment was the application of DSS to better-define the structure of the upper crust, down to about 15 km depth, in the crucial Alps-Apennines boundary zone. A second objective was to understand the potential of DSS as a complementary tool in areas of complex geology, where the results of near vertical reflection (NVR) are generally poor. The results of the experiment show that DSS, if properly planned, can continuously follow deep markers, and therefore impart a greater significance to faint and discontinuous NVR, as well as data on the Pwave velocity of the seismic units.

The collisional knot in Liguria

“…As VVL bends, near Bobbio ( Fig. 5; compare ELTER & PERTUSATI, 1973;PIgRI ~;GROPPI, 1981;CASSINIS et al, 1990) into the generally south-trending Ottone-Levanto line (OL in Figs. 6a and 8), this latter would be compressive and would be a part of the Toscanide thrust system.…”

“…3 and 4 (for location of study area and seismic lines see Figs. 1 & 2) are the expanded interpretations, in terms of velocity distributions, of refraction data already partly presented by CASSINIS et al (1990), where also the computational procedures are discussed. The best controlled is profile 7, and in the interpretation it is given special weight.…”

“…In the last ten years a large number of drillhole and geophysical data have become available which may be integrated and combined with the results of recently refined field geological studies in order to better define the constraints on any model of the tectonics of what is here called the 'Ligurian knot'. In particular, recent refraction lines in the region of the Apennine-Alpine link (BIELLA et al, 1987; ALPS-APENNINES OROGENES STUDY GROUP, 1987;LOZEJ et al, 1990;CASSINIS et al, 1990;) may be tied into the detailed subsurface data from the Po basin and its southern border (PIERI & GROPPI, 1981;CASSANO et al, 1986). In addition, the problem of the lithospheric root may be viewed in the light of the deep data collected for the European Geo Traverse .…”

An analysis of the first-arrival times picked on the DSS and wide-angle seismic section recorded in Italy since 1968

“…Several seismic sections relative to the other projects were recorded by analogical devices, then digitised and controlled by the former IR-RS Institute of Milan CNR (Biella et al, 1994;Osculati et al, 1995;Ferrari et al, 1998) and recently processed by the IDPA Institute (Corsi, 1999a,b). The procedure adopted for digitis- Fan Cassinis et al (1990) ing the data was optimised so as to obtain an accurate temporal and spatial position of the seismograms and it led to significant improvements of data quality. The data of the Sicilia68 (Cassinis et al, 1969) project were available only as record sections manually reconstructed on paper by the analogical seismograms, therefore a digitising procedure including the scanning of the waveforms, the vectorialisation and the sampling of the traces was used.…”

Geophysical interpretation of a high‐resolution seismic refraction profile in the Northern Apennines

“…The sedimentary cover consists of a pile of overthrust units and in paficular, from bottom to top, Ligurian, s u b Ligurian and Tuscan Units. AGIP explored the area by means of a reflection survey for oil (Cassano et al, 1986) and sponsored our experiment in order to complete their knowledge of the area with wideangle data. To allow the comparison with reflection data, we employed a denser coverage than usual and then we proceeded with the normal trial-andemor interpretation (Cassinis et al, 1990). Subsequently we decided to perform a 2D tomographic inversion, one of the targets of our research, taking advantage of the high density of the data.…”