GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 1.2 157 or upflow of thermal fluids through fractures. In Fig.1 we plotted the downloaded isolines of surface heat flow. The overlapping between recorded seismicity (de Lorenzo et al. , 2017) and heat flow map (Della Vedova et al. , 2001) in the Gargano area, shown in Fig. 1b, highlights an evident correspondence that we investigated using a thermo rheological model (Dragoni et al. , 1996). We subdivided the Gargano area in two zones Z NE and Z SW with different surface heat flux. In correspondence of these two zones: 1) we observed the hypocenter depth distribution from the recoderd seismicity; 2) we inferred two different geotherms from the surface heat flow values to built a thermo- rheological model that can fit the sismogenic layer depth. The seismic activity in the Z NE can be observed down to a maximum depth of about 28 km with very few deeper events, while the maximum frequency is observed at a depth of about 23-24 km. The seismic activity in the Z SW can be observed down to a maximum depth of about 9 km with a dozen deeper events while the maximum frequency in this case is observed at a depth of about 7 km. The thermo-rheological model (Dragoni et al. , 1996), using the two proposed geotherms, is able to reproduce the depth of the brittle-ductile transition from which we can infer the thickness of the seismogenic layer beneath the Gargano area. The comparison between the model results and the hypocenter depths allows us to find a match between the heat flow surface anomalies and seismicity. The results indicate that the brittle/ductile transition in the western zone Z SW is significantly shallower than it is in the eastern zone Z NE . References Camassi, R., Bernardini, F., Castelli, V. & Meletti, C. A 17th century destructive seismic crisis in the gargano area: Its implications on the understanding of local seismicity. J Earthq. Eng 12, 1223–1245 (2008). DOI 10.1080/13 632460802212774. Del Gaudio, V. et al. A critical revision of the seismicity of northern apulia (adriatic microplate - southern italy) and implications for the identification of seismogenic structures. Tectonophys. 436, 9–35 (2007). DOI 10.1016/ S0031-8914(53)80099-6. de Lorenzo, S., Michele, M., Emolo, M. & Tallarico, A. A 1d p-wave velocity model of the gargano promontory (south-eastern italy). J Seism. (2017). DOI 10.1007/s10950-017-9643-7. Della Vedova, B., Bellani, S., Pellis, G. & Squarci, P. Deep temperatures and surface heat flow distribution. In Vai, G. B. & Martini, I. P. (eds.) Anatomy of an Orogen: the Apennines and Adjacent Mediterranean Basins, chap. 7, 65–76 (Kluwer Academic Publishers, Dordrecht, 2001). Dragoni, M., Doglioni, C., Mongelli, F. & Zito, G. Evaluation of stresses in two geodinamically different areas: Stable foreland and extensional backarc. PAGEOPH 146, 319–341 (1996). Milano, G., Giovambattista, R. D. & Ventura, G. Seismic constraints on the present-day kinematics of the gargano foreland, italy, at the transition zone between the southern and northern apennine belts. GEOPH RES LETT 32, L24308 (2005). Tallarico A., Earth and Environmental Science Department, University of Bari, Italy. OTRIONS project (2013). URL http://www.otrions.uniba.it/. Trumpy, E. & Manzella, A. Geothopica and the interactive analysis and visualization of the updated italian national geothermal database. Int. J. Appl. Earth Obs. Geoinformation 54, 28–37 (2017).