GNGTS 2013 - Atti del 32° Convegno Nazionale

whole procedure is appreciable in frame c 1 , where an improvement in the continuity of the reflections, preserving the available resolution, is clearly evident. Conclusions. Source and/or receiver array simulation is widely employed in deep seismic reflection surveys to tackle the high level of source related noise that may affect the reflection records. This methodology can also be extended to near surface reflection seismic investigations, where simple energy sources such as sledgehammers or weight drops are used along with equipment of limited recording channels. In general, due to the operational flexibility of the low channel number recording spread and to the low cost energy source, it is possible to acquire a redundant number of single source – single receiver gathers with only a small additional effort in the field work. This implies just a slight increase of the acquisition time and leaves untouched the budget, laying the basis for the application of this technique. The availability of many traces pertaining to closely spaced sources and receivers allows to simulate source and/or receiver arrays that act as spatial filters aimed at attenuating the source related coherent noise. The desired array response may be attained by properly weighing the array elements and the optimal weights can be determined through the use of Chebyshev polynomials. Because of the uniform response of the polynomials in the stop-band region, Chebyshev weighted arrays prove to be more effective than equal weighted arrays in the noise attenuation even if a less restrictive notch was set. From the experience we carried out it results that simulating arrays in the processing lab brings an improvement in the data quality and can be achieved at the expense of a slight increase in the acquisition effort and in the processing work. Finally, through the array simulation we can either achieve a data reduction (for instance we can halve the number of source gathers), maintaining proper anti-aliasing conditions, or else we can keep as many simulated array source gathers as many original single blow gathers. The same applies for receiver simulated arrays. Acknowledgements. The seismic data processing was carried out using the ProMax® software of Landmark Graphics Corporation that is gratefully acknowledged. The code for the array simulation has been developed internally. We would also like to thank Prof. Alfredo Mazzotti for his useful suggestions and interesting discussion. References Carlini A. and Mazzotti A.; 1989: Optimized receiver array simulation based upon resolution constraints. Geophysical Prospecting, 37, 607-621. Federici P. R., Puccinelli A., Chelli A., D’Amato Avanzi G., Ribolini A. and Verani M.; 2002: The Large Landslide of Patigno (Northern Apennines, Italy): geological, geomorphological and geognostic integrated analysis. In Rybar, Stemberg and Wagner (eds), “Landslides”, Swets and Zeitlinger, Lisse, pp. 547-552. Ge J., Magnani M.B. and Waldron B.; 2010: Imaging a shallow aquitard with seismic reflection data in Memphis, Tennessee, USA. Part II: data analysis, interpretation and traveltime tomography. Near surface Geophysics, 8, 341- 351. DOI: 10.3997/1873-0604.2010025. Holzman M.; 1963: Chebyshev optimized geophone arrays. Geophysics, 28, 145-155. Malehmir A., Bastani M., Krawczyk C.M., Gurk M., Ismail N., Polom U. and Persson L.; 2013: Geophysical assessment and geotechnical investigation of quick-clay landslides – a Swedish case study. Near surface Geophysics, 11, 341-350. DOI: 10.3997/1873-0604.2013010 Miller R. and Steeples D.; 1994: Applications of shallow high-resolution seismic reflection to various environmental problems. Journal of Applied Geophysics, 31, 65-72. Pugin A., Pullan S., Hunter L. and Oldenborger G.; 2009: Hydrogeological prospecting using P- and S-wave landstreamer seismic reflection methods. Near surface Geophysics, 7, 315-327. DOI: 10.3997/1873-0604.2009033. Shtivelman V.; 2003: Application of shallow seismic methods to engineering, environmental and groundwater investigations. Bolletino di Geofisica Teorica ed Applicata, 44, 209-222. Steeples D. and Miller R.; 1998: Avoiding pitfalls in shallow seismic reflection surveys. Geophysics, 63(4), 1213-1224. Stucchi E., Ribolini A. and Anfuso A.; 2013: High resolution reflection seismic at the Patigno landslide, Northern Apennines, Italy. Accepted for publication in Near Surface Geophysics. Zelt C. A. and Smith R.B.; 1992: Seismic traveltime inversion for 2-D crustal velocity structure. Geophysical Journal International, 108, 16-34. 70 GNGTS 2013 S essione 3.1