Shear‐wave velocity profiling at sites with high stiffness contrasts: a comparison between invasive and non‐invasive methods

Abstract

Three sites of the Italian Strong Motion Network (RAN) have been selected for detailed S-wave profiling, using both borehole and surface wave seismic methods. At these sites, the presence of stiffness contrasts within the Soil column is found to influence the surface wave propagation profoundly. Advanced aspects in surface wave inversion such as resolution, accuracy and higher-mode interpretation must be properly taken into account to obtain realistic results from the surface wave dispersion observations. The possibility of mode misidentification and the loss of resolution with depth in surface wave interpretation are explored using synthetic modelling together with active and passive seismic data sets. With high stiffness contrasts, the possibility of mode jumps and higher mode dominance over specific frequency ranges is very probable. This is true also for normally dispersive sites, where the shear velocity increases with depth, though higher mode dominance is recognized as more common in the case of a shear-wave velocity inversion within the soil column and the sensitivity of the dispersion curves with respect to those layers beneath the low-velocity zone may be significantly reduced. Pitfalls in the inversion resulting from mode misidentification can be avoided by investigating the effective phase velocity distribution, using active data sets and full waveform seismic modelling. When an unambiguous modal identification is achieved, the results obtained by surface wave inversion are very satisfactorily consistent with borehole data

Seismic characterization and monitoring of Fucino Basin (Central Italy)

“…These deposits, partially buried, could mask the resonant effect of the underlying lacustrine sedimentary body and could be responsible for inversion of S-wave velocity in this part of the basin. The effect of velocity inversions close to the edge of an alluvial basin caused by gravel deposits has been already observed in analogous situations (Di Giulio et al 2006;Cercato et al 2010;Compagnoni et al 2010). The last station of PA profile (PA06) is located downtown Avezzano, in coincidence with the R.A.N.…”

Evaluation of site effects in the Aterno river valley (Central Italy) from aftershocks of the 2009 L’Aquila earthquake

“…1 and b Sect. 2 are inferred from geological and geotechnical studies (WorkingGroup ITACA 2010;Cercato et al 2010; Gruppo di Lavoro MS-AQ 2010); c Sect. 3 is redrawn fromBosi and Bertini (1970) using the same geological units of the other sections.…”

“…Toponyms and location of the seismic stations and the velocity profiles are also shown the structural complexity of the area, as the oldest continental deposits (AP) are displaced by sets of almost parallel, NW-SE trending normal faults to form sort of terraces suspended at various height. The cross-hole test performed at Barisciano(Cercato et al 2010, …”

L’Aquila earthquake (April 6th 2009, Central Apennine, Italy): site effect, coseismic evidence and historical development of the Collebrincioni area

“…This absence of amplification phenomena in clastic sediments has been observed in other similar geological conditions in L'Aquila Basin and can be related both to their good characteristic of the cementation and to their textural characteristic. In the Pleistocene alluvial fan deposits, like in Barisciano, it is clearly evident that the clastic deposits [mainly clast supported conglomerates (G facies in Miall 1978)] are strongly cemented and may have shear wave velocities comparable to those of the carbonate bedrock with measured velocity higher than 700 m/s (Bergamaschi et al 2011, Cercato et al 2010.…”