QUICK ESTIMATES OF SOFT SEDIMENT THICKNESSES FROM AMBIENT NOISE HORIZONTAL TO VERTICAL SPECTRAL RATIOS: A CASE STUDY IN SOUTHERN ITALY

An approach devoted to quickly assess the thickness of soft sedimentary cover in areas of unknown subsurface morphology is applied in this study. In particular, soil thickness (h) is derived by combining estimates of the resonance frequency (f _r ) relative to soft sediments with the local shear-wave velocity (V_s) profile. For this purpose, (f _r ) values are assessed from horizontal to vertical (H/V) spectral ratios of seismic noise recordings and the (V _s ) profile is obtained by considering information from shallow seismic surveys. Results obtained for a Quaternary sedimentary basin in Southern Italy are discussed. Since in the investigated area only weak independent constraints are available, special emphasis is given to the assessment of uncertainties involved in this estimate of soil thickness.     

THE BROCH CULTURES OF ATLANTIC SCOTLAND. PART 2. THE MIDDLE IRON AGE: HIGH NOON AND DECLINE c.200 BC–AD 550

The basic features of broch architecture are discussed. There were probably a large number of classic, hollow-walled, dry-stone towers, as opposed to lower, less architecturally sophisticated 'Atlantic roundhouses'. Various kinds of dating imply that most were built – probably by professionals – in the Middle Iron Age, from c.100 BC to AD 200, although a few emerged earlier in Shetland, perhaps from 400–300 BC. Wheelhouses seem to have emerged from these early Shetland brochs. The MIA material culture includes many new items found all over the province, though much of the pottery is regional. Everted Rim ware was clearly connected somehow with the spread of the brochs from Shetland. The details of the MIA mixed farming economy are reviewed, as is the varied if indirect evidence for the social organization of the broch families; a hierarchical clan society is implied. The MIA now seems to have lasted until the sixth century AD and in the west at least its end may have been precipitated by a drastic climatic downturn.