The microtremor method was trialed on soft Holocene sediments overlying glacial gravels near the Hutt River, Wellington New Zealand. A triangular four-station array of radius [Formula: see text], processed using a modified spatial autocorrelation (SPAC) method was sufficient to establish shear velocity for sediments and gravels, and a thickness of [Formula: see text] for the soft sediments. The interpretation was performed blind to geological and geophysical data, and subsequent comparison with seismic cone penetrometer and seismic refraction data shows the accuracy from the SPAC interpretation to be better than 5%. Interpretation of horizontal: vertical spectral ratio data assists with estimates of thickness of the glacial gravels (hundreds of meters) but accuracy in thickness is poor, perhaps due to uncertainty in the 2D nature of the base of the gravel-filled glacial valley.
An analysis of damage costs to domestic property in the Mw 7.2 Inangahua, New Zealand, earthquake of 23 May 1968 (U.T.) has allowed the evaluation of the vulnerability of domestic property for six intensity zones, from MM5 - MM10 inclusive. For no other earthquake worldwide has the vulnerability of any class of property been examined in so many intensity zones, and the effect of brittle chimneys on damage levels has been fully evaluated for the first time. The relative vulnerability of one and two storey houses has also been evaluated. The costs of damage were derived from about 8,000 insurance claims to the Earthquake and War Damage Commission. Damage ratios were evaluated for houses and their contents as functions of Modified Mercalli intensity. The indicators of vulnerability that were determined were the statistical distributions and mean values of damage ratios and the percentage of property items damaged for the six intensity zones. Comparisons have also been made with results from studies of other earthquakes.
In a recent study the present authors examined the damage ratios for houses and household contents in the Inangahua, New Zealand, earthquake for intensities MM7-MM10, as affected by microzoning and structural types. The present study modestly revises this work, and extends it to include the localities of Nelson (MM6.4) and Murchison (MM8.1). Four ground classes and two foundation types, i.e. unbraced piles and concrete perimeter wall foundations were considered, and also number of storeys and wall cladding. Some complexities and difficulties of reliable microzoning are revealed and discussed.
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