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If earthquakes are modelled by a stochastic process, it is possible to interpret the associated response spectrum in terms of the statistics of extreme values of oscillator response to the process. For a stationary earthquake model this interpretation leads to a relationship between the power spectral density function of the process and the response spectrum. This relationship is examined in this paper and forms the basis for two methods presented to obtain the power spectrum of the earthquake process from its response spectrum. One of these methods is approximate but leads to an explicit representation of the power spectral density function in terms of the response spectrum. The other method is exact wherein an iterative scheme for the solution of the problem is established. An example problem is solved to illustrate the use of the two methods and it is shown that for small values of damping, the approximate derivation yields a fairly accurate solution.

Six phenotypic characters and three withanolide markers were assessed in 25 accessions of Withania somnifera collected from different states of India for studying genetic variability. The variability ranges observed at phenotypic and chemotypic levels were polymorphic. Based on D 2 values and PCA (Principal Component Analysis) of phenotypic traits like plant height, no. of branches/plant, no. of seeds/berry, root length, root diameter and root yield, these 25 accessions were grouped in five clusters. The relative contribution of each character towards genetic divergence was worked out. Five accessions-AGB002 (Rajasthan), AGB003 (J&K), AGB004 (Madhya Pradesh), AGB006 (J&K) and AGB009 (Punjab) representing clusters 2 and 4 exhibited maximum intra and inter-cluster divergence. Cluster 5 representing accession AGB053 (Andhra Pradesh) was having mixed traits. Chemically most of the accessions in cluster 3 showed uniformity in presence of three marker withanolides Withaferin A, Withanone and Withanolide A in the leaves.