ANALYSIS OF DATA FROM PASSIVE SEISMIC SURVEY AT LANCEFIELD (AUSTRALIA)

Abstract

Lancefield Swamp, south-eastern Australia, is a site known for Pleistocene mega-faunal fossil deposition. The bones lying within clays in a dense, interlocked pile is known to be deposited by alluvial transportation and lie above extensive Quaternary basalt flows. Passive seismic (microtremor) methods, have been applied to profile the basement for paleochannel with a purpose to detect more bone bed sites for excavation purpose. In the present study, two methods are used to map the basement. The passive seismic data is processed with the help of MATLAB program, which is based on the methods that are used in the analysis in this project, namely Spatial Auto Co-relation method (SPAC) and Horizontal Vertical Spectral Ratio (HVSR) method. SPAC method characterized geological sections and recognised 80 m of pre-Miocene sediments below basalt cap and above granite basement. The velocity data obtained from SPAC method recognised site between station 22-23 on line B, spread 6 as a potential site of clay deposition along with station 3-5 on line A, spread 1. HVSR method validated the result of SPAC method by defining the presence of sites of interest within ‘brackets’ of sites. The working hypothesis used in the project is based on dual criteria. It also characterizes some other brackets of sites which could have low velocity layer (LVL) for which velocity data from SPAC isn’t available. Low velocity zones is obtained from SPAC methods as a reference point and show that our area of interest is bracketed by the HVSR signatures. However, HVSR gives a weak but interesting indicator of sites but velocities study of complex field process is required for further accurate results.