Multi-component Seismic Microtremor – A New Tool for Characterising the Engineering Properties of the Shallow Sub-surface

The ability to quickly and accurately determine engineering properties has significant practical implications for the design, characterisation and ultimately, the economics and legal responsibility for many urban development areas. Although traditional invasive geotechnical methods can provide this information, they are not always safe or practical to use since many areas are underlain by contaminates or large cavities. The Multi-Component Seismic Microtremor (MCSM) tool is a non-invasive method that uses ambient background noise to characterise the velocity profile (thus determining strength) of the shallow subsurface. By relying solely upon surface waves generated through noise (people, traffic, trees and distant earthquakes, etc) the need for an active source, which is often adversely affected by the high noise levels in urban areas, is eliminated. Unlike many existing surface-wave methods, the MCSM method makes use of the whole wavefield (i.e. vertically polarized Rayleigh waves and horizontally polarised Love waves). The opportunity afforded by new geophysical techniques to produce improvements in the ability to understand and characterise the sub-surface in terms of its stability, strength and general geomechanical properties will be of considerable benefit to site owners, land agencies, industry, commercial developers and, most importantly, the general public.