A brief analysis of ZTEM data from the Forrestania test site, WA

Summary

ZTEM is a helicopter-borne AFMAG system that measures the magnetic-field response in the frequency range 25-600 Hz of naturally occurring currents in the subsurface. The resolution of this system is analyzed by forward modeling and inverting synthetic ZTEM data using a 2D algorithm for a range of conductivity scenarios.

ZTEM data acquired at the Forrestania test site are compared with overlapping VTEM data. Conductivitydepth sections derived from both data sets show broad agreement, but indicate better spatial resolution for the VTEM data. The response due to bedrock conductor IR2 is strong for the VTEM system and subtle on the ZTEM profiles, which appear to be dominated by responses to larger, elongated structures. Products derived from the ZTEM data, including apparent conductivity, phase and Karous-Hjelt filtered grids appear to map geologic structure, complementing the information gathered from the VTEM data.

Key words::

• AFMAG
• airborne electromagnetics
• EM data modeling
• inversion
• natural-field EM.