Inversion of TEM responses to create a near surface velocity stucture
Permafrost in Russia occupies about 5 x 106 km2 (Brown et al., 1997), and many known mineral deposits and oil and gas fields fall within this zone. Seismic data from northern petroleum provinces, including West Siberia, may be of low quality because of perma¬frost effects. Permafrost is localized in a relatively thin near-surface layer of variable thickness and produces velocity anomalies, which have to be taken into account in interpretations. Neglect of the permafrost influence on the geometry of reflectors may cause significant errors in modelling and yield low-quality wave patterns over the entire time range (Figure 1). Correction of residual static shifts with classical methods (smoothing time variations in traveltime curves) may produce artificial synclines in the section. Long-wavelength statics com¬bined with noise pose problems to data processing (Tabakov et al., 2016). Corrections for local lateral variations in permafrost thickness can be applied by layer replacement after detailed velocity analysis. Velocity values for permafrost correction are taken along the reflectors associated with permafrost or along a conventional sub-permafrost level. We suggest a new approach to data correction, using inversion of transient electromagnetic (TEM) data to elastic properties of shallow subsurface.