Combined magnetic and surface wave analysis of a coal fire affected site at Barora, Jharia Coalfield, India: evidence of subsurface cavity and low velocity layers

The Barora Coalfield is essential to the Jharia Coalfield as it contributes significantly to India's energy sector. The nearby areas of the Barora mine are prone to geohazards due to coal fires. The present study assesses such sites using magnetic and seismic surface wave methods. The study area has been selected based on the thermal images taken near the Barora Coalfield. Initially, the site is surveyed for magnetic data. The reduce-to-pole map of the magnetic anomaly map indicates the presence of fire beneath the surface. However, the data is found to be contaminated with near-surface magnetic debris. The centroid method analysis has been performed and found that the average curie depth is ~ 10.74 ± 0.9 m, indicating active coal fire beneath this depth. The multichannel analysis of the surface wave (MASW) method shows a variation of S-wave velocity between ~ 187 m/s to ~ 654 m/s, with an average of ~ 487 m/s. The coal seam (VIIC) at the shallow depth has been identified. The velocity gradient changes drastically after a depth of ~ 11 m, indicating sudden variation in the velocity layer. The ambient noise tomography method provides similar evidence about the coal seam (VIIC); however, the deeper coal seams remain concealed. Hence, integrated analysis of passive and active seismic data has been carried out, and it has been found that the coal seams (VIIB and VIIA) situated at ~ 25 and ~ 29 m of depth have also been affected by coal fire.