Seismic Survey in Lesser Himalayan Thrust Belt, Western Nepal

Two hundred km of 2D seismic survey was carried out at the Lesser Himalayan Thrust Belts in Dailekh district, western Nepal. The main motivation is to elucidate geologic relationship between known oil and gas seeps, subsurface structure, stratigraphy area. This a challenging task which from its extreme structural geological complexity such as thrust faulting, tight folding, steep dip layers, strong lateral variations velocity. Seismic data were acquired with SERCEL 428XL system processed by GEOEAST computer software. In order increase signal-to-noise ratio (SNR), suppress interference, search for optimum acquisition parameters, series comparative tests on different charge depth size, group interval, CDP fold, geophone array, single high-sensitivity conducted. We also tested 2S3L (two lines shooting three receiving) wide line profiling. results indicate that hole 12 m, 4-16 kg size (less densely populated areas), geophone, 1S2L profiling 132 folds are parameters. On basis process experiment, processing workflow consisting preparation, prestack denoising, amplitude compensation, deconvolution, tomography static correction, velocity analysis, residual CRS stack, poststack migration, time migration (PSTM), (PSDM) selected. Maybe affected problem conflicting complex media, stack section does not show satisfactory characteristics. PSTM profile has moderate (S/N) ratio; shallow, medium, deep continuous reflections can be observed section. More details structures PSDM section, especially medium shallow layers than 3000 ms or 4000 m), but method more expensive highly consuming PSTM. So, reasonably used interpretation. By reference field mapping, characteristics, MT data, final interpretation identified interfaces 6 units (Paleoproterozoic Nabhisthan Fm., Paleoproterozoic Dubidanda Neogene Late Cretaceous Surkhet group, Carboneferous Early Cretaeous Gondwana Mesoproterozoic Upper Lakharpata Lower group) delineated Main Boundary (MBT), Ramgarh (RMT), Padukasthan (PT), (DT). bottom our top target zone about 4250 meters deep.