Shallow splay fault properties of the Nankai Trough accretionary wedge inferred from seismic inversion

Studying fault properties from reflection seismic data is essential for seismic interpretations. A three-dimensional (3D) industry standard reflection seismic volume acquired over the Nankai Trough offshore the Kii Peninsula in Japan has been used to map the splay fault system since many parts of these faults appear as strong reflectors in the stacked seismic data. However, some parts of the splay faults are too steep to be well imaged by reflection seismic data. This may cause misinterpretation of the splay fault properties and seismogenesis. To better interpret the data, we applied a model-based inversion which combines seismic data with well log data to obtain elastic properties and rock properties. Our inversion uses both a low-frequency initial model and a hybrid which considers the fractal statistics of the well log data. The latter shows better estimation of model parameters and thus can provide us with more confidence in interpreting the impedance. The inverted results show that seismic inversion is able to provide clear images of the elastic and rock properties of the regions around and at the well locations. Impedance anomalies along the shallow splay faults suggest the change of fluids, weakness and other physical parameters. Interpretation of one strong reflector cutting through the drilling site C0001 based on the seismic images alone is ambiguous since it can be interpreted either as a sedimentary bed or a splay fault. Our inverted results demonstrate that this reflector is more likely splay fault breached.