Seismic inversion for splay fault interpretation in the Nankai Trough accretionary wedge, Japan

Abstract

The updip limit of the seismogenic zone is known to occur along splay faults within accretionary complexes. In this paper, we analyze 3D seismic data from Nankai Trough, a convergent plate boundary where the Philippine Sea plate is subducting beneath Eurasian plate, to characterize the splay faults. Many parts of these faults are characterized as strong reflectors which can be directly observed in 3‐D seismic images, making these data ideal for studying fault properties that control thrust mechanics and seismogeneis at an active continental margin. To better interpret the data, we applied prestack seismic inversion to obtain elastic properties and rock properties of the splay faults structures. 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 splay fault with lateral spatial variation surrounding a series of boreholes drilled by the Integrated Ocean Drilling program. We observe that upper splay faults are characterized by high impedance with an underlying low impedance layer. Interpretation of one strong reflector cutting through the drilling site C0001 based on the seismic images alone is ambiguous (sedimentary bed or a splay fault). Our inverted results demonstrate that this reflector is more likely a splay fault. Based on the inverted results, we propose several possible interpretations related to fault activities.