Free water input into the New Britain subduction zone in Solomon Sea estimated from reflected seismic data

Abstract

AbstractIt is of great significance to examine the distribution of the fluid within the subduction zone to estimate the water flux into the subduction zone and to study the motion state of the subducting plate. The interaction of the Western Pacific Plate and the Indo‐Australian Plate controls the subduction and expansion of the Solomon Basin where the mechanisms governing plate activity remain unclear but are typically associated with high pore fluid pressures and stabilizing frictional conditions. Combining the long streamer seismic data (200) and nine well logs inside the work area, we used constrained sparse spike inversion to obtain the P‐wave impedance profile. Then we constructed reservoir rock physics models to predict the fluids distribution in New Britain Trench subduction system in Solomon Sea. The genetic algorithm was used to guide the inversion of the pore fluid distribution. The water content profile revealed the shallow structure of the New Britain Trench subduction system in Solomon Sea, including the water content within the basalt layers. We determined that in certain cases, faults identified from the reflection data were associated with low‐impedance anomalies, and this may indicate that they are zones of high porosity that act as conduits for fluid flow. The continuity of the distribution of water content under the New Britain Trench suggests that there is a large amount of free water that subducts deeply and may be important in controlling the motion state of the subducting plate. We assume that the water saturation is 1. Therefore, the free water flux entering the deep circle with the subducting plate is estimated to be 158 Tg/Ma/m totally, including 53.724 Tg/Ma/m in the sediment and 105.06 Tg/Ma/m in the basalt. This study provides insight into the structure of free water in the New Britain subduction zone and reveals the potential for the direct estimation of the 2D structural distribution of water content using geophysical survey data.