Reverse Time Migration and Kinematic Migration Approaches for Imaging the Moho in the Outer-Rise Region of the Japan Trench

Imaging of the Moho discontinuity in the trench-outer-rise region of the Japan Trench is a challenging task due to the structural changes that occur in the oceanic crust. This area is shaped by bending-related faults and petit-spot volcanism, which introduce fractures, hydration, and high porosity to the crust. These processes influence seismic velocities and disrupt sedimentary layers. Volcanic activity adds further complexity by creating uneven structures like cracks, dikes, and sills, which weaken seismic signals and make it harder to detect the Moho. These structural changes call for advanced seismic techniques and detailed data to accurately map the crust-mantle boundary.

In this study we examine the structure of the oceanic plate near the Japan Trench, focusing on identifying the Moho discontinuity and related crustal features. Our study relies on a 100-kilometer-long 2D seismic dataset collected by JAMSTEC in 2017. The data were gathered using 40 Ocean-Bottom Seismometers (OBS) placed 2 kilometres apart, capturing wide-angle seismic signals. Such acquisition setting provides a robust framework for analysing the subsurface with the imaging techniques employed in this study.

We employ two imaging techniques that complement each other in addressing the geological complexities of the region. First, we use Reverse Time Migration (RTM) - wavefield-based imaging approach - to produce highly detailed image of discontinuities in the crust and uppermost mantle. RTM was instrumental in identifying the high-resolution Moho and characterizing the variations in the crust-mantle interface. The method allows for handling areas with complex geological structures, such as those affected by bending-related faults and volcanic intrusions, making it an invaluable tool for this study. In addition, we address the challenges of conventional seismic imaging in regions with highly fractured crusts caused by subduction-related bending. To overcome these challenges, we employ the second technique, known as kinematic migration of slope data. The slope represent the horizontal component of the slowness vector at reciprocal receiver position (air-gun shot position) and is calculated as the difference of picked arrival times of the Moho reflection divided by the receiver distance. This approach significantly reduces uncertainties in identifying the Moho discontinuity.

The combination of RTM and kinematic migration proved highly effective in imaging the Moho discontinuity and revealed valuable details about the crust-mantle boundary. By leveraging these complementary techniques, the study successfully overcame the challenges posed by the region's geological complexity. These results demonstrate the importance of high-resolution imaging in advancing our understanding of Earth's interior. The ability to map the Moho with precision not only improves interpretations of subsurface structures but also contributes to broader tectonic and geophysical research. This study underscores the critical role of innovative methodologies in exploring complex geological environments, paving the way for future discoveries.