Seafloor Erosion induced by overbanking flow derived by a 2.5D high resolution sparker seismic dataset, uppermost Kaoping Submarine Canyon, southwestern offshore Taiwan

The Kaoping submarine canyon (KPSC) originates from Kaoping River, southwestern Taiwan that extends about 250 kilometers long from the Kaoping River mouth down to the Manila Trench. It can be divided into three major sections: upper reach (meandering), middle reach (NW-SE trending and V-shaped canyon) and lower reach (meandering). Based on recent a swath bathymetric data in the uppermost KPSC, an obvious seafloor depression can be observed in the eastern bank of the canyon. The eastern bank of the canyon reveals about 30-50 meters in average lower than western bank. The mechanism is blurred. In this study, to investigate fine sedimentary structures in 3D point of view, we used marine sparker seismic method. The seismic source frequency varies from 100 to 1200 Hz which can provide about 0.6 meters vertical resolution (i.e. central frequency 600 Hz and 1,600 m/s Vp). We have collected 75 in-lines across the canyon and 3 cross-lines perpendicular to the in-line. The data went through conventional marine seismic data processing procedures such as bad trace kill, band-pass filter, 2D geometry settings, NMO stacking, swell correction, match filter and predictive deconvolution. The 2D dataset was reformatted by applying 3D geometry settings to create a 3D seismic cube. The result shows that a wide incision channel was first found in the north of Xiaoliuchiu islet. Through depth, this channel becomes two narrower channels divided by a mud diapir. This down cutting can be traced down to transgressive sequence in prior to LGM (Last Glacial Maximum). In addition, a deep-towed sub-bottom profiler shows an obvious down-lapping structures heading off canyon that indicates over banking flow may be a key role to cause this erosional event.