[S-CG46] Uncovering stress accumulation and fault strengthening of megathrust earthquakes

[SCG46-P10] Submarine Fissures in the Accretionary Prism Offshore Taiwan: Evidence of Extensional Deformation

*Tzu-Ting Chen¹, Charles K. Paull², Ho-Han Hsu^1,3, Char-Shine Liu^1,3 (1.Institute of Oceanography, National Taiwan University, Taipei, Taiwan, 2.Monterey Bay Aquarium Research Institute, Moss Landing, California, USA, 3.Ocean Center, National Taiwan University, Taipei, Taiwan)

Keywords:Submarine fissures, Accretionary prism, Extensional deformation, Mega-earthquakes, SW Taiwan

High-resolution autonomous underwater vehicle (AUV) surveys reveal bands of fissures on the flat-floored surface of a closed sediment basin in the accretionary prism offshore southwestern Taiwan. These fissures, 1.5–17.0 m wide, 0.5–3.2 km long, and 0.15–3.50 m deep, are undetectable by shipboard multibeam at >1,150 m water depth. Sub-bottom profiles show a blurred east-dipping reflector beneath eastern fissures, suggesting near-vertical fractures associated with transient extensional deformation. We propose that these fissures formed due to short-lived extensional stress during the megathrust earthquake cycle, likely in the coseismic or postseismic phase, when slip on the Good-Weather Fault induced extension in the overriding plate. ROV observations indicate that the fissures have low-angle walls and are partially filled by collapsed sediment, suggesting progressive modification over multiple seismic events. Their presence provides evidence of how stress is accommodated within the accretionary prism, offering new insights into fault behavior and megathrust earthquake deformation over thousands of years.