重新估計應變之間的分配沿班達弧南部的帝汶海槽和韋塔逆衝斷層

Abstract

正面和背面構造之間的應變分配機制以及分配比例長期以來一直是板塊構造演化和地震危險性評價研究的重點。 作為前後向構造對之一，南部的帝汶海槽和北部的韋塔爾斷層共同吸收和分隔了澳大利亞板塊和巽他板塊沿班達海南緣的板塊輻合運動。 早期的大地測量模型和運動模式 GPS 觀測表明，大部分板塊運動是沿著韋塔斷層發生的，使得帝汶海槽相對不活躍，不會產生大型俯衝帶地震。 在本研究中，我們採用了ESA Sentinel-1衛星的連續GNSS觀測和InSAR形變時間序列來獲取帝汶島的位移場。 我們還建立了二維後滑模型來估計正面和背面結構之間的應變分配，以評估該地區的地震危險性。 模擬結果表明，只有帝汶海槽的耦合才能解釋帝汶島的垂直運動，而韋塔爾逆衝斷層的耦合可以更好地解釋海溝的正常水平運動。 事實上，這兩種結構都不能同時適應水平和垂直運動，這表明這兩種結構都在積極適應板塊邊界的縮短。 這一發現還表明帝汶海槽沿線有可能發生大型板塊邊界地震。

The mechanism for strain partitioning between the frontal and the back structure, as well as the proportion of partitioning, has long been of great interest to the study of plate tectonic evolution and seismic hazard evaluation. As one of such front-rear structure pairs, the Timor Trough to the south and the Wetar Fault to the north together absorb and partition the plate convergence motion between the Australian plate and the Sunda plate along the southern rim of the Banda Sea. Earlier geodetic modeling with campaign-mode GPS observations suggests that the majority of plate motion has been taken up along the Wetar Fault, leaving the Timor Trough relative inactive and free from generating large subduction zone earthquakes. In this study, we adopted continuous GNSS observations and InSAR deformation time-series from ESA’s Sentinel-1 satellites to obtain the displacement field of Timor Island. We also carried out 2D back-slip models to estimate the strain partitioning between the frontal and the back structure in order to assess the seismic hazard in the region. Modeling suggests the Timor trough can accommodate vertical slip, the Wetar thrust can accommodate trench normal slip, and neither can accommodate both. Our findings have significant implications for the earthquake potential at the Timor trough.