Structural Analysis of Onshore and Offshore Northeast Taiwan (II)

依據反射震測剖面所顯示的地質構造形 態，台灣東北部外海至南沖繩海槽之間的區 域，可分為西北部的東海陸架區，東南的沖 繩海槽區，以及其間的台灣新畿褶皺帶。 東海陸架區以東北－西南走向的正斷層 為主，形成一系列的半地塹式盆地，主要的 活動期在古第三紀，其後至今的活動趨於微 渺。沖繩海槽區也以東北－西南走向的正斷 層為主，形成一系列的地塹與地壘，主要的 活動期自晚上新世至今。台灣新畿褶皺帶也 以東北－西南走向，晚上新世－第四紀的正 斷層為主，然而它們是晚第三紀逆斷層轉化 而來。台灣新畿褶皺帶的地質構造可分別向 南連接至台灣陸上的褶皺衝斷帶，向東南延伸至沖繩海槽張裂盆地。綜合而言，整個研究區域中，第三紀壓 縮型的構造已不再活動，逆斷層多被轉化成 第四紀正斷層，全區處於琉球島弧系統的伸張型大地應力狀態。大地構造; 構造地質; 反射震測; 台灣東北部; 琉球Based on the seismic reflection profiles collected between offshore northeast Taiwan and south Okinawa Trough, 3 structural regions are recognized, namely the East China Sea Shelf in the northwest (ECSS), Okinawa Trough in the southeast (OT), and Taiwan-Sinzi Folded Zone (TSFZ). ECSS is dominated by Paleogene NE-SW normal faults and associated half-graben basins. OT is dominated by NE-SW noraml faults and associated grabens and horsts having been activating since late Pliocene. TSFZ is dominated by Pliocene-Quaternary NE-SW normal faults reacitvated from Neogene reverse faults. The geological structures in TSFZ can be traced southwards to the fold-and-thrust belt in onshore Taiwan, and southeastwards to rifting basins in the Okinawa Trough. It is found that the studied onshore and offshore northeast Taiwan is subjected to undergoing extensional tectonism associated with the Ryukyu Arc system