碩士 / 國立臺灣大學 / 地質科學研究所 / 106 / Distinct staircase topography of marine terraces along the eastern flank of the Coastal Range obviously denotes the active tectonic uplift of the Huatung coast in Holocene. Differences of marine terrace occurrences between the northern and the southern Huatung coast indicate that uplift mechanisms of the terrace system vary from place to place. Previous researches put much efforts on calculating long-term uplift rates in order to scrutinize how tectonic structures deform the coastline, but the environmental evolution and how marine terraces were formed remained equivocal due to the cover of alluvial and fluvial deposits on top of the terrace surface. Since that formation of marine tarraces are strongly influenced by underlying structures, clarification of how Holocene marine terraces were formed increases the understanding of related fault systems. Field excursions across coastal and river profiles from Linding to Chengkung are conducted in this research, trying to discover record of terrace evolution. By measuring height of paleo wave-cut platforms, recognizing sediment occurrences and collecting samples for 14C dating, we reconstruct how paleo sea level change and tectonic upift affected terrace formation which imply the tectonic signature of the Huatung marine terraces.
By comparing differences of terrace occurrences, including width of terrace surface and height of terrace riser, we classify marine terraces into two groups, T1-T6 for terraces in the north (Lindind to Zhangyuan area), and TI-TV for those in the south (Baxian cave to Chengkung area). Four tectonic sub-regions are identified with different long-term uplift rates, naming Lingding, Shinshe, Changbin and Shitiping region, with uplift rates ranging 2.5, 4.5-4.8, 6.3-6.4, and 4.5-5.0 mm/yr, respectively. As sea level rose quickly in 16-8 ka, all these sub-regions undergone relative transgression, accumulating thick marine deposits on the bedrock. As sea level reached its culmination at 7 ka and persisted stable since then, tectonic uplift became the dominant forcing for shaping the coast, turning the environment into relative regression. Forming with dissimilar uplift rates, marine terraces of four sub-regions occurred in different types. In Lingding and Shinshe region, marines terraces usually consist of narrow terrace surfaces and high terrace risers, suggesting that terraces were uplifted by locked faults with big coseismic uplift, possibly earthquakes of millenial time scale. In Changbin and Shitiping region, terraces are composed of wide terrace surfaces and low terrace risers, indicating deformation of creeping faults with small coseismic and fast interseismic uplift.
Although the spatial distribution of four sub-regions well correlates with the segmentation of the Longitudinal Valley Fault, vertical displacements of paleo-earthquakes recorded in the Huatung Valley didn’t show much evidence of coastline uplifting events. Through the elastic half-space modelling proposed by Okada(1985), we find out that once the earthquake magnitude (Mw) reaches 7.4, the coseismic uplift of Linding and Ruisui fault could attain 2-3 m around coastal area, which matches heights of terrace risers in the north. For terraces in the south, as proposed by results of modelling, the 1.4 m terrace riser should be uplifted by a Mw 7.2 event, a magnitude that is hard to reach for Chihshang fault, an active creeping faults. Terraces in the south should be developed by high erosion rate accompanied with frequent small coseismic uplift and fast steady interseismic uplift.
| Identifer | oai:union.ndltd.org:TW/106NTU05138027 |
| Date | January 2018 |
| Creators | Ching-Yuan Yang, 楊清淵 |
| Contributors | Wen-Shan Chen, 陳文山 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 171 |
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