Turbidite paleoseismology along the active continental margin of Chile - Feasible or not?
Turbidite paleoseismology along the active continental margin of Chile - Feasible or not?
复制标题
智利活动大陆边缘的浊积古地震学——可行与否？
DOI：
10.1016/j.quascirev.2015.04.001
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发表时间：
2015
影响因子：
4
通讯作者：
Strecker
中科院分区：
文献类型：
--
作者：
Bernhardt;Melnick;Hebbeln;Lueckge;Strecker
利用陆地、湖泊和海洋古地震资料估算俯冲带大地震和巨地震复发间隔的研究取得了很大进展。最近的详细记录表明，这些地震可能有不同的复发周期和震级，形成超周期。了解地震超周期需要长期的古地震档案，记录这些事件的时间和震级。浊积岩古地震档案可能会延长过去的地震记录更新世，因此可以补充通常较短期的陆地档案。然而，为了明确地建立经常性的地震活动作为浊流的触发机制，浊积岩的同步沉积在广泛的间隔，孤立的沉积中心必须加以确定。本文通过对智利大陆边缘沿着950 km的8个海洋沉积岩样的分析，探讨了利用浊流岩资料编制详细、连续的古地震记录的可行性。我们的研究结果表明，沉积广泛，同步浊积岩触发地震活动在很大程度上是由沉积物供应，因此，邻近的陆上设置的气候和地貌条件。编制浊积岩古地震记录的可行性取决于充足的沉积物供应和足够低的沉积速率之间的微妙平衡，沉积物供应提供在地震震动期间频繁失效的材料，沉积速率足够低，以允许同时代的浮游有孔虫积累用于高分辨率放射性碳测年。（29-32.5°S）全新世浊流古地震学是不可行的，因为来自半干旱大陆的沉积物供应量很低，并且在岩芯中几乎没有发现全新世浊流沉积。相反，在南纬36 °和38°之间的潮湿地区，频繁的全新世浊积岩沉积通常与古地震事件相对应。然而，高陆源沉积速率阻碍了高分辨率放射性碳测年。南纬32.5 ~ 36°之间的气候过渡区似乎最适合浊流古地震学研究。
Much progress has been made in estimating recurrence intervals of great and giant subduction earthquakes using terrestrial, lacustrine, and marine paleoseismic archives. Recent detailed records suggest these earthquakes may have variable recurrence periods and magnitudes forming supercycles. Understanding seismic supercycles requires long paleoseismic archives that record timing and magnitude of such events. Turbidite paleoseismic archives may potentially extend past earthquake records to the Pleistocene and can thus complement commonly shorter-term terrestrial archives. However, in order to unambiguously establish recurring seismicity as a trigger mechanism for turbidity currents, synchronous deposition of turbidites in widely spaced, isolated depocenters has to be ascertained. Furthermore, characteristics that predispose a seismically active continental margin to turbidite paleoseismology and the correct sample site selection have to be taken into account.Here we analyze 8 marine sediment cores along 950 km of the Chile margin to test for the feasibility of compiling detailed and continuous paleoseismic records based on turbidites. Our results suggest that the deposition of areally widespread, synchronous turbidites triggered by seismicity is largely controlled by sediment supply and, hence, the climatic and geomorphic conditions of the adjacent subaerial setting. The feasibility of compiling a turbidite paleoseismic record depends on the delicate balance between sufficient sediment supply providing material to fail frequently during seismic shaking and sufficiently low sedimentation rates to allow for coeval accumulation of planktonic foraminifera for high-resolution radiocarbon dating.We conclude that offshore northern central Chile (29–32.5°S) Holocene turbidite paleoseismology is not feasible, because sediment supply from the semi-arid mainland is low and almost no Holocene turbidity-current deposits are found in the cores. In contrast, in the humid region between 36 and 38°S frequent Holocene turbidite deposition may generally correspond to paleoseismic events. However, high terrigenous sedimentation rates prevent high-resolution radiocarbon dating. The climatic transition region between 32.5 and 36°S appears to be best suited for turbidite paleoseismology.
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