Foraminiferal evidence for the amount of coseismic subsidence during a late holocene earthquake on Vancouver Island, West Coast of Canada
Foraminiferal evidence for the amount of coseismic subsidence during a late holocene earthquake on Vancouver Island, West Coast of Canada
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加拿大西海岸温哥华岛全新世晚期地震期间同震沉降量的有孔虫证据
DOI：
10.1016/s0277-3791(96)00058-3
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发表时间：
1996
影响因子：
4
通讯作者：
M. Lapointe
中科院分区：
文献类型：
--
作者：
J. Guilbault;J. Clague;M. Lapointe
在不列颠哥伦比亚省温哥华岛西海岸托菲诺附近的一个海湾海岸上，两个相距6公里的地点的有孔虫数据允许对100-400年前大地震期间的同震沉降量进行估计。这两个地点的采样沉积物序列相似;代表以前沼泽表面的泥炭突然被潮间泥覆盖，潮间泥向上渐变为现在沼泽的泥炭。在其中一个地点，一层被解释为海啸存款的沙子，局部地将被掩埋的泥炭与上覆的潮间带泥分开。泥炭-泥的突然接触记录了地震时地壳的突然沉降。通过比较其有孔虫组合与已知海拔的现代组合，估计每个化石样本的古海拔。现代组合获得了从表面样品收集的沿着横截面横跨沼泽附近的化石样品的网站。使用传递函数进行统计比较。根据埋藏泥炭顶部上下的古海拔差异，估计同震沉降的范围为20厘米至1米，最有可能的值为55-70厘米。震后地壳反弹在地震后不久就开始了，可能在几十年后基本完成。
Foraminiferal data from two sites, 6 km apart, on the shores of an inlet near Tofino on the west coast of Vancouver Island, British Columbia, allow estimates to be made of the amount of coseismic subsidence during a large earthquake 100–400 years ago. The sampled sediment succession at the two sites is similar; peat representing a former marsh surface is abruptly overlain by intertidal mud grading upward into peat of the present marsh. At one of the sites, a layer of sand, interpreted to be a tsunami deposit, locally separates the buried peat from the overlying intertidal mud. The abrupt peat-mud contact records sudden crustal subsidence during the earthquake. The paleoelevation of each fossil sample was estimated by comparing its foraminiferal assemblage with modern assemblages of known elevation. The modern assemblages were obtained from surface samples collected along transects across the marsh near the fossil sample sites. Comparisons were made statistically using transfer functions. Estimates of coseismic subsidence, based on differences in paleoelevations just above and below the top of the buried peat, range from 20 cm to 1 m, with the most likely value in the 55–70 cm range. Post-seismic crustal rebound began soon after the earthquake and may have been largely complete a few decades later.