SGER: Geomorphic Response to the September1999 Taiwan Earthquake: Evolution of River Profiles Across the Scarp and Inference about Earthquake Recurrence Intervals

人们普遍认为，山地地貌演化的迪特里希构造强迫是通过沿山脉边界的断层形成的临界点的河流网络上游传播而发生的。1999年9月21日台湾7.6级地震提供了一个难得的机会来研究构造抬升信号是如何通过不断演变的地貌传递的。沿着中山西麓底部的60公里长的地表破裂，在几条主要河流上形成了2到8米高的瀑布。在我们工作的这一初步探索阶段，PIS将测量初始陡坎剖面和水道几何形状，测量河床沉积物尺寸分布，收集基岩样本进行强度和耐磨性测试，并记录过去隆起事件的地貌特征。他们预计，由于下伏泥岩和砂岩较弱，年降雨量大，粗泥沙负荷大，跨越海峡的断层崖将迅速演化。他们将利用现场调查和实验室测试的结果，在基岩河道切割的数值模型中，预测上游临界点的传播速度和方式。在随后的野外活动中，他们将重新调查不断演变的断层陡坎和航道条件，以与模型预测进行比较。除了提供对隆起事件如何在地貌中传播的洞察外，这项工作还可能有助于限制这种规模的地震的重复间隔，这些信息对研究这场灾难的工程师具有相当重要的实际意义。

0000893Dietrich Tectonic forcing of the evolution of mountainous landscapes is widely thought to occur through the upstream propagation through the river network of knickpoints created by faulting along range boundaries. The September 21, 1999, magnitude 7.6 earthquake in Taiwan offers a rare opportunity to study how the signal of tectonic uplift is transmitted through an evolving landscape. The 60 km long surface rupture, along the base of the western foothills of the Central Range, created waterfalls from 2 to 8 m high across several major rivers. In this initial exploratory phase of our work PIs will survey the initial scarp profiles and channel geometry, measure bed sediment size distributions, collect bedrock samples for strength and abrasion resistance testing, and document geomorphic features from past uplift events. They anticipate rapid evolution of the channel-crossing fault scarps because of the weak underlying mudstones and sandstones, the high annual rainfall and high coarse sediment load. They will use the results of the field surveys and laboratory testing in a numerical model of bedrock channel incision, to predict the rate and style of upstream knickpoint propagation. In subsequent field campaigns they will re-survey the evolving fault scarps and channel conditions to compare with model predictions. In addition to providing insight into how an uplift event propagates through a landscape, this work may help constrain the recurrence interval for earthquakes of this magnitude, information of considerable practical importance to engineers studying this disaster.