A semi-automated algorithm to quantify scarp morphology (SPARTA): application to normal faults in southern Malawi
A semi-automated algorithm to quantify scarp morphology (SPARTA): application to normal faults in southern Malawi
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DOI：
10.5194/se-10-27-2019
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发表时间：
2019-01
期刊：
影响因子：
3.4
通讯作者：
M. Hodge;J. Biggs;Å. Fagereng;A. Elliott;H. Mdala;F. Mphepo
中科院分区：
文献类型：
--
作者：
M. Hodge;J. Biggs;Å. Fagereng;A. Elliott;H. Mdala;F. Mphepo
抽象的。陡坎形态的沿走向变化反映了断层地貌和构造发育的差异，因此可以指示断层破裂历史和机械分段。定义悬崖形态的参数（高度、宽度、坡度）通常是手动测量或计算的。耗时的手动方法降低了测量的密度和客观性，并可能导致忽略以不切实际的分辨率发生的小规模形态变化。此外，在手工方法的不一致性也可能导致未知的差异和不确定性之间，也内，个别故障陡坎的研究。在这里，我们的目标是通过开发半自动Scarp PARameTer算法（斯巴达）来提高计算悬崖形态参数的效率、透明度和均匀性。我们将我们的研究结果与传统的手动分析进行比较，并使用一系列数字高程模型（DEM）分辨率评估算法的性能。然后，我们将我们的新算法应用到12米分辨率TanDEM-X DEM的四个南部马拉维断层陡崖，位于南部的东非裂谷系统的末端：比拉Mtakataka故障（BMF）和三个以前未报告的陡崖- Thyolo，Muona和Malombe。除了Muona外，所有的Muona都在其表面表现出一阶结构分割。通过使用从Bilila-Mtakataka断层崖的高分辨率（50 cm像素-1）Pleiades立体卫星图像获得的5 m分辨率DEM，我们量化了二级结构分割。我们对所有四个断层陡坎的陡坎高度计算表明，如果每个陡坎都是由一次完整的破裂形成的，那么每次地震的滑动长度比都超过了世界各地历史上正常断层地震中观察到的最大典型值。因此，高滑动长度比意味着马拉维断层陡坎可能形成于多次地震。陡坎高度分布意味着BMF和Thyolo断层的结构段通过几个地震周期的离散断层破裂（硬链接）合并，Malombe断层的段通过分布的变形区（软链接）连接。因此，对于这里研究的所有断层，地震破裂的长度可能超过每一段的长度。因此，我们的研究结果揭示了新的光在马拉维南部的地震灾害，表明一些大（Mw 7-8）的史前地震的证据，以及提供了一个新的半自动化的方法（斯巴达）计算陡崖形态参数，可用于其他断层陡崖，以推断结构的发展。
Abstract. Along-strike variation in scarp morphology reflects differences in a fault's geomorphic and structural development and can thus indicate fault rupture history and mechanical segmentation. Parameters that define scarp morphology (height, width, slope) are typically measured or calculated manually. The time-consuming manual approach reduces the density and objectivity of measurements and can lead to oversight of small-scale morphological variations that occur at a resolution impractical to capture. Furthermore, inconsistencies in the manual approach may also lead to unknown discrepancies and uncertainties between, and also within, individual fault scarp studies. Here, we aim to improve the efficiency, transparency and uniformity of calculating scarp morphological parameters by developing a semi-automated Scarp PARameTer Algorithm (SPARTA). We compare our findings against a traditional, manual analysis and assess the performance of the algorithm using a range of digital elevation model (DEM) resolutions. We then apply our new algorithm to a 12 m resolution TanDEM-X DEM for four southern Malawi fault scarps, located at the southern end of the East African Rift system: the Bilila–Mtakataka fault (BMF) and three previously unreported scarps – Thyolo, Muona and Malombe. All but Muona exhibit first-order structural segmentation at their surface. By using a 5 m resolution DEM derived from high-resolution (50 cm pixel−1) Pleiades stereo-satellite imagery for the Bilila–Mtakataka fault scarp, we quantify secondary structural segmentation. Our scarp height calculations from all four fault scarps suggest that if each scarp was formed by a single, complete rupture, the slip–length ratio for each earthquake exceeds the maximum typical value observed in historical normal faulting earthquakes around the world. The high slip–length ratios therefore imply that the Malawi fault scarps likely formed in multiple earthquakes. The scarp height distribution implies the structural segments of both the BMF and Thyolo fault have merged via rupture of discrete faults (hard links) through several earthquake cycles, and the segments of the Malombe fault have connected via distributed deformation zones (soft links). For all faults studied here, the length of earthquake ruptures may therefore exceed the length of each segment. Thus, our findings shed new light on the seismic hazard in southern Malawi, indicating evidence for a number of large (Mw 7–8) prehistoric earthquakes, as well as providing a new semi-automated methodology (SPARTA) for calculating scarp morphological parameters, which can be used on other fault scarps to infer structural development.