Seismic monitoring of soft-rock landslides: the Super-Sauze and Valoria case studies
Seismic monitoring of soft-rock landslides: the Super-Sauze and Valoria case studies
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DOI：
10.1093/gji/ggt039
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发表时间：
2013-06-01
影响因子：
2.8
通讯作者：
Joswig, Manfred
中科院分区：
文献类型：
--
作者：
Tonnellier, Alice;Helmstetter, Agnes;Joswig, Manfred
本文主要研究粘土页岩滑坡中观测到的震源特征。两个滑坡被认为是：超级索泽（法国）和瓦洛里亚（意大利）。这两个滑坡都是在改造后的粘土页岩中发育的，但在规模和位移速率上有所不同。尽管材料的地震衰减很大，但一个小型地震阵列已识别出数千个地震信号。测试了几种检测方法。通过与人工检测的对比，验证了半自动检测方法的有效性。根据地震信号的频率含量、视速度和纵横波的分异，将地震信号分为三类。假设第一组地震信号与滑坡体内部的剪切或断裂事件有关，而第二组地震信号可能对应于岩崩或泥石流。最后一组对应外部地震。采用自动波束形成定位方法定位震源。来源集中在滑坡的几个部分，与地貌观测一致。我们发现，在强降雨或融雪期后，岩崩和断裂事件的发生率增加。微震活动率和落石活动率也与滑坡位移率呈正相关。外部地震对微震活动和滑坡运动没有影响，可能是由于地震地面运动太弱，在观测期间没有触发滑坡事件。
This work focuses on the characterization of seismic sources observed in clay shale landslides. Two landslides are considered: Super-Sauze (France) and Valoria (Italy). The two landslides are developed in reworked clay shales but differ in terms of dimensions and displacement rates. Thousands of seismic signals have been identified by a small seismic array in spite of the high-seismic attenuation of the material. Several detection methods are tested. A semiautomatic detection method is validated by the comparison with a manual detection. Seismic signals are classified in three groups based on the frequency content, the apparent velocity and the differentiation of P and S waves. It is supposed that the first group of seismic signals is associated to shearing or fracture events within the landslide bodies, while the second group may correspond to rockfalls or debris flows. A last group corresponds to external earthquakes. Seismic sources are located with an automatic beam-forming location method. Sources are clustered in several parts of the landslide in agreement with geomorphological observations. We found that the rate of rockfall and fracture events increases after periods of heavy rainfall or snowmelt. The rate of microseismicity and rockfall activity is also positively correlated with landslide displacement rates. External earthquakes did not influence the microseismic activity or the landslide movement, probably because the earthquake ground motion was too weak to trigger landslide events during the observation periods.