首页> 外文期刊>Engineering Geology >Microtremor HVSR study for assessing site effects in the Bovec basin (NW Slovenia) related to 1998 M_W5.6 and 2004 M_W5.2 earthquakes
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Microtremor HVSR study for assessing site effects in the Bovec basin (NW Slovenia) related to 1998 M_W5.6 and 2004 M_W5.2 earthquakes

机译:用于评估与1998年M5.6级地震和2004年M5.2级地震有关的Bovec盆地(斯洛文尼亚西北部)场地影响的微震HVSR研究

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摘要

The Bovec basin, which is filled with glacial and fluvial sediments, has recently been struck by two strong earthquakes (1998 and 2004) which caused extensive damage (VII-VIII EMS-98). Strong site effects resulted in large variations in damage to buildings in the area, which could not be explained by the surface variations in Quaternary sediments. The microtremor horizontal-to-vertical-spectral ratio (HVRS) method was therefore applied to a 200 m dense grid of free-field measurements to assess the fundamental frequency of the sediments. Large variations in the sediment frequency (3-22 Hz) were obtained, with most of the observed values in the range 6-12 Hz. The observed frequencies cannot be related to the total thickness of Quaternary sediments (sand, gravel), but can be explained by the presence of conglomerate or lithified moraine at shallow depths. The results were compared also with the velocity structure derived from seismic refraction data. Microtremor measurements performed in several two and some three- and four-storey houses (masonry with RC floors), which prevail in the Bovec basin, have shown that the main building frequencies in the area are in the range 7-11 Hz. This indicates that damage to houses in both earthquakes in some parts of the basin was enhanced by site amplification and soil-structure resonance. Areas of possible soil-structure resonance were identified in the settlements Bovec-Brdo, Bovec-Mala vas, Cezsoca and Kal-Koritnica. Considerable changes in fundamental frequencies within short distances were established in the town of Bovec. Their values are as high as 22 Hz in the central part of the town, but diminish to 6-11 Hz in the adjacent Brdo and Mala vas districts. This is in agreement with the distribution of damage in both earthquakes, which was considerably higher in Brdo and Mala vas, although the houses in the central part of the town are older. Microtremor investigations have proved an effective tool for assessment of site effects in cases of complex geological structure commonly encountered in young Alpine basins filled with glaciofluvial sediments which are partly cemented. Lithified layers can considerably change the fundamental frequency and, consequently, the site effects. By taking additional measurements in buildings possible soil-structure resonance can be identified.
机译:充满冰川和河流沉积物的博韦茨盆地最近遭受两次强烈地震(1998年和2004年)袭击,造成了广泛破坏(VII-VIII EMS-98)。强烈的场地效应导致该地区建筑物破坏的变化很大,这不能用第四纪沉积物的表面变化来解释。因此,将微震水平与垂直光谱之比(HVRS)方法应用于200 m密集网格的自由场测量,以评估沉积物的基频。获得了沉积物频率的较大变化(3-22 Hz),大多数观测值在6-12 Hz范围内。观测到的频率与第四纪沉积物(沙,砾石)的总厚度无关,但可以由浅深度存在砾岩或石化冰ora来解释。还将结果与从地震折射数据得出的速度结构进行了比较。在Bovec盆地盛行的几栋两层以及三层和四层的房屋(带RC地板的砖石房屋)中进行的微震测量表明,该地区的主要建筑频率在7-11 Hz范围内。这表明场地放大和土壤结构共振加剧了该盆地某些地区两次地震对房屋的破坏。在Bovec-Brdo,Bovec-Mala vas,Cezsoca和Kal-Koritnica等定居点确定了可能的土壤结构共振区域。在Bovec镇,近距离内的基本频率发生了相当大的变化。在镇中心,它们的值高达22 Hz,但在邻近的Brdo和Mala vas地区减小到6-11 Hz。这与两次地震中的破坏分布是一致的,尽管该镇中部的房屋较旧,但在Brdo和Mala vas中的破坏程度要高得多。对于在充满部分胶结的冰川河流相沉积物的年轻阿尔卑斯盆地中常见的复杂地质结构情况下,微震研究已证明是评估现场影响的有效工具。锂化层会大大改变基频,从而改变位点效应。通过在建筑物中进行其他测量,可能会发现土壤结构共振。

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