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首页> 外文会议>Symposium on the Application of Geophysics to Engineering and Environmental Problems >DISCOVERING BURIED BEDROCK VALLEYS USING THE HVSR PASSIVE SEISMIC METHOD IN THE PICTURED ROCKS NATIONAL LAKESHORE AREA, MICHIGAN
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DISCOVERING BURIED BEDROCK VALLEYS USING THE HVSR PASSIVE SEISMIC METHOD IN THE PICTURED ROCKS NATIONAL LAKESHORE AREA, MICHIGAN

机译：使用HVSR被动地震方法在岩石国家湖岸地区，密歇根州发现埋藏的基岩山谷

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The horizontal-to-vertical spectral ratio (HVSR) passive seismic technique uses what is traditionally considered seismic noise or microseisms as a source. The sensitive broadband three-component sensors record ambient (passive) seismic activity at single stations for a set amount of time (~1030 minutes). HVSR analysis is then performed, in which the average of the frequency spectra from the two horizontal components is divided pointwise by the spectrum from the vertical component. A high-amplitude peak in the resulting spectral ratio represents the primary resonance frequency and has an empirical relationship with bedrock depth. Over 350 passive seismic stations were occupied within and adjacent to Pictured Rocks National Lakeshore in Michigans Upper Peninsula as part of a glacial geomorphology study to determine the glacial drift thickness and general bedrock topography of the region. Unconsolidated drift is thinner (26 m) in the western portion of our study area (near Munising, MI) and thickens to the NE (reaching 4060 m west of Grand Marais, MI). Hidden below this blanket of glacial drift are at least five buried bedrock valleys. All are fairly linear, oriented approximately north-south, and extend between 1 km and more than 12 km south of the Lake Superior shoreline. The maximum depths of the valleys increase from 55 m in the west to almost 120 m in the east. It is likely that they connect to the deep north-south valleys visible in bathymetry of the floor of Lake Superior. While the two western valleys were previously identified, the central valley had only been speculated upon but was unconfirmed, and the eastern two were unknown until this study. Gravity transects over the central valley confirm the existence of a deep valley with low-density fill. These valleys have significant implications to understanding the glacial history and hydrogeology of this region.
机译：水平到垂直的光谱比（HVSR）被动地震率使用传统上认为地震噪声或微痉挛作为源的东西。敏感的宽带三分传感器在单个站中记录单个站的环境（被动）地震活动，以设定一定的时间（〜1030分钟）。然后执行HVSR分析，其中来自两个水平分量的频谱的平均值通过来自垂直分量的光谱划分。所得到的光谱比中的高幅度峰值代表初级谐振频率，并且与基岩深度具有经验关系。超过350被动地震站被占用的内并且邻近彩岩国家湖滨在密歇根上半岛作为冰川地貌研究，以确定冰漂移厚度和该区域的一般基岩地形的一部分。在我们的研究区的西部（靠近Munision，Mi）并沉入NE（达到4060米以西，达到Grand Marais，MI以西4060米），不统一漂移是更薄的（26米）。隐藏在冰川漂移的毯子下面至少有五个埋没的基岩谷。所有人都相当线性，朝南大约朝南，距离湖泊南部的南北有1公里，超过12公里。山谷的最大深度从西方的55米增加到东部的近120米。它们很可能连接到深度南北山谷，在湖泊湖的浴室上可见。虽然前两家西方谷以前被识别出来，但中央山谷才推测，但未证实，而东两者未知，直到这项研究。重力横断中心谷确认具有低密度填充的深谷存在。这些山谷对理解该地区的冰川历史和水文地质有重大影响。

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