A network of north–south linear troughs occupies the eastern portion of the Lake Superior basin. Morphology suggests these features are tunnel valleys that formed through erosion as subglacial conduits and conveyed meltwater to a former glacial margin. We demonstrate the southern continuation of these valleys onshore into the central Upper Peninsula of Michigan by mapping bedrock topography using the Horizontal-to-Vertical Spectral Ratio (HVSR) passive seismic method. This is a single location, noninvasive seismic technique that records ambient signal. HVSR data are used to estimate subsurface elevation of the sediment-bedrock contact at each site. Regional bedrock topography was estimated using HVSR data from 347 locations. We delineated, for the first time, eight buried (or partially buried) bedrock valleys with geometric characteristics (width, depth, orientation, and continuity) suggesting a southward extension of the Lake Superior tunnel valley network. The largest valleys terminate near the crest of the Munising/Grand Marais upland. This association suggests the upland was constructed by deposition of sediment-laden meltwater at the terminal ends of these tunnel valleys as fans (or heads of outwash). Episodic erosion of the largest valleys likely began during the Two Rivers phase (∼13 ka) and were again active during the Marquette phase (∼11 ka). The smallest valleys developed later during final regional deglaciation following the Marquette phase.

一个南北线性槽网络占据了苏必利尔湖盆地的东部。形态学表明，这些特征是隧道谷，它们通过侵蚀形成冰下管道，并将融水输送到前冰川边缘。我们通过使用水平垂直光谱比 (HVSR) 被动绘制基岩地形图，展示了这些山谷向南延伸到密歇根州上半岛中部。地震法。这是一种记录环境信号的单一位置、非侵入性地震技术。HVSR 数据用于估计每个地点沉积物-基岩接触的地下高程。使用来自 347 个地点的 HVSR 数据估计了区域基岩地形。我们首次描绘了八个具有几何特征（宽度、深度、方向和连续性）的埋藏（或部分埋藏）基岩山谷，表明苏必利尔湖隧道山谷网络向南延伸。最大的山谷终止于 Munising/Grand Marais 高地的顶部。这种关联表明，高地是通过在这些隧道谷的末端沉积的富含沉积物的融水作为风扇（或外流头）而建造的。最大山谷的阶段性侵蚀可能在两条河流阶段（~13 ka）开始，并在 Marquette 阶段（~11 ka）再次活跃。最小的山谷在最后的区域后期发展Marquette 阶段之后的冰川消融。