The complex postdetonation geologic structures that form after an underground nuclear explosion are hard to constrain because increased heterogeneity around the damage zone affects seismic waves that propagate through the explosion site. Generally, a vertical rubble‐filled structure known as a chimney is formed after an underground nuclear explosion that is composed of debris that falls into the subsurface cavity generated by the explosion. Compared with chimneys that collapse fully, leaving a surface crater, partially collapsed chimneys can have remnant subsurface cavities left in place above collapsed rubble. The 1964 nuclear test HADDOCK, conducted at the Nevada test site (now the Nevada National Security Site), formed a partially collapsed chimney with no surface crater. Understanding the subsurface structure of these features has significant national security applications, such as aiding the study of suspected underground nuclear explosions under a treaty verification. In this study, we investigated the subsurface architecture of the HADDOCK legacy nuclear test using hybrid 2D–3D active source seismic reflection and refraction data. The seismic data were acquired using 275 survey shots from the Seismic Hammer (a 13,000 kg weight drop) and 65 survey shots from a smaller accelerated weight drop, both recorded by ∼1000 three‐component 5 Hz geophones. First‐arrival, P‐wave tomographic modeling shows a low‐velocity anomaly at ∼200 m depth, likely an air‐filled cavity caused by partial collapse of the rock column into the temporary postdetonation cavity. A high‐velocity anomaly between 20 and 60 m depth represents spall‐related compaction of the shallow alluvium. Hints of low velocities are also present near the burial depth (⁠∼364 m⁠). The reflection seismic data show a prominent subhorizontal reflector at ∼300 m depth, a short‐curved reflector at ∼200 m⁠, and a high‐amplitude reflector at ∼50 m depth. Comparisons of the reflection sections to synthetic data and borehole stratigraphy suggest that these features correspond to the alluvium–tuff contact, the partial collapse cavity, and the spalled layer, respectively.

中文翻译：

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内华达州国家安全站点的旧式地下核试验的密集地震阵列研究

地下核爆炸后形成的复杂的爆炸后地质结构很难约束，因为损坏区周围非均质性的增加会影响在爆炸现场传播的地震波。通常，在地下核爆炸后，形成一个称为烟囱的垂直碎石填充结构，该结构由落入爆炸产生的地下空腔的碎屑组成。与完全塌陷的烟囱相比，留下一个表面的火山口，部分塌陷的烟囱在塌陷的瓦砾上方可能有剩余的地下洞。1964年在内华达试验场（现为内华达国家安全局）进行的核试验HADDOCK形成了部分坍塌的烟囱，没有表面火山口。了解这些特征的地下结构具有重要的国家安全应用，例如在条约验证下协助研究可疑的地下核爆炸。在这项研究中，我们使用2D–3D混合有源地震反射和折射数据研究了HADDOCK传统核试验的地下结构。地震数据是使用地震锤的275个测量镜头（重量减轻13,000公斤）获得的，地震数据是通过较小的加速重量的测量获得65张，两者均由约1000个三分量5 Hz地震检波器记录。首次到达的P波层析成像模型显示，在约200 m的深度处出现了一个低速异常，这可能是由于岩石柱部分塌陷到临时的爆炸后腔中而导致的充满空气的腔。深度在20至60 m之间的高速异常代表浅冲积层的剥落相关性压实。在埋葬深度附近（？〜364m⁠）也存在低速的提示。反射地震数据显示，在〜300 m深度处有一个突出的水平下反射器，在〜200m⁠处有一个短曲线的反射器，在〜50 m处有一个高振幅反射器。通过将反射剖面与合成数据和井眼地层进行比较，可以看出这些特征分别对应于冲积层与凝灰岩的接触，部分塌陷腔和剥落层。以及约50 m深度的高振幅反射器。通过将反射剖面与合成数据和井眼地层进行比较，可以看出这些特征分别对应于冲积层与凝灰岩的接触，部分塌陷腔和剥落层。以及约50 m深度的高振幅反射器。通过将反射剖面与合成数据和井眼地层进行比较，可以看出这些特征分别对应于冲积层-凝灰岩接触，部分塌陷腔和剥落层。