Shallow sediments can respond non-linearly to large dynamic strains and undergo a subsequent healing phase as the material gradually recovers following the passing of seismic waves. This study focuses on the physical changes in the subsurface caused by the shaking from a buried chemical explosion detonated in a borehole in Nevada, USA, as a part of the Source Physics Experiment Phase II. The explosion damaged the shallow subsurface and modified the frequency content recorded by 491 geophones and 2240 Distributed Acoustic Sensing (DAS) channels within 2.5 km from surface ground zero. We observe a gradual shift of resonance frequencies in the 10-25 Hz frequency band in the hours following the explosion and develop a method to characterize the related logarithm-type healing process of the shallow (i.e., upper similar to 25 m) subsurface. We find that stronger levels of ground motion increase the relative degree of damage and duration of the subsurface healing; with the spall region exhibiting the largest degree of damage and longest healing recovery time. We observe coherent spatial patterns of damage with the region located to the southeast of the explosion exhibiting more damage than the southwest region. This study demonstrates that both DAS and co-located geophones capture similar temporal changes associated with the physical processes occurring in the subsurface, with the high-density sampling of DAS measurements enabling a new capability to monitor the fine-scale changes of the Earth's shallow subsurface following the detonation of a buried explosion. Strong seismic waves can damage the soft sediments that compose the shallow layers of the ground. A healing phase of the sediments generally follows the passing of the seismic waves as the medium gradually recovers with time. We study the spatio-temporal response of the subsurface in the vicinity of a large buried chemical explosion that was detonated in a borehole at the Nevada National Security Site, USA. The explosion, which was part of the Source Physics Experiment Phase II, was well instrumented along a surface fiber-optic cable with Distributed Acoustic Sensing (DAS) and hundreds of geophones. We find that the explosion, which generated a spallation of the shallow Earth, primarily damaged the upper similar to 25 m of the subsurface. We characterize the healing of the sediments and find a correlation between the duration of the healing phase and the level of maximum shaking. The high density of sensors also allows us to study spatial variations in the response of the shallow subsurface. This study demonstrates that both DAS and geophone continuous data similarly capture the spatio-temporal variations of the Earth's physical properties following strong ground motions, with DAS enabling meter-scale measurements of the subsurface changes. Shallow subsurface damage and subsequent healing caused by a buried chemical explosion are constrained with DAS and geophone data The explosion caused a relative drop of the average S-wave velocity in the Earth's shallow layers of a few percents The logarithm-type healing process of the subsurface exhibit a longer duration within the spall region

A nuclear explosion in the rock mass medium can produce strong shock waves, seismic shocks, and other destructive effects, which can cause extreme damage to the underground protection infrastructures. With the increase in nuclear explosion power, underground protection engineering enabled by explosion-proof impact theory and technology ushered in a new challenge. This paper proposes to simulate nuclear explosion tests with on-site chemical explosion tests in the form of multi -hole explosions. First, the mechanism of using multi -hole simultaneous blasting to simulate a nuclear explosion to generate approximate plane waves was analyzed. The plane pressure curve at the vault of the underground protective tunnel under the action of the multi -hole simultaneous blasting was then obtained using the impact test in the rock mass at the site. According to the peak pressure at the vault plane, it was divided into three regions: the stress superposition region, the superposition region after surface re flection, and the approximate plane stress wave zone. A numerical simulation approach was developed using PFC and FLAC to study the peak particle velocity in the surrounding rock of the underground protective cave under the action of multi -hole blasting. The time-history curves of pressure and peak pressure partition obtained by the on-site multi -hole simultaneous blasting test and numerical simulation were compared and analyzed, to verify the correctness and rationality of the formation of an approximate plane wave in the simulated nuclear explosion. This comparison and analysis also provided a theoretical foundation and some research ideas for the ensuing study on the impact of a nuclear explosion. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY -NC -ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).