ISSN:
1365-246X
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Geosciences
Notes:
The generation of long period (20–50s) surface waves by an explosion on an island, inside a mountain, or near a material discontinuity is studied using 2-D axisymmetrical finite difference calculations. The generation of surface waves can be reduced substantially if the explosion is close to a vertical boundary such as a material velocity reduction, mountain slope, or island/ocean boundary. This occurs because surface waves from a shallow explosion are generated primarily by the horizontal stress components which are reduced at the boundary.Three sets of finite difference calculations were performed for an ‘island’ surrounded by an ‘ocean’ of air, water, and a low-velocity solid. The surface waves were measured on ‘land’ on the other side of the ‘ocean’ . A ‘solid’ calculation with a uniform structure was also performed for comparison. Calculations include ‘ocean’ depths of 3 and 6 km, and the ‘island’ varies in diameter from 6 to 48 km. For a 48 km island, the material boundary has little effect on the surface waves. For an island width equal to the ocean depth, however, the surface wave generation is reduced by an order of magnitude for air and water, and reduced by more than a factor of 2 for the low-velocity solid. Comparisons with the geography of the Amchitka and Mururoa island test sites show that this effect is small for explosions at those sites, however, the effect appears to be important for Novaya Zemlya and other sites where explosions are detonated inside mountains, and at sites with strong material variations.To estimate the effect of a high-velocity boundary surrounding a low-velocity source region, we performed a calculation for an explosion in a sedimentary basin modelled after Yucca Valley at the Nevada Test Site. In order to include finer details of the source region, a finely gridded finite difference calculation was performed in the source region, and surface waves exterior to the calculation were calculated using the representation theorem. We find that surface waves are amplified by about a factor of 2 by the high-velocity interface surrounding the low-velocity basin.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1365-246X.1993.tb06986.x
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