Free-Field and Free Surface Ground Motions from Nuclear Explosions, Their Spatial Variations, and the Constraint of Physical Source Mechanisms
- Steven R. Taylor,
- Howard J. Patton and
- Paul G. Richards
Published Online: 18 MAR 2013
Copyright 1991 by the American Geophysical Union.
Explosion Source Phenomenology
How to Cite
Stump, B. W. and Reinke, R. E. (1991) Free-Field and Free Surface Ground Motions from Nuclear Explosions, Their Spatial Variations, and the Constraint of Physical Source Mechanisms, in Explosion Source Phenomenology (eds S. R. Taylor, H. J. Patton and P. G. Richards), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM065p0047
- Published Online: 18 MAR 2013
- Published Print: 1 JAN 1991
Print ISBN: 9780875900315
Online ISBN: 9781118663820
- Underground nuclear explosions—Detection—Congresses;
Near-source waveforms from explosions detonated at the Nevada Test Site (NTS) are reviewed. Data are separated into four types: free-field strong (FFS), representative of the region where material strength dominates; free-field weak (FFW), the region where weakly nonlinear properties and transition from plastic to elastic response are important; free surface spall (FSS), where material tensile strength is important; and free surface elastic (FSE), where most seismic observations begin. Data from Pahute Mesa (FSS & FSE), Rainier Mesa (FFW & FSE), and Yucca Flats (FSS & FSE) are specifically considered. Each of the data types is explored as to its resolution of important physical processes in the source region and resultant seismic radiation. Specific attention is paid to the variability of these motions. Single and scaled multiple explosion peak accelerations from Pahute Mesa and Yucca Flats show as much as a factor of 6–8 scatter with range. Large scatter in single explosion data suggests a propagation path effect while large amplitudes for a scaled explosion from below the water table supports a coupling difference between explosions. Data scatter decreases at long periods as exemplified by long period moments which have a multiplicative error of 1.49 for Pahute Mesa. Numerical models of body and surface wave propagation in realistic one-dimensional Pahute Mesa models indicate strong effects of velocity structure near the shot point for body waves traveling to the free surface at short offset (<2 depths of burial). Synthetic waveform difference between a site specific model and an average model decrease with increasing source-receiver offset or increasing period where near-source surface waves are emphasized. Comparison of free-field and free surface data from the same explosion at Rainier Mesa supports significantly reduced scatter in free-field data. Removal of the weathered layer as a dominant effect in the free-field data can explain the reduced scatter. Analysis of data spanning the transition from FSS to FSE regions indicates that explosion geometry plays a strong role in the decay of free surface data. These data and extended reflectivity calculations appropriate for Pahute Mesa predict that strong spall zone motions come from a region out to a free surface range just beyond one depth of burial for explosions with standard scaled depths of burial.