Article,
Characterization of mining explosions at regional distances: Implications with the International Monitoring System
Reviews of Geophysics, 40 (4): 1011 (Dec 31, 2002)
DOI: 10.1029/1998RG000048
Abstract
The International Monitoring System (IMS) being constructed in support
of the Comprehensive Nuclear-Test-Ban Treaty introduces new opportunities
to nuclear test monitoring by providing open access to global data
from seismic, hydroacoustic, infrasonic, and radionuclide sensors.
These sensors will detect myriad natural and man-made events and
can be used to identify those that have explosive characteristics
and therefore might be clandestine nuclear tests. Detection and identification
of seismic events must be conducted at a lower magnitude threshold
(mb = 3.5 and lower) than has been previously considered. Concomitant
with the lower monitoring threshold will be an increased number of
events that must be scrutinized. This collection will be largely
composed of regional observations in which the seismic waves have
traversed complex geological structures. High-fidelity regional,
geophysical models will be needed to support accurate location and
source identification. Source identification will not be limited
to the separation of single-fired nuclear explosions from earthquakes
as in previous testing treaties. The lower-magnitude threshold and
increased reliance on regional observations assures that mining explosions
will be detected by the monitoring system. It is important that the
signals from mining explosions are properly identified to avoid false
alarms of the monitoring system. Cooperation with the mining industry,
including deployment of close-in instrumentation and extensive documentation
of the explosions, provides critical information for interpreting
the performance of regional discriminants. Linkage of these observations
to appropriate physical models of the blasting process is also enhanced
through this cooperative research effort. A number of discriminants
for characterizing mining explosions have been identified including
P to Lg ratios at high and low frequencies, surface wave to high-frequency
body wave amplitudes, Rg at short distances, high- and low-frequency
time-independent spectral modulations, signal correlation, and temporal
clustering. Variable performance of individual discriminants results
from such factors as mine-specific blasting practices and the complexity
of the regional wave propagation. This variability attests to the
need for a suite of region-specific discriminants. Regional calibration
with modest-size, single-fired contained chemical explosions can
provide a basis for developing region-specific procedures. Broadband
data provide the basis for the most robust set of discriminants.
The inclusion of infrasonic data as part of the IMS introduces a
potential for the combined use of seismic and infrasonic data for
the identification of near-surface explosions. The generation and,
to a greater extent, the propagation of mining explosion infrasonic
signals is not well understood, but empirical data attest to its
future utility. Evidence for the accidental, near-simultaneous detonation
of a large amount of explosives during standard delay-fired explosions
is presented. Events such as these have single-fired characteristics
and may prove to be problematic in discrimination analysis.
