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Restatement of the Problem
The DOE Working Group draft report examined the nature of seismic signals related to domestic mining activities. The report then indicated that it was desirable to reduce the visibility and ambiguity of these seismic signals. Although measures to reduce both were mentioned, the recommendations clearly stressed reducing the level of visibility. The proposed solutions indeed would reduce the amount of energy placed in the ground. The difficulty is that the recommendations encourage changing mining practices without an examination or recognition of the economic consequences to the industry. Whereas the quantification of these costs is difficult and best performed on a case-by-case basis, most mines operate in a highly cost-competitive environment and over time have optimized their practices. The NRC committee believes that major departures from current operating practices in light of the working group's recommendations can likely have adverse economic consequences.
The NRC committee, therefore, favors an approach that reduces ambiguity, or uncertainty, of seismic sources. This may be a more practical solution than one that seeks primarily to reduce visibility, although reducing visibility may be the preferred solution in some limited instances. Moreover, as suggested in the next chapter, reducing the ambiguity of seismic signals would be less intrusive to the U.S. mining industry and is more likely to secure the voluntary cooperation of mine operators in promoting the confidence-building objectives of the CTBT.
With the availability of accurate, mine-specific information, seismic signals that create ambiguity probably will occur only infrequently. Because of their irregular and unplanned nature, seismic signals produced by rock bursts and coal bumps will tend to be more ambiguous than those resulting from blasting operations.
Figure 4 is a graphical depiction of the likely seismic visibility of domestic mines demonstrating roughly the proportion of operating mines that may be visible to the CTBT monitoring network. A large majority of mines would be invisible. Among those visible mines, most could be calibrated through a voluntary exchange
Figure 4
Conceptual distribution of U.S. mines in terms of their seismic visibility under the CTBT monitoring regime. The percent of “visible” mines probably is exaggerated. On the right are a series of cooperative steps that could be undertaken at “visible” mines, starting with their identification for purposes of complying with the confidence-building measures provisions of the treaty. Passive cooperation would involve active mines providing accurate data on their largest blasts and collapses, as proposed in Chapter 4 of this report. Active cooperation would include the on-site monitoring (“fingerprinting”) activities that are proposed in the DOE Working Group report, and could include the fielding of calibration explosions. Before making a decision to modify mining or blasting practices, a company could choose to consult with seismic, blasting, or underground engineering experts to identify ways to eliminate its anomalous signals. In all cases, the program should be voluntary.
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Sample Calibration System for On-Site Blast Monitoring “The main design goals for the calibration system are that it must be deployable by one or two people in approximately one to two hours at a remote site. The minimum source information it must provide is the shot time and location of the event. Since a supplemental goal of the system is a quantification of the character of the source, in the case of surface explosions, information associated with the design and detonation of the explosions is useful. Video and acoustic measurements that supplement the primary seismometers are included for this purpose. The system should be able to run unattended for hours to days depending on the particular application. The requirement for unattended operation is to accommodate safety issues in the mine at the time of detonation. The ability to record data over a period of days (excluding video) provides the opportunity to use the system to monitor activity in a mine or mining district for an extended period of time with little or no intrusion on the commercial activities.” “The total cost of [a] portable system [described in the DOE Working Group report] is approximately $25,000…Thus, a moderate-cost portable system is available that can be used to obtain ground truth information from a number of different sources in widely separated geographical locations with a minimum of impact on the mine.” Extracted from March 1997 DOE Working Group draft report, Ambiguity and Visibility of Seismic Signals from Mining Activities: Benefits to the Mining Industries and to the Communities Monitoring the Comprehensive Test Ban Treaty (CTBT), pp. 4-25-4-27. |
of information (see Chapter 4) between the mining industry and the U.S. agency responsible for CTBT monitoring. An example would be the one-time provision of data from a few large blasts. Most of the remaining mines producing potentially ambiguous, visible events could be “fingerprinted” through a relatively unobtrusive program of active cooperation such as that proposed in the DOE Working Group report (see text box), whereby multimedia, on-site monitoring of blasts by a designated agency would be performed. Only a small fraction of mines—perhaps none—would need to consider the modification of mining practice as a viable alternative. Of course, the mine operator would consider the cost of lost production and the inconvenience of a possible on-site inspection in the context of other measures to resolve the problem.
A strength of the DOE Working Group report is in identifying and documenting the potential impact that blasting in the mining industry may have on compliance monitoring for the CTBT. The possibility that commercial mine blasting could cause difficulty in CTBT compliance is unfamiliar to most mining executives. Thus, the report might be revised primarily to describe and document this problem. In this form, it would be a valuable resource document to aid in gaining support for a voluntary cooperative program (see Chapter 4) for reducing the ambiguity of mining-related seismic signals.
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