The Conference on Disarmament of the U.N. General Assembly is currently working to draft a Comprehensive Test Ban Treaty (CTBT) which will prohibit all nuclear testing. Because seismology remains as the primary monitoring technique for verifying treaty compliance with respect to underground nuclear tests, it is appropriate at this time to once again review the current state of understanding regarding the seismic identification of such explosions. It is evident that no practical seismic monitoring system will ever insure identification of all conceivable underground nuclear tests and, therefore, it is important to begin any such assessment of capability by recognizing that it is first necessary to establish a monitoring threshold goal, which will ultimately represent some compromise between system cost and various political and military considerations.

In September 1996, the United Nations General Assembly adopted the Comprehensive Nuclear-Test-Ban Treaty (CTBT), prohibiting nuclear explosions worldwide, in all environments. The treaty calls for a global verification system, including a network of 321 monitoring stations distributed around the globe, a data communications network, an international data center, and onsite inspections, to verify compliance. The problem of identifying small-magnitude banned nuclear tests and discriminating between such tests and the background of earthquakes and mining-related seismic events, is a challenging research problem. Because they emphasize CTBT verification research, the 12 papers in this special volume primarily addresses regional data recorded by a variety of arrays, broadband stations, and temporarily deployed stations. Nuclear explosions, earthquakes, mining-related explosions, mine collapses, single-charge and ripple-fired chemical explosions from Europe, Asia, North Africa, and North America are all studied. While the primary emphasis is on short-period, body-wave discriminants and associated source and path corrections, research that focuses on long-period data recorded at regional and teleseismic distances is also presented Hence, these papers demonstrate how event identification research in support of CTBT monitoring has expanded in recent years to include a wide variety of event types, data types, geographic regions and statistical techniques.

Negotiators from more than 35 countries are attempting to formulate a nuclear test-ban treaty and delineate a system from monitoring compliance. This book covers: (1) the desirable characteristics and capabilities of seismic monitoring stations; (2) recommendations on the flow paths and handling of the data, which are to be unclassified; and (3) the types and extent of research that will be needed in the next decade. The primary focus of the book is to explore how basic seismological research and test ban monitoring can be mutually beneficial.

On September 1996, the United Nations General Assembly adopted the Comprehensive Nuclear-Test-Ban Treaty (CTBT), prohibiting nuclear explosions worldwide, in all environments. The treaty calls for a global verification system, including a network of 321 monitoring stations distributed around the globe, a data communications network, an international data center (IDC), and on-site inspections to verify compliance. Seismic methods play the lead role in monitoring the CTBT. This volume concentrates on the measurement and use of surface waves in monitoring the CTBT. Surface waves have three principal applications in CTBT monitoring: to help discriminate nuclear explosions from other sources of seismic energy, to provide mathematical characterizations of the seismic energy that emanates from seismic sources, and to be used as data in inversion for the seismic velocity structure of the crust and uppermost mantle for locating small seismic events regionally. The papers in this volume fall into two general categories: the development and/or application of methods to summarize information in surface waves, and the use of these summaries to advance the art of surface-wave identification, measurement, and source characterization. These papers cut across essentially all of the major applications of surface waves to monitoring the CTBT. This volume therefore provides a general introduction to the state of research in this area and should be useful as a guide for further exploration.

To verify compliance with a Comprehensive Test Ban Treaty (CTBT), low energy seismic activity must be detected and discriminated. Monitoring small-scale seismic activity will require regional monitoring capabilities (within approximately 2000 km, U.S. Congress (1988)). The reliable discrimination of small-scale seismic events requires a multi-dimensional representation of the seismic signal. A multi-dimensional characterization might include wave arrival times, magnitudes, and incidence and azimuth angles. These measurements can be used singly or combined to form discriminants, which are then subjected to a set of discrimination rules to categorize the source event. Statistical discrimination methods of this type require a training sample, i.e., a set of real or simulated seismic data used to optimize or tune the discrimination algorithm by assigning weights to the various discriminants, or by modifying the structure of the algorithm. Identifying the signatures of various seismic sources also requires a geologic characterization of the shallow structure of the earth in each particular region of interest. The results can be used to construct seismic signals representing nuclear test sources. These synthetic or simulated signals can be combined with empirical signals of earthquakes and mining activities to form a training sample for each region. This paper identifies several statistical issues that must be resolved in order to address the CTBT verification mission. These are all associated with uncertainties in the multidimensional characterization measurements or in the correlations among them.

The Comprehensive Test Ban Treaty (CTBT) requires the location and identification of seismic events which might be associated with small potential underground nuclear explosion tests. For monitoring the CTBT at low magnitude thresholds, reliance must be placed on regional seismic measurements. Various regional discrimination techniques have been shown to be effective for identifying events in some areas, but the transportability of such methods into uncalibrated source areas remains a problem. This research developed procedures which could be useful for transporting regional phase spectral ratio discriminant measures by accounting for propagation path effects using prior knowledge of attenuation. We have found that by correcting for attenuation the scatter in Lg spectral ratio observations between stations could be reduced. However, these measurements still show considerable overlap between different source types which weakens the reliability of the discriminant. It might be possible to improve the reliability of regional phase spectral ratios by limiting effects of noise on the measurements by focusing on nearer stations, limiting the frequency band over which the ratios are formed.