We develop a Regional Seismic Travel Time (RSTT) model and methods to account for the first-order effect of the three-dimensional crust and upper mantle on travel times. The model parameterization is a global tessellation of nodes with a velocity profile at each node. Interpolation of the velocity profiles generates a 3-dimensional crust and laterally variable upper mantle velocity. The upper mantle velocity profile at each node is represented as a linear velocity gradient, which enables travel time computation in approximately 1 millisecond. This computational speed allows the model to be used in routine analyses in operational monitoring systems. We refine the model using a tomographic formulation that adjusts the average crustal velocity, mantle velocity at the Moho, and the mantle velocity gradient at each node. While the RSTT model is inherently global and our ultimate goal is to produce a model that provides accurate travel time predictions over the globe, our first RSTT tomography effort covers Eurasia and North Africa, where we have compiled a data set of approximately 600,000 Pn arrivals that provide path coverage over this vast area. Ten percent of the tomography data are randomly selected and set aside for testing purposes. Travel time residual variance for the validation data is reduced by 32%. Based on a geographically distributed set of validation events with epicenter accuracy of 5 km or better, epicenter error using 16 Pn arrivals is reduced by 46% from 17.3 km (ak135 model) to 9.3 km after tomography. Relative to the ak135 model, the median uncertainty ellipse area is reduced by 68% from 3070 km 2 to 994 km 2 , and the number of ellipses with area less than 1000 km 2 , which is the area allowed for onsite inspection under the Comprehensive Nuclear Test Ban Treaty, is increased from 0% to 51%.

Seismic monitoring for underground nuclear explosions answers three questions for all global seismic activity: Where is the seismic event located? What is the event source type (event identification)? If the event is an explosion, what is the yield? The answers to these questions involves processing seismometer waveforms with propagation paths predominately in the mantle. Four discriminants commonly used to identify teleseismic events are depth from travel time, presence of long-period surface energy (m b vs. M S ), depth from reflective phases, and polarity of first motion. The seismic theory for these discriminants is well established in the literature (see, for example, Blandford [1982] and Pomeroy et al. [1982]). However, the physical basis of each has not been formally integrated into probability models to account for statistical error and provide discriminant calculations appropriate, in general, for multidimensional event identification. This article develops a mathematical statistics formulation of these discriminants and offers a novel approach to multidimensional discrimination that is readily extensible to other discriminants. For each discriminant a probability model is formulated under a general null hypothesis of H 0 : Explosion Characteristics. The veracity of the hypothesized model is measured with a p-value calculation (see Freedman et al. [1991] and Stuart et al. [1994]) that can be filtered to be approximately normally distributed and is in the range [0, 1]. A value near zero rejects H 0 and a moderate to large value indicates consistency with H 0 . The hypothesis test formulation ensures that seismic phenomenology is tied to the interpretation of the p-value. These p-values are then embedded into a multidiscriminant algorithm that is developed from regularized discrimination methods proposed by DiPillo (1976), Smidt andMcDonald (1976), andFriedman (1989). Performance of the methods is demonstrated with 102 teleseismic events with magnitudes (m b ) ranging from 5 to 6.5. Example p-value calculations are given for two of these events.

On 16 June 1992, an mLg 2.3 earthquake occurred in southwestern Indiana, near Evansville. This area is part of the Illinois Basin coal belt, an area of active surface mines with numerous strip-mine blasts daily. The co-location of earthquakes and strip-mine blasts enable spectral comparisons without significant concern for differences due to path propagation effects. Discriminating between the two types of events can be done visually due to the distinctive appearance of the Rg phase in strip-mine blasts and high frequency coda of earthquakes. A strong Rg phase is indicative of shallow source depths. However, earthquakes previously located at shallow depths elsewhere within the Illinois Basin do not exhibit a distinctive Rg phase, indicating either poor control in focal depth determination or a fundamental difference in source mechanism. Visual and spectral examination shows that earthquakes are richer in energy at higher frequencies than strip-mine blasts. Earthquakes have significant energy at 20–30 Hz, while the significant energy content of blasts is closer to 10 Hz. The significant difference compared to previous earthquake-nuclear explosion discriminant studies is that the chemical explosion has reduced high frequency content compared to the earthquake.

For the past several years, Quantum Technology Sciences (QTSI) and U.S. Army Engineering Research and Development Center (ERDC) have been developing a system to actively sustain present and future artillery ranges at zero unexploded ordnance (UXO) gains. With the Department of Defense (DoD) using over two million high-explosive (HE) munitions per year with a significant fraction as UXO, reducing costly range remediation and environmental restoration efforts will offer significant savings. The developed Seismic Acoustic Impact Monitoring Assessment (SAIMA) system is not designed for past ranges, but as a complementary technology to detect, locate within two meters, and classify UXO in near real-time to aid existing cleanup technologies. Feasibility and descriptions of system components have been previously provided ( VanDeMark et al., 2009 , 2010 , 2013 ). The current system is composed of multiple buried seismic arrays encircling a mortar or artillery impact area, communications from the arrays to a central processing station, and a processing unit that employs an algorithm suite based in the seismology and statistical analysis disciplines to detect, locate, and classify the HE or UXO impact. Recent deployments of the SAIMA system have demonstrated hardware maturity and algorithm refinements to nearly enable the goal of locations within two meters. A field deployment at Ft. Sill, Oklahoma, in June 2012 demonstrated acoustic locations at a large range ( QTSI, 2012 ). Subsequent systems tests with five arrays using a synthetic UXO source (kinetic source only; no acoustic phases) on a small field (80 m by 80 m) resolved locations within 0.5 m of ground truth with coverage ellipses at 0.1 m2 (time and azimuth). On a small mortar field, approximately 365 m by 480 m, simulated UXO (inert rounds) were located within an average mislocation distance of 4.1 m and confidence ellipses on the order of 5.8 m by 3.8 m. Scheduled field testing in the near future will validate the system.

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