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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%.

The relationship between physical activity self-efficacy and participation in vigorous physical activity by high school students is examined in this article. Self-efficacy is hypothesized to be positively related to participation in three settings (physical education class, other school-related activities, and outside of school). The effects of age, gender, perceived barriers, and actual barriers are also examined. The sample consists of 1,041 grade 9 and 11 students from a large Metropolitan Toronto school board. Factors derived from a previous (factor) analysis were used to examine the effects of self-efficacy, perceived barriers, and life strain (an actual barrier). The results of multiple regression analysis indicate that physical activity self-efficacy, despite external barriers (but not internal barriers), is predictive of physical activity participation in the hypothesized direction. Other results show consistent age and gender effects on physical activity participation and some support for the hypothesized relationship between perceived barriers and participation.

Background:The decline in physical activity during adolescence is a key public health concern. This comparative study assesses whether the age-related decline in physical activity among high school students occurs similarly in the United States (US) and Ontario, whether the decline in physical activity is steady throughout the age range, or whether any declines are age-specific.Methods: Data are based on self-reports of 9 th -to 12 th -graders derived from the 2001 Youth Risk Behavior Survey (n=13,503) and the 2001 Ontario Student Drug Use Survey (n=1,322). Physical activity is measured by the number of days of vigorous physical activity during the past 7 days. Results:In both samples, there was a dominant and steady decline in physical activity between ages 14 and 18 years. The number of activity days was higher in the US than in Ontario holding constant age and sex. However, a significant sample-by-age interaction showed that the decline in the percentage of US students reporting 3 or more physical activity days was greater than it was in Ontario.Conclusions: While the pattern of decline was shown to be similar, the decline was stronger among US adolescents. Future research should examine additional factors influencing the decline in activity and the optimal timing of programs to reduce the decline.