We have developed, validated, and applied a fast and accurate, interactive, easy to use tool for estimating seismic event depth and mechanism by modeling the initial P-wave bundle. Significant features of this tool include its applicability over a broad band of frequencies (f≤2 Hz) and magnitudes (mb≥4.5), its ability to provide accurate high-resolution depth estimates, and its ability to provide constraints on event mechanism including isotropic contributions. It also provides estimates of random and model errors and can be used to test hypotheses and investigate sensitivity to and trade-offs between model parameters. We validated this tool and its algorithms by showing that our estimated depths and mechanisms are in excellent agreement with ground-truth depths and mechanisms based on local and regional data. We find that depth can usually be estimated to an accuracy of a few km with a small number of stations. Although complete mechanisms are sometimes poorly resolved, we find that two out of three of the mechanism parameters (strike, dip, rake) are usually well constrained. We illustrate the potential of this technique for regional calibration, special event analysis, and event screening by comparing estimated depths and mechanisms of events in the Middle East and North Africa with those of the National Earthquake Information Center (NEIC) and by comparing our depth and mechanism estimates for the May 11, 1998 India nuclear explosion and a November 8, 1991 earthquake that occurred in the same region. ¿ 1999 American Geophysical Union