Locating and discriminating explosions from earthquakes become progressively more difficult as magnitude decreases. We can no longer rely on teleseismic identification for events at about Mw<4.3 and we can expect only a few, perhaps one, digital stations reporting usable data in regional distance. We need to obtain more information from these regional seismograms than just arrival times and amplitude ratios. Here we introduce a new method of estimating source parameters using as few as one broadband station in conjunction with other available data. We will refer to these solutions as regional event parameters (REP) to distinguish them from other source estimates, such as Ground Truth (GT) location and Centroid Moment Tensor (CMT) location. The method employs an adaptive grid-search of matching three-component waveform records against synthetics to establish source location and depth. The basic matching procedure contains a trade-off of source mechanism with location. The better the constraint on mechanism and depth, the better the location. The locations of GT10 and GT25 events can also be improved if CMT's and other independent depth estimates are available. We propose a concentrated effort to develop an interactive semi-automated code that can take a variety of data and determine source parameters. To establish proof-of-concept, we will conduct a validation test on the PASSCAL data sets collected in Pakistan and Tibet. We will test our method against the locations of the GT5 and GT10 events. The effective accuracy in locations produced from the analysis of one broadband station plus first arrivals at other stations can be checked against the whole network locations. This code could be used systematically to refine existing locations. Researchers in the various SSSC calibration projects could use such a code to help establish the ground truth events in their regions. Moreover, independent locations by different methodologies could be used to more fully address the true uncertainties in location. This study will result in a methodology to yield ground truth information for small magnitude events using a number of short-period stations for polarity and onset times of P waves in conjunction with a broadband station. The proposed method is applicable in any tectonic environment provided that the regional structure is calibrated. Thus, following the Phase-I of this study, it will be possible to apply this method to reduce ambiguity in the epicentral locations of small magnitude events, which is needed by the OSI requirements. Also, we will be able to extend this method to smaller events with added confidence thus will yield a larger populations of GT events producing a better coverage of the geographic regions of the monitoring interests.
