Formation of Ground Truth Databases and Other Studies for Regional Seismic Research

Abstract : In the second year of this project, the main objective continues to be the formation of databases providing ground truth for regional seismic research conforming to the latest Center for Monitoring Research (CMR) schema. The effort focuses on events in the CMR Calibration Event Bulletin (CEB) from China, the former Soviet Union, and North America. Selected CEB events are re-analyzed using the seismic analysis software geotool starting with the Reviewed Event Bulletin (REB) solutions. Modifications to the original REB results include mostly arrival phase re-timings and adding missed phases, including depth phases. New waveform data are retrieved and analyzed from available IRIS stations mostly within 25 degrees distance. A modified version of LocSAT, called Locate, which uses a graphical user interface and allows interactive processing to generate location results, is used to locate the CEB events. Two sets of location results per event are derived: the first by using only the revised IDC arrivals, and the second by using both the IRIS and revised IDC data. Analysis of datasets of 70 CEB events in China and 80 CEB events in the former Soviet Union (FSU) has been completed. Re-analysis of the Chinese data included using waveforms from over 140 IDC stations contributing over 4000 arrivals, supplemented by nearly 3800 waveforms from over 130 IRIS stations providing nearly 2300 additional arrivals. Similarly, the FSU data included not only waveforms from about 130 IDC stations contributing over 4000 arrivals, but also nearly 4000 waveforms from more than 160 IRIS stations providing over 2300 new arrivals. The most important contribution of the IRIS data is the addition of a large number of arrivals from regional phases. Similar analysis of CEB events in North America, based on the use of both IDC and IRIS stations, is in progress.