Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO)

The experimental SEL0 system of the CTBTO’s Preparatory Commission (Le Bras et al., 2006) now includes a moment tensor (MT) and moment magnitude estimate. The SEL0 system rapidly detects and locates events. The effort to include further processing of large natural events, and get a better size estimate for large natural events than the mb magnitude was started in the summer of 2005. The basic scientific software that performs the MT inversion was acquired from Y. Yagi from Tsukuba University, Japan. It performs a time-domain, long-period body-waves MT inversion soon after an event is automatically detected and located, within about 20 minutes after its occurrence. We wrote signal processing scripts to prepare the broad-band International Monitoring System (IMS) vertical seismic data for MT inversion, including deconvolution of the complete instrument responses. We included the scientific software into the Commission’s environment and have now achieved its seamless integration through the web page displaying the results of the SEL0 bulletin. The addition of the moment tensor inversion module allows us to estimate the size and focal mechanism of the detected events, which is of interest for better characterization of the event in a limited time frame. This is important since the only available measure of the size of the earthquake for SEL0 events was the mb scale, which saturates for larger events. We have been able to interactively run a number of inversions and we present case examples and statistics from selected events since December 2006