Demonstration of Advanced Concepts for Nuclear Test Monitoring Applied to the Nuclear Test Site at Lop Nor, China

Starting in October 2001 the Center for Monitoring Research (CMR) engaged in an advanced concept demonstration (ACD) to improve nuclear-explosion monitoring capability, focused on the Chinese test site at Lop Nor. A demonstration prototype system was developed by integrating innovative techniques gleaned from recent research and development advances. Emphasis was in the areas of detection, location and identification of underground nuclear explosions with particular attention to techniques applicable to regional seismology in and around the Chinese test site. The demonstration prototype system was tested against a very large uniform and calibrated database of seismic recordings from over 200 explosions and earthquakes in the vicinity of Lop Nor. The data set, which was assembled from approximately 100,000 event recordings (~ 100 GB) from some 60 different seismic stations sampling the near-regional to teleseismic distance range, provides an unprecedented data resource that can be used to conduct appropriate and meaningful scale tests to quantitatively assess new monitoring techniques for this region. The above referenced data were supplemented by theoretically scaling selected event recordings of historical nuclear explosions and earthquakes down to levels of mb = 3.5, mb = 3.0 and mb = 2.5. This permitted, for the first time, realistic assessments of frequency dependent event detection and identification capability at low thresholds. The scaled waveforms were embedded in actual background noise and integrated into a database specifically designed for processing with a standard automated and interactive analysis pipeline compatible with those currently employed by the International Data Centre (IDC) and the United States National Data Center. With respect to the final version of the processing and analysis tools delivered to the IDC by CMR, innovations in the ACD demonstration prototype system include site-specific threshold monitoring and the F-statistic detector to facilitate automated detection. Origin information and waveform data from the underground nuclear explosions historically conducted at Lop Nor were assembled and used to facilitate improved location, including: • Development of static travel-time test-site corrections • Calibration of regional travel times, i.e. Site-Specific Stations Correction (SSSCs) developed by the Defense Threat Reduction Agency (DTRA) Group 1 and Group 2 calibration consortia and integrated into the ACD • Development of a waveform cross-correlation tool, used for making very accurate arrival picks • Master event and joint hypocenter determination (JHD) relocation algorithms • Non-gaussian confidence area visualization To extend the applicability of the mb:Ms discriminant to low thresholds, phase-matched filtered-surface wave detection was integrated into the ACD demonstration prototype system. In the area of depth phase utilization, a number of innovations were integrated, including depth phase stacking and the use of F-statistic and probability traces. Regional 3-component amplitude ratios were calibrated specifically for the Lop Nor area and fused with other discriminants (depth, mb:Ms) to form event identifications based on multivariate syntheses. The tuned ACD demonstration prototype system was applied to the systematic analysis of the events in the Lop Nor data sets. The results have confirmed that significant improvements in detection, location and identification capability in this region are achievable as a result of this effort. 302 24th Seismic Research Review – Nuclear Explosion Monitoring: Innovation and Integration