Identification and Validation of Reference Events Within the Area Being Regionally Monitored by IMS Stations in Asia and North Africa

High-resolution cluster analysis is applied to explosions and earthquake sequences in Asia and North Africa for which one or more of the associated events is known to an accuracy of 5 km or better (GT5). In particular, we analyze phase data reported to the ISC and NEIC for the 1997 Ghaen-Birjand earthquake sequence in eastern Iran and the 1997 Jiashi swarm in western China. In both cases, reference event data is available from short-term portable seismograph deployments following the initiation of seismic activity in those regions. For the cluster analyses we used 92 events of the Iran sequence and 123 events of the Jiashi swarm, ranging in magnitude from 3.4 to 7.1. The analyses produce new locations (relative to the centroid) and 90% confidence ellipses that sharpen the spatial relationship of the earthquakes to known faults and modes of deformation in these regions. Shifting the centroid to match reference event locations produces source-station path corrections (to ak135) for regional seismic phases recorded by IMS and surrogate stations in Asia. The standard error of these path corrections is typically only a few tenths of seconds. Hence, these data can be used to validate 3-D models and to support the calculation of travel-time curves and source-specific station corrections for the Asian and north African regions.
Proceedings of the Annual DoD/DOE Seismic Research Symposium (22nd): Planning for Verification of and Compliance with the Comprehensive Nuclear-Test-Ban Treaty (CTBT) held in New Orleans, Louisiana on 13-15 September 2000. U.S. Government or Federal Rights. The original document contains color images.