Seismicity of Central Asia as Observed on Three IMS Stations

Four months of interactive seismic data analysis were conducted to describe the station characteristics of three International Monitoring System (IMS) seismic stations (MKAR, SONM, and BVAR) located in central Asia. Specific study objectives included the location of all local and regional seismic events observed on the three stations, including single station events; identification of seismic sources routinely observed at each station; background noise characterization; identification of any biases in station azimuth, time, and slowness, etc. Additionally, these data provided a baseline for a separate study for evaluation, tuning, and enhancement of automatic and interactive processing functions at the International Data Centre (IDC). During this project, notes were kept on the thresholds necessary at each station for a given event to be recorded at one of the other stations, trends in azimuth and velocity, and any timing errors. A total of 120 days of data were reviewed (July 20-October 17, 2006; January 1-30, 2007). Over 9,000 events with at least one of the three stations at an epicentral distance less than 20? were human-analyst reviewed, including phase identification and event location. About six percent of the located events included arrival times from all three stations, while about 16% included data from at least two stations. Thirty-nine event clusters, based on geographic and temporal distribution, were identified. The three stations MKAR, SONM, and BVAR are all high-quality seismic arrays. Noise levels at the stations are generally acceptable for the period reviewed, except during the following conditions: (1) a 4.5-Hz intermittent noise source at MKAR, (2) periodic high-frequency bursts on portions of the SONM array, and (3) a monochromatic ring occasionally observed on BVAR. Trends in observed biases were catalogued for each station based on azimuthal distribution. Presented at the Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies (30th) held in Portsmouth, VA on 23-25 Sep 2008. Published in the Proceedings of the Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies (30th), p366-375, 2008. Sponsored by the National Nuclear Security Administration (NNSA) and the Air Force Research Laboratory (AFRL). The original document contains color images.