The Gazli cluster is named for the town of Gazli in northwest Uzbekistan. The source region was nearly aseismic until April 8, 1976 when a large (Ms 7.0) earthquake initiated several years of very active seismicity, including another Ms 7.0 event in May 1976 and a third Ms 7.0 event in March 1984. Low-level activity continues currently. It is generally believed that the sequence represents an episode of induced seismicity related to large-scale gas extraction industry in the area. The cluster is formed mainly from events that have depth control from teleseismic relative depth phases, plus one event, on June 25, 1991, that was recorded by a temporary seismic network (operated by LGIT, Grenoble, France) and was well-enough recorded at teleseismic distances to be included in the cluster. Data from this deployment were kindly provided by Remy Bossu. To obtain the calibrated location for this event, a cluster of 60 events from the temporary deployment was relocated using direct calibration, yielding calibration levels of 1-2 km. Very little arrival time data at local distances is available for the main gazli cluster, but it includes a half dozen small events in 2014-2015 that do have some local-distance readings. These events have no teleseismic depth phase data, so they are held at a default depth of 13 km. Direct calibration using these data (along with the readings from the 1991 event) is stable but results in uncertainty that is too large (~9 km in the epicentroid) for the GCCEL. Therefore the calibration is done indirectly, shifting the cluster in space (~5 km south) and time (-0.4 s) to match the location of the 1991 calibration event that is based on the temporary French network.
Number of events: 69
Calibration type: indirect calibration on 1 calibration events; hypocentroid calibration level = 3.3 km
Epicentral calibration range: 3 - 5 km
Date range: 19760408 - 20150810
Latitude range: 39.995 - 40.536
Longitude range: 63.109 - 64.125
Depth range: 6.0 - 20.0
Magnitude range: 3.7 - 7.0
