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...
The Valparaiso cluster is named for the nearby city of Valparaiso, Chile. The cluster is based on a set of arrival time readings from a deployment of ocean bottom seismometers, hydrophones and a temporary land-based stations for several months in 2001 that were kindly provided by Frederik Tilmann (GeoForschungsZentrum). Most of the recorded events are fairly small, the largest having magnitude 4.8mb, but 34 events could be well located with free-depth solutions and linked to larger events in the region through readings at permanent seismograph stations. The remaining events in the cluster are ones for which depth control is available from at least one station close to the epicenter, i.e., within a distance of 1-1.5...
The Jiashi cluster is named for Jiashi County of the Xinjiang Autonomous Region of NW China. It is composed mainly of events related to the earthquake sequence in early 1997, including two M5.9 events on January 21 and an M6.1 event on April 11. There were many other moderate-sized events in the sequence, which occurred near the western margin of the Tarim Basin and the border with Kyrgyzstan. As a result this cluster is very rich in arrival time data at far-regional and teleseismic distances. Number of events: 125 Calibration type: direct calibration using data to 1.2 degrees; hypocentroid calibration level = 2.7 km Epicentral calibration range: 3 - 5 km Date range: 19771218 - 20041007 Latitude range: 39.303...
The Aqaba cluster is named for the Gulf of Aqaba, between the Sinai Peninsula and Saudia Arabia. The cluster includes significant earthquake sequences in 1993 (5.8 MS) and 1995 (7.1 MS). After the 1995 sequence a number of seismic stations were installed around the Gulf and readings from those stations for more recent events form the basis for the calibration. Number of events: 49 Calibration type: direct calibration using data to 1.0 degrees; hypocentroid calibration level = 1.7 km Epicentral calibration range: 2 - 5 km Date range: 19930730 - 20161129 Latitude range: 28.488 - 29.345 Longitude range: 34.530 - 34.979 Depth range: 12.0 - 30.8 Magnitude range: 3.7 - 7.1
The Magna cluster is named for the town of Magna, Utah, U.S.A., on the southern shore of the Great Salt Lake and the northwestern suburbs of Salt Lake City. The cluster is built around a 5.7 Mw earthquake there on March 18, 2020. The next largets event is a 4.6 Mw aftershock. The local network is quite dense so small, earlier events in the area could be included in the cluster. 18 of those events were relocated in a free-depth inversion to refine the crustal velocity model and event depths. All events in the cluster have depth control from near-source and local distance arrival times. Number of...
The Simeulue cluster is named for the island of Simeulue off the north coast of Sumatra, Indonesia. The cluster is based on 33 events recorded by a temporary network of OBS's from October 2005 to February 2006 to record aftershocks of the Mw 8.6 earthquake of March 28, 2005 (Nias-Simeulue), which was itself probably triggered by the great Sumatra earthquake of December 26, 2004 (Mw 9.1). The Nias-Simeulue earthquake is included in the cluster. Readings from the OBS network (kindly provided by Frederick Tilmann, GFZ Potsdam) provide the calibration of the cluster, which was expanded with moderate-sized events since 2006 to improve the set of teleseismic arrival time data. Many events in the cluster have good datasets...
The Toktogul cluster is named for town of Toktogul, Kyrgyzstan, and the nearby Reservoir of the same name. The cluster is divided into two subclusters, one north of the reservoir and one to the south. The cluster includes the Ms 7.3 earthquake on August 18, 1992 that devastated the town of Susamyr about 40 km to the east, and a half-dozen of the larger aftershocks. On December 22, 2009 a large (4.4 mb) chemical explosion was used in the construction of the hydroelectric dam that created the Toktogul Reservoir. The shot, known as "Kambarata" and included in the cluster, was well instrumented and serves as a calibration event for the cluster. Calibration of the cluster is done with direct calibration, but the ground...
The Chiles cluster is named for Chiles Volcano in northern Ecuador. The cluster is composed mainly of earthquakes associated with a seismic crisis at the volcano in 2014, including a 6.0 mb event on October 20, 2014. About half the events are recorded at teleseismic distances. The station coverage is reasonably good and all events have depth control. Number of events: 31 Calibration type: direct calibration using data to 1.0 degrees; hypocentroid calibration level = 1.8 km Epicentral calibration range: 2 - 4 km Date range: 19970219 - 20150124 Latitude range: 0.439 - 1.250 Longitude range:...
The Nurek cluster is named for the Nurek Dam and Reservoir along the Vakhsh River in Tajikistan. The cluster includes several earthquakes in the low-5 magnitude range. Most of the seismicity appears to be associated with the reservoir and some of the seismicity may have been induced by the filling of the reservoir. It is notable that the the period 1999-2010 produced no earthquakes large enough to be included in the cluster. Number of events: 43 Calibration type: direct calibration using data to 1.2 degrees; hypocentroid calibration level = 1.2 km Epicentral calibration range: 2 - 5 km Date...
The Tocopilla cluster is named for the city of Tocopilla in northern Chile that is on its southern edge. The cluster includes an Mw 6.3 earthquake on September 11, 2020. A few small events that were recorded only locally are included to improve the statistical power of the calibration, but most events are observed to teleseismic distances. All events have depth control from readings at near-source or local distances, and about one third of the events also have teleseismic depth phases readings that are consistent with the inferred depths. Number of events: 48 Calibration type: direct calibration...
The Okinawa cluster is named for the island of Okinawa in the Ryukyu Islands. Although there are deeper events in the area, only events with depths less than about 35 km were retained in the cluster. The cluster contains one large event, an Ms 6.5 event on March 2, 1980 to the west of the island that is likely associated with back-arc spreading. All events have depth constraint from arrivals at near- or local-distances, or from teleseismic depth phases in a few cases. Although the setting is broadly oceanic, the Ryukyu Islands are thought to be part of a remannt continental sliver, so it is not so surprising that a crustal model very close to ak135 fits the observed arrival time data well. ...
The Siah Kuh cluster is named after the village of Siah Kuh (Black Mountain) in Gilan Province, Iran. It consists of only 16 events, the largest being the M4.3 event on September 5, 2005. There's a fairly large azimuthal gap to the east, but the cluster is well calibrated at a level of 1.4 km by using data up to 1.6 degrees. Focal depths of almost all events are constrained with local-distance readings, except for the oldest event in the cluster (January 6, 2005) which is set to a default of 11 km. Number of events: 16 Calibration type: direct calibration using data to 1.6 degrees; hypocentroid...
The Hakodate cluster is named for the city of Hakodate at the south end the island of Hokkaido, Japan. The cluster extends southward to the northern tip of Honshu. Over half the events in the cluster are associated with an earthquake swarm in late March 2000 on the southern flank of Mt. Usu, an active volcano in southern Hokkaido. The distribution of stations is quite good and location calibration is straight-forward. Number of events: 39 Calibration type: direct calibration using data to 1.0 degrees; hypocentroid calibration level = 1.1 km Epicentral calibration range: 1 - 2 km Date range:...
The Ahel cluster is named for the village of Ahel in Fars Province, Iran. This cluster consists of 184 events including the October 31, 1956 Gowdeh earthquake (Magnitude 6.6) and fourteen more older events prior to 1980. Calibration is greatly aided by data from a temporary network deployed by Farzam Yamini-Fard (IIEES). A.R. Ghods (IASBS) repicked many of the arrival times from Iranian networks, including S-P data from the INSM network of accelerometers (BHRC). Focal depths of 23 events are constrained with near-source data, 15 are set by local-distance data, and reminder are fixed to a cluster default of 12 km. Further information about this cluster is contained in: Karasözen et al. (in preparation), Seismotectonics...
The Turt cluster is named for a small settlement on the northeastern shore of Lake Khovsgol in northern Mongolia. The cluster crosses the border with Russia, into Buryatia. The cluster was formed around a 6.7 Mw earthquake on January 11, 2021. This event was followed by a large number of aftershocks which could have been included in the cluster but the coverage from local stations for these events was unbalanced and the location calibration tended to become unstable when a large number of them were included. Most of them were only recorded at regional distances. Several of the largest aftershocks are included. It was difficult to obtain adequate azimuthal coverage for this cluster but the final selection of events...
The Potenza cluster is named for the city of Potenza in the region of Basilicata in southern Italy. It includes the Irpinia earthquake (Ms 6.8) on November 23, 1980, and includes a number of moderate-sized events in recent years. The number of seismic stations in the source region increased markedly in 1999 and again in 2010, making direct calibration very easy. The velocity structure was refined with a subset of recent events for which free-depth relocations could be done. All events have depth constraint from near-source or local distance readings, or for a couple events, teleseismic depth phases. ...
The Kaki cluster is based on the Mw 6.2 mainshock on April 9, 2013, a few tens of km southeast of Bushehr in southern Iran. It's named after a village near the epicenter. The 2013 sequence, including one foreshock and aftershocks through the end of the year, comprises over half of the cluster. Arrival time readings from a temporary seismic network deployed by F. Yamini-Fard (IIEES) to monitor aftershocks are of critical importance to calibrating this cluster. The calibration of this cluster is done by both with direct and indirect technique; near-distance readings up to 0.4 degrees are used for the direct calibration and 18 well calibrated events located by the temporary seismic networks are used for indirect calibration....
The Kobe cluster is named for the city of Kobe, Japan. The cluster is based on the Ms 6.9 earthquake on January 16, 1995 and its aftershocks but it includes more recent events as well. Fitting the pattern of arrivals at local distances required an unusually low crustal P velocity. Number of events: 60 Calibration type: direct calibration using data to 1.0 degrees; hypocentroid calibration level = 0.6 km Epicentral calibration range: 1 - 1 km Date range: 19950116 - 20140805 Latitude range: 34.107 - 35.158 Longitude range: 134.672 - 135.802 Depth range: 14.0 - 22.0 Magnitude range: 3.5...
The Samaria cluster is named for the old community of Samaria, Idaho and the Samaria Mountains in southeastern Idaho. The cluster straddles the border with Utah. It contains one large earthquake, an M6.1 event on March 28, 1975, but none of the other events exceeds 4.6 in magnitude. The M6.1 (USGS) earthquake is often referred to as the Pocatello Valley earthquake. About half of the events are from the 1970s and the quality and quantity of arrival time data are poorer than for modern events; in particular they have few S readings. Focal depths are established by free depth relocation but they are rather unstable and the uncertainties are larger than usual. Depths span a large range, roughly from zero to 20 km,...
The Zahle cluster is named for the city of Zahle, Lebanon, but it covers most of the country and includes some offshore events as well. Most events are small and there are few arrival time data beyond ~30° epicentral distance. The distribution of stations is quite good and the calibration analysis is robust. All events have depth constraint. Depths range through most of the crust. Number of events: 69 Calibration type: direct calibration using data to 0.7 degrees; hypocentroid calibration level = 1.0 km Epicentral calibration range: 1 - 3 km Date range: 19950423 - 20180107 Latitude range: ...
