Earthquake
See also: List of earthquakes in ArmeniaThe source of the event was a fault rupture 40 kilometers (25 mi) south of the Caucasus Mountains, a mountain range that has been produced by the convergence of the Arabian and the Eurasion tectonic plates. The range is situated along an active seismic belt that stretches from the Alps in southern Europe to the Himalayas in Asia. The seismicity along this belt is marked by frequent major earthquakes from the Aegean Sea, through Turkey and Iran, and into Afghanistan. Though the recurrence of seismic events in Armenia does not reach the high frequency that is seen in other segments of this zone, rapid crustal deformation there is associated with active thrust faulting and volcanic activity. Mount Ararat, a 5,137 m (16,854 ft) dormant volcano, lies 100 kilometers (62 mi) to the south of the quake's epicenter in Turkey.
The earthquake occurred along a known thrust fault with a length of 60 kilometers (37 mi). Its strike was parallel to the Caucasus range and dipped to the north-northeast. Bruce Bolt, a seismologist and a professor of earth and planetary science at the University of California, Berkeley, walked the length of the fault scarp in 1992 and found that the vertical displacement there measured 1 m (3 ft 3 in) along most of the length with the southwest end reaching 1.6 m (5 ft 3 in). During the earthquake, the northeast-facing side of the Spitak section rode up and over the southwest-facing side.
Its depth was determined to be 5 kilometers (3.1 mi) (established from waveform modeling) and the epicenter was located on the Alavar thrust fault on the slopes of the Lesser Caucasus mountains north of Mount Aragats. The mainshock produced surface rupture and propagated to the west with a separate strike-slip sub-event occurring two seconds later that propagated to the southeast. Going westward the fault split into two branches, a north-dipping reverse fault (north branch) and a right slip fault (south branch), but neither produced surface rupture. A total of five sub-events occurred in the first eleven seconds and an aftershock measuring 5.8 (local magnitude) occurred four minutes and twenty seconds later.
Read more about this topic: 1988 Spitak Earthquake
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