2008 Qeshm earthquake

2008 Qeshm earthquake
Date September 10, 2008
Magnitude 5.9 Mw
Depth 8 kilometers (5.0 mi)[1]
Epicenter 26°50′35″N 55°55′08″E / 26.843°N 55.919°ECoordinates: 26°50′35″N 55°55′08″E / 26.843°N 55.919°E[2]
Areas affected Iran, United Arab Emirates
Tsunami none
Casualties at least 7 dead, 30 injured[3]

The 2008 Qeshm earthquake occurred at 14:30 IRST (11:00 UTC) on 10 September. It had an epicenter on the island of Qeshm, close to the location of the 2005 Qeshm earthquake. It had a magnitude of 5.9 on the moment magnitude scale and caused seven deaths and 30 injuries. It was followed by five aftershocks of M 5.0 or greater over the next ten months.[4]

Geological setting

Iran lies within the complex zone of collision between the Arabian Plate and the Eurasian Plate;[5] near Qeshm the rate of convergence is about 25 millimeters annually.[6] Part of this convergence is accommodated by shortening within the Zagros fold and thrust belt, with the remainder occurring to the north of the Iranian Plateau. The most active part of the Zagros is the 'Simply Folded Belt', which is characterised by large folds formed above a layer of Neoproterozoic Hormuz salt, which locally reaches the surface in the crests of some anticlines as salt diapirs.[5] The sedimentary rocks above the salt layer comprise a basal Cambrian conglomerate and a thick sequence of limestones of Palaeozoic to Upper Cretaceous age, known together as the 'Competent Group' due to their relatively high competence, followed by a sequence of mechanically weaker marls and interbedded limestones of latest Cretaceous to Lower Miocene age topped by Neogene sandstones and conglomerates. There is evidence of intermediate level detachment at some of the weaker layers, leading to folds at different stratigraphic levels have different locations, orientations or wavelengths.[7] Earthquake focal mechanisms and hypocentral depths show that shortening is accommodated by a mixture of high-angle and low-angle reverse faulting, within either the lowest part of the sedimentary cover or in the basement beneath the Hormuz salt.[5]

The island of Qeshm is elongated WSW–ENE, parallel to the coastline and the regional trend of the main fold axes. It is formed of Neogene sediments apart from a diapir of Hormuz salt that pierces through to the surface at the western end of the island. The sediments are affected by a series of large, mainly anticlinal folds that show a variety of trends in the central part of the island. The axis of the Laft anticline runs mainly NW–SE, while the Salakh anticline trends roughly W–E and the Suza anticline and Ramkan syncline trend SW–NE. The island shows clear evidence of recent uplift in the form of marine terraces, with the highest terrace identified at 220 meters (720 ft) above sea level. An uplift rate of 0.2 millimeters annually has been estimated from Uranium series dating of aragonite from corals on the terraces.[8]

Earthquake

The earthquake had a magnitude of 5.9 on the moment magnitude scale, making it the largest in the region since 2005. The hypocentral depth is estimated as 8 km from body wave modelling. The calculated focal mechanism indicates reverse faulting with a small component of strike-slip, on two possible fault planes, either dipping 43° to the north or 52° to the southeast.[9]

Uplift associated with the earthquake has been measured using SAR interferometry. The results are consistent with a fault that did not reach the surface. A simple fault plane model with a width of 12.8 km dipping to the southeast makes a reasonable match with the observed uplift pattern. However, the best fit to both the results from body wave modelling and SAR interferometry comes from a model with two contiguous fault segments, one to the northeast with a strike of 025°, and the other to the southwest with a strike of 065°, both with an overall southeasterly dip. It has been suggested that this earthquake and the 2005 Qeshm event may have ruptured adjacent parts of the same fault.[10]

Damage

The effects were concentrated on Qeshm, where several buildings were destroyed, although minor damage was reported around Bandar Abbas. All of the seven reported deaths occurred on Qeshm, with the injured being transferred to Bandar Abbas by boat. There were no reports of damage to oil industry facilities in the area.[11] High-rise buildings in Dubai swayed during the earthquake, causing some of them to be evacuated, but there were no reports of damage.[12]

References

  1. ↑ Nissen et al. 2010, p. 186.
  2. ↑ Nissen et al. 2010, pg 186.
  3. ↑ Nissen et al. 2010, p. 190.
  4. ↑ Nissen et al. 2010, p. 190.
  5. ↑ 5.0 5.1 5.2 Talebian et al., pp. 506–526.
  6. ↑ Nissen et al. 2007, pg 2.
  7. ↑ Nissen et al. 2010, p. 183.
  8. ↑ Nissen et al. 2007, pp. 2–3.
  9. ↑ Nissen et al. 2010, p. 190.
  10. ↑ Nissen et al. 2010, p. 192.
  11. ↑ BBC (10 September 2008). "Earthquake strikes southern Iran". BBC News. Retrieved 30 December 2012.
  12. ↑ National Geophysical Data Center. "Comments for the Significant Earthquake". Retrieved 30 December 2012.

Bibliography