Thursday, 17 September 2015

Magnitude 8.3 earthquake, central Chile, 16th September 2015

USGS Shakemap: available here
A great earthquake struck central Chile yesterday, with severe to extreme shaking felt in the Coquimbo region. The initial magnitude is estimated at 8.3, making this larger than the 2014 Iquique earthquake and the largest to strike Chile since the magnitude 8.8 earthquake of 2010.

The earthquake occurred along the Chilean Subduction Zone, a fault between the Nazca and South American Plates. The Nazca Plate subducts beneath South America, with the strain that accumulates over time episodically released during earthquakes. Great subduction zone earthquakes such as this are accompanied by intense shaking that may last several minutes. They also frequently generate tsunamis, which may be damaging both close to the source and across ocean basins. Wave heights of over 4m have been reported in Chile. The Pacific Tsunami Warning Centre suggests large waves are unlikely for most Pacific countries, however Chile and French Polynesia remain on alert for waves exceeding 1m.

The 2015 earthquake occurred to the north of the area that ruptured during the 2010 earthquake and in a similar location to an earthquake that occurred in 1943. A paper by Lomnitz (1970) describes the impact of this earlier event. The main points:

  • Extensive damage to towns and villages close to the epicentre, but also as far away as Santiago
  • Large landslides blocked roads
  • Minor tsunami that damaged boats in the fishing village of Los Vilos
  • Numerous aftershocks which caused additional damage
  • Magnitude estimated at 8.3

Similar impacts may be expected from the 2015 earthquake. Initial reports suggest that the tsunami may have been larger than that of 1943, with wave heights exceeding 4m recorded at the Coquimbo tide gauge.

Tide gauge record of the tsunami hitting Coquimbo
Aftershocks are inevitable and have been reported at up to magnitude 7 so far. The strength and number of these is expected to decline over time.

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