Saturday 14 January 2017

Magnitude 5.5 Earthquake in the Central Highlands of Madagascar.

The United States Geological Survey recorded a Magnitude 5.5 Earthquake at a depth of 8.7 km, roughly 42 km to the east of the town of Betafo in Vakinankaratra Region, in the Central Highlands of Madagascar, slightly after 1.05 am local time on Thursday 12 January 2017 (slightly after 10.05 pm on Wednesday 11 January 2017, GMT). There are no reports of any damage or casualties associated with this event, but it was felt across much of central Madagascar, and caused considerable alarm and consternation in a country where large Earthquakes are not common. 

The approximate location of the 11 January 2017 Madagascar Earthquake. USGS.

Madagascar is a former chunk of the ancient continent of Gondwana, that was formerly wedged between Africa, Antarctica, India and the Seychelles. It split away from Africa from about 182 million years onwards and from the other continents between about 115 and 120 million years ago. It currently sits in the western Indian Ocean forming part of the Somali Plate (the eastern chunk of the African Plate, which is currently splitting in two along the East African Rift). However this Indian Ocean segment can be seen as a number of smaller tectonic blocks, such as the Seychelles Microplate and Madagascan Plate, which are being squeezed together by the active rifting on the East African Rift and Indian Ocean Ridge.

The position of Madagascar on the Somali Plate. Wikimedia Commons.

Madagascar itself has two main centres of seismic activity, the Alaotra-Ankay Rift Valley, which is slowly splitting the Central Plateau of Madagascar in half, and which is considered by some to be an extension of the East African Rift, and the Ankaratra Plateau, which is a shield volcanic structure located on this rift, which has reached about 2700 m above sea level in a series of prehistoric lava flows. This volcano have not undergone any eruptive activity in recorded history, but does undergo periodic bouts of seismic activity (Earthquakes).

A hill bisected by rifting in the Central Highlands of Madagescar. Bukla Tours.

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organisation Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.

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