The United States Geological Survey recorded a Magnitude 5.4 Earthquake at a depth of 120.3 km beneath the island of West Nusa Tenggara, in the southern Lesser Sunda Islands, slightly after 6.30 am local time on Monday 31 October 2017 (slightly after 10.30 pm on Sunday 30 October GMT). Quakes at this depth are seldom dangerous, but are often felt over a wide area, and this one was reportedly felt as far away as Bali in the west and Flores in the East.
The approximate location of the 31 October 2017 West Nusa Tenggara Earthquake (USGS).
West and East Nusa Tenggara form part of the Lesser Sunda Islands, which are located on the northern part of the Timor Microplate. This is trapped between the converging Eurasian and Australian Plates, both of which are being subducted beneath it. In the south the Australian Plate is passing under the island of Timor, with material from the subducted plate melted by the friction and the heat of the Earth's interior rising through the Timor Plate to feed the volcanoes of the island. In the north the Eurasian Plate is being subducted in the same way, feeding the volcanoes there.
The subduction zones beneath the Timor Microplate. Hamson (2004).
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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