The United States Geological Survey recorded a Magnitude 5.4 Earthquake at a depth of 125 km about 2 km off the northwest coast of the island of Guam, a US possession in the Mariana Islands, slightly after 5.50 am local time on Wednesday 10 May 2017, local time (slightly after 7.50 pm on Tuesday 9 May, GMT). There are no reports of any casualties this event, though people have reported feeling the event across much of the northern part of the island.
The approximate location of the 23 April 2017 Guam Earthquake. USGS.
The volcanic Mariana Islands are located on the eastern margin of the Philippine Plate, close to its margin with the Pacific Plate. The Pacific Plate is being subducted beneath the Philippine Plate along the Mariana Trench. This is not a smooth process, an the plates constantly stick together then break apart again as the pressure builds up, resulting in Earthquakes.
Simplified diagram of the subduction of the Pacific Plate beneath the Philippine plate, and how this fuels the volcanos of the Mariana Islands. NOAA Ocean Explorer.
Witness accounts of quakes can help geologists to understand these events and the rock structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) you can report it to the USGS here.
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