Major Quake, Northern Marianas

A powerful earthquake struck deep below the Pacific Ocean in the northern part of the Mariana Islands this morning.

Saturday, 30th July 2016

A magnitude 7.7 earthquake struck 31 km south-south-west of Agrihan, Northern Mariana Islands at 9:18 this morning, New Zealand Standard Time. The quake was 212 km deep, too deep to generate a tsunami.

Mariana quake trace on GeoNet's seismograph network

Mariana quake trace on GeoNet’s seismograph network


[click for larger image] The powerful earthquake left a strong trace on GeoNet’s New Zealand seismographs. The depth and great distance from New Zealand meant that the energy generated by the earthquake reached most of New Zealand’s seismic instruments at about the same time – a few minutes before 9:30 this morning.

The United States Geological Survey reports that the earthquake was probably due to the release of stress in the distorted Pacific Plate 200 km west of the Mariana Trench where the Pacific tectonic plate begins to slide beneath the Philippine Sea plate. It is thought that the quake resulted from the slip of a fault area 110 km long and 40 km wide, 210 km beneath the Pacific Ocean.

Over the past century, four other earthquakes over magnitude seven have occurred within 250 km of today’s event.

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