Bismark Sea, January 20 : An earthquake of magnitude 6.1 rattled Bismark Sea on Tuesday, a statement by the National Center for Seismology (NCS) said.
The earthquake occurred at a shallow depth of 10km, making it susceptible to aftershocks.
In a post on X, the NCS said, "EQ of M: 6.1, On: 20/01/2026 12:51:50 IST, Lat: 5.20 S, Long: 146.03 E, Depth: 10 Km, Location: Bismarck Sea."
https://x.com/NCS_Earthquake/status/2013517168223363116?s=20
Shallow earthquakes are generally more dangerous than deep earthquakes. This is because the seismic waves from shallow earthquakes have a shorter distance to travel to the surface, resulting in stronger ground shaking and potentially more damage to structures and greater casualties.
The Australia-Pacific plate boundary is over 4000 km long on the northern margin, from the Sunda (Java) trench in the west to the Solomon Islands in the east.
The eastern section is over 2300 km long, extending west from northeast of the Australian continent and the Coral Sea until it intersects the east coast of Papua New Guinea. The boundary is dominated by the general northward subduction of the Australia plate, as per USGS.
Along the South Solomon trench, the Australia plate converges with the Pacific plate at a rate of approximately 95 mm/yr towards the east-northeast. Seismicity along the trench is dominantly related to subduction tectonics and large earthquakes are common: there have been 13 M7.5+ earthquakes recorded since 1900.
On April 1, 2007, a M8.1 interplate megathrust earthquake occurred at the western end of the trench, generating a tsunami and killing at least 40 people. This was the third M8.1 megathrust event associated with this subduction zone in the past century; the other two occurred in 1939 and 1977.
Further east at the New Britain trench, the relative motions of several microplates surrounding the Australia-Pacific boundary, including north-south oriented seafloor spreading in the Woodlark Basin south of the Solomon Islands, maintain the general northward subduction of Australia-affiliated lithosphere beneath Pacific-affiliated lithosphere.
Most of the large and great earthquakes east of New Guinea are related to this subduction; such earthquakes are particularly concentrated at the cusp of the trench south of New Ireland. 33 M7.5+ earthquakes have been recorded since 1900, including three shallow thrust fault M8.1 events in 1906, 1919, and 2007, as per USGS.
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