Very strong and shallow M7.1 earthquake hit off the coast of Papua New Guinea and Solomon Islands

Very strong and shallow M7.1 earthquake hit off the coast of Papua New Guinea and Solomon Islands

A very strong and shallow earthquake registered by Geoscience Australia as M7.1 at a depth of 23 km hit off the coast of New Britain, Papua New Guinea and Bougainville Island, Solomon Islands at 07:10 UTC on May 7, 2015. USGS is reporting M7.1 at a depth of 22.1 km (13.7 miles).

Epicenter was located 130 km (81 miles) SW of Panguna, 143 km (89 miles) SW of Arawa, 414 km (257 miles) SE of Kokopo, 536 km (333 miles) ESE of Kimbe, Papua New Guinea, and 628 km (390 miles) WNW of Honiara, Solomon Islands.

There are no people living within 100 km radius.

Based on the preliminary earthquake parameters, hazardous tsunami waves are possible for coasts located within 300 km of the earthquake epicenter, PTWC said.

USGS issued green alert for shaking-related fatalities and economic losses. There is a low likelihood of casualties and damage.

Overall, the population in this region resides in structures that are vulnerable to earthquake shaking, though some resistant structures exist.

Recent earthquakes in this area have caused secondary hazards such as tsunamis and landslides that might have contributed to losses.

This is the fourth very strong earthquake in this region since April 30, 2015.

Image credit: USGS

Earthquakes recorded by USGS from April 30 to May 7, 2015
  1. 7.2149km SW of Panguna, Papua New Guinea2015-05-07 07:10:22 UTC22.1 km
  2. 4.8128km S of Taron, Papua New Guinea2015-05-07 02:15:03 UTC35.0 km
  3. 4.4130km WSW of Panguna, Papua New Guinea2015-05-06 12:39:07 UTC62.7 km
  4. 5.2144km S of Kokopo, Papua New Guinea2015-05-06 07:06:48 UTC46.6 km
  5. 4.715km ESE of Kandrian, Papua New Guinea2015-05-06 06:05:17 UTC75.9 km
  6. 5.4127km SSW of Taron, Papua New Guinea2015-05-06 03:17:16 UTC46.3 km
  7. 4.691km SSW of Taron, Papua New Guinea2015-05-06 01:52:50 UTC44.0 km
  8. 5.038km ESE of Kandrian, Papua New Guinea2015-05-06 01:35:12 UTC44.6 km
  9. 4.8140km S of Taron, Papua New Guinea2015-05-05 21:19:31 UTC32.8 km
  10. 4.8150km S of Kokopo, Papua New Guinea2015-05-05 21:13:27 UTC35.0 km
  11. 5.0142km S of Kokopo, Papua New Guinea2015-05-05 20:39:48 UTC62.0 km
  12. 4.7100km S of Kokopo, Papua New Guinea2015-05-05 17:28:56 UTC74.3 km
  13. 4.5129km S of Kokopo, Papua New Guinea2015-05-05 17:28:16 UTC40.4 km
  14. 4.7111km SW of Kokopo, Papua New Guinea2015-05-05 16:39:44 UTC76.6 km
  15. 4.6117km WSW of Kokopo, Papua New Guinea2015-05-05 15:07:49 UTC59.0 km
  16. 5.0147km S of Kokopo, Papua New Guinea2015-05-05 08:47:08 UTC61.1 km
  17. 5.3129km S of Kokopo, Papua New Guinea2015-05-05 08:16:58 UTC42.8 km
  18. 4.9126km S of Kokopo, Papua New Guinea2015-05-05 06:11:04 UTC51.6 km
  19. 4.9143km SSW of Taron, Papua New Guinea2015-05-05 05:07:29 UTC40.0 km
  20. 5.286km S of Kokopo, Papua New Guinea2015-05-05 05:03:01 UTC55.7 km
  21. 5.2130km S of Kokopo, Papua New Guinea2015-05-05 03:55:51 UTC51.8 km
  22. 5.2124km SSW of Kokopo, Papua New Guinea2015-05-05 02:40:23 UTC33.9 km
  23. 4.4138km S of Taron, Papua New Guinea2015-05-05 02:33:39 UTC35.0 km
  24. 5.6103km S of Kokopo, Papua New Guinea2015-05-05 01:58:20 UTC57.5 km
  25. 5.9109km SSW of Kokopo, Papua New Guinea2015-05-05 01:54:05 UTC64.5 km
  26. 7.5130km SSW of Kokopo, Papua New Guinea2015-05-05 01:44:05 UTC42.0 km
  27. 4.727km SSW of Finschhafen, Papua New Guinea2015-05-04 20:16:35 UTC66.1 km
  28. 5.1143km SSW of Kokopo, Papua New Guinea2015-05-04 08:09:14 UTC60.8 km
  29. 4.6102km SSW of Kokopo, Papua New Guinea2015-05-04 01:04:48 UTC63.3 km
  30. 5.2132km SSW of Kokopo, Papua New Guinea2015-05-03 23:40:56 UTC35.1 km
  31. 5.1133km SSW of Kokopo, Papua New Guinea2015-05-03 22:50:47 UTC46.1 km
  32. 5.5142km SSW of Kokopo, Papua New Guinea2015-05-03 22:35:11 UTC67.9 km
  33. 5.6144km SSW of Kokopo, Papua New Guinea2015-05-03 22:32:42 UTC35.0 km
  34. 5.2150km SSW of Kokopo, Papua New Guinea2015-05-03 20:21:56 UTC76.0 km
  35. 4.8148km SSW of Kokopo, Papua New Guinea2015-05-03 19:28:54 UTC61.0 km
  36. 4.3137km SSW of Kokopo, Papua New Guinea2015-05-03 07:24:28 UTC56.6 km
  37. 5.093km SSW of Kokopo, Papua New Guinea2015-05-02 10:53:06 UTC103.4 km
  38. 4.9124km ESE of Kimbe, Papua New Guinea2015-05-01 19:55:56 UTC44.5 km
  39. 6.8106km SSW of Kokopo, Papua New Guinea2015-05-01 08:06:04 UTC57.0 km
  40. 6.7125km SSW of Kokopo, Papua New Guinea2015-04-30 10:45:05 UTC48.9 km
Updated: 07:49 UTC on May 7, 2015.

Seismotectonics of the New Guinea Region and Vicinity

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.

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.

The western end of the Australia-Pacific plate boundary is perhaps the most complex portion of this boundary, extending 2000 km from Indonesia and the Banda Sea to eastern New Guinea. The boundary is dominantly convergent along an arc-continent collision segment spanning the width of New Guinea, but the regions near the edges of the impinging Australia continental margin also include relatively short segments of extensional, strike-slip and convergent deformation. The dominant convergence is accommodated by shortening and uplift across a 250-350 km-wide band of northern New Guinea, as well as by slow southward-verging subduction of the Pacific plate north of New Guinea at the New Guinea trench. Here, the Australia-Pacific plate relative velocity is approximately 110 mm/yr towards the northeast, leading to the 2-8 mm/yr uplift of the New Guinea Highlands.

Whereas the northern band of deformation is relatively diffuse east of the Indonesia-Papua New Guinea border, in western New Guinea there are at least two small (<100,000 km²) blocks of relatively undeformed lithosphere. The westernmost of these is the Birds Head Peninsula microplate in Indonesia's West Papua province, bounded on the south by the Seram trench. The Seram trench was originally interpreted as an extreme bend in the Sunda subduction zone, but is now thought to represent a southward-verging subduction zone between Birds Head and the Banda Sea.

There have been 22 M7.5+ earthquakes recorded in the New Guinea region since 1900. The dominant earthquake mechanisms are thrust and strike slip, associated with the arc-continent collision and the relative motions between numerous local microplates. The largest earthquake in the region was a M8.2 shallow thrust fault event in the northern Papua province of Indonesia that killed 166 people in 1996.

The western portion of the northern Australia plate boundary extends approximately 4800 km from New Guinea to Sumatra and primarily separates Australia from the Eurasia plate, including the Sunda block. This portion is dominantly convergent and includes subduction at the Sunda (Java) trench, and a young arc-continent collision.

In the east, this boundary extends from the Kai Islands to Sumba along the Timor trough, offset from the Sunda trench by 250 km south of Sumba. Contrary to earlier tectonic models in which this trough was interpreted as a subduction feature continuous with the Sunda subduction zone, it is now thought to represent a subsiding deformational feature related to the collision of the Australia plate continental margin and the volcanic arc of the Eurasia plate, initiating in the last 5-8 Myr. Before collision began, the Sunda subduction zone extended eastward to at least the Kai Islands, evidenced by the presence of a northward-dipping zone of seismicity beneath Timor Leste. A more detailed examination of the seismic zone along it's eastern segment reveals a gap in intermediate depth seismicity under Timor and seismic mechanisms that indicate an eastward propagating tear in the descending slab as the negatively buoyant oceanic lithosphere detaches from positively buoyant continental lithosphere. On the surface, GPS measurements indicate that the region around Timor is currently no longer connected to the Eurasia plate, but instead is moving at nearly the same velocity as the Australia plate, another consequence of collision.

Large earthquakes in eastern Indonesia occur frequently but interplate megathrust events related to subduction are rare; this is likely due to the disconnection of the descending oceanic slab from the continental margin. There have been 9 M7.5+ earthquakes recorded from the Kai Islands to Sumba since 1900. The largest was the great Banda Sea earthquake of 1938 (M8.5) an intermediate depth thrust faulting event that did not cause significant loss of life. (USGS) More information on regional seismicity and tectonics

Featured image credit: USGS

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