Earth Watch Report - Earthquakes
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2013-06-26 22:59:04 UTC
Event Time
- 2013-06-26 22:59:04 UTC
- 2013-06-27 06:59:04 UTC+08:00 at epicenter
- 2013-06-26 17:59:04 UTC-05:00 system time
Location
0.154°S 124.995°E depth=57.5km (35.7mi)
Nearby Cities
- 116km (72mi) SE of Lolayan, Indonesia
- 161km (100mi) S of Tondano, Indonesia
- 165km (103mi) S of Tomohon, Indonesia
- 178km (111mi) S of Bitung, Indonesia
- 931km (578mi) N of Dili, East Timor
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2013-06-27 08:38:09 UTC
Event Time
- 2013-06-27 08:38:09 UTC
- 2013-06-27 16:38:09 UTC+08:00 at epicenter
- 2013-06-27 03:38:09 UTC-05:00 system time
Location
1.095°N 127.112°E depth=130.6km (81.1mi)
Nearby Cities
- 44km (27mi) NW of Kota Ternate, Indonesia
- 45km (28mi) NW of Ternate, Indonesia
- 122km (76mi) SW of Tobelo, Indonesia
- 218km (135mi) E of Bitung, Indonesia
- 1070km (665mi) SW of Koror Town, Palau
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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.
More information on regional seismicity and tectonics
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