Crustal structure in a profile off the pacific coast of Northeastern Japan by the refraction method with ocean bottom seismometers.

The region of the Explorer spreading centre off Vancouver Island, British Columbia, has been studied through a marine geophysical survey. Earthquake epicentres located by three ocean bottom seismometers confirm that the boundary between the Pacific plate and the Explorer plate (the northern extension of the Juan de Fuca plate) at present lies along the Sovanco fracture zone, the Explorer ridge, and the Dellwood Knolls. The epicentres of earthquakes in this area as determined by the onshore seismic network are found to be subject to significant errors. The ocean bottom seismometers also have been used for a detailed seismic refraction line just to the north of the Explorer spreading centre employing explosives and a large airgun as sources. A preliminary analysis of the data indicates a fairly typical crustal structure but a shallow and low velocity mantle near the ridge crest, and illustrates the value of ocean bottom seismometers in oceanic refraction studies. A new geothermal heat flux probe was employed in this study that permitted repeated 'pogostick' penetrations without raising the instrument to the surface. Six profiles with a total of 112 penetrations provided valuable data on the nature of hydrothermal circulation in the oceanic crust. Eleven standard heat probe stations provided some restraints on the poorly known age of the oceanic crust along the margin. Seismic reflection profiles using a 3.5 kHz system, a high resolution pulser profiler, and a large airgun were used as aids in the interpretation of the seismic and heat flow data.

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Significant tsunami observed at ocean-bottom pressure gauges during the 2011 off the Pacific coast of Tohoku Earthquake

Earth Planets and Space ◽

10.5047/eps.2011.06.005 ◽

2011 ◽

Vol 63 (7) ◽

pp. 803-808 ◽

Cited By ~ 152

Author(s):

Takuto Maeda ◽

Takashi Furumura ◽

Shin’ichi Sakai ◽

Masanao Shinohara

Keyword(s):

Pacific Coast ◽

Tohoku Earthquake ◽

Ocean Bottom ◽

Bottom Pressure ◽

Ocean Bottom Pressure ◽

The Pacific

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Pre-, Co-, and Post-Seismic Deformation of the 2011 Tohoku-Oki Earthquake and its Implication to a Paradox in Short-Term and Long-Term Deformation

Journal of Disaster Research ◽

10.20965/jdr.2014.p0294 ◽

2014 ◽

Vol 9 (3) ◽

pp. 294-302 ◽

Cited By ~ 17

Author(s):

Takuya Nishimura ◽

Keyword(s):

Pacific Coast ◽

Postseismic Deformation ◽

Plate Interface ◽

Northeastern Japan ◽

The Pacific ◽

Constant Rate ◽

Geologic Time Scale ◽

Seismic Deformation ◽

Coseismic Subsidence

The 2011 Tohoku-oki earthquake caused large eastward displacement and subsidence along the Pacific coast of northeastern Japan. This earthquake partly solved a well-known paradox holding that sense and rate of deformation differ greatly between geologic and geodetic estimates. A paradox remains, however, in explaining long-term uplift along the Pacific coast on a geologic time-scale. Geodetic data show that coastal subsidence continued at a nearly constant rate of ∼5 mm/yr with small fluctuations associated with M7-8 interplate earthquakes for ∼120 years before the Tohoku-oki earthquake. In an area near the Oshika Peninsula where coseismic subsidence is largest, extrapolation of a logarithmic function fitting observed postseismic deformation suggests that coseismic subsidence may be compensated for by the postseismic uplift for several decades but it is difficult to expect the postseismic uplift exceeding 2 meters, so it is implausible that the observed rapid subsidence continued throughout an entire interseismic period in a great megathrust earthquake cycle. We propose a hypothetical model in which the sense of vertical deformation changes from uplift to subsidence during the interseismic period. Using simple elastic dislocation theory, this model is explained by the shallow coupled part of a plate interface in an early interseismic period and the deep coupled part of a late interseismic period.

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Government’s Response to the Great East Japan Earthquake and Tsunami

Journal of Disaster Research ◽

10.20965/jdr.2012.p0517 ◽

2012 ◽

Vol 7 (sp) ◽

pp. 517-527 ◽

Cited By ~ 2

Author(s):

Atsushi Koresawa ◽

Keyword(s):

Pacific Coast ◽

Recovery Process ◽

Japanese Government ◽

Great East Japan Earthquake ◽

Northeastern Japan ◽

The Pacific ◽

Hyogo Framework For Action ◽

One Year

This paper analyzes how the Japanese government has responded to the March 11, 2011, Great East Japan Earthquake and subsequent tsunamis that devastated cities and towns along the Pacific coast of northeastern Japan claiming many precious lives and causing extremely extensive destruction. The resilience of a society depends largely on how it identifies existing gaps, how it addresses them in the recovery process, and how it integrates solutions in the existing disastermanagement system as a result. From such a perspective, this paper examines the government’s response to the disaster for approximately the first one year following it by taking stock of progress made versus the priorities of the Hyogo Framework for Action 2005-2015.

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