A reexamination of earthquakes previously thought to have occurred within the slab between the trench axis and double seismic zone, northern Honshu arc.

Seno, Tetsuzo; Kroeger, G.

doi:10.4294/jpe1952.31.195

Cited by 18 publications

(9 citation statements)

References 28 publications

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“…Kawakatsu and Seno [ 1983] compiled earthquakes of M>5.5 in the area and found no events within the 50-km area from the trench axis to the west. Seno and Kroeger [1983] have redetermined hypocenters and focal mechanisms of six large events (M>5.3) landward of the trench axis. They utilized depth phases and modeled long-period synthetic waveforms to constrain focal depths to +2 km errors.…”

Section: Large Earthquakes and Focal Mechanismsmentioning

confidence: 87%

“…Their hypocenter depths are, however, systematically 3-4 km deeper than our estimated plate boundary. This apparent discrepancy vanishes if we use our wave speed model ( Figure 15), which is about 20-30% lower in average wave speed than the model adopted by Seno and Kroeger [1983]. Five out of six events studied by Seno and Kroeger [1983] were interplate thrust-type events rather than intraplate normal-type.…”

Section: Large Earthquakes and Focal Mechanismsmentioning

confidence: 87%

“…This apparent discrepancy vanishes if we use our wave speed model ( Figure 15), which is about 20-30% lower in average wave speed than the model adopted by Seno and Kroeger [1983]. Five out of six events studied by Seno and Kroeger [1983] were interplate thrust-type events rather than intraplate normal-type. It is clear that the thrust events only start to occur 50-70 km from the trench axis, which is well past the overriding unconsolidated sediment prism (circles in Figure 15).…”

Section: Large Earthquakes and Focal Mechanismsmentioning

confidence: 91%

“…How this inflection is related to the structure and seismicity is unclear and requires future studies. We note at this point that the change in dip must occur approximately where the continental side mantle wedge pinches out and downdip compression intraplate events occur deeper relative to the plate boundary than the events at deeper depths (Figure 15) [Kawakatsu and Seno, 1983]. Our results show the Pacific Ocean crust gradually increases its dip to about 7 ø, 110 km landward of the trench axis.…”

Section: Large Earthquakes and Focal Mechanismsmentioning

confidence: 99%

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Crustal structure and seismicity beneath the forearc off northeastern Japan

Suyehiro¹,

Nishizawa²

1994

J. Geophys. Res.

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Marine seismological and other data in the Japan Trench area (north of 38.5°N) were used to infer the relation of subducting plate structure, seismicity, and focal mechanisms especially at the aseismic to seismogenic zone along the interface between the two interacting plates. Previous crustal models from ocean bottom seismographic refraction (OBS) surveys were improved by taking into account the relative seismic amplitude characteristics and constraining the shallow structure using multichannel seismic data. A wave speed discontinuity in these models is interpreted to be the contact zone of the crust of the overriding plate and the subducting Pacific plate crust. Its dip angle increases to about 7°, 110 km landward of the trench axis. A large increase beneath the deep sea terrace is required to reach the well‐defined angle of 25° beneath the Tohoku east coast. A large wave speed gradient within layer 2, commonly observed under normal oceans, seems to vanish beneath the inner trench slope at about 10‐km depth. Within the overriding plate, apparently brittle material with a P wave speed of ∼6 km/s can be found as near as 35 km from the trench axis. The upper limit of the seismogenic zone of interplate low‐angle thrust events is about 15‐km depth from OBS seismicity and large‐event analyses. Both the strength of the crust of the overriding plate and the characteristics of subducting sediments must be investigated to define the seismic coupling of interacting plates.

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Section: Large Earthquakes and Focal Mechanismsmentioning

confidence: 87%

Section: Large Earthquakes and Focal Mechanismsmentioning

confidence: 87%

Section: Large Earthquakes and Focal Mechanismsmentioning

confidence: 91%

Section: Large Earthquakes and Focal Mechanismsmentioning

confidence: 99%

See 2 more Smart Citations

Crustal structure and seismicity beneath the forearc off northeastern Japan

Suyehiro¹,

Nishizawa²

1994

J. Geophys. Res.

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“…Even if the depths rely on the identification of the pP phase, they are often inaccurate because misidentification of this phase with pwP or other depth phases is common (Yosmi, 1979 a;FORSYTH, 1982). The incorrect depths may lead to incorrect calculation of the take-off angles to local stations and thus result in incorrect fault plane solutions (SENO and KROEGER, 1983). Therefore, previous studies of trench-outer rise events (HERMANN, 1976;CHEN and FORSYTH, 1978;FITCH et al, 1981;STEIN et al, 1982;FORSYTH, 1982;CHINN and ISACKS, 1983;WARD, 1983;CHRISTENSEN and RUFF, 1987) have emphasized that these events must be studied individually using waveform analysis.…”

Section: Introductionmentioning

confidence: 99%

Faulting caused by earthquakes beneath the outer slope of the Japan trench.

Seno

Gonzalez

1987

J,Phys,Earth

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We determined fault plane solutions and focal depths for seven events which occurred in the Japan trench outer slope, using comparison between synthetic and observed long-and short-period teleseismic seismograms. The five normal fault solutions obtained in this study have nearly vertical nodal planes parallel to the trench and their depth range, 2-16 km below the seafloor, is in accord with bending of the oceanic lithosphere prior to subduction. The occurrence of both types of normal faulting, downthrow of both the continental and oceanic sides, is likely to be associated with the formation of horst-graben structures in the outer trench slope near the trench axis.One normal fault solution (31 km below the seafloor) that is significantly deeper than the other normal fault solutions has a nearly vertical nodal plane striking parallel to the ENE magnetic anomaly lineations in the region. This event is also characterized by its lower stress drop or slower rupture than the other events. This event would represent a reactivation of the initial structural fabric inherited from the accretion at the mid-oceanic ridge and indicates that the bending stress is small at this depth. One reverse fault solution, 41 km below the seafloor, is in accord with the compressional bending stress in the deeper portion of the lithosphere. These events indicate that a neutral surface of bending stress is around 30 km depth in this region at least for the past few decades, consistent with the elastic thickness of lithosphere in adjacent regions. This implies that the lithosphere is not entirely in deviatoric tension in this region, suggesting that the 1933 Sanriku earthquake may be a large bending event.

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The Great Tohoku-Oki Earthquake and Tsunami of March 11, 2011 in Japan: A Critical Review and Evaluation of the Tsunami Source Mechanism

Pararas-Carayannis

2013

Pure Appl. Geophys.

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A reexamination of earthquakes previously thought to have occurred within the slab between the trench axis and double seismic zone, northern Honshu arc.

Cited by 18 publications

References 28 publications

Crustal structure and seismicity beneath the forearc off northeastern Japan

Crustal structure and seismicity beneath the forearc off northeastern Japan

Faulting caused by earthquakes beneath the outer slope of the Japan trench.

The Great Tohoku-Oki Earthquake and Tsunami of March 11, 2011 in Japan: A Critical Review and Evaluation of the Tsunami Source Mechanism

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