Mapping the crustal thickness in southwest Japan using Moho-reflected waves

Salah, Mohamеd K.; Zhao, Dapeng

doi:10.1016/j.pepi.2003.10.002

Cited by 34 publications

(32 citation statements)

References 39 publications

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“…The use of multiple reflected waves in the crust (SmS, sSmS) results in a high-resolution crustal tomography with only two stations . The use of Moho reflected waves (PmP) in tomography leads to a better mapping of the lower crustal structure and the crustal thickness (e.g., Salah and Zhao, 2004;Xia et al, 2007;Sun et al, 2008;Gupta et al, 2009b;Lei et al, 2011). The addition of various types of later phases in the mantle and core in global tomography enables a better imaging of deep mantle plumes (Zhao, 2001c(Zhao, , 2007(Zhao, , 2009.…”

Section: Discussion and Future Perspectivesmentioning

confidence: 99%

Tomography and Dynamics of Western-Pacific Subduction Zones

Zhao¹

2012

Monogr. Environ. Earth Planets

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We review the significant recent results of multiscale seismic tomography of the Western-Pacific subduction zones and discuss their implications for seismotectonics, magmatism, and subduction dynamics, with an emphasis on the Japan Islands. Many important new findings are obtained due to technical advances in tomography, such as the handling of complex-shaped velocity discontinuities, the use of various later phases, the joint inversion of local and teleseismic data, tomographic imaging outside a seismic network, and P-wave anisotropy tomography. Prominent low-velocity (low-V ) and high-attenuation (low-Q) zones are revealed in the crust and uppermost mantle beneath active arc and back-arc volcanoes and they extend to the deeper portion of the mantle wedge, indicating that the low-V /low-Q zones form the sources of arc magmatism and volcanism, and the arc magmatic system is related to deep processes such as convective circulation in the mantle wedge and dehydration reactions in the subducting slab. Seismic anisotropy seems to exist in all portions of the Northeast Japan subduction zone, including the upper and lower crust, the mantle wedge and the subducting Pacific slab. Multilayer anisotropies with different orientations may have caused the apparently weak shear-wave splitting observed so far, whereas recent results show a greater effect of crustal anisotropy than previously thought. Deep subduction of the Philippine Sea slab and deep dehydration of the Pacific slab are revealed beneath Southwest Japan. Significant structural heterogeneities are imaged in the source areas of large earthquakes in the crust, subducting slab and interplate megathrust zone, which may reflect fluids and/or magma originating from slab dehydration that affected the rupture nucleation of large earthquakes. These results suggest that large earthquakes do not strike anywhere, but in only anomalous areas that may be detected with geophysical methods. The occurrence of deep earthquakes under the Japan Sea and the East Asia margin may be related to a metastable olivine wedge in the subducting Pacific slab. The Pacific slab becomes stagnant in the mantle transition zone under East Asia, and a big mantle wedge (BMW) has formed above the stagnant slab. Convective circulations and fluid and magmatic processes in the BMW may have caused intraplate volcanism (e.g., Changbai and Wudalianchi), reactivation of the North China craton, large earthquakes, and other active tectonics in East Asia. Deep subduction and dehydration of continental plates (such as the Eurasian plate, Indian plate and Burma microplate) are also found, which have caused intraplate magmatism (e.g., Tengchong) and geothermal anomalies above the subducted continental plates. Under Kamchatka, the subducting Pacific slab shortens toward the north and terminates near the Aleutian-Kamchatka junction. The slab loss was induced by friction with the surrounding asthenosphere, as the Pacific plate rotated clockwise 30 Ma ago, and then it was enlarged by the slab-edge pinch-off b...

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Section: Discussion and Future Perspectivesmentioning

confidence: 99%

Tomography and Dynamics of Western-Pacific Subduction Zones

Zhao¹

2012

Monogr. Environ. Earth Planets

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“…First, we combine both radial and transverse RFs with a time-shift referred to the slab Moho depth estimated by Shiomi et al [2008] for computing the Ps moveout associated with initial P wave incidence [Park and Levin, submitted manuscript, 2008]. The depth of island-arc Moho is estimated to be 30 km [e.g., Salah and Zhao, 2004] but this depth is almost the same as that of slab Moho beneath the southern part of Kii Peninsula. However, travel time tomography result by Matsubara et al [2008] shows clearly the existence of a dipping low-velocity layer, which corresponds to the subducting oceanic crust.…”

Section: Receiver Function Stackingmentioning

confidence: 99%

Structural features of the subducting slab beneath the Kii Peninsula, central Japan: Seismic evidence of slab segmentation, dehydration, and anisotropy

Shiomi¹,

Park²

2008

J. Geophys. Res.

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Seismic evidence of lithospheric slab segmentation, dehydration, and anisotropic rocks beneath the Kii Peninsula, central Japan, is detected with receiver function (RF) analyses. By stacking radial and transverse RFs with moveout perturbations, we estimate the downdip azimuth, dip angle, and depth of the slab Moho beneath each seismic station. Comparing the downdip azimuth to the slab convergence azimuth, we can classify the slab into three segments. The segments correspond to both the fault zones of past megathrust earthquakes and to the spatial distribution of intraslab seismicity. The slab Moho lies just above the intraslab seismicity in the southwestern Kii Peninsula. Slab Moho lies deeper at the eastern part of the peninsula, at the bottom of seismicity. This suggests that earthquakes occur only within the slab mantle under the southern Kii Peninsula. The dip angle of slab Moho becomes steeper at 40‐ to 50‐km depth, perhaps caused by dehydration transformation of basalt to eclogite. At some stations located in the western part of the Kii Peninsula, RF‐estimated dip angle of the interface is much steeper than that estimated by spatial trends in seismicity. Since the local seismicity distribution reflects well the larger‐scale geometry of the slab, the RF‐estimated dip angle may imply anisotropic wave speeds within strongly sheared and/or hydrated media around the slab Moho. These detailed features of the slab may be one key in distinguishing the source regions of megathrust earthquakes in the Nankai region.

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“…The results of the two previous studies are generally consistent with this study, though the Moho depth by Zhao et al (1992) is deeper by 2-3 km. Both Zhao et al (1992) and Salah and Zhao (2004) found no local structural variations beneath Biwa Lake perhaps due to the lower spatial resolution of their data sets. Salah and Zhao (2003) revealed lateral velocity variations of up to 5% beneath this area (Fig.…”

Section: Discussionmentioning

confidence: 87%

“…The Biwa models show depths of 19 and 31 km for the Conrad and Moho, respectively, which are deeper than the corresponding non-Biwa paths by 1-3 km. Salah and Zhao (2004) inverted the Pm P-P differential times and estimated the Moho depth in this area as 31-32 km under the land area and 29-30 km under the Japan sea coast. Zhao et al (1992) estimated the Conrad and Moho depth distribution and found their ranges to be 15-18 and 32-34 km, respectively, for SW Japan.…”

Section: Discussionmentioning

confidence: 99%

Waveform modelling of local earthquakes in southwest Japan

Abdelwahed

Zhao

2005

Earth Planet Sp

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The crustal structure beneath southwest Japan is investigated through waveform modellings of four local crustal earthquakes by using the generalized ray theory. High-quality seismograms recorded by the Hi-net seismic network are used. The focal mechanism solutions of the events used are estimated by using the first P-wave polarity data. Twenty-nine paths are used to characterize the crustal waveguide in SW Japan. Optimal 1-D velocity models for different paths are derived individually by waveform modelling. Synthetic tests are conducted to study the effects of different model parameters and to confirm the focal mechanism solutions. Modelling the waveforms individually is proven applicable for the heterogeneous regions. The resulted synthetics match the observed seismograms well. Considerable variations of the Conrad and Moho depths are found in the study area. The Conrad depth ranges from 14.8 to 19.7 km, and the Moho depth ranges from 28.4 to 33.4 km. Considerable variations in the crustal structure are found for the eastern portion of the study area where Biwa Lake lies. The effects of Biwa Lake on different paths are examined in detail.

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Mapping the crustal thickness in southwest Japan using Moho-reflected waves

Cited by 34 publications

References 39 publications

Tomography and Dynamics of Western-Pacific Subduction Zones

Tomography and Dynamics of Western-Pacific Subduction Zones

Structural features of the subducting slab beneath the Kii Peninsula, central Japan: Seismic evidence of slab segmentation, dehydration, and anisotropy

Waveform modelling of local earthquakes in southwest Japan

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