Seismicity and structure of the Kamchatka Subduction Zone (original) (raw)
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A double-planed seismic zone in Kamchatka from local and teleseismic data
Geophysical Research Letters, 1994
The fine structure of a double-planed deep seismic zone is studied over a wide area of the Kamchatka peninsula. This prominent feature of deep seismic zone configuration is ascertained through the analysis of microearthquake hypocenters from the local seismic network of the Institute of Volcanology of Kamchatka and 22 focal mechanism solutions from the formal inversion of long-period P and SH waves for events with m•>_5.5. Additionally, 11 focal mechanism solutions estimated from the first motion of P-waves and 12 centroid moment tensor solutions of Harvard University are used. The maximum depth of the double seismic zone is 170-180 km. The two planes of seismicity are separated by 40 km at a depth of 50 km, and by 10-15 km at 180 km depth. The focal mechanism solutions of shallow earthquakes show an abrupt change from the thrust events to down-dip compressional events at approximately 60 km depth at the upper boundary of the descending slab. Within the descending slab, the earthquakes with down-dip tensional axis form the lower plane of the double-planed deep seismic zone. Several earthquakes with down-dip tensional axis are discovered in a narrow area of the upper seismic zone at the depth of about 50 km. The double seismic zone is revealed clearly in the area between ~52øN to ~54øN and probably extends up to --56øN. 1675 alexei @ ollin.igeofcu.unam.mx)
Journal of Geodynamics, 2001
The study addresses the depth distribution of stresses in the Kamchatka Wadati-Benioff zone, based on detailed geometry of the deep seismically active structures, homogeneous data of earthquake focal mechanisms and the inverse technique by . An improved method for determining the regional stress tensor using earthquake focal mechanism data: application to the San Fernando earthquake sequence. J. Geophys. Res. 89, 9305-9320). The used data set includes 205 CMT Harvard solutions for earthquakes which belong to the Wadati-Benioff zone and 17 for a deep-seated subduction segment. The inverse technique used allows for determining the best fit principal stress directions 1 , 2 , 3 and the ratio R= 2 À 1 / 3 À 1 in several depth intervals in the Wadati-Benioff zone and for the deep-seated slab segment considered as a single body. The depth ranges 0-40 and 41-60 km are characterized by maximum compressive stress 1 which is essentially horizontal and trends SE, indicating the NW-SE convergence between the Pacific and Eurasian lithospheric plates. The minimum compression s 3 in the above depth ranges is down-dipping due to the slab pull. The stress tensors obtained for the depth layer 61-80 km and K2, the lower part of the subduction zone, indicate a heterogeneous stress field. Further analysis of the above sub-volumes showed that the stress heterogeneity is attributed to different stress regimes in the frontal and in-slab parts of the Wadati-Benioff zone: the frontal part is under slab-parallel compression and extension which dips at approximately 40 to SE; the in-slab part is subjected to down-dipping to slab-parallel extension and shallow dipping to SE compression. This stress distribution suggests unbending of the subducting plate at depths greater than 61 km. The stresses in the depth range 81-90 km are of similar orientations to those in the in-slab parts of 61-80 and 91-230 km but of different dips. The deep-seated slab segment is characterized by compression which is parallel to the dip 0264-3707/01/$ -see front matter # direction of this volume and by nearly horizontal extension of SE trend. These results show that the main geodynamic forces which drive the presently active processes at different depths in the Kamchatka and Northern Kurille region are the NW-SE convergence between the Eurasian and Pacific plates (ridge push) causing the observed almost horizontal compression of SE trend at 0-60 km depth, the slab pull, unbending forces at depths 61-230 km causing the observed slab-parallel compression in the frontal part of the Wadati-Benioff zone and down-dip to slab-parallel extension in the in-slab part. #
Geophysical Monograph Series, 2000
We present a review of great earthquakes and seismicity patterns along the Alaska-Aleutian and Kamchatka-Kurile arcs as an overview of one of the longest subduction zone complexes on the planet. Seismicity patterns, double seismic zones and focal mechanism solutions are described and used to illustrate the distribution of stress in the Pacific plate as it collides with North America and Eurasia. Seismicity along the Alaska-Aleutian arc is relatively shallow as compared to the Kamchatka-Kurile arc where the plate is considerably older and thicker prior to entering the sub duction zone. Tomographic inversions of the slab generally show high velocity anomalies where seismicity is high, presumably tracking the cold subducting lithosphere.
Thermal modeling of subducted plates: tear and hotspot at the Kamchatka corner
Earth and Planetary Science Letters, 2004
Pacific plate subduction at the Aleutian-Kamchatka juncture, or corner, could be accommodated by either a large bend or a tear in the oceanic lithosphere. In this paper, we describe a number of observations which suggest that the Pacific plate terminates abruptly at the Bering transform zone (TZ). Seismicity shoals along the subduction zone from Southern Kamchatka (600 km) to relatively shallow depths near the Kamchatka-Bering Fault intersection (100-200 km). This seismicity shoaling is accompanied by an increase in the heat flow values measured on the Pacific plate. Moreover, unusual volcanic products related to adakites are erupted on Kamchatka peninsula at the juncture. Simple thermal modeling shows that a slab torn and thinner along the northern edge of the Pacific plate would be compatible with the observations. Delayed thickening of the lithosphere due to the Meiji-Hawaiian hotspot may be responsible for the required thinning. D
Studia Geophysica et Geodaetica, 1984
S u m m a r y : The morphology of the Wadati-Benioff zone in the region of Kamchatka and Northern Kuriles, based on the distribution o f 1102 earthquake foci, verified the existence of an intermediate depth aseismie gap and its relation to active andesitie volcanism. A system o f deep seismically active fracture zones, genetically connected with the process of subduction, was delineated in the continental plate and confirmed by the results of deep aeismie sounding. Two of these fractures, dipping toward the subduction zone, may be considered as the principal feeding channels for active and Holoeene volcanoes of the continental volcanic belts of Kamchatka.
Tomography and Dynamics of Western-Pacific Subduction Zones
Monographs on Environment, Earth and Planets, 2012
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 by the asthenospheric flow. The stagnant slab finally collapses down to the bottom of the mantle, which may trigger upwelling of hot mantle materials from the lower mantle to the shallow mantle. Suggestions are also made for future directions of the seismological research of subduction zones.
Mantle flow at a slab edge: Seismic anisotropy in the Kamchatka Region
Geophysical Research Letters, 2001
The junction of the Aleutian Island and the Kamchatka peninsula defines a sharp turn in the boundary of the Pacific and North American plates, terminating the subduction zones of the northwest Pacific. The regional pattern of shear-wave birefringence near the junction indicates that trench-parallel strain follows the seismogenic Benioff zone, but rotates to trench-normal beyond the slab edge. Asthenospheric mantle is inferred to flow around and beneath the disrupted slab edge, and may influence the shallowing dip of the Benioff zone at the Aleutian junction.
Thermal models, magma transport and tomographic imaging for the Kamchatka subduction zone
2005
Abstract A finite element method is applied to model the thermal structure of the subducted Pacific plate and overlying mantle wedge beneath the southern part of the Kamchatka peninsula. A numerical scheme solves a system of 2D Navier-Stokes equations and a 2D steady state heat transfer equation. A model with the izoviscous mantle exposed very low temperatures (~ 800 ºC) in the mantle wedge, which cannot account for the magma generation below the volcanic belt.