远震数据显示贝加尔裂谷带北穆伊斯克(Severomuysk)段地壳和上地幔的精细结构

doi:10.13745/j.esf.sf.2022.2.1

摘要/Abstract

摘要：

通过贝加尔裂谷系统北穆伊斯克(Severomuysk)段的密集地震台站线性网络获得的远距离强震记录,并利用P波接收函数技术,揭示了地壳和上地幔顶部的复杂分层块状结构。横波速度的分布表明构成北穆伊斯克地壳的地块具有不同性质。这些地块的西部聚散和地壳下部的分层证实了该地区隆起的堆积-碰撞起源。位于西伯利亚克拉通变薄的倾斜边缘上的北穆伊斯克段解释了该地区地壳碰撞效应的强度。2015年地震的震中深度与Muyakan 凹陷地壳上部的明显速度差异存在令人信服的相关性。

关键词: 地球物理学, P-波接收函数, 地震速度剖面, 西伯利亚克拉通, 贝加尔裂谷带

Abstract:

The records of distant strong earthquakes, obtained by way of a dense linear network of seismic stations in the Severomuysk segment of the Baikal rift system, revealed a complex layered-block structure of the Earth’s crust and subcrustal mantle using the longitudinal receiving function. The distribution of cross-wave velocities indicates that the properties of the blocks that make up the Severomuysk Earth’s crust differ. The western vergence of these blocks and the stratification of the lower part of the Earth’s crust confirm the accretion-collision origin of the uplift. The intensity of the collision effect on the Earth’s crust of the region is explained by the location of the Severomuysk segment on the thinned inclined edge of the Siberian Craton. A convincing correlation was found between the focal depths of earthquakes in 2015 and contrasting velocity heterogeneities in the upper part of the Earth’s crust of the Muyakan depression.

Key words: geophysics, P-receiver function, seismic velocity sections, Siberian Craton, Baikal rift zone

Valentina V. MORDVINOVA, Maria A. KHRITOVA, Elena A. KOBELEVA, Mikhail M. KOBELEV, Evgeniy Kh. TURUTANOV, Victor S. KANAYKIN. 远震数据显示贝加尔裂谷带北穆伊斯克(Severomuysk)段地壳和上地幔的精细结构[J]. 地学前缘, 2022, 29(2): 378-392.

Valentina V. MORDVINOVA, Maria A. KHRITOVA, Elena A. KOBELEVA, Mikhail M. KOBELEV, Evgeniy Kh. TURUTANOV, Victor S. KANAYKIN. Detailed structure of the Earth’s crust and upper mantle of the Severomuysk segment of the Baikal rift zone according to teleseismic data[J]. Earth Science Frontiers, 2022, 29(2): 378-392.

图/表 9

Fig.1 Diagram of the fault structures of the Severomuysk region of the BRZ and seismicity for the period of 2014-2016. 1—epicenters of earthquakes with K ≥ 10 (M ≥ 3); 2-4—active faults: 2—interblock (I—Severo-Muysky, II—Verkhnemuysky), 3—intra-blocks (III—Perevalny, IV—Angarakansky, V— Muyakansky, VI—Yuzhnomyakansky), 4—local intra-blocks; 5—railway; 6, 7—local and regional (SVKR) seismic stations. The inset shows permanent seismic stations located at a distance of < 500 km from the activation area.

Fig.2 Epicenter density (left) and depth profile of section A-B (right) for the observation period of January 19-31, 2015. N is the average number of earthquakes on an averaging site, measured as φ = 0.01° and λ = 0.02°.

Fig.3 Three-component seismogram of the ARK station. The earthquake of February 16, 2015 off the east coast of Fr. Honshu: earthquake moment is 23:06:28; coordinates are 39.86°S, 142.88°E; magnitude M = 6.7; epicenter distance is 25.10°; depth is 23 km; backward azimuth BAZ is 118.3°.

Fig.4 Layout of seismic observations in the Severomuysk region of the BRZ. TN1, TN3, SVM, ARK, ULG—short-period stations of the temporary location network; SVKR—stationary short-period seismic station; TNV, SVM—temporary broadband stations.

Fig.5 Receiving functions of the ARK station (Q, L, T components) obtained by summing the components of the records of 16 earthquakes

Fig.6 P-receiving functions of SV waves (Q-component) for stations of the “TN1-ULG” profile. The circles indicate the variants of S-exchange at the coromancy border under the corresponding stations along the profile.

Fig.7 Velocity sections of stations of the “TN1-ULG” profile (results of inversion of the receiver function). A thin line shows the starting model, a thick line shows the restored model.

Fig.8 Two-dimensional vS-model based on the results of inversion of receiving functions and topography along the Severomuysk profile. Triangles with corresponding codes indicate the positions of seismic stations. Contours were drawn in the increments of 0.2 and 0.1 km/s in the speed ranges of 2.2-3 and 3-4.6 km/s, respectively.

Fig.9 Seismic-gravity deep section. (A) Granitoid batholith (red) and enclosing rocks (yellow). Dotted line is the boundary of the seismic profile in the density section. (B) Relief along the seismic profile. Triangles with letter codes indicate the position of seismic stations along the profile. Black line shows the isostatic anomaly of gravity. (C) Seismic-gravity deep section. Red line outlines the sole of granitoids of “batholith”. Black lines are the S-wave velocity isolines corresponding to the color velocity scale.

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