十. 岩石圈结构与大陆动力学
(负责人：滕吉文 孙荀英 李惠民)
(Conveners: TENG Jiwen SUN Xunying LI Huimin)
1.中国东北及其邻区三维S波速度结构的面波层析成象
李平① 王椿镛① 许厚泽② 陈运泰① 卢造勋③ 王飞①
①中国地震局地球物理研究所,北京 100081
Surface Wave Tomography of 3-D S Wave Velocity Structure in Northeastern China and Its Adjacent Area
LI Ping1), WANG Chunyong1), HSU Houtze2), CHEN Yuntai1), LU Zaoxun3), WANG Fei1)
1)Institute of Geophysics, China Seismological Bureau, Beijing, 100081, China;
2)Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan, 430077, China;
3)Seismological Bureau of Liaoning Province, Shenyang, 110031, China
ABSTRACT
Many observational seismic surface wave records covering northeastern China and its adjacent area from CDSN and others are processed by means of FTAN and selected. One of the important characteristics in this research is that we apply Occam technique and developed geophysical robust estimation to the inversion to improve the reliability of the solution. We use ray distribution, ray density, ray resolution ellipses and the resolution images of the solution to assess the reliability of the inversion solution. The tomography demonstrates that the S wave velocity distribution is horizontally and vertically inhomogeneous in the research area. There exist obvious interfaces among different kinds of structures.
2.安徽省深部构造特征
王建伟1 王晓莺2 周传公1
（1安徽省物化探院 合肥 230022 2安徽地质调查院 合肥 230001）
摘要
应用区域重力场及地震资料计算MoHo面深度，剖面拟合产状，提出深部构造认识。安徽省MoHo面起伏约7km，皖南幔坳深35～37km，皖江幔隆带32～34km，大别幔坳35～39km，皖北幔坡区33～35.5km。东至～宁国地区为华夏与扬子块对接带，呈向北下插态势。郯庐带深部效应南强北弱，落差1～3km，中段呈断陷，且由南往北逐段西推。大别造山带形成机制：前期扬子块向北俯冲，后期郯庐带左行，华北反向下楔，大别前缘北淮阳对接带推覆、主体挤压抬升。
We calculate the Moho discontinuity’s depth and imitate attitude of rocks on the section with the regional gravity field and seismic data, so that we understand some deep structures. The undulation of Anhui Moho discontinuity is about 7km. The depth of the earth mantle subside is 35～37km in Wannan ; 35～39km in Dabie. The earth mantle uprise zone in Wanjang is 32～34km deep, the area of earth mantle slope in Wanbei is 33～35.5km deep. The area of from Dongzhi to Linguo is convergent boundary between Cathaysian and Yangtze, and it shows a state of inserting down to the north. The effect of deep Tanlu fracture zone is strong in south and weak in north, and the difference in depth is 1～3km. The middle of fracture zone shows fault subsidence and is pushed westwards one by one from south to north. The forming mechanism of the Dabie orogenetic belt: The Yangtze plate dived toward north previous and in the late time the Tanlu zone moved sinistraly and Huabei plate wedged down reversedly, the north Huaiyang convergent boundary of the Dabei forefront was pushed , covered and piled and so that main body was extruded and raised.
3. Present-day Tectonic Stress
Map for Eastern Asia Region
Xu
Zhonghuai
(Institute of Geophysics, China Seismological Bureau, Beijing 100081)
Accumulation of earthquake focal mechanism data in
recent years offers a
new basis to compile a stress map for eastern Asia region. The 4351 stress
indicators we used include (1) 2,999 seismic moment solutions of shallow
(< 60 km) earthquakes issued by Harvard, among which are a batch of plate
boundary shallow earthquakes; (2) 404 focal mechanism solutions of earthquakes
in China; (3) 91 mean stress axes deduced from composite fault plane solutions
of earthquakes; (4) 47 borehole breakout orientations of deep (>1,000 m)
wells.
Two maps showing the maximum and minimum principal
compressive stress
axes, respectively, are drawn on color topographic background map. In
constructing the map, when the maximum or minimum principal stress axis is
vertical in somewhere the intermediate stress axis plotted instead. The
stress regime at a particular place can be identified by inspecting which
stress axis is vertical therein. The original stress data are smoothed for
every 200 km x 200 km area by taking the average orientation of all stress
indicators within this sub-region, and two maps showing mean stress
orientations are also given.
4. Depth Changes of the Core-mantle Boundary
in China
and Its Adjacent Area
Liu
Xiqiang Zhou
Huilan
（Seismological Bureau of Shandong Province Jinan 250014）
Graduate School, University of Science and Technology of China, Beijing 100039)
Abstract
ScS-S differential travel times are idea for imaging lower-mantle velocity structure and depth changes of the core-mantle boundary. Based on digital middle period recording data of wide frequency band and high precision which the twenty three stations of GDSN (USGS),IRIS(IDA),RIS(USGS) and CDSN networks recorded , and wavelet method identifying weak earthquake phases, we got the phase onsets of ScS and S wave. Putting the IASPEI91 as standard reference model, we got the anomaly changes of ScS-S differential travel times and corresponding space change image. Then, we analyses the results.
5. The Upper Mantle
Anisotropy Study in China and Its Adjacent Area
Liu
Xiqiang Zhou Huilan
（the Seismological Bureau of Shandong Province Jinan 250014）
Graduate School, University of Science and Technology of China, Beijing 100039)
Mainly studies the characteristics of ScS(epicenter distance is less than 40 degree ) and SKS waves(epicenter distance is more than 85 degree) splitting in China and its adjacent area. Based on theory studied results, discusses the characteristics of Scs or SKS wave splitting parameters in all propagation directions, some propagation directions parallel or vertical fast shear wave polarization direction included. Compares observation results with the motion direction of each sub-plate on the basis of new structure circumstance in China and others relative studied results. Studied results reveal that characteristics of anisotropic medium do not obvious change with depth, do not exist two anisotropic medium layers, distribution range of the thickness of anisotropic layer is from 80 to 220 kilometers which locates lithostrome or lithostrome and asthenosphere. Observed results are caused by fossil anisotropy and asthenosphere anisotropy.
6. 中国大陆及海域大地热流分布特征及岩石圈热结构
汪
洋 汪集扬 熊亮萍 邓晋福
(中国地质大学(北京)地球科学与资源学院，北京，100029)
terrestrial Heat
flow pattern and lithospheric thermal structure of china continent and its
marginal seas
WANG Yang1 WANG Jiyang2 XIONG Liangping2 DENG Jinfu1
(1 School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China; 2 Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China)
To date, altogether 822 heat flow values were obtained in China continent, and 598 in marginal seas of China. Heat flow pattern in China exhibits significant lateral variation. Generally, it is characterized by a northward-decreasing trend in western China, and by an eastward-increasing trend in eastern China. The lowest heat flow appears in the NW part of China; for instance, the average heat flow in Tarim basin is 45 mW/m2. The highest values have been observed in southern Tibet and eastern Taiwan where the mean values reach up to 80 mW/m2. The heat flow values in rifting area of eastern China vary from 65-80 mW/m2; and the heat flow in central China is in range of 50-65 mW/m2. It is observed that the good correlation between heat flow and the last tectonothermal events of the terrain. The relatively high heat flow is observed in orogens formed in Meso-Cenozoic era, and in old terrain affected by Cenozoic tectonothermal events. The mean heat flow value of China continent and shelf is 63 +/- 15 mW/m2, which is very close to the global continental mean of 65 +/- 1.6 mW/m2 (Pollack et al., 1993).
The pattern of thermal structure of lithosphere in China is similar to that of surface heat flow. The mantle heat flow values are in range of 35-45 mW/m2 in eastern China and shelf basins, and in 14-20 mW/m2 in central Yangtze and NW China, and 22 mW/m2 in Ordos basin. Meanwhile, our numerical modelling shows that it needs higher mantle heat flow to generate the geotherm that is required for the formation of Cenozoic leucogranites in southern Tibet. The thickness of thermal lithosphere in Tarim and central Yangtze platform reaches 200 km or more, but it is less than 85 km beneath Cenozoic extensional basins in eastern China, and generally 130 km or less in other regions.
of
The Lanzhou Ring-shaped Structure
Gao
pengfei
Liang yueming Yu
xuezheng
(
National Geologic
(Aero Geophysical Survey
Environmental Monitor Center) & Remote Sensing Center)
The Lanzhou ring-shaped structure is situated in the center of Dingxi. It is close to round and the radius is about 250km. There is a magnetic low zone surrounded by magnetic high on the magnetic field pattern. The magnetic field strength is between –50nT and 200nT. It is the reflection of the Lanzhou ring-shaped structure. In this paper it is described that the basement is formed of metamorphic rock of Proterozoic and there is discontinuous ring-shaped volcanic rock of Caledonian stage around the basement. Based on the synthesis study of geophysical information, it has been concluded that the earth crust is thin on the ring-shaped structure and wave speed is low on the upper mantle. It is showed that the upper mantle had been gone through obvious heat activity. It is the heat expansion that formed Lanzhou ring-shaped structure.
8. 俯冲带几何特征的一些研究
姚华建 陈敏 肖翔 徐果明
中国科学技术大学地球和空间科学系 合肥 230026
The
Study of the Geometrical Character of the Subduction Boundaries
Yao Huajian, Chen Min et al
The Study of the Geometrical Character
of the Subduction Boundaries
[Abstract] In plate tectonics a plate subducting below another plate may forms different kinds of subduction boundaries as a result of the different physical and chemical properties of the subducting and subducted plates. We establish two kind of the subduction model—slab subduction model & sphere subduction model—to simulate two main subduction boundaries (Japan Trench & Izu Trench). Slab subduction model is fit for dealing with such boundaries as Japan Trench., however sphere subduction model is for the boundaries like Izu. Trench. As a primary step, we consider the subducted plate on the lithosphere as the part of the spherical surface. The center and radius of the sphere is the same as Earth’s. In slab subduction model, the intersectant line is the subduction boundaries and the dip angle is the angle between two normals. In sphere subduction model, we could obtain another kind of subduction boundaries (Izu Trench). And we discuss the dip angle difference between calculated from the model and the angle of the Benioff-Wadati zone today.
[Key words] Subduction boundaries, Benioff-Wadati zone, dip angle
9.
Application of Receiver Function Method
to
Estimate the Buried Depths of Discontinuities in the Upper
Mantle
Beneath China and Adjacent Area
YANG
Yi , ZHOU Huilan
(Graduate
School at Beijing, University of Science
and Technology of China, Beijing, 100039)
Receiver
function is efficacious to determine the deep structure beneath
a
seismic station. With the method, we processed the teleseismic body
waves
recorded at the stations in China and adjacent area. P660S and P410S could be evident in the receiver
functions. According to the prior
work, a
velocity
model of the medium beneath a station was designed for making
synthetic
receiver function. With the
comparison between the observed and
synthetic
receiver function, we adjust the depths of 410-km and 660-km
discontinuities
in the model, until the synthetic one is good fit the
observed.
At last we got the estimations of the buried depths of upper
mantle
discontinuities in the study area .
AND GEODYNAMICS IN EARTH’S INTERIOR
Zhu Jieshou
(Chengdu University of Technology Chengdu 610059)
The CMB (Core-Mantle Boundary) is the important boundary of the physical and chemical boundary in deep earth interior. The contrast of density, velocity and temperature at this boundary implied that the CMB be the thermal and chemical evolution field. The huge thermal engine at the CMB is the source of driving mantle convection and plates motion.
The new generation of high-resolution seismic tomographic images of lower mantle and core-mantle boundary region has provided amazing insights for global tectonics and the dynamic processes of the earth. The ancient oceanic lithospheric slabs sank into the bottom of the lower mantle, and the material of remnants slabs accumulated at the core-mantle boundary. The model of convective flow of the whole mantle was supported by the new seismic images. The D" discontinuity above the core-mantle boundary has a fine and complicated structure and interpreted as a chemical or phase transition zone, and add the possibility that the cold thermal anomaly associated ancient slabs leads to the velocity anomaly. One of the most exciting discovery is the ultralow velocity zone (ULVZ) which close the core-mantle boundary in lower mantle side, it possible be the partial molten layer and the sources of the upwelling plume which cause the hot spots at the earth's surface.
The continental lithosphere of the earth had been
convergented towards to two places of East Asia and Central America. The high
velocity region in lower mantle is coincided with subduction of lithospheric
slabs, cause the amalgamation of plates since Paleozoic time. The low velocity
region in lower mantle is coincided with mantle upwelling in south Pacific and
West Africa. The discoverers of lateral heterogeneous D” layer and the ULVZ may
provide a new approach for the global tectonics research.
11．THE HIGH RESOLUTION SURFACE WAVE
TOMOGRAPHIC IMAGES IN QINGHAI-TIBET
PLATEAU
Zhu Jieshou Cao Jamin Cai Xuelin Cao Xiaolin
(Chengdu University of Technology, Chengdu, China, 610059)
The Qinghai-Tibet plateau and Himalaya, Hindu Kush, Karakoram ranges are spectacular results of the continent-continent collision of Indian plate with Eurasian plate, which characterized by a thick crust and lithosphere. The high resolution seismic surface wave tomographic inversion has been conducted for studying the 3D velocity structure of crust and upper mantle in these areas. The seismic surface waveform data are from the archives of the CDSN, GSN and GEOSCOPE. About 1200 long period surface waveform recordings are available for both dispersion and waveform tomographic inversion. The block inversion by grid 1°×1°in Qinghai-Tibet plateau and 2°×2°in the surrounding areas were adapted. The resulting maps show the high resolution 3D shear wave velocity variation from earth's surface to 400km depth.
The images of S-wave velocity at different depths in the crust and upper-mantle show significant characteristics of lithosphere/asthenosphere structure in Qinghai-Tibet plateau and its surrounding areas. In the 16-32 km depth of the upper-mid crust of the Qiangtang terrane indicates extremely low velocity. In the 40-70 km depth of mid-lower crust, the low velocity areas are extended to the surrounding terranes. In the 85-130 km depth of the upper mantle of Qiangtang terrane, however, the Lahsa terrane has a relatively high velocity. Those implicates the crustal flow in Qinghai-Tibet plateau and the subducted detached Indian lithospheric mantle beneath the plateau. The location of collision of Indian lithospheric mantle with Eurasian is along the Jinsajiang suture zone.
12．The Pattern of lithospheric
Structure and Geodynamics
In the Eurasia and West Pacific Region
Cai xueling Zhu jieshou Cao jamin Liang chuntao
(Chengdu University of Technology, Chengdu, 610059)
Based on the surface wave tomography 3D velocity analysis, and on the structural geological analysis, eight kinds of textural styles for the lithosphere of the Eurasia and Western Pacific region are defined. The concepts of “high-speed block” and “mantle block” are suggested; furthermore, both the geodynamic model and the evolution and transformation model of the ocean-continent-ocean lithosphere are discussed.
Cao Jamin Zhu Jieshou Cai Xuelin
(Chengdu University of Technology, Chengdu, 610059)
In order to study the 3D structure and geodynamics of the earth’s deep interior in China and adjacent areas, and to generate the first version of a digital, electronic database for geosciences general purpose, and to provide a reference model for geophysical inversion by seismic, gravity and geoid data. We constructed the 3D earth’s model in Eurasia and West Pacific region ranges from 10°S to 80°N in latitude and from 0°E to 180°E in longitude. The model giving the “point model”on each junction point of the 2°×2° degree grid that covers the studied area. For each “point model”, it divided 80 layers from top to bottom(depth of 0-2800 km) within the crust, lithospheric mantle，asthenosphere，transition zone，lower mantle.
The database of “point model”formed by the currently available information: existing geological maps, total 722200 km profiles of deep seismic sounding in Eurasian continent and west Pacific regions, gravity and magnetic data, the seismic tomographic images in upper mantle(depth of 50, 70, 100, 130, 170, 210, 250, 300, 400 km) and lower mantle(depth of 650, 1000, 1350, 1700, 2100, 2350, 2750 km) from body and surface waves inversion. The Combinations of all of the data mention above to construct the “point model”of 3-D structure of the Earth that called Initial database, which means the whole 3-D mapping starting with it .
The database for each selected geographic point contains the following parameters as a function of the depth from the geoid: the topographic/bathymetric height of solid surface relative to the geoid, the depth H, the density r, the compression-wave velocity Vp, the compression-wave anelasticity (frequency-independent Qp factor)，the transverse-wave velocity Vs，the transverse-wave anelasticity (frequency-independent Qs factor) and so on.
14．The application of CRT on 3D velocity model of East Asia and West
Pacific
Liang
Chuntao, Zhu Jieshou, Cao Jiaming
(Chengdu
University of Technology, Chengdu, 610059)
The complete ray tracing, CRT for short, consists of two main parts, 1.Calculating the ray path and travel time 2. Calculating vector amplitude by means of ray propagating matrix (Dynamic ray tracing). In the first step, by solving the differential equation tracing system (Cerveny e.t.c), the ray path and travel time on every point along the ray can be got. Shooting method is used in this algorithm, and a station is shot successfully when the endpoint of a ray is located in the circle with the radius as 0.00314. The 3D velocity model in this research spans from 10N to 50N in latitude, 60E to 150E in longitude, from 0 to 2800km in depth. Most of the materials used in this research come from ISC bulletin, and some records of stations in China which are not included in ISC bulletin are added in. On the basis of the ray tracing, we can rebuild the velocity model and eventually deduce the 3D crust and mantle structure in East Asia and West Pacific. (The CRT program is mainly coded by Cerveny, Ludek Klimes, Petr Bulant group, and modified by Liang Chuntao)