用GPS和VLBI数据检测固体地球的体积和形状变化

本文利用2003年GPS和VLBI组合的站坐标、站速度及它们的误差估计,采用Delaunay算法生成的三角形来逼近地形表面,研究了地球的表面积、体积及它们的变化趋势,并利用板块运动模型插值方法得到的全球分布均匀的台站对检测方法进行了检核.结果表明,实测的和插值后的数据给出的结论是一致的,即若以赤道为界,北半球在压缩,南半球在膨胀;若以0°～180°经线为界,东半球处于挤压变形中,西半球处于扩张变形中;若以90°～270°经线为界,包含太平洋的半球处于压缩状态,而包含大西洋的半球则处于扩张变形中.这种变形证明地球仍处于非对称变形中.根据GPS和VLBI组合的数据解算的体积变化率达到 -15937×1012?m3·a-1,相当于地球半径每年大约缩短3～4 mm,表明地球整体上处于压缩变形中.     

Evaluation of micro-behavior of strain field in Chinese mainland with the GPS time series

Introduction In the last 20 years, with observation technique development in space monitoring to Earth, a large progress has been made in monitoring crustal movement. This makes it possible for us to study crustal movement and the present geodynamic. Continuous GPS observation conducted in Chinese mainland and its neighboring region provides us for studying the present strain field of crustal micro-behavior tectonic. Crustal micro-behavior tectonic means that we can study the dif-ference bet…     

Horizontal movement and strain characteristics in Tianshan and its adjacent region with GPS deformation data

Introduction The Tianshan Mountain is the youngest cordillera in the present-day continental Asia, and its tectonic evolution is closely related to the collision and subduction between Indian Plate and Eurasian Plate in the Himalayas orogen since Cenozoic…     

基于GPS应变与震源机制解应力反演喜马拉雅构造带现今地壳形变特征

喜马拉雅构造带及其临近区域是印度板块与欧亚大陆板块挤压碰撞的前缘地带.本文利用GPS实测速度场与震源机制解数据分别计算了研究区域现今地壳岩石圈表面的GPS应变场及岩石圈内部的主应力分布,研究了印度板块持续挤压作用下板块边界带地壳岩石圈现今地壳形变的空间分布特征.结果显示,南北向的剧烈挤压变形与东西向的拉伸变形是现今青藏高原南缘地壳岩石圈的主要变形特征.其中南北向的地壳挤压变形主要集中在主前缘冲断带与雅鲁藏布江缝合带之间.东西方向上,南北走向的亚东—谷露断裂是区域地壳东西向伸展变形的重要分界断裂.75°E是研究区域地壳形变的另一条显著不连续边界,其西侧地壳主压应变强度低、方向弥散且最大主压应力方向一致性较差,而东侧地壳主压应变方向与主压应力方向以及地壳水平运动速度场方向均具有较好的一致性.布格重力异常的小波多尺度辨析结果显示该分界带与循喜马拉雅西构造结楔入欧亚大陆的印度板块密切相关.     

3-D velocity structure of P wave in the upper mantle beneath southwestern China and its adjacent areas

IntroductionSouthwestern China and its adjacent areas studied in the paper is the range of 10(N-36(N, 70(E-110(E, which includes southwestern areas of China (Sichuan, Xizang, Yunnan, Guizhou, Guangxi Provinces, southwestern Shaanxi Province and so on), India, Myanmar, Thailand, Vietnam, Laos and Cambodia countries and oceanic areas of Bay of Bengal and Beibu Gulf. The collision and extrusion of India plate and Eurasia plate makes the geological tectonic complex in this area (Figure 1…     

Crustal deformation before the 2008 Wenchuan MS8.0 earthquake studied using GPS data

We used GPS velocities from approximately 700 stations in western China to study the crustal deformation before the Wenchuan M_S8.0 earthquake. The processing methods included analyses of the strain rate field, inversion of fault locking and the GPS velocity profiles. The GPS strain rate in the E-W direction in the Qinghai-Tibet block shows that extensional deformation was dominant in the western region of the block (west of 92.5° E), while compressive deformation predominated in the eastern region of the block (from 92.5° E to 100° E). On a regional scale, the hypocentral region of the Wenchuan earthquake was located at the edge of an intense compression deformation zone of about 1.9 × 10⁻⁸/a in an east-west direction. The characteristic deformation in the seismogenic fault was compressive with a dextral component. The compression deformation rate was greater in the fault's western region than in its eastern region, and the strain accumulation was very slow on the fault scale. The results of a fault locking inversion show that the locking fraction and slip deficit was greater in the middle-northern section of the seismogenic fault than in the southern section. The GPS velocity profile before the Wenchuan earthquake shows that the compression deformation was smaller than the dextral deformation, which is asymmetrical with respect to the distribution of co-seismic displacement. These deformation characteristics should provide some clues to the Wenchuan earthquake which occurred in the later period of the earthquake cycle.     

Current horizontal strain field in Chinese mainland derived from GPS data

Introduction In the years when the reliable data could not be obtained and in the analysis of strain property and magnitude in history, the intensity, property and activity pattern of strain field were mainly inferred on the bases of geometric characters of surface traces and behaviors (especially the faults) as well as the characteristics of petrology (XIE, et al, 1993; Molnar, Tapponnier, 1975, 1977; Tapponnier, Molnar, 1977; FU, et al, 2000). However, they are the averaged results accumu…     

Numerical analysis of contemporary hori-zontal tectonic deformation fields in China from GPS data

Introduction To correctly understand the tectonic deformation of continental lithosphere, its dynamical mechanics and seismic activity, we should firstly acquire the velocity field and strain field of lithospheric tectonic motion with fine resolution and consistent accuracy (Molnar and Lyon-Caen, 1989; Molnar, 1990). And the quality, distribution and density of observed data are the basis for studying crustal tectonic deformation. In the past, crustal deformation is usually determined indi-r…     

Present-day tectonic movement in the northeastern margin of the Qinghai-Xizang (Tibetan) plateau as revealed by earthquake activity

Characteristics of present-day tectonic movement in the northeastern margin of Qinghai-Xizang plateau (Tibetan) are studied based on earthquake data. Evidence of earthquake activity shows that junctures between blocks in this area consist of complicated deformation zones. Between the Gansu-Qinghai block and Alxa block there is a broad compressive deformation zone, which turns essentially to be a network-like deformation region to the southeast. The Liupanshan region, where the Gansu-Qinghai block contacts the Ordos block, is suffering from NE-SW compressive deformation. Junction zone between the Ordos and Alxa block is a shear zone with sections of variable trend. The northwestern and southeastern marginal region of the Ordos is under NNW-SSE extension. The above characteristics of present-day tectonic deformation of the northeastern Qinghai-Xizang plateau may be attributed to the northeastward squeezing of the plateau and the resistance of the Ordos block, as well as the southeastward extrusion of the plateau materials. Foundation item: State Natural Science Foundation of China (49732090) and the Development Program on National Key Basic Researches under the Project Mechanism and Prediction of Continental Strong Earthquakes (95-13-02-05). Contribution No. 00FE2003, Institute of Geophysics, China Seismological Bureau.     

Earth’s deformation due to the dynamical perturbations of the fluid outer core

The elasto-gravitational deformation response of the Earth’s solid parts to the perturbations of the pressure and gravity on the core-mantle boundary (CMB) and the solid inner core boundary (ICB), due to the dynamical behaviors of the fluid outer core (FOC), is discussed. The internal load Love numbers, which are formulized in a general form in this study, are employed to describe the Earth’s deformation. The preliminary reference Earth model (PREM) is used as an example to calculate the internal load Love numbers on the Earth’s surface, CMB and ICB, respectively. The characteristics of the Earth’s deformation variation with the depth and the perturbation periods on the boundaries of the FOC are also investigated. The numerical results indicate that the internal load Love numbers decrease quickly with the increasing degree of the spherical harmonics of the displacement and depend strongly on the perturbation frequencies, especially on the high frequencies. The results, obtained in this work, can be used to construct the boundary conditions for the core dynamics of the long-period oscillations of the Earth’s fluid outer core. Foundation item: State Natural Science Foundation of China (40174022 and 49925411) and the Projects from Chinese Academy of Sciences (KZCX2-106 and KZ952-J1-411).     

Strong motion simulation by the composite source modeling： A case study of 1679 M8.0 Sanhe-Pinggu earthquake

In this study, a composite source model has been used to calculate the realistic strong ground motions in Beijing area, caused by 1679 MS8.0 earthquake in Sanhe-Pinggu. The results could provide us the useful physical parame-ters for the future seismic hazard analysis in this area. Considering the regional geological/geophysical background, we simulated the scenario earthquake with an associated ground motions in the area ranging from 39.3°N to 41.1°N in latitude and from 115.35°E to 117.55°E in longitude. Some of the key factors which could influence the characteristics of strong ground motion have been discussed, and the resultant peak ground acceleration (PGA) distribution and the peak ground velocity (PGV) distribution around Beijing area also have been made as well. A comparison of the simulated result with the results derived from the attenuation relation has been made, and a suf-ficient discussion about the advantages and disadvantages of composite source model also has been given in this study. The numerical results, such as the PGA, PGV, peak ground displacement (PGD), and the three-component time-histories developed for Beijing area, have a potential application in earthquake engineering field and building code design, especially for the evaluation of critical constructions, government decision making and the seismic hazard assessment by financial/insurance companies.     

Superlong-period oscillations of sunspots according to SOHO MDI data

The work is devoted to the study of the oscillation properties of the magnetic and velocity fields of sunspots with typical periods of up to about 10⁴ min. These oscillations were revealed at the beginning of the 1980s (Gopasyuk, 1981) but remain understudied. Using SOHO MDI data and a technique that allows for measurements of magnetic field H and the heliographic coordinates of sunspots φ and λ with higher accuracy than direct measurements of individual pixels, we have studied 72 sunspots observed on the Sun’s visible hemisphere during no less than 9–11 days (±60–70° from the central meridian) with a time resolution of 1 min. Estimates of random errors of a measurement give σ _H ≈ 60 Gs, σ_φ ≈ 0.055°, and σ_λ ≈ 0.050°. It is found that the main periods of the maximum superlong-period oscillations of sunspots are equal to eight days, according to earlier ground-based measurements. Space observations allow the effect of the Earth’s atmosphere to be totally eliminated; therefore, on the basis of recent data, one can conclude that long-period oscillations of sunspot parameters are a real Sun phenomenon.     

Middle and upper crust shear-wave velocity structure of the Chinese mainland

In order to give a more reliable shallow crust model for the Chinese mainland, the present study collected many short-period surface wave data which are better sensitive to shallow earth structures. Different from traditional two-step surface wave tomography, we developed a new linearized surface wave dispersion inversion method to directly get a 3D S-wave velocity model in the second step instead of inverting for 1D S-velocity profile cell by cell. We convert all the regionalized dispersions into linear constraints for a 3D S-velocity model. Checkerboard tests show that this method can give reasonable results. The distribution of the middle-and upper-crust shear-wave velocity of the Chinese mainland in our model is strongly heterogeneous and related to different geotectonic terrains. Low-velocity anomalies delineated very well most of the major sedimentary basins of China. And the variation of velocities at different depths gives an indication of basement depth of the basins. The western Tethyan tectonic domain (on the west of the 95°E longitude) is characterized by low velocity, while the eastern Tethyan domain does not show obvious low velocity. Since petroleum resources often distribute in sedimentary basins where low-velocity anomaly appears, the low velocity anomalies in the western Tethyan domain may indicate a better petroleum prospect than in its eastern counterpart. Besides, low velocity anomaly in the western Tethyan domain and around the Xing’an orogenic belt may be partly caused by high crustal temperature. The weak low-velocity belt along ~105°E longitude corresponds to the N-S strong seismic belt of central China.     

Determination of active units with different kinematic property and their activity pattern in North China based on the data from GPS remeasurements

Based on the high-accuracy data obtained from the GPS measurements carried out in 1992, 1995 and 1996, the isochronous active units with different kinematic property inside the North China area have been distinguished, 4 active units and 1 transition zone with distinct differential movement have been determined. They are Ordos-Yinshan unit, Yanshan unit, Shanxi-Hebei-Shandong (Jin-Ji-Lu) unit, Jiaodong-Liaoning-Shandong (Jiao-Liao-Lu) unit and Yanshan-Hebei (Yan-Ji) transition zone. The relative movements among the neighboring units in this period have been given. 1 The compressive movement between Ordos-Yinshan unit and Yanshan unit is not obvious with an amount of 0.4±1.3 mm/a. 2 Jin-Ji-Lu unit moves E40°S off the Ordos-Yinshan unit and the magnitude is 4.4±1.0 mm/a. 3 Relative to the Yan-Ji transition zone of differential movement, Yanshan unit shifts W38°N with a value of 2.4±1.3 mm/a and Jin-Ji-Lu unit moves eastward 35° by south with an amount of 2.3±0.9 mm/a. 4 Jin-Ji-Lu unit has a tensional left-lateral movement of 4.7±1.4 mm/a in the direction of E37°S relative to Yanshan unit. 5 Some area near Tanlu belt which is located in the southern part of Jin-Ji-Lu block has a southward movement 14° by west with a magnitude of 1.5±1.1 mm/a off the Jin-Ji-Lu unit. 6 Relative to Jin-Ji-Lu unit, Jiao-Liao-Lu unit has a trend of clockwise movement with a tensional right-lateral motion at the north end which neighbors Yanshan unit and a compressive motion at the south end. It should be noted that the errors given in the paper are obtained based on the divergence among the displacements of the sites in the unit, rather than the value calculated from the displacement error of the sites. The analyzed results indicate that: 1 Shanxi tectonic zone and Yan-Ji transition zone are the major tectonic active zones to show the frame and magnitude of interior relative movement in North China area, and others are the secondary tectonic active zones; 2 The complete horizontal deformation in the North China area is not homogeneous nor successive; 3 The kinetic model of North China area might be "mantle dragging plus boundary coupling". Foundation item: The National Key Basic Research Project Mechanism and Prediction of Continental Earthquakes (G1998040700).     

Effects of shock pressure and temperature on titanomagnetite from ICDP cores and target rocks of the El’gygytgyn impact structure,Russia

The aim of this study was to investigate the effect of meteorite impacts on magnetic properties including magnetic susceptibility and the Verwey transition of Ti-poor titanomagnetite of volcanic rocks from the 3.6 Ma old El’gygytgyn impact structure located in the Okhotsk-Chukotka volcanic belt in north-eastern Russia. The target rocks consist mainly of rhyolite with some andesites, and is a rare example of impact structures within volcanic target rocks on Earth. 27 samples from outside the crater, the crater rim and from the depth interval 316 to 517 m below lake bottom (mblb) of the El’gygytgyn ICDP drilling were studied. A significant decrease of the average specific magnetic susceptibility by around 90% was observed between felsic volcanic rocks from the surface (18.1 × 10^-6 m³/kg) and the drill cores from near the crater central uplift (1.9 × 10^-6 m³/kg). Ferrimagnetic Fe-Ti oxide assemblages (Verwey transition temperature, T_V: -161 to -150°C, Curie temperature, T_C: 451 to 581°C), occurring in all studied samples, differ significantly. At the surface titanomaghemite is ubiquitously associated with titanomagnetite. The drill cores lack titanomaghemite, but either show a transformation into titanomagnetite and ilmenite or a strong fragmentation associated with a second T_V between -172 and -188°C. Reversible curves of temperature dependence of magnetic susceptibility in the suevite indicate high depositional temperatures of at least 500°C. In the polymict and monomict impact breccia mechanical deformation of titanomagnetite and temperatures of at least 200-350°C related to the shock are suggested from temperature dependent magnetic susceptibility cycling. Lowtemperature oxidation along strongly brecciated grain surfaces in titanomagnetite is suggested to cause the lower TV and we suggest that this phenomenon is related to postimpact hydrothermal activity. The strong magnetic susceptibility decrease at El’gygytgyn is mainly influenced by shock, and post-impact hydrothermalism causes a significant additional depletion. These observations explain why magnetic lows are a ubiquitous phenomenon over impact structures.     

Lg Wave Attenuation in the Isparta Angle and Anatolian Plateau (Turkey)

We estimate Lg wave attenuation using local and regional seismic phases in the Isparta Angle and the Anatolian Plateau (Turkey). The Isparta Angle (IA) is a tectonically active zone forming the boundary between the African Plate and the Anatolian Plateau, and is currently undergoing N–S extensional deformation. The Anatolian Plateau contains many intra-continental faults including the North Anatolian Fault Zone and the East Anatolian Fault Zone as well as the Menderes Massif. A large waveform data set was compiled from a variety of local and regional seismic networks including 121 digital seismic stations (broad-band and short period) between 1999 and 2008 spanning the IA, the Anatolian Plateau and Azerbaijan. The data set was used to determine the nature of Lg wave propagation and characterize the nature of seismic attenuation within the crust of these regions. Lg waveforms were used to calculate the frequency-dependent Lg-Q _o and Lg- $ \eta $ . A wide range of Lg-Q _o values was obtained between ~52 ± 6 and 524 ± 227. Low Lg-Q _o values (~90–155) are calculated towards the north of IA, Iskenderun Gulf and its vicinity, Bingöl-Karl?ova, Izmit and its vicinity. Lg-Q _o values are especially low (<90) along the Menderes Massif and the Aksehir-Simav Fault Zones. This may be due to intrinsic attenuation of Lg associated with the partially molten crust and young volcanism. The high Lg-Q _o values (~350) are probably caused by the crust not being subject to large amounts of extensional deformation like the Antalya Gulf and apparently being thick enough to support Lg propagation. Relatively higher values along the border of this subduction zone and plate boundary might be related to the Taurus Mountain belts and Bitlis-Zagros Suture Zone. The lateral frequency dependency Lg- $ \eta $ is also consistent with high tectonic activity in this region.     

Moment Tensor Solutions of Earthquakes in the Indian Ocean from Surface Waves and their Tectonic Implications

—Rayleigh and Love waves generated by sixteen earthquakes which occurred in the Indian Ocean and were recorded at 13 WWSSN stations of Asia, Africa and Australia are used to determine the moment tensor solution of these earthquakes. A combination of thrust and strike-slip faulting is obtained for earthquakes occurring in the Bay of Bengal. Thrust, strike slip or normal faulting (or either of the combination) is obtained for earthquakes occurring in the Arabian Sea and the Indian Ocean. The resultant compressive and tensional stress directions are estimated from more than 300 centroid moment tensor (CMT) solution of earthquakes occurring in different parts of the Indian Ocean. The resultant compressive stress directions are changing from north-south to east-west and the resultant tensional stress directions from east-west to north-south in different parts of the Indian Ocean. The results infer the counterclockwise movement of the region (0°–33°S and 64°E–94°E), stretching from the Rodriguez triple junction to the intense deformation zone of the central Indian Ocean and the formation of a new subduction zone (island arc) beneath the intense deformation zone of the central Indian Ocean and another at the southern part of the central Indian basin. The compressive stress direction is along the ridge axis and the extensional stress manifests across the ridge axis. The north-south to northeast-south west compression and east-west to northwest-southeast extension in the Indian Ocean suggest the northward underthrusting of the Indian plate beneath the Eurasian plate and the subduction beneath the Sunda arc region in the eastern part. The focal depth of earthquakes is estimated to be shallow, varying from 4 to 20 km and increasing gradually in the age of the oceanic lithosphere with the focal depth of earthquakes in the Indian Ocean.     

菲律宾海板块的整体旋转线性应变模型与板内形变-应变场

用菲律宾海板块上7个站ITRF2000的速度建立了菲律宾海板块的整体旋转线性应变模型. 结果认为菲律宾海板块的现今运动是顺时针方向旋转,与NNR_NUVEL_1A估计的旋转方向一致,但与NNR_NUVE_1A估计的旋转极位置和旋转角速度有较大差别. 本文模型与Sella等建立的刚体运动模型相比能更精确地描述菲律宾海板块的现今构造运动与板内形变. 菲律宾海板块内部存在强烈的形变-应变场. 在板块上存在一致的向东形变,形变速率在中央构造线附近小,东、西边界附近大,南、北两端小,中部大,在Mariana弧上向东的形变速率达到484 mm/a. 板块上南北方向的形变,东、西部存在明显差别,东部的南北向形变速率很小,西部在Manila海沟附近南北向形变速率较大,北端向北的形变速率为113 mm/a,南端向南的形变速率为293 mm/a. 板块的中央构造线把板块的主应变场分为东、西两个区. 东区存在非常强烈的张应变,压应变则很弱. 主张应变为近东西方向,从中央构造线向东主张与主压应变率逐渐增加,板块东南边界附近（148°E,15°N）主张应变率最大为858×10-8/a. 在西区,存在很强的主压应变而主张应变则较弱,主压应变为NW-SE方向,主压与主张应变率呈现从中央构造向西逐渐增加的特征,在板块西北边界（122°E,23°N）附近,主压应变率最大为571×10-8/a. 菲律宾海板块主应变场的空间变化与板块内部及周围的构造背景密切相关,是构造应力场的反映.     

Crustal Strain Patterns in the Satpura Mountain Belt,Central India: Implications for Tectonics and Seismicity in Stable Continental Regions

The Satpura Mountains of central India represents an ancient orogenic belt of the Mesoproterozoic time. It has a distinct sygmoidal (S-shaped) geometry with long EW and short NE–SW alignments. The mountain belt has been affected by tectonic activities throughout the geological past. The association of high seismicity, high heat flow and high Bouguer gravity anomaly with high topography of the region is a very distinct feature of the mountain range. Present analysis demonstrates that the average velocity for central India has a value of ~54 mm/year towards N050°. The velocity field vector can be partitioned into an eastward component parallel to the Satpura Mountain Belt and a northward component across the belt. The partitioned components provide evidence for sinistral strike–slip deformation of anomalously high shear strain rate of ~3 × 10⁻⁹/year in the region. Similar high shear strain rates are also found from the strain determined by GPS data. An extremely high rate of extensional strain (~600 × 10⁻⁹/year), which is comparable to that of the continental rift systems, is recorded from geodetic data of the Satpura Mountain Belt and the adjacent regions. Regional sinistral shape of the Satpura Mountains involved in a sinistral-slip transtension regime is interpreted to be the cause of high extensional and shear strain regime of the area. The occurrence of normal faulting detected in several deep seismic sounding profiles, the Moho upwarp, crustal thinning, high heat flow and high seismicity of the Satpura region are explained by this tectonic model.     

Velocity constraints for the inner core inferred from long-period PKP amplitudes

Long-period PKP amplitudes from 16 earthquakes in the distance range 110– 170° are compared with theoretical amplitudes which are derived from synthetic seismograms calculated for 56 systematic modifications of Earth model 1066B in the inner core. A suitable normalization procedure allows for the common representation of all observed amplitudes as a function of epicentral distance. Using the theoretical amplitude distributions it can be shown that the parameters of a regression line through the logarithmic and normalized amplitudes between 110 and 134° are related to the velocity and density jump at the inner-core boundary (ICB). The analysis shows that the dominant influence on the PKP amplitudes is the P-velocity jump which can be restricted to 0.64 ± 0.05 km s^?1. There exists a trade-off between the S-velocity jump and the density jump. Restricting the latter to the reasonable range 0–1.2 g cm^?3 the S-velocity jump at the ICB can be inferred to be 2.5–3.0 km s^?1. A rather strong S-velocity gradient below the ICB follows from the condition that the S-wave travel-time through the inner core agrees with that implied by free oscillation observations. This leads to central S-velocities between 3.81 and 4.15 km s^?1, assuming a parabolic velocity law.