Studies of geochemical proxies, such as carbonate d(18)O and TEX86, show that the Earth's climate has changed significantly during the Cretaceous Period. However, knowledge about the sea surface temperature (SST) history of the eastern Tethys is limited. Based on the calcareous nannofossil record of the Nirang section, Tethys Himalayas, this paper attempts to establish the biostratigraphic framework and SST evolution of the Cretaceous Period in the southern Tibet. A total of 131 species were identified from the studied succession. Twelve bioevents were recognized, allowing for early Albian to the early Campanian (CC8 to CC18 biozones) in the section. Meanwhile, a disconformity within 81-71 Ma was also identified. The SST evolution was analysed by the calcareous nannofossils modified temperature index (mTI), and the results reveal that the long-term SST changes in the Tethys Himalayas of southern Tibet experienced progressive warming from the early Albian to the early Turonian and the warm interval persisted until the early Campanian. Short-term warming and cooling events, e. g., rapid warming in the early and late Albian, subsequent cooling in the latest Albian and peak warmth at the Cenomanian-Turonian transition, are also recorded in the study area. The SST history of the Albian-Cenomanian in the eastern Tethys can be well correlated to the western Tethys (central Italy). However, the compilation of TEX86 data indicates substantial global cooling during the Coniacian to Campanian. This study suggests that the northward drift of the Indian continent towards the equator is likely to be responsible for the sustained warmth in the Tethys Himalayas from the middle Turonian to the early Campanian.

The Albian Age is characterized by frequent short-lived perturbations of the global carbon cycle, including a series of Oceanic Anoxic Events (OAEs). Carbon Isotope Excursions (CIEs) document these OAEs in detail. A strong influence of orbital forcing on oceanographic and climatic conditions in the Albian has been documented, but the relationship between orbital changes and the carbon cycle is still unclear. The Albian CIEs are well recorded globally, except in the eastern Tethys. The major forcing mechanisms of Mesozoic carbon cycling have long remained a conundrum. Here, we present bulk carbon (813Ccarb) and oxygen (818Ocarb) isotope data, magnetic susceptibility (MS) and total organic carbon (TOC) data from the Nirang Section in the Tethyan Himalaya of southern Tibet, China. The 813Ccarb record for the first time documents the long-term secular var-iations in 813C during the Albian in the Tethyan Himalaya in high resolution. The 813C curve obtained in Nirang can be correlated well with reference sections in other basins. OAE1b and 1c were identified as troughs in the 813C profile in the lowermost and upper part of the section. Cyclostratigraphic analysis of MS, 813Ccarb and TOC content from the Nirang Section reveals the imprint of the orbital cycles of eccentricity (-100 kyr and -405 kyr) and a long-term amplitude modulation of either obliquity or eccentricity (-1.2 Myr). The band-pass filters of the-100 kyr periodicity in MS provide the estimation of 563 kyr for the duration of OAE 1c and 677 kyr for that of the negative shift between OAE 1b and 1c. A detected-1.1 Myr periodicity is the most significant cycle, providing strong evidence for astronomically paced climate change in the eastern Tethys during the Albian. The band-pass filters of the-1.1 Myr periodicity in MS and TOC display a close correspondence, suggesting that the productivity and/or preservation potential of organic matter was likely controlled by orbitally forced changes in terrigenous input. Increasing 813C values correspond to higher values of MS and TOC content and vice versa, indicating that the 813C values of the eastern Tethys during the Albian were influenced by the intensity of the terrigenous flux and the subsequent burial of organic matter paced by orbital change. This work implies that cyclic changes in carbon reservoirs in the low latitudes of the Southern Hemisphere during the Albian were controlled by seasonal variations in terrigenous input driven by the influence of orbital cycles on regional hy-drological processes.

SUMMARYIn this study, we use continuous waveforms recorded by 258 seismic stations from permanent and temporary networks in Northeast China from September 2009 to August 2011. Using ambient noise cross-correlations and time–frequency phase-weighted stacking based on the S-transform, we retrieve the P waves reflected on 410-km and 660-km discontinuities, we employ a 3-D P-wave velocity model as references to make time–depth conversion and then obtain the lateral depth variations of the two mantle discontinuities. Our results show that beneath the Changbaishan volcano, the 410-km discontinuity is depressed and is relatively thin, indicating the presence of high-temperature materials above the discontinuity. This implies that the Changbaishan volcano formed by upwelling of mantle melting associated with dehydration of the subducting Pacific slab. In the southeast margin of the study region, the 660-km discontinuity is depressed by ∼21 km, indicating the existence of low-temperature materials above the discontinuity. These results support the hypothesis that the Pacific slab has subducted beneath Northeast China and has stagnated at the bottom of the mantle transition zone. In addition, we determine that the 660-km discontinuity at 123.6°E–126.2°E, to the west of this stagnant slab, is slightly uplifted at a small scale, which may have been caused by upwelling melting formed by vertical tearing of the stagnant slab. Moreover, we preliminarily investigate the discontinuities beneath the northern part of the study region. The results show that the 410-km discontinuity is significantly depressed beneath the northeastern margin of the study region, which we attribute to reflected P-wave signals on the boundary between hydrous and anhydrous wadsleyite. The large-scale depression of the 660-km discontinuity observed beneath the northeastern part of the study region may be related to the existence of the stagnant slab.

H-k stacking method is a standard receiver-function method to detect crustal thickness. But this method can not be applied in low-velocity sedimentary basins. To solve this problem, we propose an improved sequential H-k stacking method. The improved method needs two sequential stacks. Firstly, sediment structure is calculated using converted waves and multiples on the bottom boundary of sediments. Secondly, the sedimentary results are applied to calculate the crustal structure. Theoretical calculations and “recovery tests” indicate that the improved method can obtain accurate estimates in sedimentary basins. With the teleseismic data of North China Craton, the structure of sediments is thick in the depression and thin in the uplifted area, which is consistent with Deep Seismic Sounding results. The crust to the west of the North-South Gravity Lineament is relatively thick and has a low average Poisson ratio, whereas the east is relatively thin and has a high average Poisson ratio. This result and the structural feature from data regression imply that the eastern crust of the North China Craton has experienced wide extension, which reflect the crustal response to the severe destruction and deformation in that area compared to the western crust.

根据川滇地区已有的地震各向异性研究结果,利用体波、面波资料的结果,分析川滇地区不同构造尺度、不同深度的地震各向异性特征.对比不同方法研究川滇地区介质各向异性的特点,探讨了该地区的介质连续性及壳幔耦合状态.分析认为,地壳上地幔各向异性的差异表明,川滇地区具有复杂的地壳及上地幔形变机制.因此,对于川滇地区壳幔地震各向异性的深入理解,需在理论上和高密度数据资料基础上加强量化分析和综合研究.

PreviousNext No AccessInternational Geophysical Conference, Qingdao, China, 17-20 April 2017The crustal anisotropy in North-South seismic zone using the data from temporary seismic arrayAuthors: Yi ZhangYuan GaoYi ZhangKey Laboratory of Earthquake Prediction, Institute of Earthquake Science, China Earthquake Administration, BeijingSearch for more papers by this author and Yuan GaoKey Laboratory of Earthquake Prediction, Institute of Earthquake Science, China Earthquake Administration, BeijingSearch for more papers by this authorhttps://doi.org/10.1190/IGC2017-344 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract In this paper, the data from temporary seismic stations in the North-South seismic zone set up under the project ChinaArray Phase I (2011. 01-2014. 06 ) and the project ChinaArray Phase II (2013. 02-2015. 12) are analyzed with the Systematic Analysis Method of shear-wave splitting ( SAM method )in crust of the North-South seismic zone. The environment of regional stress and the characteristics of the tectonic revealed by shear-wave splitting parameters are discussed as well as the relationships between regional principal compressive stress directions and fracture distributions. The results show that the fast shear-wave polarization directions are consistent with the regional principal compressive stress directions, which are gradually varied from NE to NNW from north to south. The NE and WNW or NW faults also have a great influence on the directions of principal compressive stress. The polarization directions of fast shear-waves at stations near the strike-slip faults are parallel to the fault strikes, and a part of these shear-wave polarization directions are nearly perpendicular to the fault strikes, which are similar with the regional principal compressive stress directions. Several stations exhibit complex features, reflecting the complexity of tectonic environment in the study area. The delay times of slow shear-waves in the south part are higher than the north part, reflecting that the southern section has a greater degree of anisotropy in crust and the tectonic deformation is more intense. Keywords: crustal structure, anisotropy, arrays, shear wave, tectonicsPermalink: https://doi.org/10.1190/IGC2017-344FiguresReferencesRelatedDetails International Geophysical Conference, Qingdao, China, 17-20 April 2017ISSN (online):2159-6832Copyright: 2017 Pages: 1525 publication data© 2017 Published in electronic format with permission by the Society of Exploration Geophysicists and Chinese Geophysical SocietyPublisher:Society of Exploration Geophysicists HistoryPublished Online: 31 May 2017 CITATION INFORMATION Yi Zhang and Yuan Gao, (2017), "The crustal anisotropy in North-South seismic zone using the data from temporary seismic array," SEG Global Meeting Abstracts : 1344-1347. https://doi.org/10.1190/IGC2017-344 Plain-Language Summary Keywordscrustal structureanisotropyarraysshear wavetectonicsPDF DownloadLoading ...

The tectonic source for widespread volcanism in northeast China has not been completely understood. We develop a 3‐D SH velocity model in NE China that provides new constraints to the origin of the volcanism. The 3‐D model is constructed from fundamental mode Love waves at the periods of 20–125 s recorded at 269 broadband seismic stations. The Changbai Mountain is characterized by a significant low velocity in the lower crust and uppermost mantle, which probably results from mantle upwelling due to the subduction of the Pacific plate. A fast and thin mantle lid of ~75 km is present beneath the Songliao Basin, indicating lithosphere extension from back‐arc rifting. The slow velocity in the middle and fast velocities in the south and north at 75–115 km depths in the Songliao Basin suggest complex mantle flow with upwelling and downwelling. Unlike the other volcanic fields (Changbaishan volcano, Jingpohu volcano, and Abaga volcano), the Halaha volcano has high velocity in the lower crust and upper mantle, implying a limited melt supply from mantle source recently. The subduction‐induced upwelling leads to complicated small‐scale mantle convection, which is responsible for the intraplate magmatism in northeast China.

In this paper, the data from temporary seismic stations in the North-South seismic zone set up under the project ChinaArray Phase I (2011-01-2014-06) and the project ChinaArray Phase II (2013-02-2015-12) are analyzed with the Systematic Analysis Method of shear-wave splitting (SAM method) to study the crustal anisotropy of the North-South seismic zone. The environment of regional stress and the tectonic characteristics revealed by shear-wave splitting parameters are discussed as well as the relationships between regional principal compressive stress directions and fracture distributions. The results show that the fast shear-wave polarization directions are consistent with the regional principal compressive stress directions, which gradually varied from NE to NNW from north to south. The NE and WNW or NW faults also have a great influence on the directions of principal compressive stress. The polarization directions of fast shear-waves at stations near the strike-slip faults are parallel to the fault strikes, and a part of these shear-wave polarization directions are nearly perpendicular to the fault strikes, which are similar with the regional principal compressive stress directions. Several stations exhibit complex features, reflecting the complexity of tectonic environment in the study area. The delay times of slow shear-waves in the south part are higher than the north part, reflecting that the southern section has a greater degree of anisotropy in crust and the tectonic deformation is more intense. Compared with the upper mantle anisotropy of the North-South seismic zone, it is inferred that there may exist a complicated crust-mantle coupling phenomenon inside of the Sichuan-Yunnan rhombic block. The shear-wave splitting in the crust can not only reflect the regional stress characteristics, but also can reveal the regional tectonic information.

We have measured radial anisotropy in the crust beneath the northern part of North China by jointly inverting Rayleigh and Love wave phase velocities at periods less than 35 s from 14 months of ambient noise data recorded by 222 broad-band seismic stations. We also estimate the azimuthal anisotropy of phase velocity from Rayleigh wave data. The fast direction of azimuthal anisotropy varies with periods, NE-SW orientation at short and intermediate periods (10-16 s) and NW-SE orientation at periods larger than 20 s. The NE-SW oriented fast direction of azimuthal anisotropy may be related to the fossilized structural fabrics due to the compression during the Indosinian orogeny from late Palaeozoic to middle Mesozoic. The NW-SE trend of anisotropic fabric in the lower crust and uppermost mantle is probably associated with the later lithospheric extension. The observed radial anisotropy also shows a two-layer feature, negative radial anisotropy (Vsh < Vsv) in the upper crust and positive (Vsh > Vsv) in the middle-lower crust. The compressional tectonics from late Palaeozoic to middle Mesozoic may cause crustal materials align vertically throughout the crust. This vertical fabric could make Vsh slower than Vsv. However, the lithospheric extension in the late Mesozoic to Cenozoic time could overprint the older fabric in the middle and lower crust by magma intrusion and underplating. Horizontal alignment of the material or intruded melt sills due to the extension probably produce the observed strong positive radial anisotropy in the middle and lower crust.

基于现场调查,并结合震害方面的经验,对滁州城区量大面广的老旧房屋的特点、抗震薄弱环节进行了评述；运用易损性概率分析法对所调查的老旧房屋进行了震害预测；进一步搜集了大量震害资料,总结了类似房屋的震害矩阵,对震害预测结果进行了对比检验.所得结果可供同类城市震害预测借鉴参考.

By means of three-component geomagnetic surveying,the processing and analyzing of data in the juncture region of Jiangsu-Shandong-Henan-Anhui provinces and the South Yellow Sea region,surface spline models for total intensity and horizontal intensity of the geomagnetic field and geomagnetic anomaly field are calculated,and the corresponding geomagnetic field charts and geomagnetic anomaly charts are drawn.Characteristics of variation in regional geomagnetic field are researched.The study shows that three-component geomagnetic survey can not only deliberately describe space distribution of geomagnetic field but also provide scientific data and background field for earthquake prediction.

通过在苏、鲁、豫、皖交界及南黄海地区开展地磁基本场矢量测量、数据处理和分析，计算了该区域地磁基本场和地磁异常场总强度和水平强度的曲面样条模型，并绘制相应的地磁图和地磁异常图，探索研究局部地磁基本场的变化特征。分析结果表明，通过区域地磁基本场矢量测量，能相对精细地反应区域地磁基本场空间分布，分辨存在的地磁基本场异常，为地震中长期预报提供科学数据和相关地球物理场变化背景。