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Impact of Topography and Land-Sea Distribution on East Asian Paleoenvironmental Patterns

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Advances in Atmospheric Sciences 2006年第2期23卷 258-266页

作者：张仲石王会军郭正堂姜大膀 institute of Geology and geophysics Nansen-Zhu International Research Center

Much geological research has illustrated the transition of paleoenvironmental patterns during the Cenozoic from a planetary-wind-dominant type to a monsoon-dominant type, indicating the initiation of the East Asian monsoon and inland-type aridity. However, there is a dispute about the causes and mechanisms of the transition, especially about the impact of the Himalayan/Tibetan Plateau uplift and the Paratethys Sea retreat, Thirty numerical sensitivity experiments under different land-sea distributions and Himalayan/Tibetan Plateau topography conditions are performed here to simulate the evolution of climate belts with emphasis on changes in the rain band, and these are compared with the changes in the paleoenvironmental patterns during the Cenozoic recovered by geological records. The consistency between simulations and the geological evidence indicates that both the Tibetan Plateau uplift and the Paratethys Sea retreat play important roles in the formation of the monsoon-dominant environmental pattern. Furthermore, the simulations show the monsoon-dominant environmental pattern comes into being when the Himalayan/Tibetan Plateau reaches 1000-2000 m high and the Paratethys Sea retreats to the Turan Plate.

关键词： Paratethys Sea retreat Himalayan/Tibetan Plateau uplift paleoenvironmental pattern precipitation field Turan Plate

Study on noise in simultaneous geomagnetic difference data caused by the effect of S_q local-time variation

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Acta Seismologica Sinica(English Edition) 2006年第1期19卷 87-92页

作者：任熙宪 institute of geophysics China Earthquake Administration Beijing 100081 China

A new concept is suggested on tectonomagnetic research about the noise in simultaneous geomagnetic difference data caused by the effect of Sq local-time variation, together with the method of theoretical calculation. The level of the noise and its contribution to the total noises of the differences data are analyzed. The result indicates that the noise increases linearly with the increase of the distance between the two stations in the range of 40° longitude-difference, and its increasing rate is about 0.4 nT/（°）at latitude 40°N. The example calculated at a pair of sites with longitude-difference 0.357°, shows that the noise is about one fifth of the total noises of the difference data on geomagnetic quiet-day.

关键词： solar-quiet-day variation Sq local-time variation same latitude simultaneous difference data noise

Crustal P-wave velocity structure in Lower Yangtze region: Reinterpretation of Fuliji-Fengxian deep seismic sounding profile

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Chinese Science Bulletin 2006年第19期51卷 2391-2400页

作者： BAI Zhiming WANG Chunyong institute of Geology and geophysics Chinese Academy of Sciences Beijing 100029 China institute of geophysics China Earthquake Administration Beijing 100081 China

The finite-difference inversion method and RayInvr technique had been employed to inter- pret the wide-angle seismic reflection/refraction data of the Fuliji-Fengxian deep seismic sounding (DSS) profile in Lower Yangtze region, hence the velocity structure was acquired and conclusions were sum- marized as follows: (1) The velocity model along this profile can be divided into three large layers vertically (upper, middle and lower crusts) and six blocks laterally, and this velocity distribution agrees with the feature of stable platform. (2) The depth of Moho discontinuity is 30―36 km. The thickness of the upper crust is 10.5―13.0 km, where the lateral velocity varies strongly, and the velocity increases to 6.2 km/s?1 at bottom. Besides, the velocity distribu- tions in the bottom layer of middle crust and lower crust have an apparent inhomogeneity. The velocity in upper layer of middle crust, lower layer of middle crust, lower crust and uppermost mantle is 5.9―6.2, 6.3―6.4, 6.6―7.0 and 8.06―8.29 km/s?1, respec- tively. (3) On two sides of the Tanlu fault belt (TFB), the mid-crustal velocity structure is quite different, nevertheless no apparent discrimination in velocity distribution and boundary topography exhibits in lower crust, hence it is inferred that the Jiashan segment of TFB had probably cut through whole crust in the Mesozoic, and the fault behaviour in lower crust had disappeared due to the low viscosity produced by the orogenic extension or crustal bal- ance, while the fault features in the rigid middle-uppercrust have been preserved up to the present. (4) The moderate earthquakes with Ms > 5.0 nearby Zhen- jiang are related to the deep faults extending into the lower crust, and the earthquakes were probably induced by the energy been transferred from man- tle lithosphere to upper-mid crust along the deep faults, and aggregated at some preferable tectonic positions.

关键词：华东地区地壳应力地震资料速度结构长江流域

Technique development of PC104 embedded module and its application in the geophysical instrument design

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Acta Seismologica Sinica(English Edition) 2002年第4期15卷 439-446页

作者：滕云田张炼王彦刘晓芹马延妮 institute of geophysics China Seismological Bureau Beijing 100081 China

The mainstream embedded resolutions widely adopted in the geophysical observation device are discussed in this paper. The advantages and its applicability of the PC104 embedded module are demonstrated through its performance description, technique development and its applications in the design of the fluxgate magnetometer, the movable seismograph and the GPS steering device.

关键词： microprocessor PC104 embedded module observation device

Differential patterns of SH and P wave velocity structures in the transition zone beneath northwestern Tibet

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Science China Earth Sciences 2011年第10期54卷 1551-1562页

作者： ZHANG RuiQing WU QingJu LI YongHua ZENG RongSheng institute of geophysics China Earthquake Administration Beijing 100081 China

Triplicate waveform modeling is used to resolve SH （Vs） and P （Vp） wave velocity structures in the upper mantle transition zone （TZ） beneath northwestern （NW） Tibet. Focal depth move out stacking is proposed to enhance the identification of triplicate phases, and can be used to test consistency of our data. Our results show that the Vs and Vp structures are decorrelated, and that a large Vs jump occurred across the 660-km discontinuity, with a small Vs gradient above it. Conversely, the Vp model is characterized by a relatively small contrast across the discontinuity, accompanied by a high Vp gradient in the TZ. There seem no significant depth anomalies of the 660-kin discontinuity in both models. The seismic structures in TZ beneath NW Tibet are similar to recent studies beneath the central Qiangtang and western Lhasa terrains. Taking the lower TZ structures under India as references, Vs is normal but Vp appears slightly high, and thus a high ratio of Vp/Vs was indicated beneath NW Tibet. Combined results with experiment information from mineral studies, we suggest that the differential anomalies of Vp and Vs can be attributed to a chemical heterogeneity, such as increased A1 content in the lower TZ. Considering the tectonic evolution of Tibet, the chemical heterogeneity may be associated with subduction or detachment of the Tethys oceanic slab.

关键词： mantle transition zone seismic velocity northwestern Tibet

Studies on Gravity Tides in King George Island, Antarctica

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Science China Chemistry 1993年第3期36卷 350-357页

作者：吕纯操许厚泽郝兴华倪志宏 institute of Geodesy and geophysics Academia Sinica Wuchang 430077 PRC

By utilizing LCR-G gravimeter, 342-day available gravity tide observations were obtained in King George Island, Antarctica. Analytical results show that mean errors of tidal factor δ and phase delay △φ for main waves are less than 0.6% and 0.3° respectively. By using the Schwiderski cotidal map to make oceanic tide correction, we discover that the effect on M_2 wave by oceanic tide reaches 20% of body tide magnitude, and leading phase is 6.7°. The obtained gravity tidal factors of this region areδ_(O_1)=1.2178±0.0061, △φ_(O_1)=2.13±0.25°,δ_(M_2)=1.2350±0.0045, △φ_(M_2)=-0.53±0.16°.

关键词： gravimeter calibration tidal factor phase delay harmonic analysis tide correction.

Magnitude and rupture duration from high frequency teleseismic P wave with projected landweber deconvolution

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Science China Earth Sciences 2013年第1期56卷 13-21页

作者： ZHENG Yong NI SiDao CHEN Yong TAN Ying Don HELMBERGER State Key Laboratory of Geodesy and Earth's Dynamics Institute of Geodesy and Geophysics Chinese Academy of Sciences institute of geophysics Chinese Earthquake Administration Seismological Laboratory California Institute of Technology

Earthquake magnitude and rupture duration are among the most important parameters characterizing an earthquake for the purpose of early tsunami warning. While they can be routinely determined from broadband P waveforms with iterative inver- sion procedures, the inversion procedures may fail when the rupture either lasts longer than the interval between P and later ar- rivals or requires too much time or human intervention. Little contaminated by later arrivals, high frequency P waves are useful for modeling earthquake source processes, though the envelope waveform is affected by strong scattering in lithosphere. With high frequency envelopes from aftershocks as Empirical Green＇s Function （EGF）, the coda effects can be removed and more accurate relative source time function （RSTF） of the main shock can be obtained. Assuming that RSTFs cannot be negative, we use the projected Landweber deconvolution method （PLD） to obtain high frequency RSTFs because PLD method has the ad- vantage of non-negativity, causality, and compactness （finite duration）. We are able to determine rupture durations of four large earthquakes： the 2004 Sumatra-Andaman earthquake, the 2005 Nias event, the 2006 Java event, and the 2011 Tokuko earthquake. The rupture durations of the Sumatra-Andaman, Nias, and Tohuko events are found to be around 550, 1 i0, and 120 s respectively, consistent with previous studies. The rupture duration of the Java event is about 130 s, supporting that the Java event is a tsunami earthquake. The magnitudes of these earthquakes are found to depend on both the amplitude and the duration of the deconvolved waveforms, and can be approximated by integrating these waveforms.

关键词： high frequency deconvolution rupture duration magnitude

Relocation of the M8.0 Wenchuan earthquake and its aftershock sequence

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Science China Earth Sciences 2008年第12期51卷 1703-1711页

作者： HUANG Yuan WU JianPing ZHANG TianZhong ZHANG DongNing institute of geophysics China Earthquake AdministrationBeijing 100081China

We relocated M8.0 Wenchuan earthquake and 2706 aftershocks with M≥2.0 using double-difference algorithm and obtained relocations of 2553 events. To reduce the influence of lateral variation in crustal and upper mantle velocity structure, we used different velocity models for the east and west side of Longmenshan fault zone. In the relocation process, we added seismic data from portable seismic sta-tions close to the shocks to constrain focal depths. The precisions in E-W, N-S, and U-D directions after relocation are 0.6, 0.7, and 2.5 km respectively. The relocation results show that the aftershock epi-centers of Wenchuan earthquake were distributed in NE-SW direction, with a total length of about 330 km. The aftershocks were concentrated on the west side of the central fault of Longmenshan fault zone, excluding those on the north of Qingchuan, which obviously deviated from the surface fault and passed through Pingwu-Qingchuan fault in the north. The dominant focal depths of the aftershocks are between 5 and 20 km, the average depth is 13.3 km, and the depth of the relocated main shock is 16.0 km. The depth profile reveals that focal depth distribution in some of the areas is characterized by high-angle westward dipping. The rupture mode of the main shock features reverse faulting in the south, with a large strike-slip component in the north.

关键词： Wenchuan earthquake Longmenshan fault zone earthquake relocation regional velocity model first arrival

ZHANG Heng’s Seismometer and Longxi earthquake in AD 134

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Acta Seismologica Sinica(English Edition) 2006年第6期19卷 704-719页

作者：冯锐俞言祥 institute of geophysics China Earthquake Administration Beijing 100081 China

Longxi earthquake was the only earthquake example, which ZHANG Heng＇s Seismometer had detected. Therefore this event attracted the attention of the academic circle and also served as crucial evidence to examine the rationality of the reconstructed model of the seismometer. But for a long time, owing to the fact that the Jincheng-Longxi earthquake on February 28, AD 138 was mistaken as the event went against the historical records, it was refuted by the researches of both in China and abroad. By making careful textual research of historical records, especially by analyzing the description of Longxi earthquake of Houhan Shu, by studying the historical background exposed by historical literatures at that time, ZHANG Heng＇s biography, his poems and place names of Han Dynasty, by comparing five earthquakes occurred in Qing Dynasty and their attenuation of seismic intensity, the conclusion can be drawn that the Longxi earthquake should take place on December 13, AD 134 （the third year of Yangjia reign）. As a rough assessment, the epicenter was in Tianshui area and the magnitude was about 7. Due to the political corruption and inability to scientifically explain earthquake phenomenon at the end of Eastern Han Dynasty, a tragedy occurred during the later years of ZHANG Heng＇s life that had direct relations with the earthquake successively occurred in AD 133 and AD 134 after invention of seismometer in AD 132. In order to analyze the ground motion at Lingtai caused by the event in AD 134, the digital broad-band seismic records of three Longxi earthquakes in recent years recorded by Luoyang seismic station are used. The numerical modelings are made from three aspects of seismic magnitude definition, digital broad-band seismograms and empirical Green＇s function method. The results have shown that the maximum horizontal displacement at Lingtai is between 6-8 mm, and the maximum acceleration is less than 10^-2 m/s^2. These results have played an important role in quantitative te

关键词： ZHANG Heng's Seismometer Longxi earthquake research on historical records numerical modeling historical earthquakes