Upper mantle P wave velocity structure of the northern part of China and Mongolia

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Crustal Structure Along the Lawrencepur-Astor Profile in the Northwest Himalayas

During the Pamir Himalayan project in the year 1975 seismic refraction and wide-angle reflection data were recorded along a 270 km long Lawrencepur-Astor (Sango Sar) profile in the northwest Himalayas. The profile starts in the Indus plains and crosses the Main Central Thrust (MCT), the Hazara Syntaxis, the Main Mantle Thrust (MMT) and ends to the east of Nanga Parbat. The seismic data, as published by Guerra et al. (1983), are reinterpreted using the travel-time ray inversion method of Zelt and Smith (1992) and the results of inversion are constrained in terms of parameter resolution and uncertainty estimation. The present model shows that the High Himalayan Crystallines (HHC, velocity 5.4 km s⁻¹) overlie the Indian basement (velocity 5.8–6.0 km s⁻¹). The crust consists of four layers of velocity 5.8–6.0, 6.2, 6.4 and 6.8 km s⁻¹ followed by the upper mantle velocity of 8.2 km s⁻¹ at a depth of about 60 km.     

Experimental studies on elastic and rheological properties of amphibolites at high pressure and high temperature

The experimental studies done at high temperature and high pressure find that increased temperature can lead to dramatic velocity and strength reductions of most of rocks at high confining pressure[1,2]. What causes this phenomenon? Is it due to dehydrati…     

地震折射法中波场延拓技术的应用

从波动方程出发,推导出平面波场传播基本公式,阐述了利用地表观测波场反演地球内部波速结构的理论关系.观测波场可通过-p 变换分解为地表平面波场,其最大振幅的轨迹能稳定地反映出地球内部波速随深度变化的趋势,这一特征可用来对反演解空间进行约束.波场延拓技术可以充分地利用观测波场中包含的丰富信息,在迭代反演中不仅能简单快速地得到反演解,而且所得解具有良好的稳定性,较少受主观因素影响,这是一种很好的反演技术.对波场延拓进行了理论分析与数值模拟,采用了同态反褶积等改善资料信噪比的措施,使解的分辨能力得到了提高.文中对南海北部一个声纳折射剖面进行了分析和计算.结果表明:该区1.4km 深处,存在一个从1.76km/s 到2.21km/s 的速度间断面.间断面上下两层的速度梯度分别为0.54kms-1/km,0.63kms-1/km.最后,从构造演化的角度对浅海构造特征进行了探讨.      

Receiver function study in northern Sumatra and the Malaysian peninsula

In this receiver function study, we investigate the structure of the crust beneath six seismic broadband stations close to the Sunda Arc formed by subduction of the Indo-Australian under the Sunda plate. We apply three different methods to analyse receiver functions at single stations. A recently developed algorithm determines absolute shear-wave velocities from observed frequency-dependent apparent incidence angles of P waves. Using waveform inversion of receiver functions and a modified Zhu and Kanamori algorithm, properties of discontinuities such as depth, velocity contrast, and sharpness are determined. The combination of the methods leads to robust results. The approach is validated by synthetic tests. Stations located on Malaysia show high-shear-wave velocities (V _S) near the surface in the range of 3.4–3.6 km s^− 1 attributed to crystalline rocks and 3.6–4.0 km s^− 1 in the lower crust. Upper and lower crust are clearly separated, the Moho is found at normal depths of 30–34 km where it forms a sharp discontinuity at station KUM or a gradient at stations IPM and KOM. For stations close to the subduction zone (BSI, GSI and PSI) complexity within the crust is high. Near the surface low V _S of 2.6–2.9 km s^− 1 indicate sediment layers. High V _S of 4.2 km s^− 1 are found at depth greater than 6 and 2 km at BSI and PSI, respectively. There, the Moho is located at 37 and 40 km depth. At station GSI, situated closest to the trench, the subducting slab is imaged as a north-east dipping structure separated from the sediment layer by a 10 km wide gradient in V _S between 10 and 20 km depth. Within the subducting slab V _S ≈ 4.7 km s^− 1. At station BSI, the subducting slab is found at depth between 90 and 110 km dipping 20° ± 8° in approximately N 60° E. A velocity increase in similar depth is indicated at station PSI, however no evidence for a dipping layer is found.     

Subcrustal Low Velocity Layers in Central India and their Implications

A 2-D subcrustal velocity model for the central Indian continental lithosphere has been derived by travel time and relative amplitude modeling of a digitally normalized analog seismic record section of the Hirapur-Mandla DSS profile, using a ray-tracing technique. Some prominent wave groups with apparent velocities slightly higher than the Moho reflection phase (P_MP) are identified on the normalized record sections assembled with a reduction velocity of 6 km s⁻¹. We interpret these phases as the wide-angle reflections from subcrustal lithospheric boundaries. Comparison of synthetic seismograms with the observed record section shows that the observed phases cannot be explained either by multiples or by the P-to-S converted phase (P_MS) from the Moho. Subcrustal velocity models either with a velocity increase or with a single low velocity layer (LVL) also do not provide a satisfactory fit. We infer that a subcrustal velocity model with two alternate LVLs (velocity 7.2 km s⁻¹), separated by a 6-km thick high velocity layer (velocity 8.1 km s⁻¹), can satisfy both the observed travel times and amplitudes. The prominent reflection phases are modeled at depths of 49, 51, 57 and 60 km. It is inferred that the subcrustal lithosphere in the central Indian region has a lamellar structure with varying structural and mechanical properties. The alternating LVLs, occurring at relatively shallow depths below Moho, may be associated with the zones of weakness and lower viscosity suggesting continued mobility, with a possible thermal source in the upper mantle. This explains the source of observed high heat flow values in the central Indian region.     

Rupture process of the M L=4.1 earthquake in Huailai Basin on July 20, 1995

On July 20, 1995, an earthquake of M _L=4.1 occurred in Huailai basin, northwest of Beijing, with epicenter coordinates 40.326°N, 115.448°E and focal depth 5.5 km. Following the main shock, seismicity sharply increased in the basin. This earthquake sequence was recorded by Sino-European Cooperative Huailai Digital Seismograph Network (HDSN) and the hypocentres were precisely located. About 2 hours after the occurrence of the main shock, a smaller event of M _L=2.0 took place at 40.323°N, 115.447°E with a focal depth of 5.0 km, which is very close to the main shock. Using the M _L=2.0 earthquake as an empirical Green’s function, a regularization method was applied to retrieve the far-field source-time function (STF) of the main shock. Considering the records of HDSN are the type of velocity, to depress high frequency noise, we removed instrument response from the records of the two events, then integrated them to get displacement seismogram before applying the regularization method. From the 5 field stations, P phases in vertical direction which mostly are about 0.5 s in length were used. The STFs obtained from each seismic phases are in good agreement, showing that the M _L=4.1 earthquake consisted of two events. STFs from each station demonstrate an obvious “seismic Doppler effect”. Assuming the nodal plane striking 37° and dipping 40°, determined by using P wave first motion data and aftershock distribution, is the fault plane, through a trial and error method, the following results were drawn: Both of the events lasted about 0.1 s, the rupture length of the first one is 0.5 km, longer than the second one which is 0.3 km, and the rupture velocity of the first event is 5.0 km/s, larger than that of the second one which is about 3.0 km/s; the second event took place 0.06 s later than the first one; on the fault plane, the first event ruptured in the direction γ=140° measured clockwise from the strike of the fault, while the second event ruptured at γ=80°, the initial point of the second one locates at γ=−100° and 0.52 km from the beginning point of the first one. Using far-field ground displacement spectrum measurement method, the following source parameters about the M _L=4.1 earthquake were also reached: the scalar earthquake moment is 3.3×10¹³ N·m, stress drop 4.6 MPa, rupture radius 0.16 km. Contribution No. 99FE2022, Institute of Geophysics, China Seismological Bureau. This study is supported by the Chinese Joint Seismological Science Foundation (95-07-411).     

Source parameters of bohai earthquake, July 18, 1969 and yongshan earthquake, May 11, 1974 determined by synthetic seismograms of teleseismic P waves

The source parameters of the Bohai Sea earthquake, July 18, 1969 and Yongshan, Yunnan earthquake, May 11, 1974 were determined by full — wave theory synthetic seismograms of teleseismic P waves. P+pP+sP wereform were calculated with WKBJ approximation and real integral paths. One — dimensional unilateral, finite propagation source was also considered. By trail — and — error in comparing the theoretical seismograms with the observational ones of WWSSN stations, the source parameters were obtained as follow: for Bohai earthquake, φ=195°, δ=85°, λ=65°,M _o=0.9×10¹⁹Nm,L=59.9km.V _R=3.5km/s, ∧ _R =160°; for Yongshan earthquake, φ=240°, δ=80°, ∧=150°,M _o=1.3×10¹⁸Nm,L=48.8km,V _R=3km/s, ∧ _R =−10°, where φ is strike, δ dip angle, λ slip angle,M _o seismic moment,L rupture length,V _R rupture propagation speed. As III type fractures the faulting propagated along the fault planes, and ∧ _R is the angle from the strike to the propagation direction. Yongshan earthquake showed complexity in its focal process, having four sub—ruptures during the first 60 seconds. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 1–8, 1991.     

Insight into the Crustal Structure of the Eastern Marmara Region, NW Turkey

In order to investigate crustal structure beneath the eastern Marmara region, a seismic refraction survey was conducted across the North Anatolian Fault (NAF) zone in north west Turkey. Two reversed profiles across two strands of the NAF zone were recorded in the Armutlu Highland where a tectonically active region was formed by different continents. We used land explosions in boreholes and quarry blasts as seismic sources. A reliable crustal velocity and depth model is obtained from the inversion of first arrival travel times. The velocity-depth model will improve the positioning of the earthquake activities in this active portion of the NAF. A high velocity anomaly (5.6–5.8 km s⁻¹) in the central highland of Armutlu block and the low velocity (4.90 km s⁻¹) pattern north of Iznik Lake are the two dominant features. The crustal thickness is about 26 ± 2 km in the north and increases to about 32 ± 2 km beneath the central Armutlu block in the south. P-wave velocities are about 3.95 km s⁻¹ to 4.70 km s⁻¹ for the depth range between about 1 km and 5 km in the upper crust. The eastern Marmara region has different units of upper crust with velocities varying with depth to almost 8 km. The high upper crust velocities are associated with Armutlu metamorphic rocks, while the low velocity anomalies are due to unconsolidated sedimentary sequences. The western side of Armutlu block has complex tectonics and is well known for geothermal sources. If these sources are continuous throughout the portions of the crust, it may be associated with a granitic intrusion and deformation along the NAF zone. That is, the geothermal sources associated with the low velocity may be due to the occurrence of widespread shear heating, even shear melting. The presence of shear melting may indicate the presence of crustal fluid imposed by two blocks of the NAF system.     

Artificially triggered lightning and its characteristic discharge parameters in two severe thunderstorms

The lightning-induced-damages in the mid-latitude regions are usually caused during severe thunder-storms. But the discharge parameters of natural lightning are difficult to be measured. Five lightning flashes have been artificially triggered with the rocket-wire technique during the passage of two severe thunderstorms. The discharge current and close electric field of return stroke in artificially triggered lightning have been obtained in microsecond time resolution by using current measuring systems and electric field change sensors. The results show that the five triggered lightning flashes include 1 to 10 return strokes, and the average return stroke current is 11.9 kA with a maximum of 21.0 kA and a mini-mum of 6.6 kA, similar to the subsequent return strokes in natural lightning. The half peak width of the current waveform is 39 μs, which is much larger than the usual result. The peak current of stroke Ip (kA) and the neutralized charge Q(C) has a relationship of Ip = 18.5Q0.65. The radiation field of return stroke is 5.9 kV·m-1 and 0.39 kV·m-1 at 60 m and 550 m, respectively. The radiation field decreases as r -1.119 with increase of horizontal distance r from the discharge channel. Based on the well-accepted transmission line model, the speed of return stroke is estimated to be about 1.4×108 m·s-1, with a variation range of (1.1―1.6)×108 m·s-1. Because of the similarities of the triggered lightning and natural lightning, the results in this article can be used in the protection design of natural lightning.     

Analysis of the Microseismicity Induced by Fluid Injections at the EGS Site of Soultz-sous-Forêts (Alsace, France): Implications for the Characterization of the Geothermal Reservoir Properties

In June/July 2000, a hydraulic stimulation experiment took place at the geothermal EGS site of Soultz-sous-Forêts (Alsace, France) in order to enhance the permeability of the fractured granitic massif at 5 km depth. As it is well known that fluid injections tend to induce microseismic events, a downhole and a surface seismological network have been installed to monitor the seismic activity during the stimulation test. 23400 m³ of fluid have been injected in the rock volume through the open-hole section (4400 m–5000 m) of the well GPK2 at increasing rates of 30 l.s⁻¹, 40 l.s⁻¹ and then 50 l.s⁻¹. More than 7200 microseismic events in the magnitude range –0.9 to 2.6 have been precisely located through a simultaneous inversion of the seismic velocity structure and location parameters. The analysis of the behavior of the seismicity relative to the hydraulic parameters gives important information about the geothermal reservoir. It appears that the evolution of the seismicity strongly depends on the variations of the injection rate: An increase or a decrease leads to changes of the velocity structure, the number and magnitude of microseismic events. This involves different hydro-mechanical processes between the fluid flow and the fracture planes, which will control the final shape of the microseismic cloud. Moreover, the study of the variations of the b-value with time suggests that the stimulation experiment produces a large proportion of small earthquakes, but records of events of magnitude higher than 2 indicate that fluid injection could reactivate structures whose dimensions allow the generation of such earthquakes.     

Belowground carbon balance and carbon accumulation rate in the successional series of monsoon evergreen broad-leaved forest

The belowground part of terrestrial ecosystem is a huge carbon pool. It is believed that of the total 2500Gt carbon stored in global terrestrial ecosystem, soil carbon storage within the 1 m surface layer ac- counts for 2000Gt, which is 4-fold of vegetation car- bon storage[1,2]. Compared with the carbon in the vegetation, carbon in the deep soil layers is much more stable, and it will stay in soil profile permanentlyunless geological vicissitude occurs. Essentially, forest restoration is the…     

Characteristics of coda wave attenuation in Yunnan area

The characteristic of seismic coda wave attenuation in Yunnan area in 7 frequency-bands range from 1 Hz to 20 Hz was estimated by using the local earthquake's waveform data recorded from 22 Yunnan digital seismic stations.Coda attenuation Q-c1 of each station was firstly calculated by single scattering method. Then, mean free path Le and seismic albedo Bo of each station were calculated, and scattering attenuation Q-1s and intrinsic attenuation Q-1i were separated from total attenuation Q-1t by multiple lapse time window analysis based on the multiple scattering model in uniform random isotropic scattering medium. The attenuating characteristics in Yunnan show that most value of Le are in 10～30 km, with maximal within 2～6 Hz;Bo are about 0.5 at 1～2 Hz, but less than 0.5at other frequency-bands, which means Q-1i is comparable with Q-1s at 1～2 Hz, and after 1～2 Hz, Q-1i is greater than Q-1s and dominates the attenuation process. Q-1c is close to Q-1i at other frequency bands except 1～2 Hz.Results show that Q-1 especially Qs-1 varies spatially, Q-1 in eastern Yunnan zone is a bit higher than in northwestern Yunnan zone;northwestern Yunnan zone higher than southwestern Yunnan zone. Comparing with other results in global, Qs-1 in Yunnan is lower than the global average value among these results, Q-1i is higher than the global average value, and Q-1t lies the middle among these results.     

Dynamical diagnosis of the breakup of the stratospheric polar vortex in the Northern Hemisphere

The research on climate change in polar regions, especially on the role of polar in the global climate system, has gain unprecedented level of interest. It has been the key scientific issue of the International Polar Year program (IPY, 2007―2008). In this paper, we dealt with the debate upon the breakup time of the stratospheric polar vortex in boreal spring. An observational study of the relation between strato- spheric polar vortex breakup and the extra-tropical circulation was performed. The mean breakup date―when the winter westerly at the core of polar jet turns to summer easterly―is about April 10. The breakup time has large interannual variation with a time span of about 2 months. It also has a long-term trend with the 1990s and 2000s witnessing more and more late breakups of polar vortex. Composite of wind speed at the core of polar jet for the extremely early and late breakup years shows that late years have two periods of westerly weakening while early breakup years have only one. The first weakening in the late years happens in middle January with wind speed dropping sharply from more than 40 m s?1 to about 15 m s?1. This is accompanied with anomalous activities of planetary waves in both strato- sphere and troposphere; while the second weakening in the late breaking years is mainly the results of diabatic heating with very weak wave activities. In early breakup years, the transition from westerly to easterly is rapid with wind speed dropping from more than 30 m s?1 to less than ?10 m s?1 within a month. This evolution is associated with a strong bidirectional dynamical coupling of the stratosphere and troposphere. The circulation anomalies at low troposphere are also analyzed in the extremely early and late breakup years. It shows that there are significant differences between the two kinds of extreme years in the geopotential height and temperature composite analysis, indicating the dynamical cou- pling of stratosphere and troposphere with the evolution of stratospheric polar vortex.     

Correction to the crustal thickness of the northwestern China using the data of seis-mic tomography

Introduction The gravity anomaly is an indicator of the density distribution of the underground material. Therefore the gravity anomalies have been important data used for studying the deep crustal struc-ture for a long time. Many people have made detailed researches on the regional crustal structure inverted by Bouguer anomalies. In particular some empirical formulae and practical algorithms about the crustal thickness were brought forward, and a series of results were obtained (MENG, 1996)…     

Characteristics and quantitative of negative ion in salt aqueous solution by Raman spectroscopy at ?170°C

The results from Raman spectroscopy analysis of salt aqueous solutions at −170°C demonstrate that for those clearly sharp iron peaks whose Raman wavenumber is close to each other such as NO ₃ ⁻ and CO ₃ ²⁻ , their original shape could be restorable by the stripping technique, and that ice’s sharp characteristic peak 3090–3109 cm⁻¹) is steady, while the spectrum band of the complex compound (nCl⁻-[H⁺-OH⁻]_n) chlorine ion combined chemically with water molecule is 3401–3413 cm⁻¹. On the other hand, the research shows that the higher the negative iron concentration, the stronger its Raman characteristic peak intensity and the smaller the ice’s. Based on the number of data and theoretical work, the strong correlation of the molar concentration of negative ion with the S _i/S _{H 2}O band area ratio is built up. Moreover, the developed Raman method is successfully used in the component analysis of the field fluid inclusions from Silurian sandstone in Tarim basin.     

Interpretation of S-wave data from Tai’an-Xinzhou DSS profile and its relationship with Xingtai earthquakes

On the basis of S wave information from Tai’an-Xinzhou DSS profile and with reference to the results from P-wave interpretation, the 2-D structures, including S-wave velocity V _s, ratio γ between V _p and V _s; and Poisson’ s ratio σ, are calculated; the structural configuration of the profile is presented and the relevant inferences are drawn from the above results. Upwarping mantle districts (V _s≈4.30 km/s) and sloping mantle districts (V _s≈4.50 km/s) of the profile with velocity difference about −4% at the top of upper mantle are divided according to the differences of V _s, γ and σ in different media and structures, also with reference to the information of their neighbouring regions; the existence of Niujiaqiao-Dongwang high-angle ultra-crustal fault zone is reaffirmed; the properties of low and high velocity blocks (zones) including the crust-mantle transitionalzone and the boudary indicators of North China rift valley are discussed. A comprehensive study is conducted on the relation of the interpretation results with earthquakes. It is concluded that the mantle upwarps, thermal material upwells through the high-angle fault, the primary hypocenter was located at the crust-mantle juncture 30.0∼33.0 km deep, and additional stress excited the M _S=6.8 and M _S=7.2 earthquakes at specific locations around 9.0 km below Niujiaqiao-Dongwang, the earthquakes took place around the high-angle ultra-crustal fault and centered in the brittle media and rock strata with low γ and low σ values. This subject is part of the 85-907-02 key project during the “8th Five-Year Plan” from the State Science and Technology Commission.     

Variations of the geomagnetic field and the geomagnetic effects of three earthquakes ( M s>5.0) in Jiangsu Province, China

Since 1979 the repeated observations and experiments of geomagnetic total intensity and vertical component have been carried out for ten years in the geomagetic network which is located in Jiangsu Province, China. Three earthquakes aboveM _s 5.0 occurred during the decade, and some seismomagnetic effects were observed. The observation results show that the anomalies of the vertical geomagnetic component can’t be observed untill some months before the earthquake (M _s>5.0) in this area. In this paper it is suggested that a densely distributed network for continuous observation of geomagnetic vertical component may catch seismomagnetic anomalies and thus improve earthquake prediction in the light of the geomagnetic measurements of the mid — or — low latitude locations. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 80–87, 1991. This study is sponsored by the Chinese Joint Seismological Science Foundation.     

Modelling of convective turbulence with a two-equation k-ɛ turbulence closure scheme

 In this study we aim at comparing turbulence parameters from field observations and model simulations under convective conditions. The comparison is focused on the depth dependence and temporal dynamics of viscous and diffusive dissipation rates ɛ and χ. The near-surface observations were obtained by using a quasi-free-rising profiler which measured small-scale shear and temperature fluctuations to within the vicinity of the water surface. Convective conditions during the experiment are characterized by low wind speeds (between 0 and 4 m s⁻¹) and a typical heat loss of about 150 Wm⁻². We applied a state-of-the-art two-equation k-ɛ turbulence model with an algebraic second-moment closure scheme. The qualitative agreement of the turbulence quantities resulting from observations and simulations is rather good. The temporal dynamics of the temperature field is simulated correctly, whereas in the spatial dynamics some deficiencies of the model due to its local character can be seen. It is concluded that such models realistically reproduce convective turbulence and therefore represent a reasonable compromise between complexity and simplicity, so that they can be used with acceptable costs in large-scale models. Received: 31 October 2001 / Accepted: 20 September 2002 Acknowledgements The whole project was intitiated by Peter Schlittenhardt, who strongly supported the development of the observational technique in uprising mode and encouraged us to undertake the experiment in Lake Maggiore; for which we will thank him most. Performing the measurement campaign was only possible with the help of several colleagues from the Marine Environment Unit at the Joint Research Centre. Thanks to all of them, but especially to Dirk van d. Linde, Ulisse Devisioni, Bjarke Rasmussen and Hartmut Prandke. The Istituto Italiano di Idrobiologia, Verbania Pallanza, provided the boat Livia for the installation and removal of the measurement system; thanks to the master Stefano Maurizio for his engagement. Ute Tschesche provided the data evaluation and presentation software and Judith Challis helped to polish our English. Part of the study was␣supported by the PROVESS project (MAS3-CT97-0159); thanks to our sponsors at the European Commission. We are further grateful to two anonymous referees for their constructive comments. Responsible Editor: Charitha Pattiaratchi     

Variations of <Emphasis Type="Italic">δ</Emphasis><Superscript>18</Superscript>O in precipitation from the Muztagata Glacier,East Pamirs

Expeditions to Muztagata (in the eastern Pamirs) during the summer seasons of 2002 and 2003 collected precipitation samples and measured their oxygen isotopes. The δ ¹⁸O in precipitation displays a wide range, varying from −17.40‰ to +1.33‰ in June-September 2002 and from −22.31‰ to +4.59‰ in May-August 2003. The δ ¹⁸O in precipitation correlates with the initial temperature of precipitation during the observing periods. The positive correlation between δ ¹⁸O and temperature suggests that δ ¹⁸O can be used as an indicator of temperature in this region. The δ ¹⁸O values in fresh-snow samples collected from two snow events at different elevations on the Muztagata Glacier show a strong “altitude effect”, with a ratio of nearly −0.40% per 100 m from 5500 m to 7450 m.