利用直达P波测定地方震震源深度的探讨

震源深度是地震时空参数中的基本参数,是目前最难测准的参数之一。可以使用直达P波测定震源深度。要确保测定结果的精度,必须加密台网观测点,使台间距的大小与震源深度相当。利用四川省西昌和冕宁大桥水库两个遥测地震台网的直达P波资料,测定发生在其监控区域内137个地震的震源深度。结果发现,该区域地震的平均深度和深度下限存在随震级增大而增加的现象。其中有部分地震的震源深度,利用本研究方法测定的结果与使用遥测地震台网计算机定位程序输出的结果相差较大。作者认为,这部分地震使用计算机定位程序得出的震源深度有较大的误差。     

武汉市区土体剪切波速与深度的经验关系

通过对武汉市区3个主要地质单元共8 305个剪切波速数据的分析整理,分别运用线性函数、一元二次多项式函数、指数函数对武汉市区不同地貌单元不同土类的剪切波速与深度的关系进行统计回归,得到其经验关系。结果表明,武汉市区土体剪切波速与埋深相关性比较明显;一元二次多项式函数的拟合效果最好。将实测数据与利用经验关系得到的预测值进行对比检验,两者基本吻合,可供武汉市区场地剪切波速数据缺乏时参考使用。     

Assessment of the statistical significance of global changes in the annual river runoff in XXI century due to possible anthropogenic warming of climate

A number of uncertainties of forecasts of changes in the annual runoff depths at global scale, obtained using information on results of integration of 21 IPCC climate models is studied. Following possible errors of these forecasts are calculated: errors of models; differences between main (IPCC) scenarios of emission of greenhouse gases in the atmosphere and resultant changes of global temperatures; mistakes in estimates of average long-term observed values of the runoff depths for the “control” period. Global maps of a “significance index” of forecasted changes in the runoff depths (estimations of changes in the annual runoff depths divided by mean square root values of errors of these estimations) for 2025, 2050, 2075 and 2100 are presented. It is shown that the most significant global changes of the runoff depths (growth in the north of Eastern Siberia, of the Russian Far East, of North America, falling in the “Greater Mediterranean Region”) are predicted for the second quarter of 21st century. Further changes of the runoff amplify only in the Amazon basin (reduction, by 2075). Almost everywhere else (including almost all European territory of Russia, Western Siberia, south of Eastern Siberia and of the Far East) the significance of changes in the runoff depths during 21st century is negligible.     

Specific features of the seismic regime in the lithosphere: Manifestations of the deep aqueous fluid action

We considered the seismic regime in the upper 70–100 km of the lithosphere and identified the layers (at depths of about 10, 20–30, and 60–80 km) characterized by relatively reduced effective strength and increased seismicity. The existence of such layers is related to changes in the regime of fluid-rock interaction, namely, to the characteristic depths of a jump-like decrease in the effective permeability of rocks and an increase in the spatial homogeneity of a fluid-rock system.     

The depth of seismicity in the Kermanshah region of the Zagros Mountains (Iran)

A detailed microearthquake survey in a small region of the Zagros Mountains in Iran failed to detect any shocks whose depths were greater than 20 km. One third of the shocks in the same area have depths greater than 50 km when located using teleseismic observations. Because of poor azimuthal coverage and lack of local stations these teleseismic locations are probably in error. There is therefore no reliable seismic evidence for the existence of oceanic lithosphere beneath the Zagros fold belt.     

青海木里冻土区水合物稳定带的特征研究——模拟与钻探结果对比

基于青海木里冻土区的气体组成、钻孔泥浆的温度测量数据等对该区水合物稳定带的顶底深度进行了模拟计算,并将计算结果与钻探揭示的水合物产出深度进行了对比.模拟计算的水合物顶深在148.8～122.7 m 间,底深在324.6～354.8 m间,水合物厚度在175.8～232.2 m间,钻探揭示水合物及其异常产出在133～39...     

金沙江水网各观测井温度梯度的精细测量结果及其分析

Fine measurements have been conducted to temperatures and their gradients of six wells of the Jinsha River Groundwater Observational Network.The results show that the influence depths of sun radiation heat are 50m to 125m,average temperature gradients in the wells range from 0.11 to 2.81℃/hm and most are 1～2℃/hm,and the temperature gradients on varied depth sections of one well are highly changeable.Lithology of strata and their integrity,particularly high-angle crashed fault zones,have imposed major effects on the influence depths of sun radiation heat and temperature gradients of the wells.The micro dynamic characteristics of water temperature,such as coseismic effects,tidal effects and anomalies of the wells prior to earthquakes,probably depend,to a large degree,on the temperature gradients of the depths at which the water temperature sensors are settled.     

USGS地震目录中4～5级震源深度异常地震可靠性初步研究:以南北地震带若干地震为例

在南北地震带地区,USGS全球地震目录中存在一些震源深度大于30km的地震.这些地震的震源深度是否可靠,对于研究这一地区的孕震机制、岩石圈强度和构造演化等科学问题具有重要意义.本文以南北地震带2012年发生的5个4~5级地震为例,利用区域地震台网的波形数据,基于sPL深度震相、短周期瑞利面波以及CAP等独立方法测定了其震源深度.结果表明:sPL深度震相和CAP方法给出的震源深度比较一致,差别小于2~3km,能够得到比较可靠的震源深度;短周期瑞利面波及其与P波振幅比也确定了地震震源深度较浅的特征.本文研究结果显示:宁夏会宁4.7级、云南富民4.8级和四川会东4.7级地震的震源深度约为8~12km左右,仍为发生于上地壳的地震,USGS地震目录给出的30km甚至更深的震源深度存在明显偏差;对于四川隆昌4.6和4.9级地震,本文给出的震源深度为1~2km,属于极浅源地震,USGS地震目录给出的10km和35km的震源深度结果尚需进一步改进.     

Determinations of focal depths of earthquakes associated with the bending of oceanic plates at trenches

The earthquakes examined in this paper are all within the oceanic lithosphere and are associated with the bending of plates before subduction. Accurate determinations of the depth of these earthquakes are needed to study the stress pattern within a bending plate. Routinely-determined depths of shallow sub-oceanic earthquakes published in bulletins are unreliable. The depths can be accurately determined to within a few kilometers if the original seismograms from these events are studied. In some cases, the reflected phases pP and pwP can be clearly identified. There exists the possibility that the wave reflected at the water-air interface, pwP, may be misidentified as pP, leading to erroneous estimates of depth. Additional methods of analysis, such as surface wave radiation patterns or the apparent frequency-dependence of reflection at the crust-water interface, can remove this possible source of confusion. One of the most powerful techniques for depth analysis is the modelling of long-period waveforms. The pattern of stresses within the bending oceanic lithosphere revealed by the depths and focal mechanisms of these intraplate earthquakes is one of horizontal, deviatoric tension down to a depth of about 25 km, with horizontal compression at greater depths.     

西昌川32井水温传感器不同投放深度监测能力分析

西昌川32井水温传感器曾投放井下两个不同深度,在含水层的不同位置,记录地震和异常变化的能力各有不同,本文对此进行比较分析,用数据说明西昌川32井水温传感器更合理的投放位置。     

用接收函数研究川滇地区国家地震台下地壳厚度及波速比

本文利用远震接收函数的方法,对川滇地区的昆明、腾冲、成都和攀枝花等4个国家地震台的台基下方不同方向的莫霍面深度及波速比进行了研究和分析。结果表明:昆明地震台台基下方的莫霍面深度基本在50km左右,波速比为1.62～1.69,地壳厚度和波速比不因方向不同而发生明显的变化;腾冲地震台台基下方的地壳厚度有着比较明显的方向性,东北方向厚为40.7km,东南方向为49.7km,两个方向的波速比相差也很大,差值达到0.2;成都地震台台基下方莫霍面的深度在40km左右,但是东北和西南方向要加深8km,两个方向波速比相差0.13;攀枝花地震台台基下方的地壳厚度比较稳定,厚度在60km左右,波速比变化也不明显。     

Flow variability and the bankfull depth of sand-bed streams of the American midwest

The bankfull depths of 15 midwestern sand-bed streams increase with increasing variability of flow. Depths are also well represented by a simple one-dimensional model of vertical floodplain accretion. Thus, the correlation between depth and flow variability may be explained by the ability of deep, sediment-laden flows to construct high floodplains. Bankfull depths are also strongly correlated with the average annual maximum flow. Apparently, the average annual maximum flow adequately represents the cumulative influence of varying flows on rivers studied here. These observations further validate the concept of a dominant channel-forming discharge of moderate return frequency in humid temperate climates.     

基于变密度模型的位场界面反演

在波数域中用重力反演莫霍面深度时通常假定壳幔密度差为一常数,但这只是一种近似的密度模型,本文采用了密度随深度呈指数变化的变密度模型来反演莫霍面深度,给出了利用指数密度模型在波数域中计算重力异常的正演公式及界面深度的反演公式.利用指数密度模型及重力资料反演了青藏高原莫霍面的深度,分析了莫霍面的特征.结果表明,青藏高原莫霍面呈现出边缘浅、中部深的特点,边缘变化快、梯度大,中间变化梯度趋缓.中心地带的羌塘地体莫霍面深度达74 km,向四周慢慢变浅至67 km左右,边缘地区突然变浅至50km左右.通过常密度模型、变密度模型及地震反演得到的莫霍面的比较,证实变密度模型更适合于莫霍面结构的反演.     

DEPTH ESTIMATION FROM RESIDUAL BOUGUER ANOMALIES: A PROCEDURE BASED ON THE BACKUS-GILBERT MINIMUM DISTANCE CRITERION *

The minimum distance criterion of Backus and Gilbert is used to determine the depths of line masses approximating the subsurface two dimensional distribution of density differences responsible for the observed residual Bouguer anomaly values. The quantity minimized is the sum of the squared differences between the starting trial depths and the desired final depths of line masses. The search for the desired depths is limited to preset depth ranges.     

Improved tilt-depth method for fast estimation of top and bottom depths of magnetic bodies

The tilt-depth method can be used to make fast estimation of the top depth of magnetic bodies. However, it is unable to estimate bottom depths and its every inversion point only has a single solution. In order to resolve such weaknesses, this paper presents an improved tilt-depth method based on the magnetic anomaly expression of vertical contact with a finite depth extent, which can simultaneously estimate top and bottom depths of magnetic bodies. In addition, multiple characteristic points are selected on the tilt angle map for joint computation to improve reliability of inversion solutions. Two- and threedimensional model tests show that this improved tilt-depth method is effective in inverting buried depths of top and bottom bodies, and has a higher inversion precision for top depths than the conventional method. The improved method is then used to process aeromagnetic data over the Changling Fault Depression in the Songliao Basin, and inversion results of top depths are found to be more accurate for actual top depths of volcanic rocks in two nearby drilled wells than those using the conventional tilt-depth method.     

Accurate relocation of earthquakes in central-western China using the double-difference earthquake location algorithm

The double-difference earthquake relocation algorithm (DD algorithm) has been applied to the accurate relocation of 10057 earthquakes in the central-western China (21°-36°N, 98°-112E°) during the period of 1992-1999. In total, 79706 readings for P waves and 72169 readings for S waves were used in the relocation, and the source parameters of 6496 events were obtained. The relocation results revealed a more complete picture of the hypocentral distribution in the central-western China. In several seismic belts the relocated epicenters present a more defined lineation feature, reflecting the close correlation between the seismicity and the active tectonic structures. The relocated focal depths confirmed that most earthquakes (91 percent of the 6496 relocated events) in the central-western China were located at shallower depths not deeper than 20 km. The distribution of focal depths indicates that the seismogenic layer in the central-western China is located in the upper-mid crust with its thickness no deeper than 20 km.     

中国大陆余震活动深度分布及其流变学机制

本文研究了中国大陆１９６６年以来发生的５次大地震（Ｍｓ≥７．０）的余震活动深度与地热流的关系。研究表明，地热流较高的震源区，余震活动深度分布较浅，并且得出余震深度分布受地壳内部岩石脆性－韧性转变深度的流变学特征控制的推论。     

帕米尔—兴都库什深俯冲残留体对410km间断面起伏形态的影响

受俯冲残留体影响的410km间断面起伏形态的研究对于确定地球内部物质构成及地球动力学过程具有重要作用.帕米尔—兴都库什俯冲区域拥有全球少有的中、深源地震,为研究410km间断面起伏提供了良好的资源.利用日本Hi-net地震台网和美国TA台阵记录的帕米尔—兴都库什俯冲区域的6个震源深度为154.0~220.9km、震级为Mb5.6~6.4的中、深源地震的短周期/宽频带波形资料,经过4次根倾斜叠加处理,获得了36组Hi-net子台网和TA记录资料的倾斜叠加灰度图,从中提取了与410km间断面相关的次生转换震相SdP,发现受俯冲残留体影响下的410km间断面的深度位于372~398km.较之持续俯冲的西太平洋地区海洋岩石圈,研究区域俯冲滞留体对于410km间断面的相变线的影响要小得多.     

厄尔尼诺事件研究的新进展

简述了厄尔尼诺事件研究的最新进展，研究表明：强潮汐加大垂直方向和水平方向海水的混合，将太平洋深层冷水翻上表面（或使西部暖水流向东部），吸收（或释放）CO2减弱（或增强）温室效应，使海洋上方空气变冷（或变暖），产生拉尼娜冷事件（或厄尔尼诺热事件）。海底火山活动亦受强潮汐的控制。     

On heterogeneities with reduced viscosity in the mantle under the Kamchatka volcanoes according to seismological data

A seismological study of the upper mantle under the Kamchatka volcanoes using body waves from nearby earthquakes has shown local heterogencities consisting of materials with reduced elastic properties at depths from 30 to 90 km. The estimated value of the upper limit of viscosity,η, is about 6 × 10²⁰ pois for the material of the mantle aseismic zone under the Kamchatka volcanoes at depths of ～ 70–150 km. It is suggested that the magmatic chambers are rooted in the mantle heterogeneities filled with substance of reduced elasticity and viscosity.