Development of unbiased plotting position formula for General Extreme Value distributions

Expressions for the expected values of GEV order statistics have been derived in simple summation form and in terms of probability weighted moments. Using exact plotting positions from GEV order statistics a new unbiased plotting position formula has been developed for the General Extreme Value distribution. The formula can, explicitly, take into account the coefficient of skewness, (or the shape parameter, k), of the underlying distribution.The developed formula better approximates the exact plotting positions as compared to other existing formulae and is quite easy to use.     

The large volume multi-anvil press as a highP-T deformation apparatus

The rheological properties of mantle materials are being investigated up to pressures of 16 GPa and temperatures of 1600°C for times up to 24 h, using a new sample assembly for the 6–8 multi-anvil apparatus. Al₂O₃ pistons, together with a liquid confining medium, are used to generate deviatoric stress in the specimen. Strain rates are estimated by monitoring the relative displacement of the guide blocks of the multi-anvil apparatus, scaled to the total axial strain of the sample. The applied stress on the sample is estimated using grain size piezometry. Strain rates and flow stresses of approximately 10^–4 to 10^–6 s^–1 and 50 to 250 MPa respectively, are presently attainable.Preliminary results on San Carlos olivine single crystals, partially dynamically recrystallized to a grain size of 10 to 300 m, indicate that the effective viscosity of polycrystalline olivine is consistent with values obtained from olivine single crystal creep laws. Assuming a dislocation creep mechanism (n3.5) with (010)[001] as the dominant slip system, the data are best fit using a creep activation volume of 5 to 10×10^–6 m³ mol^–1.     

强震前b值与C(n)值变化的对比研究

对比研究了中国西部地区发生的６次中强地震前ｂ值与Ｃ（ｎ）值异常变化特征．６次地震前,ｂ值和Ｃ（ｎ）值都有异常显示．ｂ值异常一般出现较早,最早出现在震前１年左右;Ｃ（ｎ）值异常大多在震前半年至２～３个月出现．ｂ值曲线异常形态一般不太典型,而Ｃ（ｎ）值异常形态较典型,表现为峰值异常．地震前２种异常同时出现．还对计算上述参数的空间范围的选取及窗长和步长的选取进行了讨论．     

Determination of depths to centroids of three-dimensional sources of potential-field anomalies with examples from environmental and geologic applications

A method is developed for determining the depth to the centroid (the geometric center) of ‘semi-compact' sources. The method, called the anomaly attenuation rate (AAR) method, involves computing radial averages of AARs with increasing distances from a range of assumed source centers. For well-isolated magnetic anomalies from ‘semi-compact' sources, the theoretical AARs range from 2 (close to the sources) to 3 (in the far-field region); the corresponding theoretical range of AARs for gravity anomalies is 1 to 2. When the estimated source centroid is incorrect, the AARs either exceed or fall short of the theoretical values. The levelling-off of the far-field AARs near their theoretical maximum values indicates the upper (deeper) bound of the centroid location. Similarly, near-field AARs lower than the theoretical minimum indicate the lower (shallower) bound of the centroid location. It is not always possible to determine usable upper and lower bounds of the centroids because the method depends on characteristics of sources/anomalies and the noise level of the data. For the environmental magnetic examples considered in this study, the determined deeper bounds were within 4% of the true centroid-to-observation distance. For the case of the gravity anomaly from the Bloomfield Pluton, Missouri, USA, determination of only the shallower bound of the centroid location (7 km) was possible. This estimate agrees closely with the centroid of a previously determined three-dimensional model of the Bloomfield Pluton. For satellite magnetic anomalies, the method is appropriate only for high-amplitude, near-circular anomalies due to the inherent low signal-to-noise ratio of satellite magnetic anomalies. Model studies indicate that the AAR method is able to place depths within ±20–30 km of actual center locations from a 400-km observation altitude. Thus, the method may be able to discriminate between upper crustal, lower crustal, and mantle magnetic sources. The results from the prominent Kentucky anomaly are relatively well-resolved (centroid depth 30 km below the Earth's surface). For the Kiruna Magsat anomaly, the deleterious effects from neighboring anomalies make a determination difficult (possible depth could be between 20 and 30 km). The centroid depths are deeper for the Kursk anomaly (40–50 km). These depths may indicate that magnetic anomalies from the near-surface Kursk iron formations (a known contributor) and deep crustal magnetic sources could combine to form the Kursk Magsat anomaly.     

山西大同台短水准的异常识别

给出４点组斜率信息法的理论模型,分析了大同台短水准测量结果,证明几次中强地震前大同台短水准均有明显的中、短期异常;同时发现跨断层测站高差曲线能较好地反映震前短、临异常的变化。     

高增益复合天线在超长站距遥测地震台网中的应用

自行研制的复合阵列天线具有增高,方向性图尖锐,抗干扰能力强的特点。天线系统应用于超长距离的信号转输取得了很好的效果。乌鲁木齐遥测地震台网使用自行研制的天线系统用２．５～３．５Ｗ发射功率发射。该天线可接收新疆乌鲁木齐台网长站距,超长站距（２８０ｋｍ）２２３～２３５ＭＨｚ频段的地震信号。信号场强贮备满足规范要求,不低于３０ｄｂ从而保证了超长站距无线遥测地震信号的接收质量。     

苍山M_S5.2地震前兆异常综合加权信息熵的变化

利用山东省每年地震会商报告给出的地震前兆异常（不是取地震后的震例总结或论文给出的异常）,按“专家系统”思想对每一地震前兆异常事件进行综合评估,以每一异常的最可能发震时间来估算发震概率,计算了各类地震前兆异常群体信息熵,研究了苍山ＭＳ５．２ 地震前综合信息熵的变化特征。结果表明：震前熵值减少,系统向有序方向发展     

正环境电场中闪电先导的始发和传播

为了研究中国内陆高原雷暴正极性闪电放电的特点,中日两国科学家于１９９７年７～８月在甘肃省平凉市联合进行了人工触发闪电野外实验。利用设在离触发点约３．５ｋｍ处的高速数字化摄像系统结合在闪道底部的电流测量记录,对在正环境电场中触发的两次闪电的初始先导的发生和发展特点进行了研究。资料分析表明,这两次触发闪电都是由火箭顶部始发的上行负先导传输入云而形成短暂的连续电流放电过程,整个放电持续时间分别只有１７和２６ｍｓ。先导在垂直方向的传输速度随时间而增加,平均值约为３．５×１０５ｍ／ｓ。正环境电场中的先导在向云底传输过程中可能产生多个分枝,但它们一般只存在几毫秒时间就消亡了,只有少数分枝能够发展入云。主通道的亮度综合反映了各分枝亮度的变化,而它本身又与在闪道底部测量记录到的闪电放电电流变化存在很好的对应关系。     

地震势能剖面

地质体在应力场的作用下发生弹性形变,从而具有应变位能（势能）。应用应变位能公式,可以将位或位移转化为势能,用势能剖面代替常规地震剖面。由于势能转换能拓宽地震信号的有效频谱,具有高通滤波性质,同时又不损害低频信号,所以,同常规地震剖面相比,势能剖面在保持信噪比的前提下,有更高的纵、横向分辨率。通过势能转换的理论分析及合成数据和实际数据的势能转换处理,本文系统地研究了势能转化问题和实现方法,从而证明势能转换确实是行之有效的高分辨率地震处理方法,可用于实际地震资料的处理。     

秦岭-大别山壳幔岩石高温高压下的电性特征

首次报导了秦岭-大别山壳幔岩石高温高压下电导率的测定结果。该区中上地壳主要代表岩石(角闪岩、绢云母石英片岩、千枚岩等)在10^-25km的温压条件下,含水矿物出现脱水会引起电导率值升高,认为这是该区出现高导层体的主要原因;中下地壳代表性岩石(片麻岩、麻粒岩、榴辉岩等)由于石英从α相向β相转变,会导致电导率值(σ)下降。在下地壳的温压条件下电导率值一般为10^-2到10^-3S·m^-1;上地幔的代表性岩石由于组成矿物较为基性,电导率值比下地壳高,从0.1到1S·m^-1。