AMT野外最佳观测时间及人工源信号作用的探讨

通过对不同野外工作时间获取的音频大地电磁测量数据的对比分析,总结了天然电磁场的特点及最适宜开展音频大地电磁法野外工作的季节.最后,指出了采用人工信号源弥补天然电磁场弱信号的有效性.     

我国现有短期气候业务预测方法综述

对我国短期气候业务预测方法的综合分析表明 :我国现有的短期气候业务预测经验和统计方法仍是主要的 ;物理因子和前兆强信号结合天气气候学分析的概念预测模型方法在业务预测中发挥重要作用 ;动力模式预测方法在业务预测中取得一定效果 .随着动力模式的进一步发展 ,短期气候业务预测将逐步走向以动力模式客观预报为指导预报的新阶段     

青海省月平均气温潜在长期可预报性的估计

讨论了气候信号与气候噪声的相互关系和月平均气温预报正确率的上限问题。用青海省２５个站逐日气温的多年资料，按３种方法估计了气候信号和气候噪声的方差。结果得出，如果以绝对误差小于均方差的０．６８倍作为预报正确的标准，则青海省月平均气温预报正确率的上限约为６６％￣７２％，冬季与夏季差别不大。     

Changes in animal activity prior to a major (M = 7) earthquake in the Peruvian Andes

During earthquake preparation geophysical processes occur over varying temporal and spatial scales, some leaving their mark on the surface environment, on various biota, and even affecting the ionosphere. Reports on pre-seismic changes in animal behaviour have been greeted with scepticism by the scientific community due to the necessarily anecdotal nature of much of the evidence and a lack of consensus over possible causal mechanisms. Here we present records of changes in the abundance of mammals and birds obtained over a 30 day period by motion-triggered cameras at the Yanachaga National Park, Peru, prior to the 2011 magnitude 7.0 Contamana earthquake. In addition we report on ionospheric perturbations derived from night-time very low frequency (VLF) phase data along a propagation paths passing over the epicentral region. Animal activity declined significantly over a 3-week period prior to the earthquake compared to periods of low seismic activity. Night-time ionospheric phase perturbations of the VLF signals above the epicentral area, fluctuating over the course of a few minutes, were observed, starting 2 weeks before the earthquake. The concurrent observation of two widely different and seemingly unconnected precursory phenomena is of interest because recently, it has been proposed that the multitude of reported pre-earthquake phenomena may arise from a single underlying physical process: the stress-activation of highly mobile electronic charge carriers in the Earth’s crust and their flow to the Earth’s surface. The flow of charge carriers through the rock column constitutes an electric current, which is expected to fluctuate and thereby emit electromagnetic radiation in the ultralow frequency (ULF) regime. The arrival of the charge carriers can lead to air ionization at the ground-to-air interface and the injection of massive amounts of positive airborne ions, known to be aversive to animals.     

Data mining methods for hydroclimatic forecasting

Skillful streamflow forecasts at seasonal lead times may be useful to water managers seeking to provide reliable water supplies and maximize hydrosystem benefits. In this study, a class of data mining techniques, known as tree-structured models, is investigated to address the nonlinear dynamics of climate teleconnections and screen promising probabilistic streamflow forecast models for river–reservoir systems. In a case study of the Lower Colorado River system in central Texas, a number of potential predictors are evaluated for forecasting seasonal streamflow, including large-scale climate indices related to the El Niño–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO), and others. Results show that the tree-structured models can effectively capture the nonlinear features hidden in the data. Skill scores of probabilistic forecasts generated by both classification trees and logistic regression trees indicate that seasonal inflows throughout the system can be predicted with sufficient accuracy to improve water management, especially in the winter and spring seasons in central Texas.     

突出薄层特征的Chirp信号源浅地层剖面资料的处理研究

Chirp信号的浅地层剖面调查因其高分辨率的特点广泛应用于工程勘察、地质灾害评估、水合物调查、深海资源勘查等领域。由于Chirp信号发射频带宽度限制,互相关结果中旁瓣影响严重。常规提取包络处理能压制旁瓣,但处理后资料分辨率低。本文通过不同层厚以及不同反射系数连续薄层模型的正演、处理和定量分析,提出用线性提频处理方法压制旁瓣和提高资料的分辨率,将此方法用于理论模型和实际资料,效果显著。     

一种自动扫描地震漏检事件方法的研究与实现

地震事件的自动处理过程中会发生遗漏.台站数量越多,地震分析员在手动扫描遗漏事件时所花费的时间就越长.本文讨论了一种自动扫描漏检事件的方法,该方法利用分析员的分析经验,结合台站分布状况和地球物理学规则,重新关联那些具有很可能来自特定震源区域而未被分析员关联的信号,以形成一个待验证的事件,供分析员审定.该方法大大减少了分析员的工作量,提高了地震公报的质量.     

孔隙介质地震电磁信号的数值模拟研究

本文利用最近开发的孔隙介质震电波场算法开展了数值模拟研究,重点探讨不同结构模型中双力偶点源以及有限断层面源作用下产生的地震波及其伴随的电磁信号的时域和频域特征,考察了不同震源时间函数类型对震电波场数值模拟结果的影响,并以Ricker子波为例讨论了震电波场的频率响应特征.结果表明:地震电磁信号的波形、振幅和持续时间等都不同程度受到模型结构的影响,结构越复杂,波形也越复杂;不同震源(双力偶点源与有限断层面源、震源时间函数类型、Ricker子波峰值频率)产生的位移场和电磁场在波形和频谱响应方面整体上呈现相似的特征,但在波形和频谱的幅度和复杂程度方面存在一定差异.     

基于地震信号相似性的S变换域多次波压制技术

多次波压制是海洋地震数据处理的关键,如何保护一次反射波的同时高效准确地识别并压制多次波是地震资料处理的重点。笔者在共中心点(CMP)叠加压制多次波方法的基础上,基于CMP道集地震信号与叠加道地震信号的相似性特征在S变换域进行多次波压制。首先,利用多次波速度动校正并对CMP道集数据减去叠加道数据完成第一次多次波减除,此时,波场中残余的多次波以随机噪声的形式存在;然后,对减除多次波的地震波场应用一次波速度动校正,并以一次波速度叠加道为初始模型对CMP道集S变换谱进行相似性滤波完成第二次残余多次波去除。针对理论数据和实际数据进行了有效性测试,结果表明本文所提方法能够较好地压制多次波,提高反射波的成像精度。     

利用深度神经网络和先兆信号的江苏夏季降水客观预测方法

利用1961—2019年江苏省67个站降水量和气候指数数据集等资料,选取大气环流、海温和积雪等先兆信号的不同组合作为预测因子方案,通过对比不同机器学习方法对江苏省夏季降水开展预测试验。结果表明,深度神经网络（Deep Neural Network,DNN）较传统统计方法和其他机器学习方法有一定优势,深度神经网络结合动态权重集合因子方案对江苏省夏季降水的预测技巧最高,其独立样本检验结果稳定,2015—2019年的平均PS评分为76.0,距平符号一致率为0.62,距平相关系数达0.35,尤其对江苏省中南部的预测技巧更高,具有业务应用价值。不同预测因子方案对比分析表明,大气环流因子在江苏省夏季降水预测中做主要贡献,而海温因子和积雪等其他因子也有正贡献,说明使用综合性预测因子以及集合方案有助于提升季节预测准确率。