Snowpack disrupts relationship between young water fraction and isotope amplitude ratio; approximately one fifth of mountain streamflow less than one year old

Previous “fraction of young water” (F_yw) estimates based on relative annual isotopic amplitudes in precipitation (A_p) and streamflow (A_s) produced low F_yw values in mountain catchments, which is contrary to extensive research that reports rapid water transmission in mountains. This study investigated this discrepancy by testing the effect of snow accumulation on the model that underpins the F_yw method. A Monte-Carlo analysis of simulations for 20,000 randomly-generated catchment model configurations used 10 years of precipitation inputs for the Upper Elbow River catchment in the Rocky Mountains (Alberta, Canada) to model discharge with and without snowpack storage of winter precipitation. Neither direct nor modified precipitation input produced a 1:1 relationship between A_s/A_p and F_yw, undermining the applicability of the original F_yw method in mountain watersheds with large seasonal snow accumulation. With snowpack-modified input a given A_s/A_p ratio corresponds to a range of F_yw values, which can still provide semi-quantitative information. In the small (435 km²) Elbow River catchment a F_yw range of 7–23% supports previous findings of rapid transmission in mountain catchments. Further analysis showed that the improved discharge prediction (Nash–Sutcliffe efficiency > 0.9) correlates with higher F_yw values and demonstrated that the interannual shifts in δ¹⁸O can be used to estimate of new water (<1 year) fraction in winter streamflow, and the estimate of 20% for the Elbow River further supports rapid transmission in mountain catchments.     

基于EEMD的太阳活动对印度夏季风的多尺度胁迫分析

选取10.55~2.7 kaBP Qunf洞的Q5石笋δ¹⁸O记录作为印度夏季风的代用指标,集合经验模态分解（EEMD）多尺度分析结果揭示了印度夏季风的强弱变化和与亚洲季风减弱事件的一致性,进一步讨论了11 kaBP以来印度夏季风的逐渐增强而后减弱的发展态势。选用同时期的古树年轮¹⁴C记录作为太阳活动代用指标,调频、调幅分析结果发现印度夏季风的31 a、70 a和7 860 a尺度分量受太阳活动相应分量的调频胁迫较为显著;同时又揭示出“太阳活动71 a周期-印度夏季风31 a周期”“太阳活动1 379 a周期-印度夏季风142 a周期”和“太阳活动2 376 a周期-印度夏季风733 a周期”三对调幅胁迫。     

高阶脉冲标定器及观测系统幅频特性

在前阶段理论研究的基础上,搜寻到了几种高阶脉冲波形,其频谱的低频分量平坦,高频分量更丰富。据此制成功能完善,性能优良的标定器。用高阶脉冲标定器产生的标定电流来激励拾震器,使观测系统产生相应的响应,由计算机采集该响应,并进行富氏变换及相关运算。由此可得到系统的幅频特性Ｋ（ω）,为暂态标定结果。对于速度 平坦型观测系统暂态标定与稳定态标定所得的特性曲线完全重合,即标定精度相同。     

呼和浩特—包头盆地震源应力场状态分析

为了分析呼和浩特—包头盆地现今应力场状态,基于内蒙古地震台网记录的地震波形资料,运用振幅比方法获取2000—2016年该盆地及周边M_L≥2.7地震的震源机制解,计算其一致性参数,并反演区域应力场。结果表明,震源机制解特征主要表现为走滑特征,一致性参数空间分布处于低值状态,力轴方位基本与该区的应力场背景特征相符,即主压应力方位为北东、张应力方位为北西。     

陕西地区小微震震源机制研究

小微震事件的震源机制是区域应力场及诸多地球动力学研究的基础资料。陕西地区为多个地震带的交汇区,近些年积累了丰富的小微震波形资料。运用新近发展的适用于求解小微震震源机制的广义极性振幅技术(GPAT),结合陕西2015地壳速度模型,求解陕西测震台网2011年4月至2015年12月间记录的121次ML1.5~3.5事件的震源机制。反演结果表明:(1)以上事件的震源机制大部分为走滑及正断类型,其比例占64.5%;逆断型机制占22.3%。(2)反演震源机制得到的震源深度与定位深度具有良好的一致性;矩震级与近震震级间存在差别,且这种差别随事件的变小而增大。(3)对比渭河断陷带相关研究成果,验证了该区域震源机制以正断型为主,具有拉张应力状态。     

2016年8月24日意大利中部MW6.2地震强地面运动特征分析

对意大利国家强震台网在2016年8月24日获得的其中部拉齐奥大区阿库莫利市发生的M_W6.2地震强震动三分向记录进行处理和分析。完成原始数据基线校正、滤波等基本数据处理,回归此次地震动幅值衰减规律,发现其整体与ITA08及BA08的衰减趋势一致,但远场实际值低于预测值,不同场地条件下的衰减特性与ITA10一致,近震源幅值较大,且方向性明显;计算并回归分析几种持时,与全球经验预测方程均基本吻合;比较4个幅值较大的近震源台站的反应谱,发现其明显高于欧洲抗震设计规范中的设计反应谱。结合此次震害特点,该地区在实际建设中仍需提高抗震设防能力,以确保安全性等级。     

唐山M 4.8地震地磁谐波振幅比变化

针对2012年5月28日河北唐山M 4.8地震,采用地磁谐波振幅比方法,分析昌黎、静海、红山及承德地磁台2007年1月至2015年12月地磁观测数据,结果显示：各台站10 min周期的计算结果波动性明显,其他周期形态较为一致;距震中最近的昌黎地磁台Y_ZHx（NS）测向的10-40 min周期地磁谐波在下降至极低值后,开始转折时发生地震,而Y_ZHy（EW）测向未出现明显转折现象;位于河北平原地震带中部的静海地磁台对此次地震反应显著,2个测向在震前均出现下降-转折-上升的变化特征。通过对比位于不同地区的4个地磁台站地磁谐波振幅比变化,发现受大范围整体构造应力场作用的影响,计算结果具有相似的趋势性变化特征,具体到局部地区或断裂带内部,各台站之间显示出一定差异。     

大地电场台站日变幅年度变化趋势分析

为了直观展示大地电场日变幅年度变化趋势,获取多年尺度下数据变化形态及特征,选取2012-2015年,4个地电台网8个存在潮汐地电场变化的地电台站观测数据,进行去除台阶、异常数据及滤波处理,计算地电场日变幅。结果显示：①2012-2013年大多数台站存在春冬低、夏秋高的日变幅趋势性特征;②2014-2015年存在几种不同日变幅年度变化趋势,同时同一台站不同测道间日变幅变化趋势存在差异性,该变化趋势和差异性的存在可能与地下介质结构变化和介质的非均匀性有一定关系。     

STUDY ON FOCAL DEPTH OF THE MS5.4 CANGWU EARTHQUAKE IN GUANGXI

On July 31th, 2016, a magnitude 5.4 earthquake struck Cangwu Country, Guangxi Zhuang Autonomous Region, it was the largest earthquake recorded by Guangxi Seismological Network since it set up. The number of people affected by the earthquake had reached 20 000, and the direct economic losses caused by the earthquake were nearly 100 million Yuan. After the earthquake, USGS provided a global earthquake catalog showing that the focal depth of Cangwu earthquake was about 24.5km. However, the result given by the Global Centroid Moment Tensor showed the focal depth of this earthquake was 15.6km. However, the result obtained by Xu Xiaofeng et al. using CAP method was 5.1km. It was clear that the focal depths of Cangwu earthquake given by different institutions were quite different from each other. However, accurate focal depth of the earthquake has important significance for exploring the tectonic mechanism near the epicenter, so it is necessary to further determine the more accurate depth of the Cangwu earthquake. In order to further accurately determine the focal depth of Cangwu earthquake, we used the global search method for travel-time residual to calculate the focal depth of this earthquake and its error range, based on the regional velocity model, which is a one-dimensional velocity model of the Xianggui tectonic belt produced by the comprehensive geophysical profile. Then, we inverted the focal mechanism of this earthquake with the CAP method. Based on this, the focal depth of Cangwu M_S5.4 earthquake was further determined by the method of the Rayleigh surface wave amplitude spectrum and the sPL phase, respectively. Computed results reveal that the focal depth of this earthquake and its error range from the travel-time residual global search method is about(13±3)km, the focal depth inverted by CAP method is about 10km, the focal depth from sPL phase is about 10km, and the focal depth from Rayleigh surface wave amplitude spectrum is about 9~10km. Finally, we confirmed that the focal depth of Cangwu M_S5.4 earthquake is about 10km, which indicates that this earthquake still occurred in the upper crust. In the case of low network density, the sPL phase and Rayleigh wave amplitude spectrum recorded by only 1 or 2 broadband stations could be used to obtain more accurate focal depth. The focal depth's accuracy of Cangwu M_S5.4 earthquake in the USGS global earthquake catalog has yet to be improved. In the future, we should consider the error of the source parameters when using the USGS global earthquake catalog for other related research.     

用振幅变化长短时均值比实现地震预警中P波自动拾取

地震P波到时快速、精确的自动拾取是实现地震预警的第一步。目前所有P波到时自动拾取方法都需要进一步考虑准确度问题,据此提出用"振幅变化"长短时均值比方法拾取P波到时。研究表明引进"振幅变化"作为特征函数比Allen的"振幅变化平方"更能突显地震波初至时刻的"突变"特征。对"振幅变化长短时均值比方法"和Allen的"振幅变化平方长短时均值比方法"进行抗噪音分析表明,在较低信噪比条件下,Allen方法不能准确地拾取P波到时,而新方法依然能较准确地拾取P波到时。在较高信噪比条件下,用两种方法拾取的160个M_S4.0地震P波到时,其误差大都在允许范围内,但新方法拾取的准确度略高。新方法可以看做是对长短时均值比方法的拓展。