江苏数字地震台网P波谱震级和地震辐射能的计算

基于江苏数字地震台网的宽频带记录,对38次M≥5.0地震的P波谱震级M_P进行测定,对地震的辐射能量进行了估算。结果表明:本文测定的M_P与中国地震台网中心(CENC)测定的MS、德国地学中心(GFZ)测定的MW具有很好的一致性,与该2种震级之间的平均偏差分别约为0.17和0.10级,基本小于世界主要地震机构之间对同一震级的测定误差(约0.2级);同时,基于M_P估算的地震辐射能与基于修正G-R关系由MS震级换算获得的结果十分接近,两者平均能量之比约为1.1,表明M_P与P波群(P+pP+sP)能量流是基本等效的。因此,基于宽频带数字记录测定中强地震的P波谱震级以及地震辐射能是可行的,且测定过程简便。     

Crust and upper mantle heterogeneities in the southwest Pacific from surface wave phase velocity analysis

Direct earthquake-to-station Rayleigh and Love wave data observed on high gain broadband records are analyzed in order to improve the lateral resolution of the uppermost mantle in the southwest Pacific region. We used data of nine permanent Geoscope and Iris stations located in the southern hemisphere and nine other stations as part of two temporary networks, the first one installed in New Caledonia and Vanuatu (hereafter named Cavascope network) by ORSTOM and the EOST from Louis Pasteur University in Strasbourg (France) and the second one installed in the Fiji, Tonga and Niue islands (hereafter named Spase network) by Washington University in St. Louis (USA). In order to collect more significant details on the surficial structures, we included the analysis of short period waves down to 8 s. A multiple frequency filtering technique has been used to recover phase velocities of Rayleigh and Love waves for selected earthquakes with magnitude greater than 5.5 and with known centroid moment tensor (CMT). About 1100 well-distributed seismograms have been processed in the period range 8–100 s and corrections for topography and water depth have been applied to the observed phase velocities. The geographical distribution of phase velocity anomalies have then been computed using the tomographic method developed by Montagner [Montagner, J.P., 1986a. Regional three-dimensional structures using long-period surface waves. Ann. Geophys. 4 (B3), 283–294]. Due to a poor knowledge of dense, well-distributed, crustal thickness values and corresponding velocity models, we did not perform or speculate on the construction of an S-wave 3D velocity model; therefore, we limited this study to the interpretation of the phase velocity distribution. The location of phase velocity anomalies are well determined and the deviations are discussed within the framework of the geological context and compared with other tomographic models. At long periods, from 40 s to 100 s, our results agree well with most of previous studies: the tomographic imaging shows a large contrast between low and high phase velocities along the Solomon, New Hebrides and Fiji–Tonga trenches. The lowest phase velocity anomalies are distributed beneath northern and southern Fiji basins and the Lau basin (corresponding to the volume situated just above the dipping slabs), whereas the highest values are displayed beneath the Pacific plate and the eastern part of Indian plate downgoing under the North Fiji basin. At shorter periods, our results show that the phase velocity distributions are well correlated with the large structural crustal domains. The use of local temporary broadband stations in the central part of the studied area gives us the opportunity to observe surface waves showing well-dispersed trains, allowing extended velocity measurements down to 8 s although aliasing due to multipaths become important. The continental regions (Eastern Australia, New Guinea, Fiji islands and New Zealand) show low velocities which are likely due to thick continental crust, whereas the Tasmanian, D'Entrecasteaux, and the Northern and Southern Fiji basins are characterized by higher velocities suggesting thinner oceanic crust. Additional analysis including the anisotropic case and S-wave velocity inversion with depth is in progress.     

M_(S(BB))、M、M_(S7)震级对比

选取2009—2015年内蒙古测震台网速报的46个M≥4.1地震,依据《地震震级的规定》(GB17740—2016)中关于量取地震宽频带面波震级M_(S(BB))的各项条款,重新量取M_(S(BB)),与中国地震台网中心编目结果产出的M震级和M_(S7)震级进行对比分析,结果显示:M_(S(BB))震级与M_(S7)震级的一致性较好。     

昆明地震台地面与井下地震观测背景噪声对比

对昆明地震台山洞内放置的宽频带地震仪BBVS-60及观测井内放置的GL-S60B深井宽频带地震仪所记录的资料,进行背景噪声对比分析,得到基岩地区地面及井下背景噪声干扰,为今后在云南地区推广井下观测提供参考依据。结果显示,在1—20 Hz频段内,井下台背景噪声RM_S值比地表台小,降噪效果UD向达30%以上,EW向达50%,NS向达60%。在100—30 s频带内噪声不降反升,原因有待进一步分析。     

Well tie for broadband seismic data

The seismic industry is increasingly acquiring broadband data in order to reap the benefits of extra low‐ and high‐frequency contents. At the low end, as the sharp low‐cut decay gets closer to zero frequency, it becomes harder for a well tie to estimate the low‐frequency response correctly. The fundamental difficulty is that well logs are too short to allow accurate estimation of the long‐period content of the data. Three distinctive techniques, namely parametric constant phase, frequency‐domain least squares with multi‐tapering, and Bayesian time domain with broadband priors, are introduced in this paper to provide a robust solution to the wavelet estimation problem for broadband seismic data. Each of these techniques has a different mathematical foundation that would enable one to explore a wide range of solutions that could be used on a case‐by‐case basis depending on the problem at hand. A case study from the North West Shelf Australia is used to analyse the performance of the proposed techniques. Cross‐validation is proposed as a robust quality control measure for evaluating well‐tie applications. It is observed that when the seismic data are carefully processed, then the constant phase approach would likely offer a good solution. The frequency‐domain method does not assume a constant phase. This flexibility makes it prone to over‐fitting when the phase is approximately constant. Broadband priors for the time‐domain least‐squares method are found to perform well in defining low‐frequency side lobes to the wavelet.     

鄂西地区宽频地震台阵背景噪声特征

利用鄂西地区长时间段宽频地震台站的三分量背景噪声记录,采用波形互相关方法得到台站对间的互相关函数,并通过聚束分析获得瑞雷波和勒夫波的慢度谱,研究鄂西地区背景噪声源的时空分布特征。结果表明,5~10 s周期范围,背景噪声来源于南太平洋且没有季节变化;10~20 s周期范围,慢度谱上显示明显的能量环,表明噪声源来源于多个方向,且表现出强烈和急剧的季节变化;20~40 s周期范围,慢度谱上也存在明显的能量环,其产生机制可能与此周期下提出的次重力波机制相似。在不同的周期范围内,噪声源分布方位有所不同,但在周期10~40 s范围噪声源在各方向均有分布。因此,利用长时间段连续噪声数据计算的互相关函数在周期10~40 s范围内满足背景噪声面波层析成像的理论前提。     

基于FTIR和MODIS数据估算新疆沙漠宽波段地表比辐射率

基于FTIR和MODIS数据,建立了新疆沙漠宽波段（8～13.5 μm）地表比辐射率的最优估算模型。首先,利用傅立叶变换热红外光谱仪观测的塔克拉玛干沙漠地表比辐射率光谱数据,结合同期MODIS温度/比辐射率产品MOD11A1的29、31和32波段比辐射率值和MOD09A1的第7波段反射率值,建立宽波段地表比辐射率估算模型,并分别采用观测数据和光谱库数据验证了模型的精度,估算结果的均方根误差分别为0.0041和0.0081。其次,选择最优估算模型,利用MODIS数据,估算了新疆4个沙漠的宽波段地表比辐射率,得到了沙漠地表比辐射率的空间分布特征。结果表明：塔克拉玛干沙漠和库鲁克库姆沙漠气候干燥稳定,地表比辐射率分布较为均匀,范围为0.850～0.915;古尔班通古特沙漠受到植被和地表水分的影响,比辐射率空间分布不均匀,范围为0.890～0.915;库木塔格沙漠的地表比辐射率分布与其羽状地表类似,范围为0.860～0.910。     

VP型宽频带潮汐观测仪的研制

摆式潮汐观测仪是记录由天体相互作用力引起的地倾斜固体潮变化的地震前兆观测设备。基于VP型宽频带潮汐观测仪的研制过程论述其原理及应用,得出VP型宽频带潮汐观测仪具有频带宽、易操作、采样率高的特点。     

利用区域宽频带数据反演鲁甸MS6.5级地震震源破裂过程

基于有限断层模型反演方法,我们利用区域宽频带数据反演得到了2014年8月3日鲁甸M_S6.5级地震的震源破裂过程.反演结果显示：此次地震的发震断层走向为北北西向,破裂主要以左旋走滑为主,位移主要发生在震源左上方,最大滑动量为0.7 m,模型显示断层破裂可能接近地表,破裂长度约10 km.此次地震释放的标量地震矩为1.97×10¹⁸ N·m,相当于矩震级为M_w 6.1,地震能量主要在前15 s释放.鲁甸地震有四个显著的特点：（1）位移主要集中在浅部,从11 km起破点开始迅速向上传播,大部分位于10 km以上且最大位移位于深度3 km处,从模型来看,破裂可能接近地表,因此地表震动较为强烈;（2）应力降比较大,计算显示释放的同震静态应力降约为2.8 MPa;（3）破裂速度较快,在地表附近超过了2.5 km·s^-1;（4）主震可能发生在一个共轭断层系上.这四个特点可能是导致此次地震造成如此重大人员伤亡和财产损失的最重要的原因.     

宽频带地震台网在滑坡地质灾害监测预报中的应用

在千将坪滑坡前地震动事件分析基础上,总结滑坡前滑坡体内部岩体形变和破裂所产生地震信号的典型特征,并建立宽频带地震台,对金坪子滑坡体和早谷田危岩体进行监测实验,提取基岩类、土质类和危岩体类3种基本物质组成滑坡的微振动前兆信息特征,为地震台网在滑坡监测预报中的应用推广和监测预报系统软件的研制奠定基础.根据测震学原理,研发滑坡监测分析系统软件（Smas）,可为滑坡大规模活动前快速预警.