湖北省降水量的周期分析

结合降水量对农业生产的影响特点将全年降水量分成５个阶段,根据聚类分析的结果将不同的时段的降水量进行分区,由此对全省的降水量做自相关分析和功率谱分析,从而发现了降水量的变化周期。     

广东省逐年初台登陆时间的变化特点

通过对广东省初始登陆时间资料的分析,发现其具周期变化的特点。根据循环阶段（周期）的划分,比较满意地解释了近３年广东省初始登陆时间明显偏迟的原因。     

Spectral Estimation of Irregularly Sampled Nonstationary Multidimensional Processes by Time-Varying Periodogram

A multidimensional version of the time varying periodogram has been developed. The estimation method based on the multidimensional time-varying periodogram has been applied to a nonstationary multidimensional storm model. This work proposes that the multidimensional time varying periodogram is capable of estimating nonstationary spectral density functions in space and time.     

青藏高原积雪分布与变化特征

本文对青藏高原ＳＭＭＲ修积雪深度、ＮＯＡＡ周积雪面积、地面台站积雪深度进行了分析。结果表明青藏高原东西两侧多雪与腹地少雪形成鲜明对比,高原东部是高原积雪年际变化最显著的地区,它主导了整个高原积雪的年际变化,并且与西部多雪区年际波动呈反位相关系。从６０年代到８０年代积雪年际波动幅度有明显增加趋势,积雪变化具有３年左右准周期。随着全球变暖,青藏高原积雪将会有所增加。     

Discrimination of small earthquakes and artificial explosions in the Korean Peninsula using Pg/Lg ratios

The purpose of this study is to develop a technique to discriminate artificial explosions from local small earthquakes ( M ≤ 4.0) in the time–frequency domain. In order to obtain spectral features of artificial explosions and earthquakes, 3-D spectrograms (frequency, time and amplitude) have been used. They represent a useful tool for studying the frequency content of entire seismic waveforms observed at local and regional distances (Kim, Simpson & Richards 1994). P and S(L g ) waves from quarry blasts show that the frequency content associated with the dominant amplitude appears above 10  Hz and Rg phases are observed at close distances. P and S(L g ) waves from the Tongosan earthquake have strong amplitudes below 10  Hz. For the Munkyong earthquake, however, a broader frequency content up to 20  Hz is found.
  For discrimination between small earthquakes and explosions, Pg/L g spectral ratios are used below 10  Hz, and through spectrogram analysis we can see different frequency contents of explosions and earthquakes. Unfortunately, because explosion data recorded at KSRS array are digitized at 20  sps, we cannot avoid analysing below 10  Hz because of the Nyquist frequency. In order to select time windows, the group velocity was computed using multiple-filter analysis (MFA), and free-surface effects have been removed from all three-component data in order to improve data quality. Using FFT, a log-average spectral amplitude is calculated over seven frequency bands: 0.5 to 3, 2 to 4, 3 to 5, 4 to 6, 5 to 7, 6 to 8 and 8 to 10  Hz. The best separation between explosions and earthquakes is observed from 6 to 8  Hz. In this frequency band we can separate explosions with log ( Pg/L g ) above −0.5, except EXP1 recorded at SIHY1-1, and earthquakes below −0.5, except the Munkyong earthquake record at station KMH.     

Spectral classification methods in monitoring small local events by the Israel seismic network

We use the dense Israel Seismic Network (ISN) to discriminate between low magnitude earthquakes and explosions in the Middle East region. This issue is important for CTBT monitoring, especially when considering small nuclear tests which may be conducted under evasive conditions. We explore the performance of efficient discriminants based on spectral features of seismograms using waveforms of 50 earthquakes and 114 quarry and underwater blasts with magnitudes 1.0–2.8, recorded by ISN short-period stations at distances up to 200 km. The single-station spectral ratio of the low and high-frequency seismic energy shows an overlap between explosions and earthquakes. After averaging over a subnet of stations, the resolving power is enhanced and the two classes of events are separated. Different frequency bands were tested; the (1–3 Hz)/(6–8 Hz) ratio provided the best discriminant performance. We also estimated normalized r.m.s. spectral amplitudes in several sequential equal frequency windows within the 1–12 Hz band and applied multiparametric automatic classification procedures (Linear Discrimination Function and Artificial Neural Network) to the amplitudes averaged over a subnetwork. A leave-one-out test showed a low rate of error for the multiparametric procedures. An innovative multi-station discriminant is proposed, based on spectral modulation associated with ripple-firing in quarry blasts and with the bubbling effect in underwater explosions. It utilizes a distinct azimuth-invariant coherency of spectral shapes for different stations in the frequency range (1–12 Hz). The coherency is measured by semblance statistics commonly used in seismic prospecting for phase correlation in the time domain. After modification, the statistics applied to the network spectra provided event separation. A new feature of all the above mentioned procedures is that they are based on smoothed (0.5 Hz window), instrument-corrected FFT spectra of the whole signal; they are robust to the accuracy of onset time estimation and, thus well suited to automatic event identification.     

Raman spectral analysis and genetic mechanism of pseudotachylyte in Xiaoqinling detachment fault

Veins and clasts of pseudotachylyte developed in the microbreccias of the detachment fault along the boundary of the Xiaoqinling metamorphic core complex. The Raman spectral analysis shows that there are three kinds of textures in the matrices of the pseudotachylyte, i.e. ultracataclastic fine-grained texture, cryptocrystalline texture and both of them with minute quantity of glass. The three different textures are the results of different degrees of ultracataclasis. This demonstrates that ultracataclasis-comminution-melting is the genetic mechanism of the pseudotachylytes in the Xiaoqinling detachment fault and the ultracataclasis-comminution dominates in their formation. Project supported by the National Natural Science Foundation of China (Grant No. 49472142).     

地脉动及特殊波形的频谱特性在地震预报中的应用

利用功率谱和Ｓｏｍｐｉ谱分析方法,对大震前地脉动及震前特殊波形等记录进行了比较深入的研究,结果表明：（１）较大地震前短周期地脉动及震前特殊波形频谱的峰值频率ｆｍ,拐角频率ｆｃ相对频带宽度△ｆ相对峰值Ｓｍ／Ｓ０,高频段的斜率绝对值│ｂ│及Ｓｏｍｐｉ谱的卓越频率ｆｄ等特征量均可能出呈现出较明显的下降（少数为上升）异常变化。（２）各频谱特征量呈现异常的时间基本上同步,并与波速异常发展趋势基本相符,（３）     

On the use of microtremor recordings in seismic microzonation

Experimental methods involving microtremor recordings are useful for determining site effects in regions of moderate seismic activity where ground motion records are few, and in urban or industrial contexts where the noise level is high. The aim of this study is to establish a microzonation by using the Nogoshi–Nakamura method,[1, 2] a simple experimental technique based on microtremor recordings. Since the physical phenomena underlying the method are only partially understood, the spectral responses obtained cannot be used alone. We, therefore, complete our experimental results by comparing them with the solutions of a one-dimensional numerical simulation (SHAKE91).[3, 4] The experimental programme was carried out on a plain near the Rhone Delta (South of France). H/V spectral ratios were calculated at 137 noise measurement points. In addition, we were able to compute the numerical transfer functions from soil columns defined by geotechnical characteristics inside the studied region. A comparison of the results obtained by the experimental and numerical methods showed that the fundamental frequencies are in good agreement, but that the amplitudes obtained by the two techniques are sometimes different. The analysis of H/V spectral ratios enabled us to establish maps to characterize the region: a resonance frequency map and maps of amplification levels as a function of frequency range, leading to a seismic microzonation for the whole of the region.