地震研究

利用2008年4月28日0时至5月12日13时许昌地震台地震连续波形资料,对安德列亚诺夫群岛7.0级、日本东海岸近海7.1级和汶川8.0级地震3次M≥7.0地震前地脉动变化情况进行了频域、振幅的量化分析,得出如下结论:3次地震前三分向都记录到了地脉动异常,水平向较垂直向明显; 傅立叶谱0.2～0.3 Hz谱振幅值出现较大变化,进程上具有快速增大—达到最大值—下降—下降过程中发震的特征; 地脉动异常分别在3次地震前2.3、3.3、2.9 d出现,属临震异常。

Basing on the seismic continuous waveforms from 12:00 am on Apr.28 to 1:00 pm on May.12 in 2008 recorded by Xuchang Station,we quantitatively analyzed frequency domain and amplitude of microtremor variation before three M≥7.0 earthquakes,including Andrea Ivanov Islands M7.0 earthquake on Apr.2,2008,East coast of Honshu offshore M7.1 earthquake on Apr.8,2008 in Japan and Wenchuan M_S8.0 earthquake on Apr.12,2008 in Sichuan. The conclusions was obtained as following:the microtremor anomalies were recorded by three three-component of seismometer before three earthquakes,and was obvious in the vertical component. The 0.2 ～ 0.3 Hz spectrum amplitude value of Fourier spectral changed greatly,and the process had the characteristic that the earthquake occurred in the process of rapid increase-reach to maximum-decrease-decrease. The microtremor anomaly was appeared in 2.3,3.3,2.9 days before three earthquakes,which were impending anomaly.

引言
1 资料与方法
2 地脉动异常计算与分析
3 结论与探讨

表1 研究时段内地震参数<br/>Tab.1 Seismic parameters in the study period

表1 研究时段内地震参数
Tab.1 Seismic parameters in the study period

图1 NS向短周期地震仪幅频曲线<br/>Fig.1 Amplitude-frequency curve of NS short-period seismometer

图1 NS向短周期地震仪幅频曲线
Fig.1 Amplitude-frequency curve of NS short-period seismometer

图2 许昌台地脉动傅立叶谱0.2～0.3 Hz<br/>幅值变化曲线<br/>(a)NS向;(b)EW向;(c)UD向<br/>Fig.2 Amplitude variation curve in 0.2～0.3 Hz of Fourier spectrum of microtremor at Xuchang Station (a)NS;(b)EW;(c)UD 7 count,UD向在2.0～3.5 count。

图2 许昌台地脉动傅立叶谱0.2～0.3 Hz
幅值变化曲线
(a)NS向;(b)EW向;(c)UD向
Fig.2 Amplitude variation curve in 0.2～0.3 Hz of Fourier spectrum of microtremor at Xuchang Station (a)NS;(b)EW;(c)UD 7 count,UD向在2.0～3.5 count。

表2 研究时段3次地震前地脉动整点傅立叶谱0.2～0.3 Hz振幅随时间变化<br/>Tab.2 Fourier spectrum amplitude in 0.2～0.3 Hz of microtremor whole point value variation with time before three earthquakes in the study period

表2 研究时段3次地震前地脉动整点傅立叶谱0.2～0.3 Hz振幅随时间变化
Tab.2 Fourier spectrum amplitude in 0.2～0.3 Hz of microtremor whole point value variation with time before three earthquakes in the study period

图3 安德烈亚诺夫群岛地震前0.005～0.6 Hz一小时地脉动部分频谱(UD向:0.005～0.7 Hz)<br/>Fig.3 Part of 0.005～0.6 Hz microtremor spectrum in one hour before Andrea Ivanov Islands M7.0 earthquake(UD direction:0.005～0.7 Hz)

图3 安德烈亚诺夫群岛地震前0.005～0.6 Hz一小时地脉动部分频谱(UD向:0.005～0.7 Hz)
Fig.3 Part of 0.005～0.6 Hz microtremor spectrum in one hour before Andrea Ivanov Islands M7.0 earthquake(UD direction:0.005～0.7 Hz)

图4 日本本州东海岸近海地震前0.005～0.6 Hz一小时地脉动部分频谱(UD向:0.005～0.7 Hz)<br/>Fig.4 Part of 0.005～0.6 Hz microtremor spectrum in one hour before East coast of Honshu offshore M7.1 earthquake in Japan(UD direction:0.005～0.7 Hz)

图4 日本本州东海岸近海地震前0.005～0.6 Hz一小时地脉动部分频谱(UD向:0.005～0.7 Hz)
Fig.4 Part of 0.005～0.6 Hz microtremor spectrum in one hour before East coast of Honshu offshore M7.1 earthquake in Japan(UD direction:0.005～0.7 Hz)

图5 四川汶川地震前0.005～0.6 Hz一小时地脉动部分频谱(UD向:0.005～0.7 Hz)<br/>Fig.5 Part of 0.005～0.6 Hz microtremor spectrum in one hour before Wenchuan M8.0 earthquake in Sichuan(UD direction:0.005～0.7 Hz)

图5 四川汶川地震前0.005～0.6 Hz一小时地脉动部分频谱(UD向:0.005～0.7 Hz)
Fig.5 Part of 0.005～0.6 Hz microtremor spectrum in one hour before Wenchuan M8.0 earthquake in Sichuan(UD direction:0.005～0.7 Hz)

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备注

引言

1 资料与方法

2 地脉动异常计算与分析

3 结论与探讨

期刊信息