The characteristics of Lg waves excited by explosion source and spall based on different models
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摘要: 地下核爆炸区域及远区地震波信号中,有二次源即层裂源的贡献,其对区域震相Lg波具有调制作用.本文利用理论地震图数值模拟方法,分析爆炸源和层裂源在3种典型介质速度模型下的区域震相特征,得到了爆炸源和层裂源所激发的Lg波与介质速度模型的关系,并结合CLVD源所激发的S波随震中距的演化过程,对Lg波的形成机制进行了阐述.结果表明,CLVD源是激发地下核爆炸低频Lg波的主要因素.Abstract: Spall is defined as a secondary seismic source contributing to regional and far field seismic signals generated by underground nuclear explosions.It can modulate the regional phase,i.e.,Lg waves.This paper analyzed the characteristics of Lg waves excited by explosion source and spall based on three typical crustal models by using numerical simulation of theoretical seismograms,then obtained the relationship between the crustal velocity models and the Lg waves excited by explosion source and spall.To explain the generation mechanism of Lg waves,we investigated the variation of S waves induced directly by compensate linear vector dipole (CLVD) source with different epicentral distances.The results indicate that CLVD source plays an important role in generating low-frequency Lg waves by underground nuclear explosions.
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Keywords:
- underground nuclear explosion /
- explosion source /
- spall /
- Lg waves
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图 2 3种介质速度模型下的S波和P波速度
Figure 2. The velocities of S- and P-wave for the three velocity models
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图 3 基于3种介质速度模型的爆炸源的理论地震波形图
Figure 3. Theoretical seismograms excited by explosion source based on the three velocity models
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图 4 基于3种介质速度模型的张裂源的理论地震波形图
Figure 4. Theoretical seismograms excited by tension crack source based on the three velocity models
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图 5 基于3种介质速度模型的CLVD源的理论地震图
Figure 5. Theoretical seismograms excited by CLVD source based on the three velocity models
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图 6 基于模型1的CLVD源所激发的不同震中距(Δ)上的理论地震波形图
以震中距为100 km的波形最大振幅为基准作归一化处理，归一化参数见图右侧；同时为满足Pn震相的起始时刻相同，将所有理论地震波形图的横坐标向左平移Δ/7.84 s
Figure 6. Theoretical seismograms excited by CLVD source with different epicentral distances based on the model 1
Normalized processing is based on the maximum amplitude of waveforms with the epicentral distance 100 km, and normalized parameters are shown on the right side. At the same time, to satisfy the Pn phases having the same starting points, we define the abscissa axis of all theoretical seismograms with left-ward shift by epicentral distances divided by 7.84 seconds
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McLaughlin K L,Barker T G,Day S M,Shkoller B,Stevens J L.1988.Effects of Depth of Burial on Explosion and Earthquake Regional Seismograms:Regional Discrimination and Yield Estimation[R].S-CUBED report No.SSS-R-88-9844,Jolla,California.
Patton H J.1991.Seismic moment estimation and the scaling of the long-period explosion source spectrum[G]//AGU Geophysical Monograph 65:Explosion Source Phenomenology.San Francisco:AGU:239-252.
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