Preliminary discussion and identification of pulse-like strong motion for the 1979 Imperial Valley earthquake
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摘要: 以1979年MW6.5帝王谷地震为例，比较了小波变换法、峰点法（PPM）和零点法（ZVPM）识别近断层速度脉冲型强震记录的能力，三种方法识别出的脉冲峰值基本一致，脉冲周期略有差别。为分析速度脉冲的产生机制，包括产生时间、位置以及凹凸体的影响，借助频率-波数域格林函数法（FK法）合成近断层宽频带地震动，采用峰点法逐步识别各子源地震动叠加过程中产生的速度脉冲。通过时频方法分析叠加过程中子源地震动频率成分的变化，分析凹凸体和台站的空间关系对脉冲产生的影响，初步探讨近断层速度脉冲的产生机制。Abstract: Taking the 1979 MW6.5 Imperial Valley earthquake as an example, we compared the three methods of pulse-like strong motion identification, that is, wavelet analysis, peak-point method （PPM） and zero velocity point method （ZVPM）. The identified peak values are similar, however, the identified pulse periods are slightly different. To analyze the mechanism of the velocity pulse, including the generation time, location, and the impact of asperity, we use the frequency-wavenumber Green’s function （FK method） to synthesize broadband ground motion. PPM is used to gradually identify the velocity pulses during the superposition of the sub-source ground motions. Analyzing the changes of the frequency components in sub-fault ground motion during the superposition process by using time-frequency analysis method and the impact of the spatial relationship between the asperity and the station on the pulse generation, preliminarily discuss the generation mechanism of the velocity pulse.
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Keywords:
- velocity pulse /
- pulse identification /
- FK method /
- asperity /
- pulse indicator
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图 1 帝王谷地震震中、断层投影和台站位置 （a）及31个台站的加速度时程 （b）
Figure 1. The location of epicenter, fault projection and stations （a） and acceleration records at 31 stations （b） of the Imperial Valley earthquake
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图 2 小波变换法识别出的速度脉冲型地震动
Figure 2. Identification of pulse-like ground motion by wavelet transform
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图 4 三种方法提取RSN158台站记录的脉冲
Figure 4. Identification of pulse-like ground motion by three methods
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图 5 小波变换（a）、峰点法（b）和零点法（c）识别出的速度脉冲的台站
Figure 5. Stations with velocity pulse identified by wavelet transform （a），PPM （b），and ZVPM （c）
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图 6 帝王谷地震断层面上的错动分布
Figure 6. Slip distribution on the fault plane of the Imperial Valley earthquake
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图 7 台站RSN158 （a）和台站RSN179 （b）在破裂过程中出现脉冲的子源
Figure 7. The velocity pulse appears during rupture process at station RSN158 （a） and station RSN179 （b）
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图 8 最初产生脉冲的子源位置与凹凸体和错动量的关系
Figure 8. The relationship between the sub-source position that the pulsefirst generated， the asperity and the slip distribution
表 1 三种方法识别出的帝王谷地震中脉冲型地震动的脉冲参数
Table 1 The pulse indicators of pulse-like ground motions in the Imperial Valley earthquake identified by three methods
RSN台站编号 脉冲周期Tp/s 脉冲峰值Vp/（cm·s−1） 小波变换法 峰点法 零点法 小波变换法 峰点法 零点法 158 − 1.9 1.9 − 59 60 159 2.3 1.9 1.9 53 50 53 161 4.3 4.2 3.3 51 55 52 170 4.4 3.9 3.5 79 63 71 171 3.4 3.2 3.1 121 111 115 173 4.5 3.3 4.9 69 71 70 178 4.5 4.4 4.4 69 61 60 179 4.8 4.4 3.8 81 89 82 180 4.1 3.9 2.1 130 133 136 181 3.8 3.5 4.8 155 156 160 182 4.4 3.1 4.4 98 100 109 185 2.8 3.5 3.0 68 71 72 
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表 2 帝王谷地震的震源参数
Table 2 Source parameters of Imperial Valley earthquake
震源
机制走向/° 倾角/° 断层参数 子源个数 凹凸体 埋深
/km长度
/km宽度
/km面积
/km2沿走向 沿倾向 个数 面积
/km2长度
/km宽度
/km中心沿走向、
倾向位置/km走滑型 323 90 8 42 10.4 436.8 16 8 1 102 13 7.8 22，6.4
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