Instantaneous Seismic Attributes and Response Characteristics of Active Faults
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摘要: 活断层探测是断层活动性评判的基础，也是天然地震灾害预防的依据，而浅层地震勘探是活断层探测的有效方法之一；而目前利用浅层地震方法评判断层活动性的能力亟待提高.通过构建了不同宽度破碎带的活断层理论模型，采用二维粘弹性波动方程有限差分法进行了波场响应特征模拟，运用希尔伯特变换方法提取了瞬时频率和相位属性.结果表明：地震水平叠加剖面和瞬时属性相结合可有效获取穿过第四系活断层的响应特征和实现断层活动性评判；当相干噪声达到30%时，水平叠加和瞬时频率属性剖面已难以追踪第四系中弱反射信号，而瞬时相位属性剖面仍可有效追踪；在实际活断层判定中，水平叠加、瞬时频率与瞬时相位地震属性剖面均可判断断层的存在，而穿过第四系的断层 (或破碎带) 特征瞬时相位属性最为明显和突出，水平叠加剖面次之，瞬时相位地震属性是判定断层活动性的重要和有效的属性.Abstract: Active fault detection is not only the foundation for the fault activity evaluation, but also the basis for prevention of natural earthquake disasters. The shallow seismic exploration is one of the effective methods for active fault detection. This study aims to further improve the fault activity evaluation with shallow seismic methods. We construct theoretical models of active fault of different fracture zone widths, apply the finite difference method of two-dimensional viscoelastic wave equation to simulate wave field response characteristics, use Hilbert transform method to extract the attributes of instantaneous frequency and instantaneous phase, and analyze the performance in the field of anti-noise and effect of practical applications of method. The results show: Combination of the vertical travel time section and seismic attributes can effectively obtain the response characteristics of active faults which cut through the Quaternary and achieve the evaluation of fault activity; However, when coherent noise reaches thirty percent, it is difficult to trace and identify the weak reflection signals in the Quaternary by the vertical travel time section and instantaneous frequency section, but instantaneous phase attributes can still effectively trace and identify the weak reflection signals with a high anti-noise ability. In the practical determination of active faults, both the vertical travel time section, instantaneous frequency section and instantaneous phase section can determine the existence of faults.The instantaneous phase attribute is the most obvious and prominent to show the characteristics of faults or fracture zones which cut through the Quaternary, whereas the vertical travel time section takes the second place.It is concluded that the instantaneous phase attribute is an important and effective seismic attribute to determine the fault activity.
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图 3 非活动断层模型Ⅰ等偏移距模拟时间剖面
Fig. 3. Simulation time section in equal offset of inactive fault model Ⅰ
图 4 活动断层模型等偏移距模拟时间剖面
a、b、c和d分别为模型Ⅱ、Ⅲ、Ⅳ和Ⅴ的时间剖面，图中圆圈处为第四系地层中断层所在位置
Fig. 4. Simulation time section in equal offset of active fault model
图 5 非活动断层模型Ⅰ的瞬时属性剖面
a和b分别为瞬时频率和相位属性剖面
Fig. 5. Instantaneous attribute section of model Ⅰ
图 6 活动断层模型Ⅱ~Ⅴ的瞬时属性剖面
a、b、c和d分别为模型Ⅱ、Ⅲ、Ⅳ和Ⅴ的频率剖面，e、f、g和h分别为模型Ⅱ、Ⅲ、Ⅳ和Ⅴ的相位剖面，图中圆圈处为第四系地层中断层所在位置
Fig. 6. Instantaneous attribute section of active fault model Ⅱ~Ⅴ
图 7 模型Ⅳ加不同相干噪声后的时间剖面
a、b和c分别为加15%、30%和45%相干噪声后的时间剖面，图中圆圈处为第四系地层中断层所在位置
Fig. 7. Simulation time section with different coherent noise of active fault model Ⅳ
图 8 模型Ⅳ加不同相干噪声后的瞬时属性剖面
a、b和c分别为加15%、30%和45%噪声后的频率剖面，d、e和f分别为加15%、30%和45%噪声后的相位剖面，图中圆圈处为第四系地层中断层所在位置
Fig. 8. Instantaneous attribute section with different coherent noise of active fault model Ⅳ
图 9 实例时间剖面和瞬时属性剖面
a、b和c分别为实例时间、瞬时频率和相位剖面
Fig. 9. Time section and instantaneous attribute section of an example
表 1 非活动断层模型Ⅰ参数
Table 1. The parameters of inactive fault model
模型层号 厚度 (m) 界面深度 (m) 断层性质 断层倾角 (°) VP(m/s) VS(m/s) ρ(kg/m3) QP QS 备注 1 10 10 正 960 288 1 568 51.2 9.5 素填土层 2 10/14 20/24 正 45 1 000 300 1 600 56.0 10.4 第四系粘土层 3 10 30/34 正 45 1 400 600 1 800 117.4 44.6 风化层 4 正 45 2 000 900 2 000 257.3 107.9 基岩 注：VP、VS、ρ、QP和QS分别为纵波速度、横波速度、密度、纵波品质因子和横波品质因子. 
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表 2 活动断层破碎带模型参数
Table 2. The parameters of fracture zone in active fault model
模型
编号破碎带
厚度 (m)第四系粘土层破碎带 风化层破碎带 基岩破碎带 VP
(m/s)VS
(m/s)ρ
(kg/m3)QP QS VP
(m/s)VS
(m/s)ρ
(kg/m3)QP QS VP
(m/s)VS
(m/s)ρ
(kg/m3)QP QS Ⅱ 1.5 960 288 1 568 51.2 9.5 1 344 576 1 764 107.3 40.8 1 880 846 1 920 224.6 94.1 Ⅲ 2.9 960 288 1 568 51.2 9.5 1 344 576 1 764 107.3 40.8 1 880 846 1 920 224.6 94.1 Ⅳ 5.9 960 288 1 568 51.2 9.5 1 344 576 1 764 107.3 40.8 1 880 846 1 920 224.6 94.1 Ⅴ 11.8 960 288 1 568 51.2 9.5 1 344 576 1 764 107.3 40.8 1 880 846 1 920 224.6 94.1
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