Variations of the specific barrier model—part I: effect of subevent size distributions
Variations of the specific barrier model—part I: effect of subevent size distributions
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特定障碍模型的变体 - 第一部分：子事件大小分布的影响
DOI：
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发表时间：
2012
影响因子：
4.6
通讯作者：
A. Papageorgiou
中科院分区：
文献类型：
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作者：
B. Halldorsson;A. Papageorgiou
特定障壁模型（specific barrier model， SBM）由Papageorgiou和Aki （1983a; 1983b; 1985）提出并发展，最近由Halldorsson和Papageorgiou（2005）对不同构造区域的地震进行了重新校准，它是一种复合震源模型的特殊情况，根据该模型，地震矩基于矩和面积约束在断面上以确定性的方式分布。也就是说，它假设一个矩形断层表面充满了非重叠子事件的集合，这些子事件被模拟为直径相等的圆形裂缝，即“屏障间隔”，在该“屏障间隔”上发生了“局部应力下降”。在本工作中，我们放宽了关于SBM子事件大小的基本假设。子事件仍然建模为圆形裂缝，允许根据控制子事件大小发生频率的各种规定的概率密度函数在大小上变化。采用Joyner和Boore（1986）提出的方法推导了复合源的“远场”光谱的封闭形式表达式。单个子事件辐射的地震能量在一个时间窗口内到达一个地点，这个时间窗口的持续时间与破裂的持续时间和震源地点的几何形状有关。“到达时间”分布对复合源的光谱振幅的影响在一篇配套论文中进行了研究，称为第二部分。子事件大小分布的类型及其允许的大小范围直接影响满足矩约束所需的子事件数量。大量的子事件导致地震的“复杂性”增加，这通常导致高频源加速度谱水平相对较高。不同尺寸分布对应的高频加速度谱幅值的平台水平与SBM远场谱的平台水平没有显著差异，局部应力下降恒定。此外，在SBM及其变体的频谱振幅中观察到的差异可能小于与强震数据确定的局部应力降值相关的预期不确定性。因此，尽管SBM的假设简化了，但它似乎提供了最简单、最有效的描述，能够捕捉到复合震源的基本特征。这对于在“近断层”以及“远场”区域进行地震工程应用的一致强震建模尤其有利。
The specific barrier model (SBM), introduced and developed by Papageorgiou and Aki (1983a; 1983b; 1985) and recently re-calibrated by Halldorsson and Papageorgiou (2005) for earthquakes of different tectonic regions, is a particular case of a composite seismic source model according to which the seismic moment is distributed in a deterministic manner on the fault plane on the basis of moment and area constraints. Namely, it assumes that a rectangular fault surface is filled with an aggregate of non-overlapping subevents modeled as circular cracks of equal diameter, the ‘barrier interval’, on which a ‘local stress drop’ takes place. In the present work, we relax the basic assumption regarding subevent size of the SBM. Subevents, still modeled as circular cracks, are allowed to vary in size according to various prescribed probability density functions controlling the frequency of occurrence of subevent sizes. Closed form expressions of the ‘far-field’ spectra of the composite source are derived using an approach proposed by Joyner and Boore (1986). The seismic energy radiated by individual subevents arrives at a site in a time window the duration of which is related to the duration of rupture and the source-site geometry. The effect of the distribution of ‘arrival times’ on the spectral amplitudes of the composite source is investigated in a companion paper, referred to as Part II. The type of subevent size distribution and its allowed size range directly affects the number of subevents required to satisfy the moment constraint. A larger number of subevents leads to increased ‘complexity’ of the earthquake which generally results in relatively higher source acceleration spectral levels at high-frequencies. The level of the plateau of the high-frequency acceleration spectral amplitudes, corresponding to different size-distributions, does not differ significantly from that of the far-field spectrum of the SBM, for a constant local stress drop. Furthermore, the differences observed in the spectral amplitudes of the SBM and its variants are likely to be less than the expected uncertainty associated with local stress drop values determined from strong-motion data. Thus, despite its simplifying assumptions, the SBM appears to provide the most simple, yet effective, description that captures the essential characteristics of a composite seismic source. This is especially advantageous for consistent strong-motion modeling in the ‘near-fault’, as well as in the ‘far-field’ region for earthquake engineering applications.