应用动力学拐角频率对经验格林函数法的改进

doi:10.3969/j.issn.0253-4967.2015.02.015

摘要/Abstract

摘要：

针对大小震拐角频率的差异, 假设大震断层上每个子源的拐角频率与已破裂的子源个数平方根成反比, 基于ω²震源谱模型, 通过理论推导构建了一个函数, 将动力学拐角频率引入经验格林函数法。以汶川地震余震记录为格林函数, 分别用改进前和引入动力学拐角频率后的经验格林函数法合成5 ·12汶川大地震强地面运动。对比合成结果与观测记录, 结果表明改进前经验格林函数法合成的地震动在低频部分相对实际记录偏低; 引入动力学拐角频率之后的经验格林函数法合成的结果在高频基本保持不变, 低频部分得到提高, 并与实际记录符合。引入动力学拐角频率后, 大部分合成结果很好地符合实际记录。说明动力学拐角频率可有效改善经验格林函数法的低频合成结果, 同时验证了经验格林函数法对M_W7.9特大地震地震动合成的有效性。

关键词: 汶川地震, 经验格林函数法, 动力学拐角频率, 地震动合成, &omega, ²震源谱模型

Abstract:

In traditional empirical Green's function method, the difference between corner frequencies of large and small events is seldom considered. Since the simulation is performed by the superposition of the small events records, the results would have same corner frequencies as the small events, which contradict the fact that the corner frequency decreases with the moment magnitude. The results by traditional empirical Green's function method underestimate the low-frequency content when n² small events are added. Assuming the corner frequency of a sub-fault is inversely proportional to the square root of the numbers of ruptured sub-faults, we construct a new function to apply the dynamic corner frequency to empirical Green's function method based on the ω² source model. In the constructed function, the corner frequency of each sub-fault changes with the rupture propagation. We also develop a schematic diagram to show how the improved empirical Green's function method works.
To validate the empirical Green's function method with dynamic corner frequency, we simulate the near fault strong ground motion of Wenchuan earthquake. Three aftershocks of Wenchuan earthquake are used as Green's functions of the asperities based on their magnitude and locations. Then ground motions of Wenchuan earthquake are synthesized by traditional empirical Green's function method and the empirical Green's function method with the dynamic corner frequency respectively. Comparison between the simulated results and observed data indicates that the traditional empirical Green's function method underestimates the low-frequency content of ground motions. While the empirical Green's function method with the dynamic corner frequency boosts the low-frequency motions without changing the high-frequency content. The results from the empirical Green's function method with the dynamic corner frequency show good agreement with the observed records after the low-frequency contents are improved, which proves that the dynamic corner frequency is valid to eliminate the underestimation due to the difference between the corner frequencies of large events and small ones.
This study also proves that the empirical Green's function method with the dynamic corner frequency is a powerful tool to synthesize the near fault strong ground motions from M_W7.9 earthquake.

Key words: Wenchuan earthquake, empirical Green's function method, dynamic corner frequency, ground motion simulation, ω² source model

中图分类号:

P315.0

夏晨, 赵伯明. 应用动力学拐角频率对经验格林函数法的改进[J]. 地震地质, 2015, 37(2): 529-540.

XIA Chen, ZHAO Bo-ming. IMPROVEMENT OF EMPIRICAL GREEN'S FUNCTION METHOD USING A DYNAMIC CORNER FREQUENCY[J]. SEISMOLOGY AND GEOLOGY, 2015, 37(2): 529-540.

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