GROUND MOTION SIMULATION CONSIDERING VELOCITY DISPERSION AND ITS IMPLICATIONS FOR SEISMIC HAZARD ASSESSMENT

doi:10.3969/j.issn.0253-4967.2024.06.011

Abstract

Abstract:

Seismic hazard assessment is crucial for determining engineering fortification levels, guiding urban planning, mitigating earthquake disasters, and addressing secondary hazards such as landslides and mudslides triggered by earthquakes. Energy attenuation during seismic wave propagation is influenced by multi-angle scattering, physical dispersion, and geometric spreading. When conducting numerical simulations of post-earthquake ground motion, accounting for these factors significantly affects the accuracy of hazard assessments.

This paper examines the physical dispersion characteristics of seismic waves in viscoelastic media. Through simulations of velocity dispersion and seismic wave time distribution in a simple one-dimensional model, we explore the impact of dispersion on the spatial distribution of seismic motion and its implications for seismic hazard assessment. A case study of the 2021 Yangbi M_S6.4 earthquake further illustrates the importance of considering physical dispersion in seismic hazard analysis.

In contrast to traditional ground motion prediction equations(GMPE), physics-based simulations of ground motion provide more reliable estimates of seismic hazard levels and enhance the accuracy of hazard assessments. It is well-established that, excluding site effects, peak ground motion parameters on bedrock decrease with increasing epicentral distance. However, considering the wave field dispersion characteristics reveals that peak ground motion parameters do not always decrease monotonically with distance; in some cases, they may even slightly increase. This highlights the complexity of seismic wave propagation through viscoelastic media. Further validation of these findings through refined, scenario-based numerical simulations is necessary.

Additionally, with increasing epicentral distance, the amplitude of ground motion time histories decreases, while their duration increases. This low-frequency, long-duration seismic motion may be amplified under specific site conditions, such as in basins. The influence of the non-uniform viscoelastic medium results in varying attenuation rates for horizontal peak ground motion parameters at different angles. The findings of this study have important implications for national security, critical infrastructure, unconventional energy development, and secondary hazards such as landslides and mudslides. The integration of source physics, seismic wave theory, medium structure imaging, and structural stress analysis is essential for improving the accuracy and reliability of seismic hazard assessments.

Key words: physical dispersion, energy attenuation, ground motion simulation, 2021 Yangbi M_S6.4 earthquake, physics-based seismic hazard assessment

摘要：

地震危险性评估对于确定工程抗震设防等级、制定城市规划、减轻地震灾害及地震引发的滑坡、泥石流等其他灾害具有重要意义。在地震波场传播过程中, 能够造成波场能量衰减的因素包括多角度散射、频散及球面扩散。针对震后的地震动场空间分布特征开展数值模拟时, 是否考虑这3项因素对于实际计算结果有着直接影响。文中以地震波场在滞弹性介质中的物理频散特征为讨论对象, 通过模拟计算情景地震在简单一维模型中引起的波场频散及地震动时程分布, 讨论频散对地震动场空间分布及地震危险性分析的影响。然后, 以2021年漾濞 M_S6.4 地震为例, 进一步分析滞弹性介质的物理频散对地震危险性分析的意义。在经典地震动参数预测方程(GMPE)的基础上, 基于物理的地震动模拟对于进一步获得更加可靠的地震动水平及地震危险性的物理评估都具有重要意义。

关键词: 物理频散, 能量衰减, 地震动场模拟, 2021年云南漾濞M_S6.4地震, 基于物理的地震危险性评估

ZHANG Yan, JI Zhi-wei, ZHAI Hong-yu, WU Chun-hao. GROUND MOTION SIMULATION CONSIDERING VELOCITY DISPERSION AND ITS IMPLICATIONS FOR SEISMIC HAZARD ASSESSMENT[J]. SEISMOLOGY AND GEOLOGY, 2024, 46(6): 1408-1425.

张琰, 纪志伟, 翟鸿宇, 伍纯昊. 考虑速度频散的地震动场模拟及其对地震危险性分析的意义[J]. 地震地质, 2024, 46(6): 1408-1425.

Figures/Tables 10

Fig. 1 A diagram of fifth-order mode between two fixed points.

Fig. 2 A scheme of transmission media.

Fig. 3 Representation of phase velocity(a), group velocity(b), anelastic attenuation(c) and energy integral with 1Hz cut-off frequency.

Fig. 4 Attenuation of radial, vertical and transverse peak ground parameters with increment of epicentral distance produced by a scenario earthquake with strike/dip/slip set as 80°/30°/10°, depth 7km, and moment magnitude 6.5.

Fig. 5 Radial, vertical and transverse synthetic ground motion parameters versus epicentral distance increment.

Fig. 6 Location of the epicenter of 2021 Yangbi MW6.1 earthquake, as well as 5 seismic stations.

Table1 Source parameters of 2021 Yangbi MS6.4 earthquake

震中	25.62°N, 100.01°E
震级	M_W6.1
矩心深度	15.1km
走向/倾角/滑动角	314°/83°/170°

Fig. 7 Peak ground parameters based on characteristics of attenuation of wavefield.

Table2 Strong-ground motion stations around the epicenter

台站	代码	东经/(°)	北纬/(°)	场地	震中距/km	PGA/cm·s^-2
永平台	53YPX	99.5	25.5	土层	58.16	17.78
宾川台	53BCJ	100.6	25.8	土层	68.47	10.94
六库台	53LKT	98.9	25.8	基岩	124.82	0.4575
施甸台	53SDX	99.2	24.7	土层	136.06	21.41
仁和镇台	53YRH	101.0	26.5	土层	147.03	2.01

Fig. 8 The recorded maximum horizontal acceleration varies with the distance from the epicenter(blue line).

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