The Physics of the Earthquake Source and Radiated Waves: Frequency Dependence, Spatial Distribution, and Directivity in Elastodynamic Models of Repeated Fault Ruptures

地震源和辐射波的物理学：重复断层破裂的弹性动力学模型中的频率依赖性、空间分布和方向性

• 批准号: 0125871
• 负责人: Bruce Shaw
• 金额: $ 10.98万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-12-01 至 2003-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0125871&HistoricalAwards=false
• 关键词: Physics; Earthquake; Source; Radiated; Waves

The main thrust of this work is to seek a deeper understanding of the radiated waves emitted by earthquakes. In previous work, the investigator has examined how total radiated energy can be sensitive to the source physics, showing dfferences for slip versus velocity weakening friction in elastodynamic faults. This work was expanded to look at the frequency content and spatial dependence of the radiation. A number of important results were obtained, including: (1) A new radiating boundary condition allowing a nonuniform prestress, useful for repeated ruptures, was developed; (2) Having to assume only a physics of the tractions on the fault, the full spectra of radiated waves for events with a wide range of sizes were generated; (3) Characterizing the spectral content of the radiation, a nonlinear magnitude dependence of a second corner frequency was found, and shown to be related to fundamental source parameters; (4) Strong directivity effects for large events were exhibited in spectral ratios. With renewed support, continued research on this subject is being carried out, with a focus on three specifc projects:The first project involves further exploration of magnitude and spatial dependence of directivity effects. Initial results have shown striking amplification of acceleration spectra away from the epicentral region in large events. Further exploration of these effects includes time domain complements of the frequency domain measurements already made. This work will further develop a new theoretical tool for exploring an issue with potentially large hazard and earthquake engineering implications.The second project involves the extension of measurements made in two-dimensional models of radiated energy spectra to three-dimensional models. A further generalization of a new radiating boundary condition is being developed in two dimensions, both extending it to higher dimensions and to continuous loading, allows direct measurements at long times. This allows quantitative physical predictions of the magnitude dependence of radiated energy spectra.The third project involves the application of a new measurement developed in the models to earthquake data. The measurement takes advantage of a natural averaging measure through summing of energy spectra to convert to average acceleration spectra. In the models, the period of the peak average acceleration spectra was shown to reflect fundamental source parameters. Measurements of the magnitude dependence of this quantity in earthquakes are being carried out.

这项工作的主要目的是寻求对地震发出的辐射波有更深入的了解。在之前的工作中，研究者已经研究了总辐射能量如何对源物理敏感，显示了弹性动力断层中滑移与速度减弱摩擦的差异。这项工作扩展到研究辐射的频率含量和空间依赖性。得到了一些重要的结果，包括：(1)建立了一个新的辐射边界条件，允许非均匀预应力，适用于重复破裂；(2)只假定断层上的牵引力的物理性质，就产生了各种大小事件的辐射波的全谱；(3)表征辐射的光谱含量，发现第二角频率的非线性幅度依赖关系，并表明与基本源参数有关；(4)谱比对大事件表现出较强的方向性效应。在新的支持下，正在继续开展关于这一主题的研究，重点是三个具体项目：第一个项目涉及进一步探索指向性效应的大小和空间依赖性。初步结果表明，在大型地震中，远离震中区域的加速度谱有显著的放大。对这些影响的进一步探索包括对已经进行的频域测量的时域补充。这项工作将进一步发展一种新的理论工具，用于探索具有潜在大危害和地震工程意义的问题。第二个项目涉及将辐射能谱的二维模型的测量扩展到三维模型。一种新的二维辐射边界条件的进一步推广，将其扩展到更高的维度和连续载荷，允许长时间的直接测量。这样就可以对辐射能谱的大小依赖性进行定量的物理预测。第三个项目涉及将模型中开发的新测量方法应用于地震数据。该测量方法利用了一种自然平均的测量方法，将能量谱相加，转化为平均加速度谱。在模型中，峰值平均加速度谱的周期反映了基本源参数。目前正在对该量在地震中的震级依赖性进行测量。