The Attenuation of Fourier Amplitudes for Rock Sites in Eastern North America
The Attenuation of Fourier Amplitudes for Rock Sites in Eastern North America
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DOI：
10.1785/0120130136
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发表时间：
2014-02-01
影响因子：
3
通讯作者：
Boore, David M.
中科院分区：
文献类型：
--
作者：
Atkinson, Gail M.;Boore, David M.
我们建立了北美东部岩石遗址记录的m3 -6级地震傅立叶振幅衰减的经验模型，并讨论了其对震源参数的影响。10至500公里距离上的衰减可以用双线性模型来充分描述，该模型在50公里过渡距离上的几何扩展为1/R-1.3，在更大距离上的几何扩展为1/R-0.5。对于低频和小于50公里的距离，使用频率和震源深度相关因子对模型给出的有效几何传播进行扰动，该因子的定义方式是在震中附近增加低频的振幅，但保持1公里源振幅不变。对每个事件确定相关的非弹性衰减，其平均值由区域质量因子Q = 525f（0.45）给出。该模型提供了已知事件的地震矩与推断的R = 1 km处的低频谱幅值（通过对衰减模型进行校正获得）之间的平均匹配。从高频源项推断出的布鲁恩应力参数平均约为600巴（60 MPa），对于M > 4.5级的事件。
We develop an empirical model of the decay of Fourier amplitudes for earthquakes of M 3-6 recorded on rock sites in eastern North America and discuss its implications for source parameters. Attenuation at distances from 10 to 500 km may be adequately described using a bilinear model with a geometric spreading of 1/R-1.3 to a transition distance of 50 km, with a geometric spreading of 1/R-0.5 at greater distances. For low frequencies and distances less than 50 km, the effective geometric spreading given by the model is perturbed using a frequency- and hypocentral depth-dependent factor defined in such a way as to increase amplitudes at lower frequencies near the epicenter but leave the 1 km source amplitudes unchanged. The associated anelastic attenuation is determined for each event, with an average value being given by a regional quality factor of Q = 525f(0.45). This model provides a match, on average, between the known seismic moment of events and the inferred low-frequency spectral amplitudes at R = 1 km (obtained by correcting for the attenuation model). The inferred Brune stress parameters from the high-frequency source terms are about 600 bars (60 MPa), on average, for events of M > 4.5.