Simultaneous inversion of regional wave spectra for attenuation and seismic moment in Scandinavia
Simultaneous inversion of regional wave spectra for attenuation and seismic moment in Scandinavia
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DOI：
10.1029/jb093ib03p02019
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发表时间：
1988-03
影响因子：
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通讯作者：
T. Sereno;S. Bratt;T. Bache
中科院分区：
文献类型：
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作者：
T. Sereno;S. Bratt;T. Bache
频率相关的区域波衰减估计的大陆路径的NORESS阵列在挪威。从186个事件在200和1400公里之间的范围和当地震级在1.1和4.8之间的区域Lg和Pn谱反演地震矩和视衰减。Lg谱在1 ~ 7 Hz之间反转，Pn谱在1 ~ 15 Hz之间反转。该方法利用观测信号幅度的频谱和空间衰减来分离源和路径贡献。这些假设包括几何扩展率和源频谱由其长周期水平唯一定义。所考虑的大多数事件具有小于3.0的局部幅度，因此源拐角频率接近或超过反转带宽的上限。因此，Q结果，特别是对Lg，对我们源参数化的细节不是很敏感。反演参数是源矩（对于每个事件），整个数据集的角频率和矩的常数，以及描述该区域中Q的幂律频率依赖性的两个参数。对于固定源和扩散假设，反演定义了模型参数之间的明确权衡。这些权衡是通过添加约束，分别推导出的源参数Lg和Pn是一致的。表观衰减的“首选”估计值为QLg（f）= 560f0.26和QPn（f）= 325f0.48。这些Q值对应于假定的几何扩展速率，对于Lg为r-0.5，对于Pn为r-1.3。对于固定的Lg扩展，Pn扩展速率的限制，要求的相对Lg振幅的地震和爆炸的同一时刻是一致的，从以前的实证研究得到充分支持的结果。反演地震矩值与当地震级之间的关系与近场研究的值基本一致。由于震级不进入反演，这一结果提供了相当大的支持，导出的Q模型。无论结果的物理解释，他们肯定提供了一个精确的参数化观测振幅谱在这一地区。这是有价值的，代表波在该地区的传播，它提供了重要的数据，评估小型区域网络的事件监测能力。
Frequency-dependent regional wave attenuation is estimated for continental paths to the NORESS array in Norway. Regional Lg and Pn spectra from 186 events at ranges between 200 and 1400 km and local magnitudes between 1.1 and 4.8 are inverted for both seismic moment and apparent attenuation. The Lg spectra were inverted between 1 and 7 Hz, and the Pn spectra were inverted between 1 and 15 Hz. The method uses both the spectral and spatial decay of observed signal amplitudes to separate source and path contributions. The assumptions include the geometric spreading rate and the source spectrum to be uniquely defined by its long-period level. Most events considered have local magnitudes less than 3.0, so the source corner frequencies are near or beyond the upper limit of the inverted bandwidth. The Q results, particularly for Lg, are therefore not very sensitive to the details of our source parameterization. The inversion parameters are source moment (for each event), a constant relating corner frequency and moment for the entire data set, and two parameters describing a power law frequency dependence of Q in the region. For fixed source and spreading assumptions the inversion defines clear trade-offs among model parameters. These trade-offs are resolved by adding the constraint that the separately derived source parameters for Lg and Pn are consistent. The “preferred” estimates for the apparent attenuation are QLg(f) = 560f0.26 and QPn(f) = 325f0.48. These Q values correspond to assumed geometric spreading rates of r−0.5 for Lg and r−1.3 for Pn. For fixed Lg spreading, the Pn spreading rate is constrained by requiring that the relative Lg amplitude for earthquakes and explosions of the same moment be consistent with well-supported results from previous empirical studies. The relationship between the inverted seismic moment values and local magnitude is generally consistent with values from near-field studies. Since magnitude does not enter the inversion, this result lends considerable support to the derived Q models. Whatever the physical interpretation of the results, they certainly provide an accurate parameterization of observed amplitude spectra in this region. This is valuable for representing wave propagation in the region, and it provides important data for assessing the event monitoring capabilities of small regional networks.