SUMMARY We analysed 478 three-component strong ground motion time-series from 65 events in the moment magnitude (Mw) 3–6.5 range recorded at 111 stations at distances up to 150 km from 1997 to 2019 in the Alborz region. Non-parametric spectral functions for seismological source, path and site-effects were derived from Fourier amplitude spectra of observed acceleration time-histories using the generalized inversion technique (GIT) for the Alborz region of Iran. To characterize the spectral models in terms of the anelastic attenuation (Q), geometrical spreading, magnitude and stress parameter (Δσ), we fitted non-parametric attenuation and source functions (resulted from inversion) with the standard parametric models. The frequency-dependent non-parametric attenuation function shows a rapid decay at close distances (<60 km) and decreases monotonically at larger distances. The frequency-independent geometrical spreading follows a bilinear hinged model with a crossover distance at 70 km. For hypocentral distances Rhypo < 70 km, the geometrical spreading is ${R^{ - 1.01}}$, and for Rhypo > 70 km it is ${R^{ - 1.37}}$. The corresponding quality factor is $Q\ ( f ) = \ 146{f^{0.91}}$. The non-parametric source spectra were found in a good agreement with Brune's ω-squared model. The stress-parameter (Δσ) values were found to exhibit large variability from 0.36 to 86.7 MPa with no significant magnitude-dependence. The average Δσ was found to be 8.6 MPa. The mean value of the estimated near-surface attenuation (κ0) from high-frequency part of non-parametric source function is 0.032 s (±0.01 s). In general, there is a good agreement between subsoil resonance frequencies and amplification levels estimated from GIT and HVSR (horizontal to vertical spectral ratio). The results of this study provide updated values of seismological source, attenuation and site properties in the Alborz region of northern Iran, which are expected to improve regional seismic hazard analysis studies in the region.

中文翻译：

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伊朗北部厄尔布尔士地区地震源参数、路径衰减和场地效应的光谱模型

总结 我们分析了 1997 年至 2019 年在厄尔布尔士地区的 111 个站记录的 65 个事件的 478 个三分量强地震动时间序列，这些事件的矩震级 (Mw) 3-6.5 范围内距离高达 150 公里。使用伊朗厄尔布尔士地区的广义反演技术 (GIT) 从观测到的加速度时程的傅立叶振幅谱推导出地震源、路径和场地效应的非参数谱函数。为了根据非弹性衰减 (Q)、几何扩展、幅度和应力参数 (Δσ) 来表征光谱模型，我们用标准参数模型拟合了非参数衰减和源函数（由反演产生）。频率相关的非参数衰减函数在近距离处显示出快速衰减（< 60 公里），并在更远的距离单调递减。与频率无关的几何扩展遵循双线性铰链模型，交叉距离为 70 km。对于震源距离 Rhypo < 70 公里，几何扩展为 ${R^{ - 1.01}}$，对于 Rhypo > 70 公里是 ${R^{ - 1.37}}$。对应的品质因数为$Q\ ( f ) = \ 146{f^{0.91}​​}$。发现非参数源光谱与 Brune 的 ω-平方模型非常一致。发现应力参数 (Δσ) 值在 0.36 到 86.7 MPa 之间表现出很大的变化，没有显着的幅度依赖性。发现平均 Δσ 为 8.6 MPa。从非参数源函数的高频部分估计的近地表衰减 (κ0) 的平均值为 0.032 s (±0.01 s)。一般来说，从 GIT 和 HVSR（水平与垂直光谱比）估计的底土共振频率和放大水平之间有很好的一致性。这项研究的结果提供了伊朗北部厄尔布尔士地区地震源、衰减和场地特性的更新值，有望改善该地区的区域地震危险性分析研究。