Inversion of intermediate‐period Rayleigh waves for source characteristics of the 1968 Tokachi‐Oki earthquake
Inversion of intermediate‐period Rayleigh waves for source characteristics of the 1968 Tokachi‐Oki earthquake
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1968年十胜冲地震震源特征的中周期瑞利波反演
DOI：
10.1029/jb090ib13p11374
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发表时间：
1985
期刊：
影响因子：
--
通讯作者：
K. Shimazaki
中科院分区：
文献类型：
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作者：
J. Mori;K. Shimazaki
利用最小二乘反演技术对周期为10 ~ 25s的瑞利波进行反演，确定了1968年枥木地震震源区内矩释放的分布。反演程序试图生成与数据相匹配的合成地震图，方法是求解间隔为40公里的网格上每个点产生的力矩量。这些数据记录在距离震源地区70-200公里的低增益机械地震仪上。假设简单的单侧和双侧破裂模型，对不同的恒定破裂速度值进行反演，结果表明，这两种模型最适合3.0-3.1 km/s的数据。计算得到的表面波合成高度依赖于地壳速度模型。通过使用折射测量得到的速度结构，合成波的波形变得明显不同，这取决于我们是使用不连续面还是线性梯度来连接测量给出折射P速度的深度点。无论是不连续结构还是梯度结构都不能产生令人满意的合成物。因此，使用了一种中间结构，在表面附近具有线性梯度，而在表面以下具有不连续。反演结果表明，这些数据可以用一个由两个强子事件组成的源来模拟，这两个子事件控制着这些表面波的辐射。这两个子事件的相对位置与强震记录中看到的两个高应力降子事件的位置一致。
A least squares inversion technique was applied to Rayleigh waves with periods of 10–25 s to determine the distribution of moment release within the source region of the 1968 Tokachi-Oki earthquake. The inversion procedure attempts to produce synthetic seismograms which match the data by solving for the amount of moment generated from each point of a grid spaced at 40 km. The data were recorded on low-gain mechanical seismometers that were located 70–200 km from the source region. Assuming simple unilateral and bilateral rupture models, the inversion was run for different values of constant rupture velocity, resulting in a best fit to the data at 3.0–3.1 km/s for both models. The calculated surface wave synthetics depended strongly on the crustal velocity model. By using a velocity structure obtained from a refraction survey, the waveforms of the synthetics became significantly different, depending on whether we used discontinuities or linear gradients to connect the depth points for which the survey gives a refractor P velocity. Neither a structure of only discontinuities nor a structure of only gradients was found to produce satisfactory synthetics. Therefore an intermediate structure with a linear gradient near the surface and discontinuities below was used. The results of the inversion show that the data can be modeled with a source consisting of two strong subevents which dominate the radiation of these surface waves. The relative location of the two subevents is consistent with the locations of the two subevents of high stress drop that were seen on strong motion records.