Regional moment tensor uncertainty due to mismodeling of the crust
Regional moment tensor uncertainty due to mismodeling of the crust
复制标题
由于地壳模型错误造成的区域矩张量不确定性
DOI：
10.1016/j.tecto.2003.12.007
复制
发表时间：
2004
期刊：
影响因子：
2.9
通讯作者：
J. Šílený
中科院分区：
文献类型：
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作者：
J. Šílený
地震矩张量(MT)的反演需要知道介质的响应，即地震波从震中传播到台站。在反演长周期(LP)地震数据(远震和LP区域记录)时，一个总地球模型就足够了；随着周期的减少，需要一个更详细的模型。这是当区域距离处的弱地震的波形要被反转时的情况。大多数地中海地震的区域矩张量(RMT)是由瑞士地震勘探局(SED)使用地壳平均模型常规确定的。通过对2002年2月14日在意大利北部乌迪内附近发生的Mw=4.8地震的宽带记录的反演，我们检验了MT解对所用地球模型和震源深度位置中可能存在的误差的敏感性。我们对一维地球模型中的P和S速度和厚度在参数值的3%到30%范围内进行了摄动，给出了三个频带内MT的置信域、震源时间函数和标量矩的误差条估计。同样，这些误差特征是在假设震源深度位置错误的情况下确定的。我们发现，在25-50 S的周期范围内，该机制被很好地分辨(至少在95%的置信度下)，直到地球模型的不确定度达到30%，在通带10-25 S的范围内，其分辨率可达10%左右，但在5-10 S的周期内，这种机制是完全不确定的。震源深度的误差在10 S以上的周期内不会破坏该机制的分辨率。在SED的RMT目录中，Mw大于3.5的地震是在30 S以上的周期处理的；因此，对于所使用的地球模型中可能存在的不确定性，这些事件的解决方案是稳健的。从短周期恢复的较弱地震的机制应谨慎解释。
The retrieval of earthquake moment tensor (MT) requires the response of the medium, in which seismic waves travel from the hypocenter to the stations, to be known. In inverting long-period (LP) seismic data (teleseismic and LP regional records), a gross earth model is sufficient; with decreasing periods, a more detailed model is needed. This is the case when waveforms of weak earthquakes at regional distances are to be inverted. Regional moment tensors (RMTs) of mostly Mediterranean earthquakes are determined on a routine basis by the Swiss Seismological Survey (SED) by using averaged models of the earth's crust. By inverting broad-band records of the Mw=4.8 earthquake near Udine, N Italy, on Feb. 14, 2002, we tested the sensitivity of the MT solution with respect to possible errors in the earth model used and in the location of the hypocenter depth. We perturbed the P and S velocities and the thickness in the 1-D earth model in the range from 3% to 30% of the parameter values and constructed estimates of confidence regions of the MT and error bars of the source time function (STF) and scalar moment in three frequency bands. Similarly, these error characteristics were determined assuming a mislocation in the hypocenter depth. We found that, in the band of periods from 25 to 50 s, the mechanism is resolved well (at the confidence level 95% at least) up to an earth model uncertainty of 30%, in the passband 10–25 s up to about 10%, but it is undetermined completely at periods of 5–10 s. An error in hypocenter depth of as much as double the value reported by the location procedure does not destroy the resolution of the mechanism at periods above 10 s. In the RMT catalog of the SED, earthquakes of Mwgreater than about 3.5 are processed at periods above 30 s; thus, the solutions for these events are robust with respect to a possible uncertainty in the earth model used. Mechanisms of weaker earthquakes, retrieved from short periods, should be interpreted with caution.