【摘要】 本文基于Langston的震源机制分解方法以及Minson和Dreger修正后的近场位移的解析解表达式,给出了一种区域纯偏量矩张量的求解方法,方法使用基于Hilbert变换的波形包络作为增强约束.对该方法进行了数值试验.试验结果表明,定位准确且速度结构已知的情况下,背景高斯噪声水平达30%时,该方法仍可以得到较稳定的解;使用0.01—0.1Hz的中长周期频段进行反演,在随机震相到时误差最大±3s的情况下,近90%的情况可以得到相对准确的解.速度结构模型的干扰试验表明,平均模型接近真实地壳结构时,可以得到接近真实的解;模型与真实的地壳结构的误差在10%以内时,得到的解与真实解比较接近;误差接近20%时,矩张量解会出现很大的偏差;地震的定位误差主要影响震源深度的判定,从而导致最终解中出现虚假的非双力偶成分,但在约束为偏量矩张量的情况下,反演得到的断层面参数与真实解偏差不大;在台站方位角覆盖较差(<60°)的情况下,使用平均模型仍可以得到较为准确的解.使用该方法研究了2010年10月24日河南周口太康MW4.7地震的震源机制,结果显示矩张量解与初动符号解较为一致.更多还原

【Abstract】 Based on Langston’s decomposition theory and Minson and Dreger’s near-field displacement formula,this paper proposes a deviatoric moment tensor inversion method.Waveform’s envelop function calculated from Hilbert transform is introduced to stabilize the inversion.The method is successfully tested with synthetic data.Numerical experiment result shows that the method has decent robustness and stabilization.Specific results are as follows.(1) While the velocity structure and earthquake location are exactly known,the solution will be accurate and stable(Kagan angle<5°,the error of double couple component percent,noted as DC%,within ±5%),despite of high noise level even reaching to 30% of original signals.(2) While random disturbances on wave arrival time are limited within ±3 s,the moment tensor solutions inverted in 0.01—0.1 Hz frequency range are still entirely stable.About two-thirds of solutions can be considered to be very close to the true solution(Kagan angle<15°,DC% within ±5%),and about 90% of solutions have a small deviation to the true ones(Kagan angle<30°,DC% within ±10%).It shows that the method has good compatibility with crustal anisotropy and lateral heterogeneity.(3) The test results under various crust models show that the velocity model has important effect on inversion result.If a 1D model being close to the mean model of true crust structure is used,the inversion can retrieve near-real solution.If the model is a little different from the true model(no more than 10% error),the solution would be close to the real one;if the error exceeds 10%,even reaching to 20%,of original signals,the solution will have notable bias.(4) Earthquake location error mainly affects focal depth determination,accordingly cause spurious non-DC component in final solution.But,with the constraint of pure deviatoric moment tensor,the fault parameters retrieved from inversion have little bias from the real one.(5) In case of sparse data(3 stations at least) and worse station coverage(less than 60°),we can still get relatively correct solution from the method under mean crust model.The method is applied to 24 Oct.2010 Zhoukou--Taikang MW4.7 event in Henan province,China.The optimized solution retrieved by this method is consistent with that estimated from P wave polarity data.更多还原