应力张量反演的遗传算法及其在青藏高原东北缘的应用

A genetic algorithm for stress tensor inversion and its application to the northeast margin of the Tibetan Plateau

为准确而快速地求解区域构造应力张量,构建了基于震源机制解反演应力张量的遗传算法策略,详细介绍了计算原理,分析了以断层面上剪应力方向和滑动方向的偏差为约束反演应力张量而忽略剪应力大小偏差对反演结果的影响,表明仅考虑剪应力方向和滑动方向的偏差就可以得到正确结果.利用不同应力状态下人工合成的包含不同噪声水平的震源机制数据对该方法进行检验,并与网格搜索法得到的结果比较.表明本文方法所得结果的拟合差均小于网格搜索法结果的拟合差,并且二者相差较小,体现了本文方法的稳健性.将该方法应用于青藏高原东北缘(103-106°E,34.5-37.5°N)应力张量的估计,结果显示,该区域主要受控于青藏高原近东西向的挤压,从而导致阿拉善块体以及华南块体方向的拉张,并且向华南块体方向的拉张作用强于向阿拉善块体的拉张作用.

In order to obtain regional tectonic stress tensors accurately and quickly,the strategy of stress tensor inversion using the genetic algorithm based on focal mechanisms is constructed.Its principle is introduced in detail.We analyze the influence on the inversion results under constraint of direction deviation between shear stress and slippage on the fault plane while neglecting the shear stress magnitude deviation.The result indicates that we can obtain the correct result only under constraint of direction deviation between shear stress and slippage.The method is tested using synthetic data produced by different stress states with different noisy.We compare the result with another result obtained by agrid search algorithm.It indicates that the misfit of results obtained by the genetic algorithm are all smaller than those of results obtained by the grid search algorithm.And the difference of misfit obtained by the two method is small,which reflects the robustness of the method in this paper.We apply this method to the northeast margin of the Tibetan Plateau(103-106°E,34.5-37.5°N).The result shows that this region is mainly controlled by nearly east-west compression from the Tibetan Plateau,leading to extension towards the Alxa block and South China block.And the extension towards South China block is stronger than that towards Alxa block.