求震源机制P波初动解的格点尝试概率法

A probabilistic grid test method of determining earthquake focal mechanisms using P-wave onset polarity data

考虑到Ｐ波初动数据在震源球面上分布的不均匀性对节面解的可能影响，不用矛盾符号所占比例的大小作为选择可取节面解的标准，而是将震源球面分成许多小块，再确定有Ｐ波初动数宇的小块为正号区或负号区的概率，最后以全部有数据小块的平均概率的高低作为选择解答的标准。用此改进方法重新测定了徐纪仁等（Ｘｕｅｔ．ａｌ．，１９８８）发表的青藏高原地区９９个地震的震源机制解，从中筛选出了２０个可信的解答。

In consideration of the influence of inhomogeneous coverage of the P-wave onset polarity data over focal sphere on nodal plane solutions,we use a probability criterion,instead of the ratio of inconsistent readings,to pick up the nodal plane solutions from the grid test results.The surface of focal sphere is divided into a lot of small blocks and for each P-wave onset polarity data-filled block the probability of being theoretically in the positive or negative quadrant is calculated. Then the average probability of all the datafilled blocks is taken as the criterion, based on which the final solution is choosen.The focal mechanism solutions of 99 earthquakes in Qinghai-Tibet plateau rigion published by Xu et.al.(1988) are redetermined using the new method,and 20 reliable solutions are obtained.