Microseismic monitoring is widely used to detect hydraulic fractures. Accurate mapping of microseismic events is essential to detect such fractures enhancing productivity. The eikonal solver is an efficient forward-modelling method used to map microseismic events. However, traditional eikonal solvers do not distinguish between head and direct waves, computing only the traveltimes of the waves that arrive first. We developed a new eikonal solver that computes the traveltimes of direct waves by imposing new constraints on the conventional, vertical transverse isotropy solver. We then performed numerical experiments exploiting the traveltimes of direct waves. We used the traveltimes of only the first arrivals, and those of both first and direct arrivals, when performing inverted event mapping. The results showed that the uncertainties of event locations were minimized when both head and direct waves were analysed due to the increased both the number of available data and the travelling path diversity. Also, we found that the use of only direct-arrival traveltimes was valuable when head-wave first arrivals were difficult to detect because the signal-to-noise ratio was low.

中文翻译：

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利用在垂直横观各向同性介质中传播的头波和直达波来定位微震事件

微地震监测广泛用于检测水力压裂。对微震事件进行准确测绘对于检测此类裂缝以提高生产率至关重要。本征求解器是一种有效的正向建模方法，用于绘制微​​地震事件。但是，传统的常规求解器无法区分头波和直达波，仅计算最先到达的波的传播时间。我们开发了一种新的ekonnal求解器，它通过在常规的垂直横向各向同性求解器上施加新的约束来计算直接波的传播时间。然后，我们利用直接波的传播时间进行了数值实验。在执行反向事件映射时，我们仅使用第一次到达的旅行时间，以及第一次和直接到达的旅行时间。结果表明，由于增加了可用数据的数量和行进路径的多样性，当同时分析头波和直达波时，事件位置的不确定性降至最低。另外，我们发现，当头波的首次到达由于信噪比低而难以检测时，仅使用直接到达的旅行时间是有价值的。