区域一维速度模型对地震定位的定量影响——以2017年九寨沟M_(S)7.0地震序列为例

Quantitative effect of regional one-dimensional velocity models on earthquake relocation:Take the 2017 Jiuzhaigou M_(S)7.0 earthquake sequence as an example

利用2017年8月1日至2017年12月31日四川地震台网和甘肃地震台网记录到的发生在青藏高原东缘的731个地震事件的9 284条Pg震相到时数据,首先反演了该地区的"最小一维速度模型",并将该模型和选取的速度模型建立对比模型,以九寨沟地震序列为研究目标,定量讨论了两种速度模型分别在绝对定位和相对定位方法中对定位结果的影响。所得定位结果表明:反演获得的"最小一维速度模型"在重定位中可以有效地减小地震走时均方根残差;绝对定位比相对定位更加依赖于一维速度模型,一维速度模型会直接影响绝对定位结果中的震源分布形态,但在相对定位结果中仅起到调整地震事件相对位置的作用;在地震绝对定位中,震级越大的地震对于速度模型越敏感,而这一特点在相对定位中表现得并不明显。通过本项研究可知,在地震定位研究中,联合采用绝对定位和相对定位方法是最佳策略。

Using 9 284 Pg phase arrival times of 731 earthquakes occurred in the eastern margin of the Tibetan Plateau recorded by Sichuan and Gansu Seismic Networks from August 1,2017 to December 31,2017,this paper determine " the minimum one-dimensional velocity model" for the area by inversion. " The minimum one-dimensional velocity model" and the selected comparative velocity model are used to establish the comparative models. Taking the Jiuzhaigou earthquake sequence as the research object,we quantitatively discuss the effects of two velocity models on the positioning results in absolute seismic location and relative seismic location methods. The results show that " the minimum one-dimensional velocity model"obtained by inversion can effectively reduce the root-mean-square residuals of travel time in relocation. Absolute seismic location method is more dependent on one-dimensional velocity model than relative seismic location. Furthermore,one-dimensional velocity model will directly affect the distribution pattern of hypocenters in absolute location,but only adjust the relative position of seismic events in relative location. In absolute location of earthquakes,the earthquake with larger magnitude is more sensitive to velocity model,which is not obvious in relative location. Therefore,the combination of absolute location method and relative location method is the best strategy in earthquake relocation.