尾波干涉法在汶川地震余震定位中的应用

Application of Coda Wave Interferometry Method in Relative Location of the Wenchuan Earthquake Sequence

中小地震的震源位置及其变化对于研究地震构造、断层性质以及地震应力场的演化等问题都有极为重要的意义。然而以HypoDD双差定位法为代表的常规定位方法对地壳速度结构要求很高,且受台站分布影响较大。而尾波干涉法不需要了解速度模型的精细结构,只要求速度结构中存在各向不均一性散射体即可,且对台站分布要求低,因此适合应用在中小地震的相对位置变化的研究上。本文以汶川地震余震为例,研究利用尾波干涉法确定相似地震相对位置的可行性及其稳定性,并将其结果与双差法进行了比较。发现当台站分布较好时,其结果与双差法所得结果较为一致,而当台站分布较差时,尾波干涉法所得结果更为可靠。

Focal depths of moderate to small earthquakes and their temporal changes are critical for understanding seismogenic structures, fault characteristics and evolution of seismic stress fields. However, traditional locating methods such as double difference method （HypoDD） require high accurate crustal structure, which is usually hard to be ful- filled. Furthermore, the precisions of these methods can be also seriously affected by seis- mic station distribution. On the contrary, coda wave interferometry method （CWI） doesn ＂t need to know accurate crustal velocity structure, the only requirement for the crustal model is that there should exist relatively evenly distributed scatters, which is a very com- mon phenomenon in shallow crust. Another advantage of CWI method is that the require- ment of seismic stations distribution is also very low. Thus, the CWI method is quite suit- able for studying the variation of relative distance between earthquakes. In this paper we collected the data of the 2008 Wenchuan earthquake aftershock sequence, analyzed the possibility and stability of locating earthquakes by CWI method, and finally compared with the results obtained by double difference method. Our result shows that when the distri- bution of seismic stations are good, the result obtained by double difference method is close to that by the CWI method, however, when the distribution pattern of seismic sta- tions are not good, the CWI method can provide much more robust results than that of double difference method.