In this study, we retrieved the finite source characteristics of the October 23, 2011 Van earthquake (Mw 7.1) using the teleseismic waveforms to focus on the source location. The outstanding off-fault aftershock sequence of the Van mainshock was readily explained by calculating the Coulomb stress changes imparted to the surrounding crust. This may be accomplished through finite source modelling to examine the stress interaction between the fault, ruptured by the Van mainshock, and the surrounding fault(s) triggered by the same mainshock. In addition, to provide further support for the Coulomb failure stress changes in the off-fault area, centroid moment tensor (CMT) inversion of the off-fault aftershocks was performed and stress tensors were derived from their focal solutions. This identified the dominant fault slip, the constraints of the crustal stress fields and illuminated the crustal nature of the stress interaction. The off-fault aftershocks showed a strike-slip stress regime in rotational (to NW) and non-rotational (to N) stress fields of the upper and lower crusts, respectively. However, this was inconsistent with a horizontal compressional stress direction striking to the north. This suggests that a local source and/or rotation of lateral variation in stress magnitudes in crustal and sub-crustal structures strongly perturbed the regional stress field. It was also evident that these strike-slip aftershocks increased the intensity of stress in an off-fault area, NE of the source rupture. This revealed a uniquely triggered strike-slip motion, activated and rooted in the weak lower crust. We conclude that the Van mainshock rupture source area, associated with the stress changes imparted to the surrounding crust, had undergone anomalous modifications to generate distinctive off-fault aftershock responses in the entire crust, and also triggered and loaded the weak lower crust. We hypothesize that the strike-slip motion, the so called “transfer fault”, as a distinctly triggered slip event, was generated or selectively activated by subcrustal ductile processes in the absence of mantle lid beneath the study area. However, local slab fragmentation, tearing and cold mantle beneath the study area lead to paradigm changes in interpreting the strike-slip motion and subcrustal deformation. The presence of a small piece of oceanic lithosphere, consistent with fragmented, torn slab and cold mantle, may be an alternative hypothesis that remains to be tested. The Van earthquake, combined with careful examination of associated off-fault aftershocks, revealed new information about stress field constraints on subcrustal deformation. This investigation also provided insights into an important role of stress interaction, with a newly discovered transfer fault within the off-fault area, which extends through the entire crust beneath Lakes Van and Erçek areas.

在这项研究中，我们检索了 2011 年 10 月 23 日 Van 地震（Mw 7.1) 使用远震波形聚焦震源位置。通过计算传递给周围地壳的库仑应力变化，很容易解释范主震的突出的断层余震序列。这可以通过有限震源建模来完成，以检查由 Van 主震破裂的断层与由同一主震触发的周围断层之间的应力相互作用。此外，为了进一步支持断层外区域的库仑破坏应力变化，对断层余震进行了质心矩张量（CMT）反演，并从它们的焦点解中导出应力张量。这确定了主要的断层滑动，地壳应力场的约束，并阐明了应力相互作用的地壳性质。断层外余震分别在上地壳和下地壳的旋转（向 NW）和非旋转（向 NW）应力场中显示出走滑应力状态。然而，这与向北冲击的水平压缩应力方向不一致。这表明地壳和亚地壳结构中应力大小横向变化的局部来源和/或旋转强烈扰动了区域应力场。很明显，这些走滑余震增加了源破裂东北方向的非断层区域的应力强度。这揭示了一种独特触发的走滑运动，它被激活并植根于脆弱的下地壳。我们得出结论，范主震破裂源区，与传递给周围地壳的应力变化有关，经历了异常修改，在整个地壳中产生了独特的断层余震响应，并触发并加载了弱的下地壳。我们假设走滑运动，即所谓的“转移断层”，作为一个明显触发的滑动事件，是在研究区下方没有地幔盖的情况下由地壳下延性过程产生或选择性激活的。然而，研究区下方的局部板块破碎、撕裂和冷地幔导致解释走滑运动和地壳下变形的范式发生变化。一小块海洋岩石圈的存在，与破碎的、撕裂的板块和冷地幔一致，可能是一个有待检验的替代假设。Van 地震，结合对相关断层余震的仔细检查，揭示了关于地壳下变形应力场约束的新信息。这项调查还提供了对应力相互作用的重要作用的见解，在断层区域内新发现了一个转移断层，该断层延伸到凡湖和埃尔切克湖地区下方的整个地壳。