Earthquake nests are anomalous clusters of seismicity located far from active collisional systems in intraplate, locked suture zones, or the deep part of relic subducted slabs, challenging classic earthquake generation mechanism theories. The Vrancea Seismic Zone in Romania is such an upper-mantle seismic nest located in the SE Carpathians, releasing the largest strain in continental Europe. To better understand earthquake generation and the relationship with lithospheric deformation, we estimate earthquake source parameters in Vrancea and surrounding regions between 2014 and 2020, and determine the stress field via focal mechanism inversion and unsupervised machine learning. In the crustal domain, maximum horizontal stress is in agreement with surface fault kinematics and GPS-derived S-SE trending horizontal plate velocities relative to Eurasia, implying that tectonic stress is vertically coherent on a crustal scale. The stress regime changes from transpression beneath the orogen to transtension towards the foreland where movement is accommodated along major crustal faults, and tension further away from the epicentre, in the Moesian Platform and the North Dobrogea Orogen. Inside the seismogenic body vertical tension and an overall compressive regime dominates, implying that vertical elongation may be the driving mechanism for brittle failure and that stress is transmitted along the sinking slab to the surface. However, the retrieved stress ratios are low: ~0.2 for mantle earthquakes Mw>4 and ~0.4 for Mw<4, challenging the brittle failure assumption. Increased pore fluid pressure has been shown to lower stress ratios, implying that dehydration embrittlement may contribute to generating intermediate-depth seismicity in the Vrancea slab. Comparisons with seismic tomography and anisotropy studies show excellent correlations between maximum horizontal stress directions, possible slab strike orientation, and seismic anisotropy, especially below ~130 km depth, suggesting ambient mantle flow may also promote in-slab stress build-up and seismic potential.

地震巢是地震活动的异常簇，其位置远离板内，锁定的缝合带或遗物俯冲板的深部的主动碰撞系统，对经典的地震发生机制理论提出了挑战。罗马尼亚的Vrancea地震带就是这样的上地幔地震巢，位于东南喀尔巴阡山脉，释放了欧洲大陆最大的应变。为了更好地了解地震的产生及其与岩石圈变形的关系，我们估算了2014年至2020年之间Vrancea及周边地区的地震震源参数，并通过震源机制反演和无监督机器学习确定了应力场。在地壳区域，最大水平应力与表面断层运动学和GPS衍生的S-SE趋势相对于欧亚大陆的水平平板速度一致，这意味着构造应力在地壳尺度上是垂直相干的。应力状态从造山带之下的压变转变为向前陆的伸展，前陆沿主要的地壳断层运动，并且在莫斯平台和北多布罗加造山带中，张力进一步远离震中。在震源体内，垂直张力和总体压缩状态占主导地位，这意味着垂直伸长可能是脆性破坏的驱动机制，并且应力会沿着下沉的平板传递到地面。但是，取回的应力比很低：地幔地震Mw> 4约为0.2，而Mw <4约为0.4，这对脆性破坏假设提出了挑战。孔隙流体压力的增加已显示出较低的应力比，这意味着脱水脆化可能有助于在Vrancea平板中产生中等深度的地震活动。与地震层析成像和各向异性研究的比较表明，最大水平应力方向，可能的平板走向和地震各向异性（尤其是在〜130 km深度以下）之间存在极好的相关性，这表明环境地幔流动也可能促进平板内应力的建立和地震潜力。