Abstract The Florina basin (NW Greece) embodies sources of natural CO2 emissions, which are aligned parallel to the NE-SW striking regional major normal faults. The study area is characterized by low to moderate seismicity, as historical information and instrumental data reveal. During February 2013 to January 2014 an outburst of seismic activity emerged, consisting of more than 2000 located earthquakes, with a mainshock of Mw = 4.1 on 17 February 2013 (16:48 UTC). A local temporary network was installed in July 2013, whose recordings provided the necessary data for performing a Shear-wave Splitting (SwS) study of the upper crust. After the application of strict selection criteria, 532 SwS measurements were obtained for two stations, using a mixture of manual and fully automatic methods. Two polarization directions of the fast shear-wave were identified at one of the stations, with the main one striking NE-SW and the secondary in a NW-SE direction. The first direction is in agreement with the local stress field, as it is identified by focal mechanisms, and with the strike of faults along which soil gas CO2 concentrations are distributed and can be explained by the Anisotropic Poro-Elasticity (APE) model. The second direction is consistent with the strike of mapped local faults, inherited since the Late Miocene extension, which are responsible for the formation of the Florina basin. The SwS results at the second station revealed an almost N-S dominant polarization direction, which is not consistent with the local stress field. This direction, obtained from events belonging to the southern group of the sequence, that was probably triggered by fluid intrusion, might be interpreted by spatiotemporal patterns of seismicity and CO2 upwelling.

中文翻译：

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2013-2014 年地震危机期间，希腊弗洛里纳盆地富含二氧化碳的油田上地壳的横波分裂特性

摘要 弗洛里纳盆地（希腊西北部）体现了自然 CO2 排放的来源，这些排放源与 NE-SW 突出的区域主要正断层平行。正如历史信息和仪器数据所揭示的那样，研究区的特点是低到中等地震活动。2013 年 2 月至 2014 年 1 月期间，出现了一次地震活动爆发，包括 2000 多次定位地震，2013 年 2 月 17 日（UTC 时间 16:48）主震 Mw = 4.1。2013 年 7 月安装了一个本地临时网络，其记录为对上地壳进行剪切波分裂 (SwS) 研究提供了必要的数据。在应用严格的选择标准后，使用手动和全自动方法的混合，获得了两个站点的 532 个 SwS 测量值。在其中一个台站确定了快横波的两个极化方向，主要方向为 NE-SW，次要方向为 NW-SE。第一个方向与局部应力场一致，因为它是由震源机制确定的，并且与土壤气体 CO2 浓度沿其分布的断层走向一致，并且可以通过各向异性孔隙弹性 (APE) 模型来解释。第二个方向与绘制的局部断层走向一致，自晚中新世延伸以来继承，是弗洛里纳盆地形成的原因。第二站的 SwS 结果显示几乎为 NS 主导的极化方向，这与局部应力场不一致。这个方向，从属于该序列南部组的事件中获得，