Due to the low to moderate seismicity of the European Western Alps, few focal mechanisms are available in this region to this day, and the corresponding current seismic stress and strain fields remain partly elusive. The development of dense seismic networks in past decades now provides a substantial number of seismic records in the 0–5 magnitude range. The corresponding data, while challenging to handle due to their amount and relative noise, represent a new opportunity to increase the spatial resolution of seismic deformation fields. The aim of this paper is to quantitatively assess the current seismic stress and strain fields within the Western Alps, from a probabilistic standpoint, using new seismotectonic data. The dataset comprises more than 30 000 earthquakes recorded by dense seismic networks between 1989 and 2013 and more than 2200 newly computed focal mechanisms in a consistent manner. The global distribution of P and T axis plunges confirms a majority of transcurrent focal mechanisms in the entire western Alpine realm, combined with pure extension localized in the core of the belt. We inverted this new set of focal mechanisms through several strategies, including a seismotectonic zoning scheme and grid procedure, revealing extensional axes oriented obliquely to the strike of the belt. The Bayesian inversion of this new dataset of focal mechanisms provides a probabilistic continuous map of the style of seismic deformation in the Western Alps. Extension is found to be clustered, instead of continuous, along the backbone of the belt. Robust indications for compression are only observed at the boundary between the Adriatic and Eurasian plates. Short-wavelength spatial variations of the seismic deformation are consistent with surface horizontal Global Navigation Satellite System (GNSS) measurements, as well as with deep lithospheric structures, thereby providing new elements with which to understand the current 3D dynamics of the belt. We interpret the ongoing seismotectonic and kinematic regimes as being controlled by the joint effects of far-field forces – imposed by the anticlockwise rotation of Adria with respect to Europe – and buoyancy forces in the core of the belt, which together explain the short-wavelength patches of extension and marginal compression overprinted on an overall transcurrent tectonic regime.

中文翻译：

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西阿尔卑斯山的现代地球动力学：地震机制的新见解

由于欧洲西部阿尔卑斯山的低至中度地震活动，迄今为止该地区几乎没有可用的震源机制，相应的当前地震应力和应变场仍然部分难以捉摸。过去几十年密集地震网络的发展现在提供了大量 0-5 级范围的地震记录。相应的数据虽然由于其数量和相对噪声而难以处理，但代表了提高地震变形场空间分辨率的新机会。本文的目的是从概率的角度，使用新的地震构造数据，定量评估西阿尔卑斯山内当前的地震应力和应变场。该数据集包含 1989 年至 2013 年间由密集地震网络记录的 30 000 多次地震以及以一致方式新计算的 2200 多个震源机制。全球分布P和T 轴突确认了整个阿尔卑斯山脉西部地区的大部分横流震源机制，并结合了位于带核心的纯延伸。我们通过几种策略反转了这套新的震源机制，包括地震构造分区方案和网格程序，揭示了倾斜于带走向的延伸轴。这个新的震源机制数据集的贝叶斯反演提供了西阿尔卑斯山地震变形样式的概率连续图。发现延伸部沿带的主干聚集而不是连续的。仅在亚得里亚海和欧亚板块之间的边界处观察到明显的压缩迹象。地震变形的短波长空间变化与地表水平全球导航卫星系统 (GNSS) 测量以及深层岩石圈结构一致，从而为了解该带的当前 3D 动力学提供了新的元素。我们将正在进行的地震构造和运动机制解释为受远场力的联合效应控制——由阿德里亚相对于欧洲的逆时针旋转施加——和带核心的浮力，它们共同解释了短波长扩展和边缘压缩的补丁覆盖在整个跨流构造体系上。