The Alpine mountains in central Europe are characterized by a heterogeneous crust accumulating different tectonic units and blocks in close proximity to sedimentary foreland basins. Centroid moment tensor inversion provides insight into the faulting mechanisms of earthquakes and related tectonic processes but is significantly aggravated in such an environment. Thanks to the dense AlpArray seismic network and our flexible bootstrap-based inversion tool Grond, we are able to test different setups with respect to the uncertainties of the obtained moment tensors and centroid locations. We evaluate the influence of frequency bands, azimuthal gaps, input data types, and distance ranges and study the occurrence and reliability of non-double-couple (DC) components. We infer that for most earthquakes (M_w≥3.3) a combination of time domain full waveforms and frequency domain amplitude spectra in a frequency band of 0.02–0.07 Hz is suitable. Relying on the results of our methodological tests, we perform deviatoric moment tensor (MT) inversions for events with M_w>3.0. Here, we present 75 solutions for earthquakes between January 2016 and December 2019 and analyze our results in the seismotectonic context of historical earthquakes, seismic activity of the last 3 decades, and GNSS deformation data. We study regions of comparably high seismic activity during the last decades, namely the Western Alps, the region around Lake Garda, and the eastern Southern Alps, as well as clusters further from the study region, i.e., in the northern Dinarides and the Apennines. Seismicity is particularly low in the Eastern Alps and in parts of the Central Alps. We apply a clustering algorithm to focal mechanisms, considering additional mechanisms from existing catalogs. Related to the N–S compressional regime, E–W-to-ENE–WSW-striking thrust faulting is mainly observed in the Friuli area in the eastern Southern Alps. Strike-slip faulting with a similarly oriented pressure axis is observed along the northern margin of the Central Alps and in the northern Dinarides. NW–SE-striking normal faulting is observed in the NW Alps, showing a similar strike direction to normal faulting earthquakes in the Apennines. Both our centroid depths and hypocentral depths in existing catalogs indicate that Alpine seismicity is predominantly very shallow; about 80 % of the studied events have depths shallower than 10 km.

中文翻译：

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使用密集的 AlpArray 地震网络对阿尔卑斯山中小地震进行区域质心矩张量反演：挑战和地震构造见解

欧洲中部的高山山脉的特征是异质地壳，在沉积前陆盆地附近积累了不同的构造单元和块体。质心矩张量反演可以深入了解地震和相关构造过程的断层机制，但在这种环境中会显着加剧。由于密集的 AlpArray 地震网络和我们灵活的基于引导的反演工具Grond，我们能够针对获得的矩张量和质心位置的不确定性测试不同的设置。我们评估频带、方位角间隙、输入数据类型和距离范围的影响，并研究非双耦合 (DC) 分量的出现和可靠性。我们推断，对于大多数地震（M_w ≥3.3 ) 0.02–0.07 Hz 频带内的时域全波形和频域幅度谱的组合是合适的。依靠我们的方法学测试的结果，我们对M _w >3.0 的事件执行偏矩张量 (MT) 反演. 在这里，我们提出了 2016 年 1 月至 2019 年 12 月之间的 75 种地震解决方案，并在历史地震的地震构造背景、过去 3 年的地震活动和 GNSS 变形数据中分析了我们的结果。我们研究了过去几十年中地震活动相对较高的地区，即西阿尔卑斯山、加尔达湖周围地区和南阿尔卑斯山东部，以及远离研究地区的集群，即第纳尔迪斯山脉北部和亚平宁山脉。东阿尔卑斯山和中阿尔卑斯山的部分地区的地震活动性特别低。我们将聚类算法应用于焦点机制，同时考虑现有目录中的其他机制。与 N-S 压缩机制相关，E-W-to-ENE-WSW 走向的逆冲断层主要在南阿尔卑斯山脉东部的弗留利地区观察到。沿中阿尔卑斯山北缘和第纳尔迪斯山脉北部观察到具有类似方向压力轴的走滑断层。在 NW 阿尔卑斯山观察到 NW-SE 走向的正常断层，显示出与亚平宁山脉正常断层地震相似的走向。我们现有目录中的质心深度和震源深度都表明高山地震活动主要是非常浅的；大约 80% 的研究事件的深度小于 10 公里。我们现有目录中的质心深度和震源深度都表明高山地震活动主要是非常浅的；大约 80% 的研究事件的深度小于 10 公里。我们现有目录中的质心深度和震源深度都表明高山地震活动主要是非常浅的；大约 80% 的研究事件的深度小于 10 公里。