Abstract. 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 set-ups 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-DC components. We infer that for most earthquakes (Mw ≥ 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 MT inversions for events with Mw > 3.0. We present here 75 solutions and analyse our results in the seismo-tectonic context of historic earthquakes, seismic activity of the last three decades and GNSS deformation data. We study regions of high seismic activity, namely the western Alps, the region around Lake Garda, the SE Alps, besides clusters further from the study region, 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 focal mechanisms from existing catalogs. Related to the NS compressional regime, E-W to ENE-WSW striking thrust faulting is mainly observed in the Friuli area in the SE 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 as normal faulting earthquakes in the Apennines. Both, our centroid depths as well as 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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利用密集的AlpArray地震网络对阿尔卑斯山中小地震进行区域质心MT反演：挑战和构造认识

摘要。欧洲中部的高山山脉的特征是非均质地壳，在沉积前陆盆地附近堆积了不同的构造单元和块体。质心矩张量反演可提供有关地震和相关构造过程的断层机制的见解，但在这种环境下会大大加剧。得益于密集的AlpArray地震网络和我们灵活的基于bootstrap的反演工具Grond对于获得的力矩张量和质心位置的不确定性，我们能够测试不同的设置。我们评估频带，方位间隙，输入数据类型和距离范围的影响，并研究非直流分量的发生和可靠性。我们推断，对于大多数地震（Mw≥3.3），将时域全波形和频域幅度谱在0.02–0.07 Hz的频带中组合起来是合适的。依靠我们的方法学测试的结果，我们对Mw> 3.0的事件执行偏斜MT反演。我们在这里提出75个解决方案，并在历史地震的地震构造背景，最近三年的地震活动和GNSS变形数据中分析我们的结果。我们研究高地震活动的地区，即西部阿尔卑斯山，加尔达湖周围的SE阿尔卑斯山地区，以及距研究区域较远的群集，在第纳里德北部和亚平宁山脉。阿尔卑斯山东部和阿尔卑斯山中部地区的地震活动特别低。考虑到现有目录中的其他焦点机制，我们将聚类算法应用于焦点机制。与NS压缩方式有关，从EW到ENE-WSW的冲断断层主要发生在东南阿尔卑斯山的弗留利地区。在中部阿尔卑斯山的北缘和第纳里德北部，观察到了具有类似方向压力轴的走滑断层。在西北阿尔卑斯山观察到NW-SE走向正常断层，其走向与亚平宁山脉的正常断层地震相似。两个都，现有目录中的质心深度和震中深度表明，高山地震活动主要是很浅的。大约80％的事件深度小于10 km。