This report summarizes the seismicity in Switzerland and surrounding regions in the years 2017 and 2018. In 2017 and 2018, the Swiss Seismological Service detected and located 1227 and 955 earthquakes in the region under consideration, respectively. The strongest event in the analysed period was the ML 4.6 Urnerboden earthquake, which occurred in the border region of cantons Uri, Glarus and Schwyz on March 6, 2017. The event was the strongest earthquake within Switzerland since the ML 5.0 Vaz earthquake of 1991. Associated ground motions indicating intensity IV were reported in a radius up to about 50 km and locally approached intensity VI in the region close to the epicentre. Derived focal mechanisms and relative hypocentre relocations of the immediate aftershocks image a NNW–SSE striking sinistral strike-slip fault. Together with other past events in this region, the Urnerboden earthquake suggests the existence of a system of sub-parallel strike-slip faults, likely within in the uppermost crystalline basement of the eastern Aar Massif. A vigorous earthquake sequence occurred close to Château-d'Oex in the Préalpes-Romandes region in western Switzerland. With a magnitude of ML 4.3, the strongest earthquake of the sequence occurred on July 1, 2017. Focal mechanism and relative relocations of fore- and aftershocks image a NNE dipping normal fault in about 4 km depth. Two similarly oriented shallow normal-fault events occurred between subalpine Molasse and Préalpes units close to Châtel-St-Denis and St. Silvester in 2017/18. Together, these events indicate a domain of NE–SW oriented extensional to transtensional deformation along the Alpine Front between Lake Geneva in the west and the Fribourg Fault in the east. The structural complexity of the Fribourg Fault is revealed by an ML 2.9 earthquake near Tafers in 2018. The event images a NW–SE striking fault segment within the crystalline basement, which might be related to the Fribourg Fault Zone. Finally, the ML 2.8 Grenchen earthquake of 2017 provides a rare example of shallow thrust faulting along the Jura fold-and-thrust belt, indicating contraction in the northwestern Alpine foreland of Switzerland.

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2017年和2018年瑞士及周边地区的地震

本报告总结了2017年和2018年瑞士及周边地区的地震活动。2017年和2018年，瑞士地震局分别在所考虑的地区发现和定位了1227和955级地震。在分析期间，最强烈的地震是2017年3月6日发生在乌里州，格拉鲁斯州和施维茨州交界的ML 4.6 Urnerboden地震。该事件是自1991年ML 5.0瓦兹地震以来瑞士境内最强烈的地震。据报道，指示强度IV的相关地面运动的半径最大约为50 km，并在靠近震中的区域局部接近强度VI。立即余震的推导震源机制和相对中心重定位反映了ＮＮＷ一ＳＳＥ向左旋走滑断层撞击。与该地区过去发生的其他事件一起，Urnerboden地震表明存在亚平行的走滑断层系统，可能在东部Aar地块的最高结晶基底内。瑞士西部Préalpes-Romandes地区附近的Château-d'Oex发生了强烈地震。震级为ML 4.3，为该级地震中最强烈的地震，发生于2017年7月1日。震源机制和前后震的相对位置反映了大约4 km深度的NNE浸入正常断层。在2017/18年度，靠近Châtel-St-Denis和St.Silvester的亚高山Molasse和Préalpes单位之间发生了两次方向相似的浅层正常断层事件。一起，这些事件表明，在西部的日内瓦湖和东部的弗里堡断层之间，沿着NE-SW取向的区域从高变形向沿高变形延伸。2018年塔弗斯附近的ML 2.9级地震揭示了弗里堡断裂的结构复杂性。该事件反映了晶体基底内西北向东南的断裂带，这可能与弗里堡断裂带有关。最后，2017年的格林2.8级格伦兴地震提供了一个罕见的例子，说明侏罗纪褶皱冲断带上的浅逆冲断层，表明瑞士西北高山前陆发生了收缩。该事件成像了结晶基底内的西北-东南走向的断裂带，这可能与弗里堡断裂带有关。最后，2017年发生的ML 2.8格伦兴ML地震提供了一个罕见的例子，表明侏罗纪褶皱冲断带沿浅冲断层断裂，表明瑞士西北高山前陆发生了收缩。该事件成像了结晶基底内的西北-东南走向的断裂带，这可能与弗里堡断裂带有关。最后，2017年发生的ML 2.8格伦兴ML地震提供了一个罕见的例子，表明侏罗纪褶皱冲断带沿浅冲断层断裂，表明瑞士西北高山前陆发生了收缩。