Abstract English Channel Islands are located off Normandy coast of France within an intraplate area not associated with high seismicity rate and active tectonics. However, in July 1926 a damaging and well-documented earthquake occurred there, followed by a strongly felt event in February 1927. In this paper, we reprocess macroseismic observations, analog seismograms and bulletin data in order to re-appraise the location and magnitude of these two earthquakes. We find that the macroseismic epicentre of the 1926 Jersey earthquake is shifted to the East when compared with the location offshore South of Jersey given in both the French database SisFrance and the recent French catalog FCAT-17. Arrival-times from published data, together with our own onset-time readings, are processed in order to obtain probabilistic hypocentral locations. The maximum-likelihood instrumental epicentre of the 1926 event is located about 15 km East of Jersey Island (49.20°N, 1.82°W). This epicentre is well constrained within a 10 km radius area. The location of the 1927 epicentre is slightly south of Jersey, at a location similar to that of SisFrance, but this latter epicentre is less constrained as fewer observations are available (the Probability Density Function for the 1927 epicentre is relatively “diluted”). Focal depth remains very poorly determined for both the 1926 and 1927 events. Analysis of historical seismograms is also performed in order to determine both surface-wave and moment magnitudes, MS and MW. We find MS = 5.6 ± 0.2 for the 1926 event and MS = 5.0 for the 1927 event. Waveform fitting of some of the highest quality seismograms of the 1926 event gives us MW in the range [5.0, 5.5], depending on the chosen focal depth and focal mechanism. The 1927 Jersey earthquake is expected with an intensity magnitude MI about 0.6 smaller.

中文翻译：

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来自历史、仪器和宏观地震数据的 1926 年和 1927 年泽西地震的震源参数

摘要 英吉利海峡群岛位于法国诺曼底海岸附近的一个板块内区域，与高地震活动率和活动构造无关。然而，在 1926 年 7 月，那里发生了一次破坏性的、有据可查的地震，随后在 1927 年 2 月又发生了强烈的地震。在本文中，我们重新处理宏观地震观测、模拟地震图和公告数据，以重新评估地震的位置和震级。这两次地震。我们发现，与法国数据库 SisFrance 和最近的法国目录 FCAT-17 中给出的泽西南部近海位置相比，1926 年泽西地震的宏观震中向东移动。处理来自已发布数据的到达时间以及我们自己的起始时间读数，以获得概率性震源位置。1926 年事件的最大可能性仪器震中位于泽西岛以东约 15 公里（49.20°N，1.82°W）。这个震中被很好地限制在半径 10 公里的区域内。1927 年震中的位置在泽西岛稍偏南的位置，与 SisFrance 的位置相似，但由于可用观测数据较少，后一个震中受到的限制较少（1927 年震中的概率密度函数相对“稀释”）。1926 年和 1927 年事件的焦深仍然很差。还对历史地震图进行分析，以确定表面波和矩震级、MS 和 MW。我们发现 1926 年事件的 MS = 5.6 ± 0.2，1927 年事件的 MS = 5.0。1926 年事件的一些最高质量地震图的波形拟合为我们提供了范围 [5.0, 5.5] 的 MW，取决于所选的焦深和聚焦机制。预计 1927 年泽西地震的强度 MI 会小 0.6 左右。