Abstract. The northern margin of the Ligurian Basin shows notable seismicity at the Alpine front, including frequent magnitude 4 events. Seismicity decreases offshore towards the Basin centre and Corsica, revealing a diffuse distribution of low magnitude earthquakes. We analyse data of the amphibious AlpArray seismic network with focus on the offshore component, the AlpArray OBS network, consisting of 24 broadband ocean bottom seismometers deployed for eight months, to reveal the seismicity and depth distribution of micro-earthquakes beneath the Ligurian Sea. Two clusters occurred between ~10 km to ~16 km depth below sea surface, within the lower crust and uppermost mantle. Thrust faulting focal mechanisms indicate compression and an inversion of the Ligurian Basin, which is an abandoned Oligocene rift basin. The Basin inversion is suggested to be related to the Africa-Europe plate convergence. The locations and focal mechanisms of seismicity suggest reactivation of pre-existing rift structures. Slightly different striking directions of faults in the basin centre compared to faults further east and hence away from the abandoned rift may mimic the counter-clockwise rotation of the Corsica-Sardinia block during ~20–16 Ma. The observed cluster events support the hypothesis of strengthening of crust and uppermost mantle during rifting related extension and thinning of continental crust.

中文翻译：

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盆地反转：OBS揭示了利古里亚海的活化裂谷构造

摘要。利古里亚盆地北缘在阿尔卑斯山锋地区表现出明显的地震活动性，包括频繁发生的4级地震。地震活动在向盆地中心和科西嘉岛的近海降低，显示出低震级地震的分散分布。我们分析了两栖AlpArray地震网络的数据，重点是海上组件AlpArray OBS网络，该网络由24个部署了8个月的宽带海底地震仪组成，揭示了利古里亚海以下微地震的地震活动性和深度分布。在下部地壳和最上层地幔内，在海面以下约10 km至约16 km的深度之间出现了两个星团。逆冲断层的震源机制表明了利古里亚盆地的压缩和反转，它是一个废弃的渐新世裂谷盆地。盆地反演被认为与非洲-欧洲板块的收敛有关。地震活动的位置和震源机制表明已经存在的裂谷构造可以重新激活。与更东部的断层相比，盆地中心断层的走向略有不同，因此远离废弃的裂谷可能模仿了科西嘉-撒丁岛地块在约20-16 Ma的逆时针方向旋转。观察到的星团事件支持了与裂谷有关的伸展和大陆壳变薄期间地壳和最上层地幔强化的假说。与更东部的断层相比，盆地中心断层的走向略有不同，因此远离废弃的裂谷可能模仿了科西嘉-撒丁岛地块在约20-16 Ma的逆时针方向旋转。观察到的星团事件支持了与裂谷有关的伸展和大陆壳变薄期间地壳和最上层地幔强化的假说。与更东部的断层相比，盆地中心断层的走向略有不同，因此远离废弃的裂谷可能模仿了科西嘉-撒丁岛地块在约20-16 Ma的逆时针方向旋转。观察到的星团事件支持了与裂谷有关的伸展和大陆壳变薄期间地壳和最上层地幔强化的假说。