Generation and Destruction of Lithosphere in the Ligurian Sea

非洲板块和欧亚板块的汇合以及西地中海-阿尔卑斯山地区最近的演化形成了一个盆地(如利古里亚海)和山脉的谜团。利古里亚海是一个关键地点，因为其复杂的地球动力学环境以地壳性质和厚度的显着变化为特征。深部构造以西阿尔卑斯造山带向亚平宁系过渡和俯冲极性变化为特征。在利古里亚海之下，阿尔卑斯锋向东俯冲，而在亚平宁之下，向东俯冲，向西北推进。特别是，对于较大深度(20公里)，没有使用OBS数据进行地震成像，有关利古里亚海深部结构的知识大多是从陆地数据观测或超大规模断层成像研究中推断出来的。为了成像岩石圈结构，我们建议使用来自利古里亚海和邻近陆地站龙虾部署的33个宽带海底地震仪(OBS)站的数据。OBS站是安装在SPP 4D-MB框架内的阿尔普阵列的海洋组成部分，将于2017年5月/6月安装在利古里亚海，为期约11个月。为了估计接收器之间的经验格林函数，我们提出了地震学环境噪声互相关技术。提取的瑞雷波群速度将与远距离地震的瑞雷波相速度频散曲线互补，以提高三维剪切速度模型反演的数据集的质量。剪切波速度模型将用于区分先前假设的盆地中心性质，如蛇纹状、典型的洋壳或底板物质。特别是，盆地中洋壳的几何形状与形成它的主要地球动力学事件有关。目前利古里亚海的地震活跃率较低，4-4.5级事件，周期约为2-3年。尽管地震活动水平中等，但该区域在历史时期曾发生破坏性地震，例如1897年在盆地中心发生的英佩里亚地震(MW6.3-7.5)，造成至少600人伤亡。龙虾OBS网络将首次以均匀分辨率精确确定地震矩释放，精确到小震级事件(mL1-2)，从而识别与当前盆地开放有关的活动断层及其孕震深度。目前人们对活动断裂的位置和性质知之甚少，对当地地震活动的彻底分析将有助于揭示利古里亚盆地的浅层地质和可能的应力状态(从震源机制)。

The convergence of the Africa and the Eurasia plates and the recent evolution of the western Mediterranean-Alpine area has built a puzzle of basins (such as the Ligurian Sea) and ranges. The Ligurian sea is a key location due to its complex geodynamic setting characterized by pronounced variations in crustal nature and thickness. The deep structure is characterized by the transition from the western Alpine orogen to the Apennine system and change in subduction polarity. Beneath the Ligurian Sea the Alpine front subducts to the East while beneath the Apennine eastward subduction and subduction rollback advancing to the NW occurs. In particular for larger depths (>20 km) no seismological imaging using OBS data was carried out and the knowledge of the deep structure in the Ligurian sea is mostly inferred from land data observations or from very large-scale tomography studies. In order to image the lithospheric structure we propose to use the data from 33 broadband Ocean Bottom Seismometer (OBS) stations from the LOBSTER deployment in the Ligurian Sea and adjacent landstations. The OBS stations form the marine component of the AlpArray installed within the framework of the SPP 4D-MB and will be installed in May/June 2017 in the Ligurian sea for a period of ~11 months. We propose seismological ambient noise cross correlation techniques in order to estimate empirical Green functions between the receivers. The extracted group velocities of the Rayleigh waves will be complemented with Rayleigh wave phase velocity dispersion curves from distant earthquakes in order to enhance the quality of the dataset for the inversion of a 3D shear velocity model. The shear wave velocity model will be used to discriminate between previously hypothesed nature of the basin center such as serpentinized, typical oceanic crust or underplated material. In particular, the geometry of the oceanic crust in the basin is of special interest in relation with the major geodynamic events that shaped it.The current seismicity rate is in the Ligurian Sea is modest with magnitude 4-4.5 events with an approximate period of 2-3 years. Despite the moderate seismicity level destructive earthquakes occurred in the region in historical times such as the Imperia earthquake 1897 in the centre of the basin (Mw 6.3-7.5) with at least 600 casualties. The LOBSTER OBS network will allow for the first time precise determination of seismic moment release with homogenous resolution down to small magnitude events (Ml 1-2) resulting in the identification of active faults and their seismogenic depths involved in current basin opening. Current locations and properties of active faults are poorly known and a thorough analysis of the local seismicity will enlighten the shallow geology and possibly the stress regime (from focal mechanisms) in the Ligurian basin.