Generation and Destruction of Lithosphere in the Ligurian Sea

非洲板块和欧亚板块的融合，以及地中海西部阿尔卑斯地区最近的演化，构成了一个由盆地（如利古里亚海）和山脉组成的谜。利古里亚海具有复杂的地球动力学背景，地壳性质和厚度变化明显，是一个关键位置。深部构造以西阿尔卑斯造山带向亚平宁体系过渡和俯冲极性变化为特征。利古里亚海下为阿尔卑斯锋面东俯冲，亚平宁海下为东俯冲和北西推进的俯冲回退。特别是对于较大深度（bbb20 km），没有使用OBS数据进行地震成像，对利古里亚海深部结构的了解主要来自陆地数据观测或非常大规模的层析成像研究。为了对岩石圈结构进行成像，我们建议使用利古里亚海龙虾部署的33个宽带海底地震仪（OBS）站和邻近陆台站的数据。OBS站是安装在SPP 4D-MB框架内的AlpArray的海洋组成部分，将于2017年5月/ 6月在利古里亚海域安装，为期11个月。为了估计接收机之间的经验格林函数，我们提出了地震环境噪声互相关技术。提取的瑞利波群速度将与来自遥远地震的瑞利波相速度频散曲线相辅相成，以提高数据集的质量，用于三维剪切速度模型的反演。横波速度模型将用于区分先前假设的盆地中心性质，如蛇纹岩，典型的海洋地壳或下镀物质。特别是，盆地中海洋地壳的几何形状与形成它的主要地球动力学事件有特殊的关系。利古里亚海目前的地震活动频率一般，4-4.5级，周期约为2-3年。尽管该地区的地震活动程度中等，但在历史上曾发生过破坏性地震，例如1897年发生在盆地中心的Imperia地震（Mw 6.3-7.5），造成至少600人伤亡。LOBSTER OBS网络将首次允许以均匀分辨率精确确定小震级事件（Ml 1-2）的地震力矩释放，从而识别当前盆地打开中涉及的活动断层及其发震深度。目前人们对活动断层的位置和性质知之甚少，对当地地震活动性的深入分析将启发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.