First low-frequency 3D seismic investigation of the deep magmatic-hydrothermal system and architecture of the Campi Flegrei caldera to complement an amphibian ICDP/IODP drilling effort

在过去的几十年里，部分被淹没的Campi Flegrei火山口（CFc）是世界上火山风险最高的地区之一，由于其灾难性喷发的历史和持续的火山动荡，已经受到了重大的科学和社会关注。因此，它已成为一种两栖ICDP-IODP方法的对象。虽然ICDP提案（CFDDP）获得了批准，并且成功钻出了第一个500米长的试验井（12/2012），但相关的IODP计划仍处于提案前阶段（#671），因为（当时）合适的地震现场调查的可用性有限。从那时起，意大利和德国进行了两次联合考察，致力于多通道地震（MCS）数据采集，为两栖ICDP-IODP钻井活动的发展提供适当的数据库。特别重要的是2016年收集的3D低频MCS数据集（25 m线间距；20-200 Hz），在ICDP-IODP目标深度范围内达到了约2-3 km的信号穿透。这些新的地震数据集的获取，加上活跃的ICDP钻井以及额外的广泛研究，推动了另一次麦哲伦研讨会的举办（2/2017），从而重振了两栖钻井方法。最初的提议旨在处理和解释选定的低频MCS剖面，为两栖ICDP-IODP钻井活动的准备提供可靠的现场调查，而现在提议的24个月的项目涉及对完整3D数据（156个剖面）的全面分析。这种3D方法允许对深火山口结构和相关岩浆-热液系统的各个方面进行前所未有的检查，从而最终提供了整合和空间外推ICDP-IODP钻井结果的独特机会。这种综合策略使我们能够建立整个系统的3D结构框架，从而有可能彻底改变我们对火山口火山作用的理解。拟议项目的目的和目标遵循了2017年麦哲伦研讨会的建议，并与ICDP-IODP的工作密切相关。主要的科学重点在于了解(1)大型破火山口形成喷发的喷发机制，(2)浅层热液岩浆特征与深层地下特征之间的相互联系，(3)陆地与海洋火山活动的明显差异。为了实现这一目标，必须实施仔细的3D MCS数据处理和分析，以便识别和绘制重要特征，如火成岩矿床、岩浆特征（如侵入、馈线管道）、火山建筑、热液蚀变区、逃离通道、断裂带、最大火山口填充厚度和未受干扰的海洋沉积序列。当前提案的结果对于最终指导计划中的ICDP转移和IODP钻井地点的定位至关重要。

During the last decades, the partially submerged Campi Flegrei caldera (CFc) – one of the world’s highest volcanic risk areas – has received significant scientific and societal interest due to its history of catastrophic eruptions and ongoing volcanic unrest. Therefore, it has become subject to an amphibious ICDP-IODP approach. While the ICDP proposal (CFDDP) was approved and a first 500-m long pilot hole was successfully drilled (12/2012), the associated IODP initiative is still in the pre-proposal stage (#671) due to (at that point) limited availability of suitable seismic site surveys. Since then, two joint Italian-German expeditions dedicated to multichannel seismic (MCS) data acquisition were carried out to provide an appropriate database for the development of amphibious ICDP-IODP drilling campaign. Of particular importance is a 3D low-frequency MCS dataset (25 m line spacing; 20-200 Hz) collected in 2016, reaching a signal penetration in the range of the ICDP-IODP target depth of ~2-3 km. The acquisition of these new seismic datasets together with the active ICDP drilling as well as additional extensive research motivated to host another Magellan Workshop (02/2017), thereby revitalizing the amphibious drilling approach. While the original proposal aimed at the processing and interpretation of selected low-frequency MCS profiles to provide a robust site survey for the preparation of an amphibious ICDP-IODP drilling campaign, the here proposed 24-month project deals with a comprehensive analysis of the full 3D data (156 profiles). Such a 3D approach allows for an unprecedented examination of all facets of the deep caldera architecture and associated magmatic-hydrothermal system, thereby ultimately providing the unique opportunity to integrate and spatially extrapolate ICDP-IODP drilling results. This integrative strategy enables us to establish a 3D structural framework of the entire system, thereby holding the potential to revolutionize our understanding caldera volcanism.The aims and objectives of the proposed project follow recommendations from the 2017 Magellan Workshop and are closely linked to the ICDP-IODP effort. The main scientific focus lies on understanding (1) the eruption mechanisms of large-scale caldera forming eruptions, (2) the interconnectivity between shallow hydrothermal-magmatic features and the deep subsurface, and (3) the distinct difference between terrestrial and marine volcanic activity. To achieve that a careful 3D MCS data processing and analysis has to be implemented to allow for the identification and mapping of important features such as ignimbrite deposits, magmatic features (e.g. intrusions, feeder conduits), volcanic edifices, hydrothermally altered areas, escape pathways, fault zones, maximum caldera fill thickness, and undisturbed marine sedimentary successions. The results of the current proposal are essential for the final guidance of a planned diverted ICDP and positioning of IODP drill sites.