# Urban Seismic Networks: A Worldwide Review
## 3 Concluding Remarks  
The idea of focusing an earthquake monitoring network on a single urban areas has been widely exploited in the last decades, and has became a tool for a variety of different tasks. USNs can be settled in a relatively short time compared to traditional large-scale networks, and the costs for their maintenance in the case of long-term applications are comparatively constrained. Of course, for certain specific objectives USN performance can be reduced with respect to large-scale networks, especially compared to those designed for seismic surveillance. However, in most cases USNs represent an excellent solution in the trade-off between time and costs on the one hand and performance and reliability on the other. In this review, we provide an overview of the application of this tool, focusing in particular on the technical characteristics. In addition, we aim to provide strategies for the planning and development of USNs (presented in Table 4). Each USN objective, together with any possible secondary tasks, entails numerous possible combinations between technical and operational elements. Tables 3 and 4 provide recommendations on a wide range of such choices. Although often designed as single-task infrastructure, USNs may enable multiple functions, especially in case of strong earthquakes. USNs can represent the core of an entire chain of actions, starting in the very early aftermath of earthquake detection (early warning systems) and revealing decisive information in the short term when supporting decision-making and rescue operations is crucial (post-event damage assessment, seismic intensity mapping), while other actions may only performed later (seismic site response, structural monitoring). It is very likely that in the near future the interest in monitoring urban areas will continue to increase, driven by the expansion of urban centers and the consequent need to arrange mitigation and prevention actions [173; 174]. The capabilities of new sensing networks based on fiber-optic cables have been explored and developed in the last few years [175; 176; 177; 178; 179; 180; 181; 182; 183]. A network based on distributed acoustic sensing (DAS) represents the ideal candidate for the future generation of USNs. At this early stage for this technology, the cost for DAS interrogation units are remarkable; conversely, the possibility of exploiting existing communication infrastructure and the contained costs for cable maintenance help to balance the overall cost. Such systems are very sensitive; they allow high spatial (sub-metric) and temporal (up to kHz) resolutions. The waveforms can be reconstructed with high fidelity in the band from 0.02 to 30 Hz, making their performance comparable to broadband seismometers [178; 182; 184]. In general, the main advantages are the possibility of exploiting expanding communication infrastructure and the potentially huge amount of high quality data. According to [PERSON] and [PERSON] (2022) [159], seismic networks are evolving from research-oriented projects into public safety infrastructure. From this perspective, in the near future USNs could be integrated with other networks as components of a multi-scale and multi-parametric system in a smart city context. Such a system could carry out several roles in the disaster cycle, not only involving earthquakes, both in the pre-event (preventions) and post-event (recovery) phases. Such integration includes the possibility of sharing crucial data during the phase of post-disaster decision-making (e.g., structural monitoring, power and water grids, transportation, energy, etc.) as well as with regard to climate and environmental parameters [185]. Stakeholders, civil protection authorities, decision-makers, the scientific community, and the whole of society are among the potential beneficiaries of the outcomes of this integrated multi-scale system for the reduction of seismic risk.