A Global 3D Hydroacoustic Detectability Framework for Quantifying Submarine Volcanism Rates using CTBTO network

Submarine volcanism is estimated to account for the vast majority of Earth’s total magma output, playing a critical role in crustal formation and ocean geochemical cycles. However, despite this dominance, global eruption catalogs remain heavily biased toward subaerial events, with less than 10% of documented eruptions occurring underwater. This discrepancy highlights a massive knowledge gap in our understanding of planetary volcanic rates and magnitude-frequency distributions. Hydroacoustic monitoring offers the most promising avenue to address this deficit, utilizing the International Monitoring System (IMS) of the CTBTO. While these stations routinely detect hydroacoustic signals from magmatic activity thousands of kilometers away, the sensitivity of the global array remains unquantified for specific volcanic arcs. Without understanding the detection threshold for any given location, it is challenging to convert individual detection logs into accurate global eruption rate estimates.In this study, we present a comprehensive framework for evaluating the detectability of submarine eruptions that accounts for the complex physics of sound propagation in a heterogeneous ocean. We utilize global 3D acoustic propagation modeling to calculate Transmission Loss (TL) from potential volcanic sources to IMS hydrophone stations. Unlike standard 2D approximations, this approach accounts for critical 3D effects, including bathymetric blockage by ridges and seamounts, horizontal refraction, and diffraction effects that severely impact signal continuity. Our results provide the first global "detectability maps," quantifying the minimum Source Level required for an eruption to be registered by the IMS network. This framework allows for a rigorous assessment of the "blind spots" in the current global catalog. Furthermore, we demonstrate how this 3D modeling facilitates the optimization of station selection. By analyzing signal-to-noise ratios and transmission paths, we identify which specific stations are best suited to analyze eruptions from a given volcano, thereby providing a method for robust cross-validation of eruption signals. Beyond simple detection, this approach enhances source characterization. We present maps of travel time estimates that account for 3D path deviations, allowing researchers to correct for data shifts and accurately locate sources even over trans-oceanic distances. Additionally, we explore the effects of frequency-dependent attenuation, demonstrating how 3D propagation modeling can help distinguish between different source mechanisms, such as sustained distinct magmatic jetting versus discrete explosive impulses. To validate this framework, we apply our 3D transmission loss analysis to the Hunga Tonga-Hunga Ha’apai eruption sequence. We demonstrate the utility of data fusion by integrating recordings from the far-field CTBTO global network with near-field data from the published regional MERMAID floating seismometer dataset. By correcting for long-range propagation effects, we show that it is possible to recover original volcanic source properties from distant hydroacoustic data. These results highlight the challenges posed by complex bathymetry and underscore the necessity of 3D acoustic sound propagation modeling. Ultimately, this work provides the robust framework required to move from individual eruption detections to a comprehensive, unbiased quantitative estimate of global submarine volcanism rates.