A compact, low-impact seismic source reshapes monitoring of offshore CO₂ storage

A research group led by Prof. Takeshi Tsuji at the Graduate School of Engineering, The University of Tokyo, has developed a compact and low-impact seismic source system for monitoring offshore CO₂ storage sites. The research has been published in the International Journal of Greenhouse Gas Control.

Monitoring injected CO₂ in offshore geological formations is essential to ensure safe and long-term storage. However, conventional offshore seismic monitoring relies on large airgun sources and survey vessels, which are costly, environmentally intrusive, and difficult to operate in shallow nearshore environments. As a result, monitoring surveys are typically conducted only infrequently, limiting the ability to detect rapid or unexpected CO₂ migration.

To address these challenges, the research team developed a compact speaker-type seismic source, the Marine Portable Active Seismic Source (Marine-PASS). The system weighs less than 100 kg—approximately 1/100 the weight of conventional airgun systems—and can be deployed from small vessels or unmanned surface vehicles. Instead of generating a single strong impulsive signal, Marine-PASS emits highly repeatable, controlled vibration signals, which are stacked over time to achieve sufficient signal strength for subsurface imaging. By adopting this method, even a compact seismic source can probe deep subsurface structures. In addition, compared to conventional airgun sources, the system produces lower acoustic pressure, thereby reducing environmental impact on marine life. It is also possible to design source waveforms that avoid frequency ranges known to have strong impacts on marine organisms.

Field experiments conducted at a candidate offshore CO₂ storage site offshore Taiwan demonstrated that the system can clearly image geological structures at depths greater than 2 km beneath the seafloor. The system was also successfully integrated with Distributed Acoustic Sensing (DAS) using subsea fiber-optic cables, enabling high spatial and temporal resolution and opening the possibility for continuous monitoring.

Because Marine-PASS is extremely compact, it can be operated from small vessels, as demonstrated in the Taiwan experiments. This enables the possibility of collaborative monitoring with local fishing vessels around CO₂ storage sites. Unlike conventional surveys that rely on large vessels, this approach allows the use of local resources and existing infrastructure, contributing not only to cost reduction but also to the realization of CO₂ storage monitoring systems that coexist with local communities. In this sense, the technology proposes a new paradigm for offshore monitoring that integrates regional resources and human networks into safe and sustainable operations.

This technology represents a paradigm shift from conventional high-cost, low-frequency offshore surveys using large vessels to low-cost, high-frequency, and potentially automated monitoring systems based on compact sources and autonomous platforms. By significantly reducing environmental impact and enabling flexible deployment in nearshore environments, Marine-PASS provides a practical pathway toward scalable and sustainable monitoring of carbon capture and storage (CCS) systems. The approach also has potential applications in marine resource exploration, offshore infrastructure monitoring, and renewable energy development.

Figure 1. (Left) Conventional survey and monitoring using a large seismic source (airgun) and streamer cables equipped with receivers. (Right) Newly developed compact seismic source (Marine-PASS) operated from a small vessel.

Figure 2. Reflection seismic section acquired using Marine-PASS, showing subseafloor geological structures.

Papers

Journal: International Journal of Greenhouse Gas Control

Title: A compact, low-impact seismic source reshapes monitoring of offshore CO₂ storage

Authors: Takeshi Tsuji*, Tarek Imam, Ahmad Ahmad, Kazutoshi Sakamoto, Arata Kioka, Tetsuro Tsuru, Fernando Hutapea, Masaharu Ueki, Hao Kuo-Chen, Zhuo-Kang Guan, Chun-Hung Lin

DOI: 10.1016/j.ijggc.2026.104644