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Continental shelf agreement emerges as a new variable in Korea-Japan relations

Published: 28 May. 2025, 00:04

Shim Sang-min

The author is a research fellow at Asan Institute for Policy Studies

A decades-old resource-sharing agreement between Korea and Japan is set to become a key point of contention in bilateral relations. With the possibility of either side unilaterally ending the 1974 Joint Development Agreement (JDA) over the continental shelf, the agreement's future is now closely tied to shifts in regional geopolitics and international maritime law.

The roots of the JDA date back to a landmark 1969 ruling by the International Court of Justice (ICJ), which held that continental shelves are natural extensions of land territory. Based on that interpretation, Korea in 1970 enacted the Submarine Mineral Resources Development Act and claimed jurisdiction over the 7th Mining Zone (Block 7), stretching close to the Okinawa Trough. Japan strongly objected to Korea’s claim, but the two nations opted for a diplomatic compromise: rather than establishing a permanent maritime boundary, they agreed to jointly explore and develop the area’s undersea resources. The resulting Joint Development Agreement was signed in 1974 and entered into force in 1978.

Starting June 22, either Korea or Japan may unilaterally declare the termination of their 1974 joint development agreement for Block 7 in the southern waters off Korea. Observers say the decision could affect bilateral relations. The photo shows the West Capella conducting exploratory drilling at a promising structure in the waters off Pohang, North Gyeongsang, on the morning of December 30, 2024. [YONHAP]

Nearly half a century later, the area has yet to yield any commercially viable resource deposits.

Under Article 31, Clause 3 of the agreement, either Korea or Japan may now notify the other of its intention to terminate the pact, effective June 22. Once notice is given, the agreement will expire three years later. What once seemed a stable legal framework now appears vulnerable, as the legal environment that once favored Korea has changed dramatically.

The turning point came in 1982 with the adoption of the United Nations Convention on the Law of the Sea (UNCLOS), which allowed all signatory states, including Japan, to claim a 200-nautical-mile exclusive economic zone (EEZ) as a matter of right. Meanwhile, more recent ICJ rulings have moved away from the “natural prolongation” principle that once supported Korea’s claim that its continental shelf extends to the Okinawa Trough.

Japan has come to view the JDA as overly favorable to Korea. That perception, combined with years of Japanese hesitancy toward joint development efforts, suggests that Tokyo may be inclined to terminate the agreement when given the opportunity.

The termination clause has created a structural power imbalance. From June 22 onward, Japan will hold the unilateral legal authority to end the agreement, regardless of Korea’s position. If Korea wants to maintain the agreement, it must persuade Japan to keep it in place. This dynamic places Korea in a subordinate position — a “B party,” in effect.

It would be naive to expect Japan to forgo this advantage without extracting concessions. Even if Tokyo opts not to immediately notify termination — perhaps out of consideration for the 60th anniversary of Korea-Japan normalization or Korea’s new administration following the June 3 presidential election — it could still use the threat of termination as diplomatic leverage.

Korea’s options are clear but difficult: either make broad concessions to preserve the agreement or accept its expiration and assert a more autonomous stance. Either way, decisions must be grounded not in sentimentality or inertia but in a rigorous, interest-based assessment of Korea’s strategic priorities under international law.

Even if the agreement ends, any future delimitation in the overlapping continental shelf area among Korea, Japan, and China will require Korea’s consent. This gives Korea significant leverage in any trilateral negotiations. Unilateral drilling or resource development in these unresolved zones would constitute a violation of international law.

Should Japan pursue such a course, Korea could shift to an offensive posture, using international legal channels and even launching resource development projects of its own as a countermeasure. Such actions, if backed by legal justification, would represent a significant policy shift for Korea.

Starting June 22, either Korea or Japan may unilaterally declare the termination of their 1974 joint development agreement for Block 7 off Korea’s southern coast. Analysts say the outcome could impact bilateral relations. The photo shows the drilling ship West Capella stationed in waters off Pohang, North Gyeongsang, on December 18, 2024, to examine the presence of oil and gas. The site is located about 40 kilometers from land. [YONHAP]

Importantly, termination of the agreement would not erase Korea’s domestic designation of Block 7 under national law. In fact, the JDA has long restricted Korea’s ability to explore or develop the zone without Japanese approval. Its expiration may allow Korea to proceed with some technical activities that were previously constrained, though full-scale development would still require multilateral coordination to avoid legal infractions.

Ultimately, the fate of the JDA will rest with Korea’s incoming administration, which will have to weigh the issue as part of a broader redefinition of Korea-Japan relations. Historically, political transitions in Korea have provided opportunities for some factions to exploit Japan-related issues for electoral gain. The JDA could become an easy target for such opportunistic narratives.

To avoid falling into these patterns, Korean policymakers must approach the situation with a strategic mindset. The goal should not be the blind preservation of the agreement, but the pursuit of tangible national interest. Seen from this perspective, the expiration of the JDA may represent not a loss, but the opening of a new window of opportunity.

Translated from the JoongAng Ilbo using generative AI and edited by Korea JoongAng Daily staff.