Estimation of Ground Vibration Around Lava Tubes in Jeju Island Geopark, Korea

Lava tubes on Jeju Island, Korea, form a series of geosites with outstanding geological, ecological, historical, and cultural value. The area is a UNESCO World Natural Heritage Site and a Global Geopark. This recognition has led to much active development nearby; thus, management, regulation, and conservation measures are increasingly needed. This study proposes limits on the amounts of an explosive charge (dependent on distance from the lava tubes) that can be used during rock blasting near the lava tubes. To verify the proposed numerical analysis method, in situ tests were conducted using small charges that would not affect the geosites. The observations were compared with the numerical analysis. The allowable charge for each separation distance (50, 100, 150, and 250 m) that satisfies the 0.2 kine (cm/s) vibration criterion for geosites was determined from the numerical analysis results. For the Manjanggul lava tube, the determined maximum charges per delay are 2.0–2.6 kg at 50 m, 8.0–10.4 kg at 100 m, 18.1–23.5 kg at 150 m, and 50.4–65.5 kg at 250 m. The equivalent ranges for the Yongcheondonggul lava tube are 3.6–4.7, 14.4–18.7, 32.5–42.3, and 90–117 kg, respectively.