The Existence of Saturated Vapors in the Deep Source Region of 2017 Pohang Earthquake Evidenced from Seismic Tomography

Authors

• Jia Wei Qian, Anhui University of Science and Technology
• Hai Jiang Zhang, University of Science and Technology of China
• Lei Guo, Hebei Earthquake Agency
• Uzonna Okenna Anyiam, Hope CollegeFollow
• Changsoo Cho, Korea Institute of Geoscience and Mineral Resources
• Kang Hyeun Ji, Korea Institute of Geoscience and Mineral Resources
• Hao Ran Ma, Hohai University

Document Type

Article

Publication Date

1-1-2024

Publication Source

Earth and Planetary Physics

Volume Number

8

Issue Number

6

ISSN

20963955

Abstract

Geothermal resources are a promising approach to clean renewable energy; 90% of them are deep reservoirs of hot dry rock that require hydraulic fracturing to create a network of connections among wells to enable efficient heat exchange, known as an Enhanced Geothermal System (EGS). The Pohang EGS project in south Korea led to a devasting Mw5.5 earthquake, triggered by the reservoir’s EGS stimulation, the largest earthquake known to have been induced by EGS development. Detailed investigations have been conducted to understand the cause of the Pohang earthquake; the conclusion has been that overpressurized injected fluids migrated into an unknown fault triggering this large earthquake. Detailed velocity images for the source zone of the 2017 Pohang earthquake, which could be helpful for further understanding its inducing mechanism, are unavailable. However, we have assembled detailed aftershock data recorded by 41 local stations installed within about three months after the Mw5.5 Pohang earthquake, and have then applied the Vp/Vs model’s consistency-constrained double-difference seismic tomography method to determine the high-resolution three-dimensional Vp (compressional wave velocity), Vs (shear wave velocity), and Vp/Vs models of the source region that we report here, as well as earthquake locations within the source region. The velocity images reveal that the deep source area of the 2017 Pohang earthquake is dominated by low Vp, high Vs, and low Vp/Vs anomalies, a pattern that can be caused by overpressurized vapors due to high temperatures at these depths. Based on aftershock locations and velocity features, our studies support the conclusion that the 2017 Pohang earthquake was triggered by injected EGS fluids that migrated into a blind fault.

Keywords

EGS, low Vp/Vs, Pohang earthquake, saturated vapors, tomoDDMC

Recommended Citation

Published in: Earth and Planetary Physics, Volume 8, Issue 6, January 1, 2024.