Fault “Corrosion” by Fluid Injection: A Potential Cause of the November 2017 5.5 Korean Earthquake

Figure 6

Outcrop of Yeongdeok granite near Jipum (36.4478351°N, 129.2705272°E; near the town of Yeongdeok, ~50 km north of Pohang; Figure 1), showing its highly fractured character. Tape measure (diameter ~8 cm) provides scale. This granite is petrologically similar to the Pohang granite and part of the same Permian magmatic suite (e.g., [37]). Its highly fractured character can be considered indicative of the physical state of the Pohang granite. For the Yeongdeok granite, the typical spacing of fractures has been measured as ≤0.3 m [98]. However, many of these fractures will have been formed during the last ~1 km of erosional unloading (cf. [99]); we thus adopt a nominal fracture spacing of 0.5 m for our analysis of the Pohang granite.