Fault Rupture Model of the 2016 Gyeongju, South Korea, Earthquake and Its Implication for the Underground Fault System

• Published in: Geophysical research letters Vol. 45; no. 5; pp. 2257 - 2264
• Main Authors: Uchide, Takahiko, Song, Seok Goo
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.03.2018
• Subjects: Earthquakes; Fault lines; fault structure; finite‐fault slip inversion; Gyeongju; Korean Peninsula; Rupture; Rupturing; Seismic activity; Seismicity; Stress concentration; South Korea
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2017GL076960

The 2016 Gyeongju earthquake (ML 5.8) was the largest instrumentally recorded inland event in South Korea. It occurred in the southeast of the Korean Peninsula and was preceded by a large ML 5.1 foreshock. The aftershock seismicity data indicate that these earthquakes occurred on two closely collocated parallel faults that are oblique to the surface trace of the Yangsan fault. We investigate the rupture properties of these earthquakes using finite‐fault slip inversion analyses. The obtained models indicate that the ruptures propagated NNE‐ward and SSW‐ward for the main shock and the large foreshock, respectively. This indicates that these earthquakes occurred on right‐step faults and were initiated around a fault jog. The stress drops were up to 62 and 43 MPa for the main shock and the largest foreshock, respectively. These high stress drops imply high strength excess, which may be overcome by the stress concentration around the fault jog. Key Points Finite‐fault slip models were obtained for the 2016 Gyeongju earthquake and its largest foreshock using strong motion data The main shock and the largest foreshock ruptured the collocated parallel faults and their rupture directions were opposite to each other The high fault strength inferred from the high stress drop was probably overcome by the stress concentration around the right‐step fault