← Back to Sessions

The 2017 Pohang, Korea, Earthquake and its Largest Aftershocks: Stress Drop and Source Complexity Suggestive of Fluid-faulting Interaction

Description: 

The Pohang earthquake (Mw 5.5), which occurred in the southeastern part of the Korean Peninsula on November 15, 2017, has been reported as one of the biggest earthquakes associated with fluid injection activities. For the Pohang earthquake and its seven largest aftershocks, we determined the source spectra and source time functions using the empirical Green’s function spectral ratio approach, and computed corner frequencies and stress drops. The stress drops vary from 17 to 39 MPa, which corresponds well with the previously observed values along the Korean Peninsula when considering the Madariaga model used. We obtained a two-pulse moment rate function and bimodal spectrum for the Pohang mainshock along with plausible rupture directive effects. The aftershocks located off the main fault generated larger stress drops than those on the main fault plane, likely indicating the rupturing of new or strongly coupled/healed fault segments. The observed source spectra for the aftershocks are simpler and well explained by a circular rupture approximation. These findings indicate that the mainshock may have been caused by a complex rupture process, such as a near-simultaneous activation of differently oriented fault segments. Fault-valve mechanism along the previously unmapped fault system that intersects the causative fault would increase the coulomb static stresses reducing effective normal stresses. This could cause aftershock migrations on both sides of the intersecting faults and high stress drop events at the edge of the main fault. Our result is one of the clearest examples of fluid-faulting interaction, which is expected to be involved in migrating earthquakes, and also important in seismicity triggered/induced by hydraulic stimulation in modern enhanced geothermal systems.

Session: Earthquake Source Parameters: Theory, Observations and Interpretations

Type: Oral

Date: 4/18/2023

Presentation Time: 02:15 PM (local time)

Presenting Author: Minkyung Son

Student Presenter: No

Invited Presentation: 

Authors