Kinematic rupture model for the 2017 Mw 5.5 Pohang, South Korea, earthquake

Jeongung Woo

Submitted August 16, 2021, SCEC Contribution #11605, 2021 SCEC Annual Meeting Poster #240

Analyzing the faulting process of induced and triggered earthquakes at many unconventional hydrocarbon sites is one of the integral parts to better understand their causes, potentially related to the pre-event seismicity, aftershock activity and the temporal variations of fluid-injection. The Pohang, South Korea, earthquake (Mw 5.5) occurred on November 15, 2017 near the Pohang Enhanced Geothermal System site and it generated strong ground motions with measurable surface deformation. In this study, I investigated finite rupture models for the Pohang earthquake by using local seismic records and InSAR measurement. Three fault models with different segments were constructed based on the distribution of its aftershocks and velocity models to calculate Green’s functions for each subfault were pathwisely calibrated from the seismograms of M 3 earthquakes in the aftershock area. The fault model calculated via multiple time window method shows that the rupture nucleated near foreshocks and a stimulation well initially propagated to SW direction, followed by another ruptures to NE direction with a maximum slip at ~1.4 s. At the disconnected NE fault segment, further slip was observed at 2.8s, which may explain the dominance of the non-double-couple moment tensors of the earthquake as the rupture on multi-fault system. The size of our rupture model is far larger than the extent of pre-events, rather than matching with the dimensions of aftershocks. I suggest the rupture process itself was dominantly affected by the pre-conditions of fault parameters, apart from that the nucleation of the rupture is closed related to series of fluid injections and the slips jumping onto disconnected fault segment may be triggered by instantaneous ground motions near hypocentral area. This finding reconciles the importance of the intensive examination of the fault structure at various fluid-injection sites and shows that the interactions of multi-fault system can be a potential risk for induced earthquakes.

Key Words
finite fault model, waveform modeling, Enhanced Geothermal System, 2017 Pohang earthquake

Woo, J. (2021, 08). Kinematic rupture model for the 2017 Mw 5.5 Pohang, South Korea, earthquake. Poster Presentation at 2021 SCEC Annual Meeting.

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