A study on the dependence of focal depth of the 2017 Pohang earthquake on crustal velocity models using moment tensor inversion: Journal of the Geological Society of

초록

The 2017 Pohang earthquake (ML 5.4) is the most devastating earthquake in South Korea since modern seismometers were installed in 1978. One of the reasons why the Pohang earthquake caused more damage than the 2016 Gyeongju earthquake with ML 5.8 is due to its shallow focal depth. The focal depth of the Pohang earthquake is estimated to be between 2 ~ 10 km according to recent studies. It is necessary to quantitatively measure the exact focal depth of the Pohang earthquake because it is closely related to whether the Pohang earthquake is induced by the nearby enhanced geothermal system site or not. Travel times usually used in the estimation of focal depths suffer from the trade-off between crustal velocity models and focal depths, hampering accurate estimation of focal depths. Therefore, we applied moment tensor inversion method to waveforms from the Pohang earthquake to estimate focal depth. Furthermore, to estimate the trade-off between crustal velocity models and focal depths quantitatively, we used 8 different crustal velocity models. Our results show stable estimations of focal depth of about 3 ~ 5 km regardless of crustal models, which is very similar to the water injection depth of 4.215 and 4.340 km. © 2019 The Geological Society of Korea. All rights reserved.

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