Effective time- and frequency-domain techniques for interpreting seismic precursors in groundwater level fluctuations on Jeju Island, Korea.

An effective method, involving time and frequency domains was developed to interpret seismic precursors by comparing groundwater-level fluctuations recorded immediately and long before the occurrence of a known earthquake. The proposed method, consisting of the pre-processing (3-point filtering, band-pass filtering, and spectrum analysis) and post-processing (weighted moving average method and histogram and spectrum analyses) stages, was applied to the groundwater-level time series measured at three monitoring wells on Jeju Island, South Korea, from 00:00 on 8 September 2016 to 00:00 on 22 September 2016. The Gyeongju earthquake (Mw 5.

Contribution of nitrate-nitrogen concentration in groundwater to stream water in an agricultural head watershed.

This study characterized nitrate-nitrogen (NO-N) concentrations in groundwater and stream water in an agricultural head watershed in South Korea and identified the pollution load of NO-N as a result of the groundwater entering streams using field surveys, analyses of chemical constituents, and numerical modeling. The mean NO-N concentration in groundwater was 7.373 mg/L, which is approximately 1.