| dc.description.abstract | The local magnitude (ML) of an earthquake, calculated from the amplitude of seismic waves, can vary depending on site conditions at different recording stations. These site conditions cause different amplification effects on the recorded seismic waves, impacting the calculated ML values. To represent the ML of an earthquake event, the average magnitude value obtained from many stations is utilized. The term “dML” signifies the difference between the event magnitude and individual station magnitudes. The use of dML corrections is not currently applied by the Central Weather Administration (CWA) of Taiwan in their magnitude determinations. The observed dML values ranged widely from -0.71 to 0.92 magnitude units. When dML corrections are applied, the standard deviation of the event magnitude decreases from 0.36 to 0.22 magnitude units, indicating a more consistent and reliable magnitude determination. The application of dML corrections is especially critical for earthquakes of small magnitudes. These events are typically recorded only by stations near the epicenter, which might all be situated on similar ground conditions (e.g., all on hard rock or all on soft soil). This homogeneity can lead to systematic biases in magnitude estimates. Therefore, using dML corrections helps mitigate these biases by adjusting those stations to a united seismic site condition. This study proposes utilizing known site parameters to calculate dML. Among these parameters, VS30 showed the strongest correlation with dML in this study. Moreover, seismic instruments placed downhole substantially minimize interference from surface noise, enabling the acquisition of high-quality ground motion signals. The difference in seismic wave velocities between the layers at the surface and downhole seismometers leads to divergence in the calculated local magnitude results (DeltaML). When employing downhole recordings for local magnitude determination, an underestimation occurs due to their smaller amplitudes compared to surface recordings. The goal of this study is to explore the correlation between dML and site parameters and to evaluate the impact of dML corrections on local magnitude determinations. Additionally, we aim to evaluate differences (DeltaML) in local magnitude calculations resulting from ground and downhole recordings due to site amplification effects. | en_US |