Exploring dML Correction and Correlation with Site Parameters for Improved ML estimation in Taiwan
Chun‐Hsiang Kuo, Hsin-Yu Chen, Horng-Yuan Yen · 2024
Local magnitude (ML) is still commonly used for regional seismic networks because of it can be estimated fast and easily. To represent ML of an earthquake event, an average value obtained from a couple of stations are utilized. However, calculation of ML is influenced by diverse geological characteristics at each seismic station, leading to variations in computed values, and thus a station correction term Si had been suggested. This study analyzes a station adjustment term, i.e., dML, which indicates the difference between the earthquake event magnitude and the magnitudes obtained from individual stations. For small or medium magnitude earthquakes, which may only be recorded by stations located close to the epicenter. In such cases, all stations may be situated on either hard rock or soft soil, potentially causing bias of ML estimation without considering station adjustment. In addition, we also assess dML between surface and downhole stations for a recently installed surface-downhole network in Taiwan. Those downhole stations have better ability for recording weak seismic signals and are expected to enhance the precision of earthquake localization and monitoring capabilities, especially for regional small earthquakes. By applying dML adjustment, those high-quality downhole stations are able to be incorporated in ML estimation. Since various site parameters, like VS30 (time average S-wave velocity of the top 30-meter layers), Z1.0 (sedimentary depth), and fd (peak frequency), have been derived in Taiwan, we try to determine if it is possible to estimate the correlation between dML and the site parameters of each station. By implementing dML correction, we anticipate contributing to greater consistency in earthquake catalogs, enhancing the accuracy of seismicity rates for seismic hazard analysis.