Application of Taiwan borehole seismometers in earthquake early warning

Abstract:

Earthquake Early Warning (EEW) is an effective approach to mitigate earthquake damage. This study is the first study of using borehole seismograph in earthquake early warning in Taiwan. Since 2007, Central Weather Bureau (CWB) has been installing the borehole seismometers; currently, there are 47 operating borehole seismometers in Taiwan. We selected the inland and offshore earthquakes with M_L larger than 4.0 occurring between 2012 and 2014. We investigated the Pd attenuation relationship as a function of hypocentral distance (R) and magnitude, and obtained the following equation: log(Pd)=0.812×M_Pd−0.905×log(R)−4.795±0.322. Once the earthquake location is determined, we could use this regression equation to quickly define earthquake magnitude (M_Pd). According to the new regression equation specifically for the borehole observation in Taiwan, our result shows that the standard deviation of M_Pd is about 0.22 related to M_L. This small standard deviation of 0.22 compared to that of the free-surface one might be attributed to the neglect of the near surface effect. We propose a new robust Pd regression equation for the Taiwan borehole seismic network.