Rapid assessment of damage potential and size of an earthquake at the station is highly demanded for onsite earthquake early warning. We study the application of τ c *Pd for its estimation on the earthquake size using 123 events recorded by the borehole stations of KiK-net in Japan. The new type of earthquake size determined by τ c *Pd is more related to the damage potential. We find that τ c *Pd provides another parameter to measure the size of earthquake and the threshold to warn strong ground motion.

Earthquake early warning (EEW) is an effective approach to mitigating earthquake damage. This is the first study evaluating borehole seismograph application to EEW in Taiwan. We selected inland and offshore earthquakes with M L larger than 4.0 occurring between 2012 and 2014 for this study. We investigated the Pd attenuation relationship as a function of the hypocentral distance (R) and magnitude (M). The new Pd attenuation relationship specific for the borehole records is expressed as: log(Pd) = 0.689M L -0.741log(R) -4.608 ± 0.248. Once the earthquake location is determined, this regression equation is used to quickly estimate Pd magnitude (M Pd ). According to the new regression equation formulated specifically for borehole observations in Taiwan, our result shows that the standard M Pd deviation is about 0.21 relative to M L . This smaller standard deviation of 0.21 compared to that of the free-surface records might be attributed to the reduced influence of near-surface effects in the borehole records. We propose a new robust Pd regression equation for the Taiwan borehole seismic network.