On 6 February 2018, an $Mw$ 6.4 earthquake struck near the city of Hualien, in eastern Taiwan with a focal depth of 10.4 km. The earthquake caused strong shaking and severe damage to many buildings in Hualien. The maximum intensity during this earthquake reached VII ($>0.4g$) in the epicentral region, which is extreme in Taiwan and capable of causing damage in built structures. About 17 people died and approximately 285 were injured. Taiwan was one of the first countries to implement an earthquake early warning (EEW) system that is capable of issuing a warning prior to strong shaking. In addition to the official EEW run by the Central Weather Bureau (CWB), a low‐cost EEW system ($P$‐alert) has been deployed by National Taiwan University (NTU). The $P$‐alert network is currently operational and is capable of providing on‐site EEW as well as a map of expected ground shaking. In the present work, we demonstrate the performance of the $P$‐alert network during the 2018 Hualien earthquake. The shake maps generated by the $P$‐alert network were available within 2 min and are in good agreement with the patterns of observed damage in the area. These shake maps provide insights into rupture directivity that are crucial for earthquake engineering. During this earthquake, individual $P$‐alert stations acted as on‐site EEW systems and provided 2–8 s lead time in the blind zone around the epicenter. The coseismic deformation ($Cd$) is estimated using the records of $P$‐alert stations. The higher $Cd$ values ($Cd>2$) in the epicentral region are very helpful for authorities for the purpose of responding to damage mitigation.

Rupture directivity of earthquakes could amplify ground shaking and cause serious earthquake hazards. Its timely information is therefore of great importance for early shaking alerts and emergency responses. To this end, we test the feasibility of using near‐field (<25 km) ground motion data from a dense low‐cost seismic network in Taiwan to constrain directivity information and provide warning for far‐field areas. The method is simple and robust, based on the real‐time shaking map interpolation and directional attenuation regression analysis. Applications to 16 moderate‐ to large‐magnitude earthquakes in Taiwan and California show that the directivity can be stably obtained within 17 s and agrees well with previous studies when available. An indicator of the strength of directivity amplification is also defined and reveals a prevalence of strong directivity effect for M_L ≥ 6.0 earthquakes in Taiwan. Such near‐real‐time directivity information can therefore be useful in earthquake early warning systems for providing more accurate ground shaking alerts.

Following the recent establishment of a high-density seismic network equipped with low-cost micro-electro-mechanical system (MEMS) P-wave-alert-device (P-Alert) by the earthquake early warning (EEW) research group at the National Taiwan University, a large quantity of strong-motion records from moderate-magnitude earthquakes (M_L > 6) around Taiwan has been accumulated. Using a data preprocessing scheme to recover the dynamic average embedded within the P-Alert data, we adopted an automatic baseline correction approach for the P-Alert accelerograms to determine the coseismic deformation (Cd). Comparisons between the Cd values determined using global positioning system (GPS) data, strong-motion records from the P-Alert network, and data from the Taiwan Strong Motion Instrumentation Program (TSMIP) demonstrates that the near-real-time determination of Cd values (>2 cm), which provide crucial information for seismic hazard mitigation, is possible using records from low-cost MEMS accelerometers.