Abstract
The 2016 Kumamoto earthquake (Kumamoto earthquake sequence) is an extremely high-seismicity event that has been occurring across Kumamoto and Oita Prefectures in Japan since April 14, 2016 (JST). The earthquake early warning system of the Japan Meteorological Agency (JMA) issued warnings for 19 events in the Kumamoto earthquake sequence from April 14 to 19, under some of the heaviest loading conditions since the system began operating in 2007. We analyzed the system performance for cases where a warning was issued and/or strong motion was actually observed. The results indicated that the system exhibited remarkable performance, especially for the most destructive earthquakes in the Kumamoto earthquake sequence. In addition, the system did not miss or seriously under-predict strong motion of any large earthquake from April 14 to 30. However, in four cases, the system issued over-predicted warnings due to the simultaneous occurrence of small earthquakes within a short distance, which implies a fundamental obstacle in trigger-data classifications based solely on arrival time. We also performed simulations using the integrated particle filter (IPF) and propagation of local undamped motion (PLUM) methods, which JMA plans to implement to address over-prediction for multiple simultaneous earthquakes and under-prediction for massive earthquakes with large rupture zones. The simulation results of the IPF method indicated that the IPF method is highly effective at minimizing over-prediction even for multiple simultaneous earthquakes within a short distance, since it adopts a trigger-data classification using velocity amplitude and hypocenter determinations using not-yet-arrived data. The simulation results of the PLUM method demonstrated that the PLUM method is capable of issuing warnings for destructive inland earthquakes more rapidly than the current system owing to the use of additional seismometers that can only be incorporated by this method.
Highlights
The 2016 Kumamoto earthquake (Kumamoto earthquake sequence) consists of the collective earthquake activity that has continuously occurred in Kumamoto Prefecture and its surrounding areas in Japan since April 14, 2016, at 21:26 (JST) (e.g., Japan Meteorological Agency (JMA) 2016)
The simulation results of the propagation of local undamped motion (PLUM) method demonstrated that the PLUM method is capable of issuing warnings for destructive inland earthquakes more rapidly than the current system owing to the use of additional seismometers that can only be incorporated by this method
The integrated particle filter (IPF) and PLUM method simulations indicate that these new methods are superior to the current method and that introducing these methods would further improve the performance of the JMA earthquake early warning (EEW) system for the Kumamoto earthquake sequence, the current method itself exhibited excellent performance
Summary
The 2016 Kumamoto earthquake (Kumamoto earthquake sequence) consists of the collective earthquake activity that has continuously occurred in Kumamoto Prefecture and its surrounding areas in Japan since April 14, 2016, at 21:26 (JST) (e.g., JMA 2016). This activity has caused damages in the form of building collapses and landslides and has taken a toll of 49 lives as of June 16, 2016 (Cabinet Office, Government of Japan 2016). The Japan Meteorological Agency (JMA) reported that JMA seismic intensities of 7, which is the maximum on the JMA scale (JMA 1996), were observed during the M6.5 and M7.3 earthquakes that occurred on April 14 and 16, respectively (JMA 2016). On April 16 at 01:25, a M7.3 earthquake occurred near the epicenter of the first earthquake, causing extremely high seismicity within an approximately 120-km range across Kumamoto and Oita Prefectures
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