Abstract
The detailed source rupture process of the M 7.3 event (April 16, 2016, 01:25, JST) of the 2016 Kumamoto, Japan, earthquakes was derived from strong-motion waveforms using multiple-time-window linear waveform inversion. Based on the observations of surface ruptures, the spatial distribution of aftershocks, and the geodetic data, a realistic curved fault model was developed for source-process analysis of this event. The seismic moment and maximum slip were estimated as 5.5 × 1019 Nm (M w 7.1) and 3.8 m, respectively. The source model of the M 7.3 event had two significant ruptures. One rupture propagated toward the northeastern shallow region at 4 s after rupture initiation and continued with large slips to approximately 16 s. This rupture caused a large slip region 10–30 km northeast of the hypocenter that reached the caldera of Mt. Aso. Another rupture propagated toward the surface from the hypocenter at 2–6 s and then propagated toward the northeast along the near surface at 6–10 s. A comparison with the result of using a single fault plane model demonstrated that the use of the curved fault model led to improved waveform fit at the stations south of the fault. The source process of the M 6.5 event (April 14, 2016, 21:26, JST) was also estimated. In the source model obtained for the M 6.5 event, the seismic moment was 1.7 × 1018 Nm (M w 6.1), and the rupture with large slips propagated from the hypocenter to the surface along the north-northeast direction at 1–6 s. The results in this study are consistent with observations of the surface ruptures.
Highlights
A series of earthquakes in Kumamoto and Oita Prefectures, central Kyushu, Japan, from April 14, 2016, collectively referred to as the 2016 Kumamoto earthquakes, caused damage by strong ground motions, surface ruptures, and subsequent landslides: more than 100 people were killed, more than 2000 people were injured, and more than 38,000 houses were fully or partially destroyed (FDMA 2016)
We estimate the source process of the first large event (MJMA 6.5; hereafter called the M 6.5 event) that occurred at 21:26 JST on April 14, 2016 (12:26 UTC on April 14, 2016), and caused strong ground motions with maximum seismic intensity of 7 and maximum peak ground acceleration (PGA) over 1000 cm/s2
To analyze the source process of the M 7.3 event, we developed a realistic curved fault model
Summary
A series of earthquakes in Kumamoto and Oita Prefectures, central Kyushu, Japan, from April 14, 2016, collectively referred to as the 2016 Kumamoto earthquakes, caused damage by strong ground motions, surface ruptures, and subsequent landslides: more than 100 people were killed, more than 2000 people were injured, and more than 38,000 houses were fully or partially destroyed (FDMA 2016). The events occurred mainly within the Hinagu and Futagawa fault zones (Fig. 1), which are known to be active faults. The Hinagu fault zone consists of the Takano-Shirohata segment, the Hinagu segment, and the Yatsushirokai segment, while the Futagawa. The main target of this study is the MJMA 7.3 event (hereafter called the M 7.3 event) that occurred at 01:25 JST on April 16, 2016 (16:25 UTC on April 15, 2016). We estimate the source process of the first large event (MJMA 6.5; hereafter called the M 6.5 event) that occurred at 21:26 JST on April 14, 2016 (12:26 UTC on April 14, 2016), and caused strong ground motions with maximum seismic intensity of 7 and maximum PGA over 1000 cm/s2. We discuss the relationship between the fault rupture and the strong ground motions
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