Characteristics of Shallow Low‐Frequency Earthquakes off the Kii Peninsula, Japan, in 2004 Revealed by Ocean Bottom Seismometers

The characteristics of shallow low‐frequency earthquakes (LFEs) are related to stress changes on the shallow plate boundary, which are important for understanding the megathrust earthquake cycle. The 5 September 2004 off the Kii Peninsula earthquakes (MJMA = 7.1, 7.4) occurred near the Nankai trough...

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Bibliographic Details
Published in:Geophysical research letters 2019-12, Vol.46 (23), p.13737-13745
Main Authors: Tamaribuchi, Koji, Kobayashi, Akio, Nishimiya, Takahito, Hirose, Fuyuki, Annoura, Satoshi
Format: Article
Language:English
Subjects:
Earthquakes
Nankai Trough
Ocean bottom
Ocean bottom seismometers
Ocean floor
Oceans
Plate boundaries
Seismic activity
Seismographs
Seismometers
shallow low‐frequency earthquake
slow earthquake
Subduction
Subduction (geology)
Subduction zones
tidal response
Tides
Very Low Frequencies
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Summary:The characteristics of shallow low‐frequency earthquakes (LFEs) are related to stress changes on the shallow plate boundary, which are important for understanding the megathrust earthquake cycle. The 5 September 2004 off the Kii Peninsula earthquakes (MJMA = 7.1, 7.4) occurred near the Nankai trough subduction zone, off southwest Japan. Ocean bottom seismometer observations from 22 September to 30 November 2004 detected many shallow LFEs among the ordinary aftershocks. During the observation period, the frequency of shallow LFEs steadily decayed with the exception of episodic activities, which were very sensitive to stress changes caused by tides and the 23 October 2004 Niigata earthquake (MJMA = 6.8). We also confirmed correlations between shallow LFEs and shallow very low frequency earthquakes, which suggest that these slow events represent the same slip phenomenon. These findings will contribute to clarifying the impact of LFEs on megathrust earthquakes. Key Points We detected shallow low‐frequency earthquakes (LFEs) after the 2004 off Kii Peninsula earthquakes by using ocean bottom seismometers Some shallow LFEs are associated with very low frequency earthquakes, which suggests both slow earthquakes represent the same phenomenon Episodic shallow LFEs are stochastic yet sensitive to stress changes caused by both the 2004 Niigata earthquake and tidal effects
ISSN:0094-8276
1944-8007
DOI:10.1029/2019GL085158