Characteristics of Spatiotemporal Variations of Hypocenters and Diversity of Waveforms of Deep Low-frequency Earthquakes in Northeastern Japan (Special Issue: “Possible Effect of Mega Earthquake on Long-term Volcanic Activity” Part 2)
The characteristics of spatiotemporal variations of hypocenters of deep low-frequency earthquakes in northeastern Japan are investigated using the earthquake catalog of the Japan Meteorological Agency. The parameters of DLF10 and DLF90 are defined as depths above which 10 % and 90 % of low-frequency earthquakes occur. The findings are as follows. The thickness of the seismogenic layer of low-frequency earthquakes, the difference between DLF90 and DLF10, varies in space at distances of 100-250 km. Areas with an almost constant seismicity rate have a spacing of 100-150 km. These values are several times larger than the spacing of hot fingers that correlate well with areas of low-velocity anomalies and deep low-frequency earthquakes in the Tohoku district. No clear temporal change in the seismicity of low-frequency earthquakes is found after the 2011 Tohoku-oki earthquake, except in the Zaozan area of central Tohoku. Inactivation of seismicity suggests that the source mechanisms of low-frequency earthquakes are insensitive to a small change in stress at source depths. The diversity of waveforms of low-frequency earthquakes is then examined by grouping events using a waveform cross-correlation. Using a time window immediately after the arrival of the S-wave, it is found that closely located earthquakes tend to form a single group, which suggests a similarity of focal mechanisms among grouped events. However, the value of cross-correlation is much lower than that of ordinary high-frequency events, and many events are not grouped even if the location is near grouped events. This suggests that focal mechanisms and/or source processes of low-frequency earthquakes differ from event to event. When using time windows in later phases, the correlation takes a lower value, and grouped events are not co-located. Thus, later phases have less information on the source mechanism than the S-wave.
雑誌名
東京大学地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo
巻
92
号
2-4
ページ
63 - 80
発行年
2017
ISSN
00408972
書誌レコードID
AN00162258
著者版フラグ
publisher
出版者
東京大学地震研究所
出版者別名
Earthquake Research Institute, University of Tokyo
東北日本で発生する深部低周波地震の震源の時空間分布の特徴と地震波形の多様性 (特集:「巨大地震と火山活動」Part 2)
IHO922403.pdf
(13.48MB)
