Evidence for diurnal periodicity of earthquakes from midnight to daybreak  

作　　者：Jinlai Hao Jinhai Zhang Zhenxing Yao 

机构地区：[1]Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences

出　　处：《National Science Review》2019年第5期1016-1023,共8页国家科学评论（英文版）

基　　金：support from the Strategic Priority Research Program of Chinese Academy of Sciences(XDA17010404,XDA15011700);the National Major Project of China(2017ZX05008-007);the National Natural Science Foundation of China(41574058)for support;the Foundation for Excellent Member of the Youth Innovation Promotion Association,Chinese Academy of Sciences(2016)

摘　　要：Previously,inadequate earthquake catalogs and the lack of method made it challenging,if not impossible,to determine the dominant period of earthquake occurrence.With the advent of densely distributed seismic stations in Japan since 2002,410642 M1.0+earthquakes have been cataloged under the mainland within30-km depth,which provide a superb dataset to identify the periodicity of earthquakes.We processed this catalog using time-frequency analyses and daily stacking,which are powerful in extracting weak periodical signal from strong random noises.We concentrated on the time sector from 0:00 to 6:00(i.e.from midnight to daybreak),which is a reliable time window for much higher detectability of weak earthquakes,since it has the lowest affects from cultural noises.We successfully observed two apparent periodicities of12-and 24-hour,which are much smaller than the fortnightly periodicity presented previously in the literature.Synthetic earth tides,after intentionally ignoring the contribution from the Moon,present similar dominant periods as the earthquakes.This may indicate that the dominant period of earthquakes is statistically associated with the Sun rather than the Moon.The daily stacking number of earthquakes using a15-minute or 1-hour interval shows a peak around 1:30,rather than usually expected 3:00 to 4:00.In addition,bigger earthquakes show more evident variations in the stacking results,and the trend is very consistent for various lower limits of earthquake magnitude from M1.0 to M4.0.These discoveries settled the disputes on the existence of the periodicity of earthquakes since 1886 and may open a window to unravel the mystery of earthquakes.Previously, inadequate earthquake catalogs and the lack of method made it challenging, if not impossible, to determine the dominant period of earthquake occurrence.With the advent of densely distributed seismic stations in Japan since 2002, 410 642 M1.0+ earthquakes have been cataloged under the mainland within30-km depth, which provide a superb dataset to identify the periodicity of earthquakes.We processed this catalog using time-frequency analyses and daily stacking, which are powerful in extracting weak periodical signal from strong random noises.We concentrated on the time sector from 0:00 to 6:00(i.e.from midnight to daybreak), which is a reliable time window for much higher detectability of weak earthquakes,since it has the lowest affects from cultural noises.We successfully observed two apparent periodicities of12-and 24-hour, which are much smaller than the fortnightly periodicity presented previously in the literature.Synthetic earth tides, after intentionally ignoring the contribution from the Moon, present similar dominant periods as the earthquakes.This may indicate that the dominant period of earthquakes is statistically associated with the Sun rather than the Moon.The daily stacking number of earthquakes using a15-minute or 1-hour interval shows a peak around 1:30, rather than usually expected 3:00 to 4:00.In addition, bigger earthquakes show more evident variations in the stacking results, and the trend is very consistent for various lower limits of earthquake magnitude from M1.0 to M4.0.These discoveries settled the disputes on the existence of the periodicity of earthquakes since 1886 and may open a window to unravel the mystery of earthquakes.

关 键 词：PERIODICITY of EARTHQUAKES TIME-FREQUENCY analyses ocean TIDE earth TIDE Local Mean Time 

分 类 号：P315[天文地球—地震学]