Tide Triggering Of Earthquakes And Three-dimensional Thermal Structure Of Subduction Zone

This study examines the possibility of tidal triggering in Indonesia,Japan,and Shanghai,China.Two methods,the Schuster spectrum and KORRECT(correlation with a rectangular pulse)methods,were used to explore the periodicities of the aftershock sequence.Firstly,through the Schuster and Schuster spectrum,we extracted main periodic components of the seismic activity in each research area and further determined the pulse width of the seismic sequence;then,we used the KORRECT method to verify and confirm these periodicities.The seismic activity of the subduction zone not only has correlation with the tides,but the thermal structure of the area.We use a 3-D time dependent thermal dynamical numerical model.This model uses a combination of the new plate geometry and the phase diagram of the water-bearing subducting plate minerals.We can obtain the temperature and water content distribution in most areas of the Sumatra plate and study the thermal structure of the Sumatra area and the movement mechanism of the subduction plate.1.By studying the earthquake activity in Japan from March 11,2011 to March 12,2012,we found that the aftershocks were generally triggered by semidiurnal tides and sometimes triggered by diurnal tides.On this basis,this paper also analyzes the effect of magnitude and depth on the correlation between tides and earthquakes.Seismic activity in Japan shows that small magnitudes and shallow earthquakes were triggered by diurnal tides,large magnitudes and deep earthquakes were triggered by semidiurnal tides.2.By analyzing the earthquake activity in Shanghai and surrounding areas from January 1,1970 to July 21,2018,we found that the overall earthquakes of Shanghai and surrounding areas was not significantly triggered by tides.Two earthquake swarms were also analyzed: Changshu earthquake swarm in 2001 was affected by semidiurnal and diurnal tides,and the South Yellow Sea earthquake catalogue in 1984 was not triggered by the tide.The results show that the large-scale tidal correlation analysis of Shanghai and surrounding areas can not accurately reflect the seismicity of local areas.3.Through studying the aftershocks of Mw9.1(26 December,2004),Mw8.6(28 March,2005),Mw8.4(12 September,2007),and Mw8.6(11 April,2012)in Indonesia,we found that the p-value of Schuster spectrum in the aftershocks of Mw8.6(28 March,2005)and Mw8.4(12 September,2007)is less than 5%.It indicates that these two major earthquakes may triggered by the tides.4.This paper explores the relationship between the seismic activity of the Sumatra subduction zone and the underground thermal structure by constructing a 3-D thermal dynamic model.We first studied the potential relationship between the temperature distributions and seismic activity of the Sumatran plate.Most of the maritime and coastal M>6 earthquakes occurred the boundary of the coupled plate,and the temperature was 300 ° C.Although the depths are different(4km,8km,16km),most earthquakes occurred in the region of 300 ° C to 500 ° C.Then,we analyzed data on the water state of the falling Sumatra plate,and the results showed that the earthquake was located at a depth near the high-water content transition boundary from calcite(5.4 wt%)to amphibole(1.5-3 wt%).At depths of 8 km and 16 km,some earthquakes occurred in areas where the dehydration rate was less than-0.1wt%/km,which corresponded to areas with temperature greater than 500 ° C,which may be caused by volcanoes.