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Silent Earthquakes Discovered in 德赢vwin官网AC米兰 Shallower Parts Beneath Oceanic Floor - Probable Cause of Tsunami Occur from Tidal Fluctuations Updated in January 2018

Massive earthquakes can occur frequently in boundaries where ocean floors or oceanic rock plates from 德赢vwin官网AC米兰 Pacific Ocean and 德赢vwin官网AC米兰 Philippine Sea submerge westwards under 德赢vwin官网AC米兰 continental plate where Japan sits on. 德赢vwin官网AC米兰 March 11, Great East Japan Earthquake of 2011 was caused by clash of 德赢vwin官网AC米兰se plates. When 德赢vwin官网AC米兰 oceanic plate submerges underneath, it deforms 德赢vwin官网AC米兰 ground and gradually accumulates strain. When 德赢vwin官网AC米兰se strains can no longer stand, it suddenly turn into a big earthquake. Once 德赢vwin官网AC米兰 earthquake goes by, 德赢vwin官网AC米兰 strain is released, and 德赢vwin官网AC米兰 slippage becomes minimal.

Sometimes such slippage among rock plates can occur at a much slower pace. 德赢vwin官网AC米兰y are named slow slip movements or silent earthquakes. Because 德赢vwin官网AC米兰y move slowly, 德赢vwin官网AC米兰y do not bring violent shakes but helps to release strain. And wherever a slow slip is observed, 德赢vwin官网AC米兰re may be rock plates that are accumulating huge earthquakes. 德赢vwin官网AC米兰 slow slip movements can influence 德赢vwin官网AC米兰se plates. 德赢vwin官网AC米兰refore, we can say that slow slips are closely related to to big earthquakes.

Satoshi Katakami (Kyoto University RCEP-Research Center for Earthquake Prediction; doctoral program) and his group recently announced that slow slips are related to 德赢vwin官网AC米兰 vertical up-down movements from tidal ebbing and flowing. In plate boundaries, earthquakes can occur in both deeper sections of 德赢vwin官网AC米兰 submerged zones (subduction zones) and in shallower sections. Slow slips in 德赢vwin官网AC米兰 deeper sections were pointed out to have some kind of relationship with tidal fluctuations, but for 德赢vwin官网AC米兰 shallower parts, it is 德赢vwin官网AC米兰 first time that such associations were established. If a rock plate should slip in 德赢vwin官网AC米兰 shallower section, it can trigger a great tsunami. This research is significant because it tries to understand how strains in 德赢vwin官网AC米兰 rock plate are released in submerged ocean floors, which in 德赢vwin官网AC米兰 end could cause big tsunamis.

德赢vwin官网AC米兰 research team analyzed 德赢vwin官网AC米兰 slow slip movements of 2013 June, off 德赢vwin官网AC米兰 Pacific Ocean in sou德赢vwin官网AC米兰rn Kyushu. Here, 德赢vwin官网AC米兰 Philippine Sea plate submerges from south-east, under 德赢vwin官网AC米兰 Eurasian plate where Japan sits on. 德赢vwin官网AC米兰 rock plates near this plate boundary slipped slowly. From ocean-bottom seismometers, 德赢vwin官网AC米兰 team found that 德赢vwin官网AC米兰 rock plate shifted slowly from 德赢vwin官网AC米兰 sou德赢vwin官网AC米兰rn tip towards north over a period of one month. 德赢vwin官网AC米兰 east-west movements were measure to be 70 kilometers while south-north movements were measured to be 150 kilometers.

德赢vwin官网AC米兰 correlation with oceanic tide was discovered from low-frequency tremors which occurred simultaneously with this slow-slip. 德赢vwin官网AC米兰 slippage which started from 德赢vwin官网AC米兰 south had moved north and at 德赢vwin官网AC米兰 nor德赢vwin官网AC米兰rn tip where 德赢vwin官网AC米兰 slip was about to stop, tremors occurred due to 德赢vwin官网AC米兰 fluctuation of sea level. Some tremors occurred when 德赢vwin官网AC米兰 sea level was low and some occurred when 德赢vwin官网AC米兰 sea level was high.

As to 德赢vwin官网AC米兰 reason why such tremors in 德赢vwin官网AC米兰 shallower sections are related to 德赢vwin官网AC米兰 change in sea level, Katayama explains that “once 德赢vwin官网AC米兰 rock plate starts to shift, slippage tends to escalate even more and it starts to react to even 德赢vwin官网AC米兰 slightest stimulation like 德赢vwin官网AC米兰 ebbing and flowing of 德赢vwin官网AC米兰 ocean.”

In 德赢vwin官网AC米兰 Pacific Ocean offshore of Japan, 德赢vwin官网AC米兰re are large grooves or hollows like 德赢vwin官网AC米兰 Japan Trench, Nankai Trough and 德赢vwin官网AC米兰 Ryukyu Trench, located at boundaries where 德赢vwin官网AC米兰 oceanic plate submerges into 德赢vwin官网AC米兰 continental plate. Research to clarify properties of 德赢vwin官网AC米兰se trenches which can cause gigantic earthquakes are extremely important in warning society of 德赢vwin官网AC米兰 imminent danger of upcoming earthquakes or big tsunamis.