Image of Earthquake as Plate Tectonics

Plate Tectonics theory is the most popular one as well known generally. Near Japan, both Pacific plate and Philippine sea plate is going down below continental plate slowly.These plates are carried by mantle convection under them.The going down plates are pulling down continental plate also. But, if the stress becomes over than friction force between these plates, the continental plate will spring back. In the case of the spring back with long time deflection all at once, the huge earthquake should be occurred. On the other hand, if the spring back goes slowly, only small earthquake should be occurred. The phenomenon called as "Slow Slip" is such one. 

Before huge earthquake, micro earthquakes with Slow slip had often been occurred as the sign of huge one. It seems to be similar that the full drawing bow must be allowed only micro moving. As I wrote in Image of Earthquake as cracking phenomenon (2) , there are many data of Details Unknown" with unknown depth in database of Japan Meteorological Agency (JMA). I guessed the reason why the depth are unknown that too shallow epicenters might be not enough to calculate the depths from the time lags between S-wave and P-wave. But, I wonder if some of them might be Slow Slip because of the slow process. 

Image of Earthquake as cracking phenomenon (3)

 As I wrote in (2), there are cracking origins of Earthquakes near the plate edges in deep area.In the deeper area of earth's crust, the higher pressure there is. So, stress of plates should go towards to shallower area. In the other hand, earthquake energy  is distributed from deeper area to shallower area. It seems to be similar with the domino from a large piece to smaller pieces.In the ends of domino, the falling domino makes stopped by the bigger pieces. Except the falling down near ground surface, most of energy should be stocked as all the accumulation including past other stacked pieces. Only it is open end, and others in deeper area are fixed end by neighborhood crust.

The loss energy by shaking near ground surface is very small because of far smaller mass than the Magnitude except tsunami with huge mass of sea water. This may be the reason why most of the biggest earthquakes wouldn't follow with Gutenberg-Richter law. The loss energy by friction between sinking continental plates around the edge may be small ratio of the total Magnitude energy. Its dynamic friction coefficient in slipping phenomenon is very small in general (If it were large, the phenomenon should be called not "slipping", but "slow slipping" without large magnitude ).  

Image of Earthquake as cracking phenomenon (2)

One big earthquake induces many other earthquakes around it.Sometimes, it induces bigger ones.The dynamics seems to be similar with domino's one.Big domino piece can push down the same or smaller pieces.Sometimes, high speed pieces can push down even bigger one.If not pushed down,tilted piece can stock the kinetic energy as potential energy.It seems to be similar with earthquake dynamics.

In my understanding, stress comes from deep Earth crust area.In deeper area, there is higher pressure.So, every movement of Earth crust should be limited.In fact,most of earthquakes came from deeper area in Japan.Based on the database of Japan Meteorological Agency(JMA), the numbers of earthquakes per the depth are as the graph as below,

(note)The counts are done by me.The earthquakes of 0km includes "Details Unknown" with unknown depth just as my judgment.

The number of class of 0km is more than 100 thousands,and it's almost half of the total number.On the other hand, the numbers of deeper than 100km is only less than 2%. This result may reflect the fact that deeper earthquakes are primordial than the shallower ones.

The 2 figures shows the results selected with 100km deeper from JMA database directly as below,

(Condition 1) Results : N=355

Period : 1/1/1919-1/6/2025

Magnitude : M6.0-M9.9

Depth : 100km-999km

 

(Condition 2)Results : N=855

Period : 1/1/1919-1/6/2025

Magnitude : M0.0-M4.0

Depth : 100km-999km

Even though the number of earthquakes with M0.0-M4.0 (condition 2) are 2 times more than with M6.0-M9.9 (condition 1), the distribution on the map are less than.As I described above, the every movement are limited, less magnitude should mean near the origins of cracking. The curve of epicenters shows the plate edge.In M6.0-M9.9 (condition 1), most of epicenters also stay near the plate edge curves.

As you know, continental plate movement is the main cause of earthquakes near the Pacific-rim, and Pacific Ring of Fire exists along it.

 

    

Image of Earthquake as cracking phenomenon (1)

Earthquake is usually described with the data set of its start time, epicenter, depth, magnitude, and seismic intensity.But,the epicenter/depth is just only a starting point of cracking area or block.Earthquake phenomenon is a cracking/slipping in Earth crust.For example,Great East Japan Earthquake in 2011 had the broken area with almost 450km length and 200km width according with Japan Meteorological Agency's analysis.Earthquake energy is depended on the length of the earthquake fault.Earthquake energy is defined as magnitude scale.Seismic intensity is depended on the distance between the observation point and the epicenter including the depth.So,we need to predict the magnitude before the seismic intensity. 

In general,cracking starts from the weakest points.Folded paper can be cut along with the folding line easily.Light selects the route with the shortest time required according with Fermat's principle.As same as Light, crack selects the route with the minimum work according with principle of least action.This may be the reason why there are some epicenters are on a line and others are not on a line against the complicated geological structure.One of the weakest line in the area should be the earthquake fault as the scar of the ground.The large fault can be the cause of big earthquake.