Method for prediction of off Ibaraki M7 characteristic earthquakes based o

n seismicity change

Shozo Matsumura

(NIED)

Recent Characteristic Earthquakes off Ibaraki Prefecture

A: １９８２M7.0

B: 2008M7.0

Seamount discovered by Mochizuki et al. (2008)

27.4y 19.9y 22.4y 16.8y 25.8y

a

cd1

d2

A Bb

？

Ｃ2027 - 2035

One Century History of Characteristic Earthquakes Sequence off Ibaraki Prefecture

Micro-seismicity observed by NIED for 30 years

Event AEvent B

Micro-earthquake Density Maps before event B

Ratio of Density Maps

2007.7.8. – 2007.12.7. 2007.12.8. – 2008.5.7.

Before event B

Correlation coefficient

r(A:B) = 0.577

Degree of freedom

n = 22

Significance level

e = 0.16 %

Before event

Before event

- 0.5

- 0.4

- 0.3

- 0.2

- 0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1980 1985 1995 2000 20051990

A: 1982.7.23. B: 2008.5.8.

Cor

rela

tion

coef

ficie

nt (

r)

Ｐａｃｉｆｉｃ　Ｐｌａｔｅ

asperities

The point of this method is existence of “Preparing stage”

• Distribution of inhomogeneous asperities

• Quasi-static slipping

• Stress redistribution

- 0.5- 0.4

- 0.3- 0.2

- 0.10

0.10.2

0.30.4

0.50.6

0.70.8

0.91

B: 2008.5.8.

Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun

2007 2008

Cor

rela

tion

coef

ficie

nt (

r)

3.5 months before

4 days before

r0 = 0.53

2008 2009

- 0.4

- 0.3

- 0.2

- 0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

B: 2008.5.8.

Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb

Cor

rela

tion

coef

ficie

nt (

r)

rA

rB