session6: overvew,purpose,andscopeofoperaonal earthquake ... · 1. background: large earthquakes in...

Earthquake Sta,s,cs and Probalis,c Forecas,ng for the Southern Kanto A;er the 2011 Mw9.0 Tohoku-‐Oki Earthquake

N. Hirata1, K. Z. Nanjo2, S. Sakai1, A. Kato1, , H. Tsuruoka1 1ERI, 2 NIED

SCEC CSEP Workshop: Final Evalua,on of the Regional Earthquake Likelihood Models (RELM) Experiment and the

Future of Earthquake Forecas,ng Session 6: Overvew, Purpose, and Scope of Opera6onal

Earthquake Forecas6ng (OEF)

THURSDAY, JUNE 7, 2012, 11:00

2012/6/7 SCEC CSEP Workshop 1

１. Background: Large earthquakes in Kanto

●　Ｍ８ class ●　Ｍ７ class ●　Ｍ６ class

About 220 years

M

Genroku-‐Kanto EQ (1703)

Taisyo-‐Kanto EQ (1923)

2012/6/7 2 SCEC CSEP Workshop


Probability based on the past 5 events in 120 years

• 1894/06/20 M7.0 • 1895/01/18 M7.2 • 1921/12/08 M7.0 • 1922/04/26 M6.8 • 1987/12/17 M6.7 Average interval: 23.8 yrs à Poisson assump,on

70

Insert reference

2. Earthquake frequency and probability 　

•  In southern Kanto, we have a probability of 70% in 30 years for a M7-‐class earthquake

•  The probability is very high. A probability of being injured by a traffic accident in 30 years is 24%, houses being fired is 1.9%

•  We have more frequent small earthquakes due to the 2011 Tohoku-‐oki event. It is the case in southern Kanto.

•  The M7-‐class event has more chance to occur. –  The worst case was that there was 70 % chance in 4 years. –  But the number depends on many assump,ons and can be changes if we use different amputa,ons. However, the base line is that 70% in 30 years.

–  The probability is decreasing and eventually 70 % in 30 years.


●Probability determined by small-‐to-‐middle size events (as of August 1, 2011)

5

0 20 40 60 80 100

0 10 20 30 40 50 year

％

Probability by Earthquake Research Commihee : average in 100 years

●

●

● ●

●

●

It depends on sampled events, assump6ons on parameters

2012/6/7 SCEC CSEP Workshop


1994 east off Hokkaido （M8.2)

1952 Off Tokachi（M8.2) 1933Sanriku Tsunami （M8.1)

Elapse ,me (day)

A;er shocks of M5.0 or more

400

200

0 0

2011 Tohoku earthquake（M9.0)

2. Prominent a;ershock ac,vity

M7.0 以上 6回 M6.0 以上 98回 M5.0 以上 607回（2012/3/23 08:00 現在）気象庁資料による

0 100 200 300 hhp://www.seisvol.kishou.go.jp/eq/2011_03_11_tohoku/a;ershock/

600

3. Triggered Seismicity • Catalogue : JMA

•  Depth : 0 - 20 km •  M : 0.5 or more

• Reference period： •  2003/03/10 00:00 ～

•  2011/03/11 14:36 (約8年間) • Studied perido：

•  2011/03/11 14:50 ～ •  03/30 23:59

• Change in seismicity:β-value •  [Mahhews & Reasenberg, 1988] •  |β|>2： significant

Active：１．Northern Akita ２．Southern Akita ３．Tajiri lake ４．Yamagata ５．Aizu ６．Off Akita ７．Iwaki ８．Nrthern Ibaraki ９．Northern Kagano １０．Eastern Shzuoka

Activated：Volcanic area

Quiescent：Aftershocks of Inland EQ


1 2

3 4 5

6

7 8

10

8

Change in seismicity in the Greater Tokyo（M≧3.0）

Before A;er

47event 343 event


(0.3 events / day) (2 events / day)

About 7 6mes

Sakai et al. (2011)

Upper boundary of the Philippine Sea Plate Upper boundary of the Pacific Plate

Seismicity increase on plate boundaries

Upper boundary of the Pacific Plate Color bar shows how many ,mes seismicity increases

Depth: 50km Depth: 70km


4. Gutenberg-‐Richter law LogN=a-‐bM

Converted from P=70% for M6.7-‐7.2 events (ERC, 2004)

JMA catalog Downloaded On 25 Jan. 2012

Missing


5. Omori-‐Utsu law　 λ=K/(t+c)p

•  Applica,on of the ETAS model also shows p=0.5-‐0.6 for several cutoffs M=3.0-‐3.5.

JMA catalog Downloaded On 25 Jan. 2012


6. Probability for M6.7-‐7.2 earthquakes

•  Earthquake Research Commihee (1998) –  Combine GR & OU rela,ons àEx

–  Ex à Prob

•  Star,ng ,me of evalua,on dura,ons –  25 Jan. 2011

•  Assump,on –  Applicable to southern Kanto, outside of the rupture region

p=0.45+-‐0.09

See Fig (a)

Pre-‐quake level

Pre-‐quake level


Probability determined by small-‐to-‐middle size events (as of Jan. 25, 2012)


Period（yrs）

Probability (M6.7-7.2)

Earthquake committee

M≥3（present

study）

M≥4 (present study)

5 - 25-60% 20-60%

10 ca 30% 30-80% 30-80% 20 ca 60% 60-90% 60-90% 30 ca 70% 70-90% 70-90% 40 ca 80% 80-90% 80-90% 50 ca 90% > 90% > 90%

7. Rate-‐and-‐state dependent fric,on law

•  At t=0 – Stress step (earthquake)

•  At t>0 – Constant stress – Non-‐constant stress (fault creep) •  Increase • Decrease – Fast – Slow

Dieterich (1994)

Slow stress decrease

Fast stress decrease

Stress increase


Summary – Ac,vated seismicity a;er the Tohoku-‐Oki eq. follow •  Gutenberg-‐Richter law •  Omori-‐Utsu law with low decay rates (p=0.4-‐0.6)

–  Increased probability for M7-‐class events decays with ,me approaching to the pre-‐quake level •  High uncertainty in probability

–  Other uncertain components may cause further increase of uncertainty (study region, data selec,on, parameter es,ma,on, target period)

– According to rate-‐and-‐state dependent fric,on law •  A;erslip (fault creep) to slowly relax stress step on the plate boundaries –  Poten,al of stress redistribu,on due to the a;erslip to the surrounding regions

– Monitoring on-‐fault seismicity as well as off-‐fault seismicity 2012/6/7 SCEC CSEP Workshop 15


Omori-‐Utsu law λ=K/(t+c)p

session6: overvew,purpose,andscopeofoperaonal earthquake ... · 1. background: large earthquakes in...

Documents