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

Transcription

1 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 Earthquake Sta,s,cs and Probalis,c Forecas,ng for the Southern Kanto A;er the 2011 Mw9.0 Tohoku- Oki Earthquake N. Hirata 1, K. Z. Nanjo 2, S. Sakai 1, A. Kato 1,, H. Tsuruoka 1 1 ERI, 2 NIED 2012/6/7 SCEC CSEP Workshop 1

2 1. Background: Large earthquakes in Kanto M8 class M7 class M6 class Genroku- Kanto EQ (1703) Taisyo- Kanto EQ (1923) M About 220 years 2012/6/7 SCEC CSEP Workshop 2

3 Probability based on the past 5 events in 120 years 1894/06/20 M /01/18 M /12/08 M /04/26 M /12/17 M6.7 Average interval: 23.8 yrs à Poisson assump,on /6/7 SCEC CSEP Workshop 3 Insert reference

4 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. 2012/6/7 SCEC CSEP Workshop 4

5 Probability determined by small- to- middle size events (as of August 1, 2011) It depends on sampled events, assump6ons on parameters % Probability by Earthquake Research Commihee : average in 100 years 2012/6/7 SCEC CSEP Workshop year 5

6 2. Prominent Tohoku earthquake(m9.0) a;ershock ac,vity 400 A;er shocks of M5.0 or more east off Hokkaido (M8.2) 1952 Off Tokachi(M8.2) 1933Sanriku Tsunami (M8.1) hhp:// 2011_03_11_tohoku/a;ershock/ Elapse,me (day) 2012/6/7 SCEC CSEP Workshop 6 0

7 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 /6/7 SCEC CSEP Workshop 7

8 Change in seismicity in the Greater Tokyo(M 3.0) (0.3 events / day) (2 events / day) About 7 6mes 47event 343 event Before A;er 2012/6/7 SCEC CSEP Workshop 8

9 Seismicity increase on plate boundaries Upper boundary of the Philippine Sea Plate Upper boundary of the Pacific Plate Depth: 50km Depth: 70km Sakai et al. (2011) Upper boundary of the Pacific Plate Color bar shows how many,mes seismicity increases 2012/6/7 SCEC CSEP Workshop 9

10 4. Gutenberg- Richter law Missing LogN=a- bm JMA catalog Downloaded On 25 Jan Converted from P=70% for M events (ERC, 2004) 2012/6/7 SCEC CSEP Workshop 10

11 5. Omori- Utsu law λ=k/(t+c) p JMA catalog Downloaded On 25 Jan Applica,on of the ETAS model also shows p= for several cutoffs M= /6/7 SCEC CSEP Workshop 11

12 6. Probability for M earthquakes Earthquake Research Commihee (1998) Combine GR & OU rela,ons à Ex Ex à Prob Star,ng,me of evalua,on dura,ons 25 Jan Assump,on Applicable to southern Kanto, outside of the rupture region See Fig (a) p= Pre- quake level Pre- quake level 2012/6/7 SCEC CSEP Workshop 12

13 Probability determined by small- to- middle size events (as of Jan. 25, 2012) Period(yr s) Probability (M ) M 3(pres ent study) M 4 Earthquake (present committee study) % 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% 2012/6/7 SCEC CSEP Workshop 13

14 7. Rate- and- state dependent fric,on law Dieterich (1994) Stress increase Fast stress decrease Slow stress decrease At t=0 Stress step (earthquake) At t>0 Constant stress Non- constant stress (fault creep) Increase Decrease Fast Slow 2012/6/7 SCEC CSEP Workshop 14

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

16 Omori- Utsu law λ=k/(t+c) p 2012/6/7 SCEC CSEP Workshop 16