Forecasting Future Earthquakes from Tsunami Deposits and Simulation

Transcription

1 Forecasting Future Earthquakes from Tsunami Deposits and Simulation Kenji Satake Earthquake Research Institute The University of Tokyo

2 Contents 1. Earthquake Recurrence and Forecast 2.Tsunami Deposits and Past Earthquakes 3.Tsunami Simulation and Earthquake Model 4. Forecasting Future Tsunamis

3 Giant Earthquakes since 20 th Century

4 Earthquake Prediction and Forecast Successful Predictions need to specify 1. Where 2. When 3. How large (Magnitude) For when - Short-term prediction: hours to days - Intermediate-term prediction: months to years - Long-term forecast: decades to centuries - Earthquake Early Warning, Tsunami Warning after the occurrence

5 Earthquake Probability Earthquake occurrence Periodical Interval between eq. Random in time Poisson Process

6 Probability in next 30 yrs Earthquake Probability Earthquake occurrence Periodical Hazard rate Random in time Poisson Process Time since last earthquake

7 Earthquake Probability Earthquake recurrence Probability = a / (a + b)

8 Earthquake Recurrence along Nankai trough Ishibashi (2002)

9 Probability of Large (M~8) Earthquakes between 2003 and 2032 ~40% ~30% 1918 Mt Mw % 1893 M Mw 8.2 ~60% 1894 Mt M Mw M 8.2 HQ Earthq Res Prom, March 2003

10 Strong-motion Prediction (Probabilities in the next 30 yrs) Intensity 6- actually recorded Probability (%) Probability (%) HQ Earthq Res Prom, March 2003

11 Long-term Forecast Japanese Govt. announcement Next 30 years Miyagi-oki 99 % Nankai Trough % ISTL (inland fault) 14% most active faults < 5% Probability of Kobe eq. in 1995: % Max probability for 30 yrs 1/100 yr event ~ 90 % 1/1000 yr event ~ 20 % 1/10000 yr event ~ 2 %

12 Long-term Forecast Japanese Govt. announcement Next 30 years Miyagi-oki 99 % Nankai Trough % ISTL (inland fault) 14% most active faults < 5% Probability of Kobe eq. in 1995: % Max probability for 30 yrs 1/100 yr event ~ 90 % 1/1000 yr event ~ 20 % 1/10000 yr event ~ 2 %

13 Long-term Forecast of Large Earthquakes Past earthquakes (1) Characteristic size (Magnitude) (2) Recurrence interval (3) Date of most recent event Typical recurrence interval Interplate earthquakes: ~ 10 2 yrs historical records Inland eq. on active faults: ~ 10 3 yrs trenching studies Offshore earthquakes with longer interval: 10 2 ~ 10 3 yrs tsunami deposits

14 Kanto Earthquakes 1703 Genroku Kanto Eq Taisho Kanto Eq. (M 7.8) (M 8.2) After Hatori (1975)

15 Tsunami Deposits Past 300 yrs After 1050 yrs The age of AD is obtained from the inner bay sediments immediately below the T3 unit.

16 Contents 1. Earthquake Recurrence and Forecast 2.Tsunami Deposits and Past Earthquakes 3.Tsunami Simulation and Earthquake Model 4. Forecasting Future Tsunamis

17 Regions Discussed in This Talk This is removed because of copyrighted material. Muller et al 1997

18 Cascadia Subduction Zone Coastal paleoseismology 1990 s Photo by Brian Atwater

19 1960 Chilean Earthquake Largest eq. in 20 th century (Mw 9.5) The tsunami arrived Hawaii 15 hrs; 60 casualties Japan 23 hrs; 150 casualties Int l Tsunami Warning System Ofunato, Japan Onagawa, Japan

20 Past Earthquakes in Chile AD1960 AD1575 ~AD1300 ~AD1100 This is removed because of copyrighted material. This is removed because of copyrighted material. Giant (M~9.5) earthquakes ~300 yr interval NOT ~ 100 yr as inferred from historic data Cisternas et al. (2005 Nature)

21 Paleoseismology in Sumatra-Andaman Paleoseismological studies (corals, tsunami deposits, marine terrace, buried peat) indicate that earthquakes similar to the 2004 earthquake occurred a few hundred to a thousand yrs ago. Myanmar Andaman Thailand Tamil Nadu Sumatra

22 Paleotsunami Studies in Thailand 2004 tsunami ~AD1400 tsunami This is removed because of copyrighted material. Kruawn Jankaew et al.(2008)

23 Contents 1. Earthquake Recurrence and Forecast 2.Tsunami Deposits and Past Earthquakes 3.Tsunami Simulation and Earthquake Model 4. Forecasting Future Tsunamis

24 Forward and Inverse Problems

25 Observed Tsunami in Japan in 1700 Fault length: 1,100 km, slip: 14 m, Mo 4.6 x Nm (Mw 9.0) similar to the 2004 Sumatra-Andaman earthquake Average recurrence interval: ~500 years

26 Earthquakes along Kuril Trench 2003 M 8.0

27 Earthquake Recurrence along Kuril Trench Kiritappu Marsh

28 Kiritappu, Hokkaido 1952 tsunami

29 Kiritappu, Hokkaido 1952 tsunami 17 th century tsunami deposits

30 Multi-segment Earthquake in 17 th century Nanayama et al. (2003, Nature)

31 Contents 1. Earthquake Recurrence and Forecast 2.Tsunami Deposits and Past Earthquakes 3.Tsunami Simulation and Earthquake Model 4. Forecasting Future Tsunamis

32 Probabilistic Estimates This is removed because of copyrighted material. Rikitake and Aida (1988)

33 Probabilistic Tsunami Hazard Analysis Aleatory uncertainty (Max ~ 7 m in the past 400 years) -Due to the unpredictable random nature -A hazard curve by integration over the aleatory uncertainties. Epistemic uncertainty -Due to incomplete knowledge and data -A large number of hazard curves by logictrees representing epistemic uncertainty. Annaka et al. 2007

34 Example of PTHA Hazard curve Max wave heights in 1000 yrs This is removed because of copyrighted material. Burbidge et al. (2008)

35 Conclusions 1. Future earthquakes (location, time and size) can be forecasted from past earthquakes. Probability can be calculated from the recurrence history. 2. For earthquakes with long recurrence intervals, geological data such as tsunami deposits are useful. Gigantic earthquakes repeat at 300 to 500 years interval in the world s subduction zones. 3. Earthquake source, or fault model can be studied by an inverse approach, e.g., a comparison of tsunami deposit distribution and simulated inundation area. 4. Future tsunami hazard can be estimated by a probabilistic approach.