Takashi Furumura Tatsuhiko Saito ERI. Univ. Tokyo)

Transcription

1 CREST Workshop in 2007 An Integrated Simulation of Seismic Wave and Tsunami Propagation 古村孝志 齊藤竜彦 (東大地震研 Takashi Furumura Tatsuhiko Saito ERI. Univ. Tokyo) Hokkaido -O Izu ough r T kai Nan ch ren T ra wa a s ga Honshu Japa n Tr ench T re l i r Ku nch

2 Characteristics of two Tsunami Events in Kuril Islands 20 km 12 0k m Large M8 earthquakes occurred in Kuril Trench in 2006 and 2007; the former is an interplate event and the other is an intraplate event km 25 0 [Event 1] 2006 Nov. 15 km After Yamanaka (2006; 2007) [Event 2] 2007 Jan Hokkaido Japa n Tr h= m [Event 2] 2007 Jan. 13 Izu -O ara w a ga s h roug T i ka Nan ch Kyushu n Tr e Honshu h e nc ench r il T r u K [Event 1] 2006 Nov. 15 North American Plate Interplate Intraplate

3 JMA Tsunami Alert System Japan Meteorological Agency (JMA) made a number of tsunami simulation and made a tsunami height database for possible events occurring around Japan. Tsunami Database (JMA, 1999-) for 4000 Event * Source Depth (h=0,5,10km..) * Magnitude (M6,7,8, ) 100,000 stories 66 areas 4000 events After JMA

4 Tsunami Alert [1 st Event] 2006 Nov. 15 ( Mj7.9; Mw8.2) JMA Tsunami Alert [2 nd Event] 2007 Jan 13 (Mj8.2; Mw8.2) Large Tsunami (>3m) Tsunami (>2m) Warning (<0.5m) Tsunami (>2m) Tsunami (>2m) 60min 60min Warning (<0.5m) Warning (<0.5m) After JMA (2006;2007)

5 Observed Tsunami Tide gage record shows larger tsunami from the 1 st (2006) event and very weak tsunami from the 2 nd (2007) event. Observation: [Event 1] 2006 Nov. 15 Hachinohe: 53cm Under Estimation Hachinohe: 17cm [Event 2] 2007 Jan. 13 Over Estimation Mistake Alert! After JMA (2007)

6 Tsunami Simulation We made tsunami simulation for using a conventional tsunami generation/propagation model assuming: (1) Deformation of seafloor posed by earthquake is calculated using program of Okada (1985) assuming homogeneous, half-space. (2) Elevation of sealevel (initial tsunami) is assumed to be same as seafloor deformation (3) Propagation of tsunami is calculated by using a linear, long-wave theory. Linear long-wave equation M η = gh t x N η = gh t y Equation of continuity η t M N = x y M N = = η h η h udz vdz η: sea-level fluctuation h: depth of sea floor

7 Tsunami Simulation [Event 1] 2006 Nov. 15 [Event 2] 2007 Jan. 13 A parallel tsunami simulation code (Saito and Furumura, 2007) is used which took 30 min using 16CPU of AMD Opteron.

8 Simulation Results Simulation results are compared with the tide gauge data at offshore Tokachi. It is indicating under and overestimation of tsunami for 1 st and 2 nd events, respectively, similar to JMA alert. Height [mm] [Event 1] 2006 Nov Time [min.] 30cm 20cm BPF: ,000s Tide Gauge. Calculation [Event 2] 2007 Jan. 13 Under Estimation Height [mm] Time [min.] Tide Gauge Data: after JAMSTEC 5cm 20cm Tide Gauge. Calculation Over Estimation

9 Tsunami Simulation Conventional Assumptions: (1) Deformation of seafloor posed by earthquake is evaluated using program of Okada (1985) assuming homogeneous, half-space. (2) Elevation of sealevel (initial condition of tsunami) is assumed to be same as seafloor deformation (3) Propagation of tsunami is simulated by using a linear, long-wave theory. Deep Sea ( m) Heterogeneity Small Fault

10 Accurate Tsunami Simulation ー Challenge 2. FDM Simulation of tsunami generation/propagation -Navier-Stokkes Equations in 3D -Nonlinearity, Viscosity Friction, Dispersion, etc V (x,y,t) or P (x,y,t) Coupling (one way) V (x,y,t) Acretionary wedge Oceanic Crust OceanicMantle After IFREE/JAMSTEC 1. FDM Simulation of Seismic Waves - Equation of Motions in 3D - 3D Heterogeneous structure - Source Slip model

11 FDM Simulation of Seismic Wave /Deformation of Seabed Vertical Deformation of Seafloor posed by earthquake is calculated by FDM using heterogeneous subduction zone structure Equation of Motions: U σ xp σ yp σ zp ρ & p = + + x y z + Constitutive Equations (Stress-Strain) f p σ pq U = λ x x + U y y + U z z δ pq U + μ q p + U q p Accretionary Prism (Vp/Vs=2.2; σ=0.37) Fault Source - Low-angle reverse fault - W=30 km - Rupture Speed, Vr=3km/s 2D FDM Simulation - Staggered-grid,8 th -order - 200km*100km (D=0.25km) - T=100sec - CPU, 10 min (Opteron 2.4GHz) Depth [km] Seabed Oceanic Crust (Vp/Vs= ; σ= ) Oceanic Mantle (Vp/Vs=1.73; σ=0.25) Upper Crust Lower Crust Distance [km] (Vp/Vs= ; σ= )

12 FDM Simulation of Seismic Wave/Deformation Soft sediments in acretionary wedge cause very large deformation of seabed, which leads in large tsunami! (a) Plate Model (b) Plate + Accretionary Wedge Vertical Deformation of Seabed Vertical Deformation of Seabed Seabed Fault Oceanic Crust Upper Crust Lower Crust Accretionary Wedge (Vp/Vs=2.2; σ=0.37) Seabed Fault Oceanic Mantle Snapshots demonstrating wave propagation and deformation caused by earthquake Red: Vertical, Green: Horizontal component and top panel illustrating deformation of seabed

13 3D FDM simulation of seabed deformation (a) Half Space (Vp/Vs=1.73) (b) Plate Model (c) Plate + Accretionary Wedge Seafloor Deformation up down (a) (b) (c) Fault: L=60km, D=4m Crust Fault Oceanic Crust Oceanic Mantle Fault Accretionary Wedge (Vp/Vs=2.0) Half Space Poission Solod (Vp/Vs=1.73) Mantle

14 3D FDM Simulation Summary- Large deformation occurs when earthquake fault cut soft acretionary wedge in the trench, which should causes large tsunami This is considered the cause of unusually large tsunami during shallow subduction zone earthquakes such as 1896 Sanriku M8.5 earthquake (e.g. Fukao, 1979; Satake and Tanioka, 1999, etc. ) and may also be the case for the 1st (2006) event? [Event 1] 2006 Nov. 15 [Event 2] 2007 Jan. 13

15 Effect of Deep Sea The Long-wave, shallow water approximation used in the conventional tsunami simulation does not simulate tsunami propagation in deep ( m) sea? [Event 1] 2006 Nov. 15 [Event 2] 2007 Jan. 13 Sea Depth: m

16 Full 3D FDM Simulation of Tsunami Direct tsunami simulation without approximations - Mass continuity equation (incompressible flow) u = 0 u = (u, v, w) : velocity vector - Navier-Stokes Equation u t + ( u ) u = p + ν Δu g p: pressure, ν: kinematic viscosity coefficient, g: gravity vector - Boundary Conditions Free surface at the top Pressure at the top h h h + u + v = w t x y h (x,y): height of the top surface p ( x, y, z = h) = 0 Rigid boundary at the bottom u n = 0-3D FDM simulation of NS SOLA-SURF in 3D (e.g. Hirt et al. 1975, LLNL)

17 Numerical simulation of tsunami generation: (1) Shallow (1000m) water (a) Large Fault (W/L=20km/40km) Sea level- Top view (b) Small Fault (W/L=10km/5km) Sea level-top view Vertical Deformation of Seafloor h=1000m D0=4m Tr=5s

18 Numerical simulation of tsunami generation: (2) Deep (6000m) water Thick water column cannot push up sea level very efficiently, and so the Initial tsunami height is much lower than the vertical deformation of seabed (a) Large Fault (W/L=20km/40km) Sea level (b) Small Fault (W/L=10km/5km) Sea level Vertical Deformation of Seafloor Deep Sea (h=6000m) D0=5m W=20km, 60km

19 Simulation of tsunami propagation: (2) Deep (6000m) water Attenuation of tsunami height due to dispersion is very significant as propagating in deep sea especially for narrow tsunami (a) Wide Tsunami (W=60km) Horizontal View (b) Narrow Tsunami (W=20km) Horizontal View Tsunami 3m Tsunami Flow 6000m Flow Distance: 500km Deep Sea (h=6000m) D0=5m W=20km, 60km

20 Simulation of tsunami propagation: (1) Shallow (1000m) water Dispersion of tsunami is not sot strong in case for shallow water. (b) Wide Tsunami (W=60km) Slice View (a) Narrow Tsunami (W=20km) Slice View Tsunami 3m Tsunami Flow 1000m Flow Distance: 500km Shallow Sea (h=1000m) D0=5m W=20km, 60km

21 Tsunami Simulation - Summary Fault Size (L*W) Large Deformation in Acretionary Wedge Sea Depth Push up Sea surface Attenuation by Dispersion [Event 1] 2006 Nov. 15 Mw8.2 Large: 200km*60km may be Deep: >6000m Efficient Weak Larger Tsunami [Event 2] 2007 Jan. 13 Mw8.2 Small: 25km*120km no Deep: >6000m Not efficient Strong Weak Tsunami Sea Depth = m 60 km [Event 1] 2006 Nov. 15 [Event 2] 2007 Jan km 25 km 120 km After Yamanaka (2006; 2007)

22 Integrated Simulation for Earthquake and Tsunami Oscillation Simulation of Buildings and Tanks 2. FDM Simulation of tsunami generation/propagation Furumura et al. (2006) ew On ay Region: 800km*400km*100km (Dx=0.05km) Time: 4000s (Dt=0.1s) CPU Time: 2 hours?? (ES: 32 node) g lin p u Co Saito and Furumura (2006) Co up lin g 1. FDM Simulation of Seismic Waves Region: 800km*400km*100km (Dx=0.5km) Time: 200s (Dt=0.005s) CPU Time: 2 hours (ES: 32 node) Deformation of seabead in 3D Heterogeneous media Micro Scale Tsunami Simulation - Run up - Flood - etc

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26 FDM Simulation of Seismic Wave/Deformation (a) Plate Model Vertical Deformation of Seabed (b) Plate + Accretionary Wedge Vertical Deformation of Seabed Seabed Fault Oceanic Crust Upper Crust Lower Crust Seabed Fault Oceanic Mantle Accretionary Wedge (Vp/Vs=2.2; σ=0.37) Snapshots demonstrating wave propagation and deformation caused by earthquake Red: Vertical, Green: Horizontal component and top panel illustrating deformation of seabed

27 FDM Simulation of Seismic Wave/Deformation Soft sediments in acretionary wedge cause very large deformation of seabed, which leads in large tsunami! (a) Plate Model (b) Plate + Accretionary Wedge Vertical Deformation of Seabed Vertical Deformation of Seabed Seabed Fault Oceanic Crust Upper Crust Lower Crust Accretionary Wedge (Vp/Vs=2.2; σ=0.37) Seabed Fault Oceanic Mantle Snapshots demonstrating wave propagation and deformation caused by earthquake Red: Vertical, Green: Horizontal component and top panel illustrating deformation of seabed

28 Two Large M8 Earthquakes in Kuril Islands (1) 2006 Nov. 15, Mj7.9; Mw8.2 (2) 2007 Jan 13, Mj8.2; Mw8.2 JMA Tsunami Alert

29 2006 Nov. 15 Event(Mw8.2) Hokkaido r il T r u K h e nc Japa n Tr Honshu ench 2007 Jan 13 Event (Mw8.2) Kyushu 規模(M) 死者数 1896 明29 明治三陸地震 , 昭8 昭和三陸地震 8.1 3, 昭19 東南海地震 7.9 1, 昭21 南海地震 8.0 1, 昭35 チリ地震 昭58 日本海中部地震 平5 北海道南西沖地震 ga 地震名 -O Izu 発生年 ara w a s ough r T kai Nan nch e r T Shikoku