Simulations of Large Earthquakes on the Southern San Andreas Fault

Amit ChourasiaVisualization Scientist

San Diego Supercomputer Center

Presented to: Latin American Journalists

July 11, 2007

Global Seismic HazardGlobal Seismic Hazard

Source: Global Seismic Hazard Assessment Program

Expansion of urban centers in tectonically active areas is driving an exponential increase in earthquake risk.

Growth of Earthquake Risk

Growth of cities 2000-2015

Source: National Geographic

1

10

100

1000

10000

IncreasingLoss

Slide: Courtesy Kim Olsen

Structural vulnerability

Risk Equation

Risk = Probable Loss (lives & dollars) =

Hazard Exposure Fragility

Faulting, shaking, landsliding, liquifaction

Extent & density of built environment

Slide: Courtesy Kim Olsen

Seismic Hazard Analysis

Definition: Specification of the maximum intensity of shaking expected at a site during a fixed time interval

Example: National seismic hazard maps

• Intensity measure: peak ground acceleration (PGA)

• Interval: 50 years

• Probability of exceedance: 2%

(http://geohazards.cr.usgs.gov/eq/)(http://geohazards.cr.usgs.gov/eq/)

Slide: Courtesy Kim Olsen

“HAZUS’99 Estimates of Annual Earthquake Losses for the United States”, September, 2000

The FEMA 366 Report

• U.S. annualized earthquake loss (AEL) is about $4.4 billion/yr.

• For 25 states, AEL > $10 million/yr

• 74% of the total is concentrated in California

• 25% is in Los Angeles County alone

Slide: Courtesy Kim Olsen

Southern California: a Natural Laboratory for Understanding Seismic Hazard and Managing Risk

Tectonic diversity

Complex fault network

High seismic activity

Excellent geologicexposure

Rich data sources

Large urban population with densely built environment high risk

Extensive research program coordinated by Southern California Earthquake Center (SCEC) under NSF and USGS sponsorship

Slide: Courtesy Kim Olsen

1994 Northridge

When: 17 Jan 1994Where: San Fernando ValleyDamage: $20 billion Deaths: 57Injured: >9000

Slide: Courtesy Kim Olsen

Slip deficit on the southern SAF since last event (1690):

315 years x 16 mm/year = 5.04 m -> Mw7.7

18571857M 7.9M 7.9

~1690~1690M 7.7M 7.7

Major Earthquakes

on the San Andreas

Fault,

1690-present

19061906M 7.8M 7.8

146+91-60 yrs

220±13 yrsSlide: Courtesy Kim Olsen

TeraShake Simulation Region

600km x 300km x 80km Spatial resolution = 200m Mesh Dimensions

3000 x 1500 x 400 = 1.8 billion mesh points

Simulated time = 4 minutes Number of time steps =

22,728 (0.011 sec time step)

60 sec source duration from Denali

3D Crustal structure: subset of SCEC CVM3.0

Near-surface S-wave velocity truncated at 500m/s, up to 0.5 Hz

Computational Challenge!

TeraShake-2 Data Flow

TS2.dyn.200m30x 256 procs, 12 hrs,

TG IA-64

GPFS

GPFS

Okaya

200m Media

Okaya

100m Media

100m Reformatting

100m Transform

100m Filtering

200m moment rate

SDSC IA-64

TS2.dyn.100m10x 1024 procs, 35 hrs

Initial 200m

Stress modify

Initial 100m

Stress modify

TS2.wav.200m3x 1024 procs, 35 hrs

NCSA IA-64

Datastar p690

Datastar p655

VisualizationAnalysis

Network

TG IA-64

GPFS-wan

NCSA-SAN

SDSC-SAN

Velocity mag. & cum peak

Displace. mag & cum peak

Seismograms

Registered to Digital Library

SRB

SAM-QFS

HPSS

Datastar

GPFS

Slide: Courtesy Yifeng Cui

Challenges for Porting and OptimizationBefore Optimization Code deals up to 24 million mesh nodes Code scales up to 512 processors Ran on local clusters only No checkpoints/restart capability Wave propagation simulation only Researcher’s own code Mesh partition and solver in one Initialization not scalable, large memory need I/O not scalable, not portable

After Optimization Codes enhanced to deal with 32 billion mesh nodes Excellent speed-up to 40,960 processors, 6.1 Tflop/s Ported to p655, BG/L, IA-64, XT3, Dell Linux etc Added Checkpoints/restart/checksum capability Integrated dynamic rupture + wave propagation as one Serve as SCEC Community Velocity Model Mesh partition separated from solver 10x speed-up of initialization, scalable, memory reduced MPI-I/O improved 10x, scaled up to 40k processors

TeraShake code Total Execution Time on IBM Power4 Datastar

10.00

100.00

1000.00

10000.00

120 240 480 960 1920

Number of processors

Wal

l Clo

ck T

ime

(sec

, 101

ste

ps)

WCT time with improved I/OWCT idealWCT time with TeraShake-2WCT time with TeraShake-1

95%86% efficiency

86%

Source: 600x300x80kmM esh: 3000x1500x400Spatial resolution: 200mNumber of steps: 101Output: every time step

Slide: Courtesy Yifeng Cui

Data from TeraShake 1.1

Scalar Surface (floats)• 3000 x 1500

ie 600 km x 300 km

=17.2 MB per timestep

• 20,000 timesteps

• 3 variables Vx, Vy & Vz

Velocity components

• Total Scalar data = 1.1 TB

Scalar Volume (floats)• 3000 x 1500 x 400

ie 600 x 300 x 80 km^3

=7.2 GB per timestep

• 2,000 timesteps

• 3 variables Vx, Vy & Vz

Velocity components

• Total Vol data = 43.2 TB

Other Data – check points,etc

Grand Total = 47.4 TB

Aggregate Data : 160 TB (seven simulations)

Visualization

Movie (1.5 mb)

Comparative Visualization

Movie (11 mb)

PGV (NW-SE Rupture) PGV (SE-NW1 Rupture)

Scenario Comparison

Topography Deformation

Movie (11 mb)

Glimpse of Visualization

Movie (65 mb)

Visualization

Over 130,0000 images Consumed 40,000 hrs of compute time More than 50 unique animations

Does Viz work?

Does Viz work?

TeraShake Results

• NW-directed rupture onsouthern San Andreas Fault is highly efficient in exciting L.A. Basin

• Maximum amplification from focusing associated with waveguide contraction

• Peak ground velocities exceeding 100 cm/s over much of the LA basin

• Uncertainties related to simplistic source description.

• Extremely nonlinear dynamic rupture propagation

• Effect of 3D velocity structure: SE-NW and NW-SE dynamic models NOT interchangeable

• Stress/strength/tapering - weak layer required in upper ~2km to avoid super-shear rupture velocity

• Dynamic ground motions: kinematic pattern persists in dynamic results, but peak motions 50-70% smaller than the kinematic values due to less coherent rupture front

TeraShake-1 TeraShake-2

Slide: Courtesy Yifeng Cui

Summary

TeraShake demonstrated that optimization and enhancement of major applications codes are essential for using large resources (number of CPUs, number of CPU-hours, TBs of data produced)

TeraShake showed that multiple types of resources are needed for large problems: initialization, run-time execution, analysis resources, and long-term collection management

TeraShake code as a community code now used by the wider SCEC community

Significant TeraGrid allocations are required to advance the seismic hazard analysis to a more accurate level

Next: PetaShake!

Slide: Courtesy Yifeng Cui

References Chourasia, A., Cutchin, S. M., Olsen, K.B., Minster, B.,

Day, S., Cui, Y., Maechling, P., Moore, R., Jordan, T. (2007) “Visual insights into high-resolution earthquake simulations”, IEEE Computer Graphics & Applications (Discovering the Unexpected) Sept-Oct 2007, In press.

Cui, Y., Moore, R., Olsen, K., Chourasia, A., Maechling, P., Minster. B., Day, S., Hu, Y., Zhu, J., Majumdar, A., Jordan, T. (2007), Enabling very-large scale earthquake simulations on parallel machines "Advancing Science and Society through Computation", International Conference on Computational Science 2007, Part I, Lecture Notes in Computer Science series 4487, pp. 46-53, Springer

Olsen, K.B., S.M. Day, J.B. Minster, Y. Cui, A. Chourasia, M. Faerman, R. Moore, P. Maechling, and T. Jordan (2006). Strong shaking in Los Angeles expected from southern San Andreas earthquake, Geophys. Res. Lett. 33, L07305,doi:10.1029/2005GRL025472

TeraShake Collaboration

Large Scale Earthquake Simulation on Southern San Andreas

33 researchers, 8 Institutions Southern California Earthquake Center San Diego Supercomputer Center Information Sciences Institute Institute of Geophysics and Planetary Physics

(UC) University of Southern California San Diego State University University of California, Santa Barbara Carnegie-Mellon University ExxonMobil

Slide: Courtesy Marcio Faerman

Acknowledgements

Southern California Earthquake Center (SCEC)

San Diego Supercomputer Center (SDSC)

Funding: National Science Foundation

Thanks for your patience

Q&A

Websites: http://www.sdsc.edu/us/sac (Computation)

http://epicenter.usc.edu/cmeportal/TeraShake.html (Seismology)

http://visservices.sdsc.edu/projects/scec/terashake (Visualization)