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The SCEC Broadband Ground Motion Simulation Platform

Paul Somerville, Scott Callaghan, Philip Maechling, Robert Graves, Nancy Collins, Kim Olsen, Walter Imperatori, Megan Jones, Ralph Archuleta, Jan Schmedes, Thomas H. Jordan

Southern California Earthquake Center• Collaboration of 600+ scientists at 60+ institutions• SCEC conducts earthquake system science

– Many physical phenomena involved– Community Modeling Environment (CME) improves

computational models

2Anticipation timemonth dayyeardecadecentury week

Faultrupture

Origin time Response time 0 minute hour day year decade

------ Aftershocks -------------------------------------------------------------------

Surfacefaulting

Seismicshaking

Structural & nonstructuraldamage to built environment

Human casualties

Disease

Fires

Socioeconomic aftereffects

Landslides

Liquifaction

NucleationTectonic loading

Stress accumulation

Seafloordeformation

Tsunami

Dynamic triggering

Slow slip transients

Stress transfer

----- Foreshocks -----

Earthquake Simulations

• Scenario earthquake simulations increase understanding of ground motions

• Valuable in determining seismic hazard• SCEC performs a variety of large-scale scenario

simulations

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Broadband Platform

• Collaborative software system– SCEC research groups– CME software development

• Computes seismograms from 0-10 Hz• Can be run by scientists or engineers without

detailed knowledge of the code details• Open development and user access

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http://scec.usc.edu/scecpedia/Broadband_Platform

Features and Attributes• Transparency / Reproducibility

– Software is open and downloadable• Software Control

– Formal releases with documentation– Version control

• Flexibility– Modular architecture– Standardized data formats

• Expandability– Designed for easy addition / revision of computational

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Current Capabilities

• Can run historical earthquakes– Validate simulations against observed results

• Scenario earthquakes– Ground motions due to potential earthquakes– User supplies earthquake description

• User provides list of sites at which to perform simulations

• User selects modules to run– Multiple implementations of same functional steps– Compare and contrast codebases

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Source Description• CFM, ERF• Mw, Dimension,

Geometry

Kinematic Rupture Generator

Standard Rupture Format

• GF Libraries• Site Lists• Velocity Models

High Frequency Simulation (> 1 Hz)

Low Frequency Simulation (< 1 Hz)

Combine into BB, add Site Response

Broadband Time Series (0 – 10 Hz)

Schematic Workflow

deterministic

stochastic

Current Modules

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UCSB URS SDSU / ETH

Kinematic Rupture Generator X X1D Low Frequency Wave Modeling X X1D High Frequency Wave Modeling X X XSite Response X X XURS: Graves, R. W. and A. Pitarka (2010). “Broadband Ground-Motion Simulation Using a Hybrid Approach.” BSSA., 100, 2095-

2123, doi: 10.1785/0120100057.SDSU / ETH: Mai, P.M., W. Imperatori, and K.B. Olsen (2010). “Hybrid broadband ground motion simulations: combining long-period

deterministic synthetics with high frequency multiple S-to-S back-scattering.” BSSA, 100, 2124-2142, doi: 10.1785/0120080194.

UCSB: Schmedes, J., R. J. Archuleta, and D. Lavallée (2010). “Correlation of earthquake source parameters inferred from dynamic rupture simulations.” JGR, 115, B03304, doi:10.1029/2009JB006689.

Rupture Generation• Converts user-provided simple earthquake description into full

kinematic rupture description (SRF file)• Optional module (can supply SRF)

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MAGNITUDE = 6.67FAULT_LENGTH = 20.01DLEN = 0.2FAULT_WIDTH = 25.01DWID = 0.2DEPTH_TO_TOP = 5.0STRIKE = 122RAKE = 90DIP = 40LAT_TOP_CENTER = 34.344LON_TOP_CENTER = -118.515HYPO_ALONG_STK = 6.0HYPO_DOWN_DIP = 19.4DT = 0.01SEED = 3092096CORNER_FREQ = 0.15

Source Description Rupture with slip

Seismogram Generation• Low-frequency generation

– Generates 0-1 Hz seismograms– Deterministic, calculated from

1-D Green’s functions– Two implementations

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• High-frequency generation– 1-10 Hz seismograms– Stochastic attributes– Three implementations

Combine into Broadband

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• Matched filters at 1 Hz– Low-cut for HF– High-cut for LF– Sum to get BB

(Seyhan et al., 2011)

Site Effects• Adjusts seismograms based on site specific

properties• Current modules Vs30 based

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Before site response After site response

Optional comparisons

• Response spectra– Examine frequency behavior– Can compare against

observed or simulated results• Goodness-of-fit

– Compares response spectra from ≥3 stations

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Data Products

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Rupture PlotsVelocity and acceleration

seismograms

Station and fault trace maps

Comparison Data Products

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Spectral response

comparison Seismogram comparison

Goodness-of-fit

Software Engineering

• Modular design• Code integration• Software testing• Formal release

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Modular Design

• Each module represented by Python class• User chooses which implementation

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User input:

URSSDSUUCSB…

Workflow description

URSSDSUUCSB

…

Low freq High freq Site response

Execute modules

Construct description

URS UCSB SDSU …

Example Invocation

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# ./run_bbp_2G.py Welcome to the SCEC Broadband Platform.Please select the modules you want to run.Do you want to perform a validation run (y/n)? nDo you want to run a rupture generator (y/n)? yRupture generators:URS (1)UCSB (2)?1Using region: Southern CaliforniaChoose a low frequency module:URS (1)UCSB (2)?2Found multiple BBP station list files in the start directory. Please select one:nr_one_stat.stl (1)valid_test_stat.stl (2)nr_five_stat.stl (3)?3Choose a high frequency module:...You can find results in /home/scec-00/scottcal/bband/. . .

Code Integration

• Goal to make platform easy to run without detailed code knowledge

• Modified codes to read and write common (i.e., standardized) formats

• Simplifies addition of future modules

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Software Testing

• Need to verify platform is installed correctly• Three levels of testing

– Checksums to verify data files– Unit testing

• Each module checked for correct performance– Acceptance testing

• All combinations of modules run to check integration

• Very useful in locating problems• Gives users confidence in results

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Formal Release• Platform targeted at wide variety of users• Requires extra effort with science codes• Detailed user’s guide• Track system for bugs

• Version 11.2.0 released on February 18, 2011• Official web site

http://scec.usc.edu/scecpedia/Broadband_Platform

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Current Applications• NGA-West 2

– Footwall / hanging wall simulations• NGA-East

– Simulations to help constrain ground motion prediction equations (GMPEs)Zeng et al. 11:45 am today

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Future Plans• Reduce software dependencies (e.g. OS, compilers)• Additional modules• New modules

– 1D GF calculator– 3D GF calculator

• Parallel version• Increase support for varied execution environments

– Virtual machines– Cloud

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http://scec.usc.edu/scecpedia/Broadband_Platform

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Verification and Validation• Similar results verifies multiple complex codes

27Finite element (CMU)Finite difference (AWP-ODC)Finite difference (URS)

Small-scale simulations

• Hundreds of thousands of potential M5+ events in Southern California

• Enable individual scientists to run simulations• Compare results from multiple codebases

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Schematic

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