Particle Flow Code 2D (PFC2D v. 7.00) Model using NERC

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Team

John Shaw, Vice Provost for Research
Andreas Plesch, PI
Kristen Chiama, Research Assistant
Harvard University

Introduction

This project seek to improve our understanding of the physical processes that control the style, distribution, and intensity of ground surface ruptures on thrust and reverse faults during large earthquakes. Their study combines insights from coseismic ground surface ruptures in historic earthquakes and patterns of deformation in analog sandbox fault experiments to inform the development of a suite of geomechanical models based on the distinct element method (DEM). They explore how model parameters related to fault geometry and sediment properties control ground deformation characteristics such as scarp height, width, dip, and patterns of secondary folding and fracturing. DEM is well suited to this investigation because it can effectively model the geologic processes of faulting at depth in cohesive rocks, as well as the granular mechanics of soil and sediment deformation in the shallow subsurface. They results show that localized fault scarps are most prominent in cases with strong sediment on steeply dipping faults, whereas broader deformation is prominent in weaker sediment on shallowly dipping faults. Based on insights from 45 experiments, the key parameters that influence scarp morphology include the amount of accumulated slip on a fault, the fault dip, and the sediment strength. They propose a fault scarp classification system that describes the general patterns of surface deformation observed in natural settings and reproduced in our models, including monoclinal, pressure ridge, and simple scarps. Each fault scarp type is often modified by hanging‐wall collapse. These results can help to guide both deterministic and probabilistic assessment in fault displacement hazard analysis.

Objective: To improve understanding of ground surface ruptures during large earthquakes

Approach: Combined study of coseismic ground surface ruptures and analog sandbox fault experiments to inform geomechanical models

Method: Distinct Element Method (DEM)

Findings

Parameters affecting ground deformation characteristics: scarp dip, height, width, and patterns of secondary folding and fracturing.

Localized fault scarps are prominent in strong sediment on steeply dipping faults, whereas broader deformation is prominent in weaker sediment on shallowly dipping faults.

Key parameters influencing scarp morphologies: amount of accumulated slip on a fault, fault dip, and sediment strength.

Proposed fault scarp classification system: monoclinal, pressure ridge, and simple scarps; each type often modified by hanging wall collapse.

Implications

Results can guide deterministic and probabilistic assessment in Fault Displacement Hazard Analysis (FDHA)

DEM is a suitable method to model geologic processes of faulting and granular mechanics of soil and sediment deformation in the shallow subsurface

Potential for further research and application of findings in earthquake hazard analysis and mitigation

Used NERC Resources

  • ~800 trials run on NERC
    • Using both Windows 10 & Linux versions
    • Each trials takes ~ 5 – 9 hours
    • Each trial generates 5.6 – 11.2 GB of data
  • Flavor: gpu-a100.2
    • VCPUs: 24
    • RAM: 192 GB
    • Each trial cycles through force-balance equations for all particles and can use up to 40% CPU and 45% RAM allocated so they can run two trials in parallel on this powerful machine.

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