SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland DEM Simulation of dynamic Slip on a rough Fault Steffen Abe, Ivan Lokmer and Chris Bean Seismology and Computational Rock Physics Lab University College Dublin Ireland

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Project Scope DEM Simulation of Rupture Processes Key Question: Influence of geometric heterogeneity on rupture behavior of a fault model Approach: DEM fault model Geometric heterogeneity on two scales Simple friction law

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland The DEM Approach Spherical particles interacting with nearest neighbors Brittle-elastic “linked” interactions Can break if deformed too far Free elastic interactions Frictional interactions Coulomb friction

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland The Fault Model (I) 1D fault embedded in 2D elastic block smooth and rough patches along the fault surface -> “large scale” roughness constant normal force and shear velocity at the edge of the elastic block

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland The Fault Model (II) 375…400 particles long 200…300 particles wide Narrow band of random sized particles along fault to generate random “small scale” roughness

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Stick-Slip Dynamics of the Fault Slow stress/energy buildup Stress drop at slip events Used to identify major slip events

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Slip distribution time location along fault displacement Inhomogeneous final displacement both uni- and bidirectional propagation

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Pre-Slip Stress and Final Slip Distribution high displacement in “low stress deficit” / “close to failure” regions slip stopped by “far from failure” asperity

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Synthetic Seismograms two different approaches, both using displacement evolution recorded at the fault surface analytic extrapolation, assuming ideal elastic medium (I. Lokmer) numerical (DEM) compare results from the two methods for verification

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Synthetic Seismograms – Verification (I) main features agree differences in details Reasons: limitations of DEM used wave speeds are freq. dependent limit on frequency finite model data high pass filtered, adjusted for “best fit” velocity in DEM

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Synthetic Seismograms – Verification (II) Data band-pass filtered and scaled to fit main features good agreement in most features

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Synthetic Seismograms – Setup arbitrary locations possible 14 intermediate to far field locations chosen distance times fault length

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Synthetic Seismograms – Results

SPICE Research and Training Workshop III, July 22-28, Kinsale, Ireland Conclusions / Outlook Complex rupture patterns generated by geometrically heterogeneous fault with simple friction law Rupture extent influenced by pre- slip stress deficit/ closeness to failure Next ? 3D !