Landers 1992 "reloaded": an integrative dynamic earthquake rupture model

Stephanie Wollherr, Alice-Agnes Gabriel, & Paul M. Mai

Published August 15, 2018, SCEC Contribution #8798, 2018 SCEC Annual Meeting Poster #211

The 1992 Mw 7.3 Landers earthquake raised awareness of unexpectedly large magnitude earthquakes caused by rupture of fault networks that were previously considered unconnected. While the overall kinematics of the event are thought to be well understood, many observations regarding its complicated rupture dynamics are still unresolved.
Here, we present 3D spontaneous dynamic rupture simulations that improve our understanding of the earthquake source and ground motions of the multi-segment Landers event. The model incorporates a new degree of realism by incorporating the interplay of fault geometry, topography, 3D rheology, off-fault plasticity and viscoelastic attenuation. These model complexities are enabled by the software package SeisSol (www.seissol.org) specifically suited for handling complex geometries and for the efficient use on modern high-performance computing infrastructure.

We find that fault geometry, as well as amplitude and orientation of initial fault stresses primary control sustained rupture along all fault segments. The resulting complex source dynamics include reverse slip, direct branching, and dynamic triggering over large distances. Fault slip terminates spontaneously on most of the principal fault segments due to the underlying fault geometry.

The model reproduces a broad range of observations, including seismic moment-rate, seismic waveform characteristics and peak ground velocities. Despite the complex rupture evolution, ground motion variability is close to what is commonly assumed in Ground Motion Prediction Equations. Our simulation results suggest that an along-strike variability of the shallow slip deficit of up to 20% is possible, even for laterally constant rock cohesion and bulk friction. These variations can be attributed to different principal stress directions and complex fault geometry. Further, we observe dramatically increased off-fault deformation in the vicinity of fault bends and intersections, in excellent agreement with recent maps of fault-zone width (Milliner et al., 2015, Geochemistry, Geophysics, Geosystems).

Finally, we examine the effects of variations in modeling parameterization, e.g. purely elastic setups or models neglecting viscoelastic attenuation, in comparison to our preferred model.

Key Words
dynamic rupture, Landers, complex fault systems, ground motions, plasticity

Citation
Wollherr, S., Gabriel, A., & Mai, P. M. (2018, 08). Landers 1992 "reloaded": an integrative dynamic earthquake rupture model. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)