Surface Displacement and Ground Motion from Dynamic Rupture Models of Thrust Faults with Variable Dip Angles and Burial Depths

Sirena Ulloa, & Julian C. Lozos

Published August 14, 2019, SCEC Contribution #9671, 2019 SCEC Annual Meeting Poster #150

Historic earthquakes and empirical studies show that thrust fault ruptures produce stronger ground motion than normal or strike-slip events of the same magnitude. This is due to a combination of hanging wall effects, vertical asymmetry, and higher stress drop due to compression. Surface displacement occurs in blind thrust ruptures in addition to those with surface expression. This poses a hazard since surface displacement can potentially affect lifelines and infrastructure. Our 3D dynamic rupture modeling parameter study focuses on planar thrust faults of varying dip angles and burial depth, in order to establish a physics-based understanding of how these geometrical parameters affect surface displacement and ground motion. We vary dip angles from 20º to 70º, and burial depths from 0 km to 5 km. We conduct rupture models on these geometries using different dynamic stress drops, fault strengths, and homogeneous initial stresses vs. stresses tapered with fault depth.

We find that varying dynamic stress drop has a considerable scalar effect on both ground motion and surface displacement, whereas changing fault strength has a negligible effect. In the homogeneous initial stress case, particle velocity increases with shallower burial depths, and varying burial depth has more of an impact on peak particle velocity than varying dip angle does. In contrast, in the tapered initial stress case, ground motion generally increases as we bury the fault deeper, with the exception of surface faults. In both the homogeneous and tapered initial stress cases, peak horizontal particle velocities shift from the hanging wall toward the footwall as the dip angle increases, while the vertical components show hardly any difference between cases.

There is more surface displacement in the homogeneous initial stress case than in the tapered stress case. In the homogeneous case, both subsidence and uplift increase with burial depth, but vary depending on dip angle in the tapered case. The area uplifted in the homogeneous case shifts as we vary both dip angle and burial depth. The area of subsidence is smaller in the tapered model compared to the homogeneous case, and it increases in size as we increase dip angle and burial depth. Due to the simple geometry of a planar fault, our results can be applied to understanding basic behavior of specific real-world thrust faults.

Key Words
parameter study, dynamic rupture, thrust faults, ground motion, numeric modeling

Citation
Ulloa, S., & Lozos, J. C. (2019, 08). Surface Displacement and Ground Motion from Dynamic Rupture Models of Thrust Faults with Variable Dip Angles and Burial Depths. Poster Presentation at 2019 SCEC Annual Meeting.

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