Dueling dynamics of low-angle normal fault rupture with splay faulting and off-fault damage

Abstract

Despite a lack of modern large earthquakes on shallowly dipping normal faults, Holocene Mw > 7 low-angle normal fault (LANF; dip<30°) ruptures are preserved paleoseismically and inferred from historical earthquake and tsunami accounts. Even in well-recorded megathrust earthquakes, the effects of non-linear off-fault plasticity and dynamically reactivated splay faults on shallow deformation and surface displacements, and thus hazard, remain elusive. We develop data-constrained 3D dynamic rupture models of the active Mai’iu LANF that highlight how multiple dynamic shallow deformation mechanisms compete during large LANF earthquakes. We show that shallowly-dipping synthetic splays host more coseismic slip and limit shallow LANF rupture more than steeper antithetic splays. Inelastic hanging-wall yielding localizes into subplanar shear bands indicative of newly initiated splay faults, most prominently above LANFs with thick sedimentary basins. Dynamic splay faulting and sediment failure limit shallow LANF rupture, modulating coseismic subsidence patterns, near-shore slip velocities, and the seismic and tsunami hazards posed by LANF earthquakes.

Linked and fully-coupled 3D earthquake dynamic rupture and tsunami modeling for the Húsavík-Flatey Fault Zone in North Iceland

“…A better understanding of the complex interaction between static and time-dependent earthquake displacements, off-fault deformation, and seismic, acoustic, and tsunami amplitudes is now possible using realistic 3D scenarios. Non-linear earthquake dynamic rupture simulations combining coseismic frictional failure on prescribed faults and seismic wave propagation are powerful tools to investigate earthquake dynamics as a consequence of the model's initial conditions (e.g., Aochi and Ulrich, 2015;Wollherr et al, 2019;Ulrich et al, 2019a;Lozos and Harris, 2020;Harris et al, 2021;Taufiqurrahman et al, 2022;Biemiller et al, 2023). Empowered by high-performance computing (Ben-Zion et al, 2022), joint earthquake-tsunami modeling is now becoming applicable for the development of (probabilistic) tsunami forecasting and early warning systems (Yamamoto, 1982;Cecioni et al, 2014;Bernard and Titov, 2015;Mei and Kadri, 2017;Gomez and Kadri, 2021;Selva et al, 2021).…”