The impact of fault-bend folding on models of tsunami generation and inundation
Abstract
Megathrust earthquakes generate tsunamis due to uplift and horizontal motion of the seafloor. Here, we explore the effect of thrust fault geometry on tsunami generation. The tips of subduction megathrusts are usually characterized by steeper thrusts, dipping either landward or seaward. Slip on these thrust faults produces folding, modeled as fault-bend folds (FBF) and fault-propagation folds (FPF), with resulting uplift patterns. We assess the sensitivity of tsunami generation to near-trench slip, using detailed patterns of seafloor uplift as described FBF theory. We define three FBF models with thrust ramps dipping 30° landward, and one model with the ramp dipping seaward (a "backthrust"). We define the seafloor elevation based on the slip on the thrust combined with the possibility of erosion or sedimentation. For each model, we calculate the change in bathymetry based on a 10-m slip event, and use this as the input for a tsunami model in the COMCOT software package, assuming a cyclindrical fault extending 100 km along strike at the trench offshore Sumatra. Our simulations show that the resulting tsunamis are significant, but exhibit minimal difference in the maximum wave height (≤ 20 cm) and inundation (≤ 1m) between the four models. Our result suggests that it is important to include the effect of slip on a thrust ramp in a megathrust earthquake, but reasonable to assume a simple FBF geometry in tsunami modelling when it is not possible to know the detailed near-trench fault geometry of the study area. Our next goal is to use the same FBF-modelling approach to try to match the observed tsunami caused by the 2010 Mw 7.8 Mentawai tsunami earthquake. With this method, we hope to better understand how earthquakes that rupture in the frontal regions of subduction megathrusts can produce large tsunamis, and to better forecast the hazard associated with frontal thrusts.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMNH43E1106F
- Keywords:
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- 4304 Oceanic;
- NATURAL HAZARDSDE: 4313 Extreme events;
- NATURAL HAZARDSDE: 4341 Early warning systems;
- NATURAL HAZARDSDE: 7215 Earthquake source observations;
- SEISMOLOGY