AGU 2020 Fall Meeting Presentation by Alice Gabriel

A dynamic view on key regional factors governing megathrust
earthquakes, subduction mechanics and tsunami genesis

Alice Gabriel, Thomas Ulrich, Betsy Madden

Determining characteristics that control subduction zone earthquake and
tsunami dynamics is critical to mitigate megathrust hazards, but this is
impeded by structural complexity, large spatio-temporal scales, and scarce
instrumental coverage. Megathrust earthquake variability has been
qualitatively explained using conceptual models. Depth-varying rupture
behavior has been attributed to the presence of weaker materials in the
near trench region. Along-arc variations in tectonic loading, megathrust
interface topography, and seismic coupling have been invoked in space and
time.
Here we show that modeled tsunamigenesis and earthquake dynamics are
controlled by along-arc variability in regional tectonic stresses together
with depth-dependent variations in rigidity and yield strength of
near-fault sediments. We perform data-integrated, geometrically complex,
multi-physics earthquake-tsunami modeling to identify dominant factors
controlling megathrust hazards. To this end, we demonstrate how to unify
and verify the required initial conditions for multi-physics
earthquake-tsunami modeling from interdisciplinary geophysical
observations. We present large-scale rupture dynamics and tsunami modeling
of the 2004 Sumatra-Andaman earthquake and Indian Ocean tsunami that
reconciles near- and far-field seismic, geodetic, geological, and tsunami
observations. We specifically find that sediment strength affects
tsunamigenic trade-offs between slip to the trench, splay faulting, and
bulk yielding of the accretionary wedge: shallow and large slip to the
trench remains invisible to teleseismic and near-field geodetic
measurements, but is an important factor in dynamically sourced tsunami
models.
Our computational capabilities render possible the incorporation of present
and emerging high-resolution observations into dynamic-rupture-tsunami
models. Our findings highlight the importance of regional-scale structural
heterogeneity for earthquake dynamics and tsunami genesis. Incorporating
smaller scale heterogeneities and observational uncertainties into our
models may enhance scenario focused modeling and physics-based
probabilistic hazard assessment of the future to decipher megathrust
hazards based on the assessment of regional factors.