Speaker: Ylona van Dinther, Assistant Professor, Department of Earth Sciences, Utrecht University
“Combining physics-based models and observations to understand Tectonics and Seismicity”
Abstract: Earthquake sequence models are becoming increasingly more realistic in terms of physical ingredients and resemblance to geological observations. One such example is our seismo-thermomechanical (STM) modeling approach, which simulates tectonics and seismicity using a viscoelasto-plastic rheology with laboratory-derived parameters for different lithologies. Physics-based models can reveal their power by predicting new and verifiable observations and by making sensible fore- and hindcasts. Observations are our stronghold towards the truth, but they are indirect and limited in space and time. I will highlight different examples on how we combine STM models and observations to better understand the both earthquake sequences and tectonics.
First, geological and geophysical observations can be used to tightly constrain our STM models. In an example in the Northern Apennines, a peculiar orogenic belt driven by slab pull, we show that lower crustal rheology and deep lithospheric mantle temperatures distinctly affect crustal tectonics and seismicity. Second, STM models predicted the existence of a secondary zone of surface uplift related to great megathrust earthquakes, which were subsequently identified in the large majority of vertical displacements following four great earthquakes. Elastic rebound of crustal buckling and a mass-return flow due to accelerated subduction can explain these new observations. Ultimately, one effective way to estimate unknown state variables and parameters is by combining physics-based models and observations in a quantitative and probabilistic manner using ensemble data assimilation as used in weather forecasting. I demonstrate in a proof of concept using an analogue model that ensemble data assimilation can estimate and forecast fault stresses well. In more recent, synthetic studies this is confirmed for both slow slip events and earthquakes slipping at seismic slip rates, under the condition that a bias in frictional parameters is moderate, but not too large. Time permitting, I will also show how observations can constrain dynamic earthquake rupture models feeding the 2018 Palu bay earthquake-tsunami to identify the importance of the tectonic stress regime in inducing tsunami’s in strike-slip fault systems.