# Huihui Weng （翁辉辉）

## Postdoc, Géoazur, Université Côte d'Azur

## e-mail: weng@geoazur.unice.fr

## 250 rue Albert Einstein, 06560 Valbonne, France

My research vision is to achieve a fundamental understanding of fault mechanics, through synergistic efforts in combining theoretical, computational, and observational approaches. My long-term goals aim at answering the following essential questions: What controls the nucleation, propagation, and arrest of earthquake ruptures? Can we anticipate the size of future earthquakes? What controls the earthquake cycle? How can we improve the way seismic risk is evaluated?

What controls the rupture speed of earthquakes?

Fracture mechanics theory is an analytical tool that enables us to predict the propagation speed of a crack, in a 2D elastic medium with strike-slip or dip-slip loading. However, there are two crucial limitations in the classical 2D models: the along-depth rupture widths of the real earthquakes are finite rather than infinite and the earthquake slip can be oblique (with both strike-slip and dip-slip components). By overcoming these two limitations, we were able to establish new 3D rupture-tip-equation-of-motions and validate them by 3D dynamic rupture simulations. The new-developed 3D equation-of-motions enable us to predict the rupture speed of earthquakes on long faults.

Specifically, previous analytical models determined a forbidden speed range situated between the speed of P and S waves. However, seismological observations demonstrate that recent earthquakes had actually propagated within the forbidden range, such as the 2018 Mw7.5 Palu earthquake. Utilizing our new-developed 3D equation-of-motion of oblique slip, we were able to explain why the "forbidden speeds" are actually admissible.

How can we anticipate the size of future earthquakes?

The new 3D equation-of-motions enable us to define a function of rupture potential, a concept similar to the gravity potential in physics, which can predict the maximum size of future earthquakes on long faults. One of my on-going works is to estimate the maximum earthquake magnitude (Mmax) that could be induced by gas extraction in the Groningen gas field.

How to constrain fault properties?

The new 3D equation-of-motions demonstrate that earthquake rupture speed and size are primarily controlled by the ratio between dissipated fracture energy and potential static elastic energy. Thus, constraining the fracture energies of previous earthquakes are significant for the prevention of future earthquakes. One of my research experiences was to combine computational earthquake physics with seismological observations. As one application of the 2015 Mw7.8 Nepal earthquake, we combined the 3D dynamic rupture simulations with the near-field seismic and geodetic observations to robustly constrain the frictional properties on fault. This approach could also be applied to other earthquakes, providing more robust constraints on the fracture energies on seismogenic faults that can serve for future physics-based seismic hazard assessment.