Uncertainties in earthquake source estimates

How can we study earthquakes, these complex phenomenon occurring so deep under our feet that we cannot observe them directly ? One unfortunate aspect of the problem is that we have to rely on measurements acquired at the surface of the Earth. These observations are incomplete, and the imagery of earthquakes is subject to biases induced by numerous approximations. Most of these approximations cannot be avoided, and stem from the poor resolution of the measurements, the inherent lack of knowledge of the physics of the Earth interior, and the bias induced by our modeling procedures. The imperfections of our models question our ability to robustly investigate earthquakes rupture, and thus to understand the physics driving them. The quest for robust images needs a thorough and exhaustive examination of the uncertainties that potentially corrupt the modeling procedure and its results, at least not to interpret improbable characteristics. Although measurement errors are usually accounted for, other kinds of approximations are overlooked. Here, we show that the impact of our simplified description of the Earth’s interior on earthquake models is significant, especially for the events with a large magnitude. We concentrate on two main sources of approximation : the architecture of seismogenic faults, and the temporal complexity of seismic and aseismic processes at play on these faults. We present two methodological developments allowing to estimate and account for uncertainties deriving from these approximations in modeling procedures. In particular, we show that introducing the uncertainties deriving from our approximation of the Earth’s physics is necessary to infer robust and realistic earthquake source models. Our analyses is supported by the use of probabilistic modeling approaches, allowing to explore the diversity and uncertainties of possible models.