Geological controls on megathrust slip : the 2014 Pisagua, Chile, earthquake sequence as a natural laboratory
Most subduction zones remain poorly resolved when it comes to the study of the precise location of the far oﬀshore located updip limit of coseismic slip and its controlling parameters, which is an essential component of earthquake hazard assessment. The relative lack of seismicity on the updip limit, combined with laboratory friction studies, suggest the shallow fault is mostly velocity strengthening and likely to creep. This view is reinforced by geodetic inversions, which show low to zero coupling close to the trench. However, these locations are remote from the land; hence the models derived from terrestrial stations are not suﬃciently well constrained. Moreover, the updip region can also be seismogenic, as demonstrated by tsunami earthquakes and shallow, slow slip events. To better understand the controls on the updip limit, we analyze high-resolution seismic data to image an erosive margin with documented intense seismicity. Developing a high-resolution model of the seismic velocity and reﬂectivity of a region where we have exceptionally good knowledge of the temporal and spatial distribution of slip will provide new insights into these controls that can be transferred to studies of seismic slip and crustal structure elsewhere. These results will also have a signiﬁcant impact on statistical forecasts of future earthquake activity, which can aﬀect seismic hazard evaluation and mitigation plans. The thesis is motivated by two themes, which are interrelated and addressed in a holistic seismic approach. One theme is mainly focused on the ﬂuid-pressure variations revealed by the reﬂectivity of the seismic proﬁles along the updip limit to identify the shallow, velocity strengthening part of the plate boundary. Another theme is the study of the structure of the updip limit and the hanging upper plate caused by the subducting oceanic ridge.