Slip heterogeneity of a subduction zone from detailed repeating earthquake analysis. A 15–year–long story from northern Chile

• Applicant: Dr. Jonas Folesky
• Subject Area: Geophysics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 536179230

I propose a research project to systematically and quantitatively study repeating earthquake (RE) activity in the northern Chilean subduction zone. RE sequences are groups of events with overlapping rupture area; they are usually identified by their nearly identical waveforms, which indicate coinciding source mechanism and location. REs are studied primarily due to their specific potential to constrain motion at depth (fault creep). The first scientific objective in this work will be REs along the plate interface, which is planned to be analyzed to illuminate the current distribution of slip rate at depth and to provide valuable information on the locking pattern in the context of the megathrust earthquake cycle. The second prime objective will be the mechanism(s) of REs that are located deeper within the subducting plate. Their occurrence as of today is still enigmatic. I plan to study the temporal and spatial patterns and integrate petrophysical constraints to test different hypothetical mechanisms (role of interconnected pore networks, dehydration reactions, shear-heating) and therewith contribute to a better understanding of intermediate depth seismicity, in general. For both aims, the compilation of a long-term, complete and accurate RE catalog is fundamental. I will approach this by using template matching and machine-learning based tools, starting with the existing high-resolution event catalog for northern Chile. To minimize errors in the association of earthquakes repeatedly activating the same location I will refine the methodology of RE identification. The idea is to combine waveform similarity, high-precision relative event locations from differential travel time measurements and event-wise estimates of source dimensions from seismic moments and stress drops. In a subsequent step it is planned to improve the already existing seismic catalog with state-of-the-art and ML-based picking, denoising, association and location procedures. The proposed study region in northern Chile is of particular interest as it is considered a seismic gap hosting the potential of a severe megathrust event. In 2014 the region experienced the MW8.1 Iquique megathrust earthquake which only released part of the stored rupture potential. The area has been surveyed by the IPOC network since 2006 and a high resolution seismicity catalog with over 182,000 earthquakes including for- and aftershock series. In my latest project, I have conducted a study on stress drop variability throughout the northern Chilean subduction zone and created the first continuous, comprehensive stress drop map for an entire subduction zone. This map can now serve as important input for RE analysis to constrain their rupture structures. Please note that I have already made substantial preparatory work for the machine learning based picking and denoising, template matching and RE characterization techniques proposed for this study. Therefore, I am convinced of its feasibility.

• DFG Programme: Research Grants