Inferring heterogeneity of fault properties and stress state of a megathrust fault from dynamic stress drop variations: A feasibility study in the northern Chilean subduction zone

• Applicant: Dr. Jonas Folesky
• Subject Area: Geophysics
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 442516884

I propose a research project to systematically investigate the spatiotemporal patterns of seismic stress drop at the seismically highly active northern Chilean subduction zone. For this I plan an integrative analysis approach based on the combination of three independent stress drop estimation techniques.Recent studies indicate that stress drop relates to the fault strength and/or the stress acting on the fault. This suggests that the stress drop may be a valuable parameter to perform fault segmentation to constrain the slipping and locking behavior or to identify potential rupture barriers. However, stress drop estimates often suffer from large uncertainties, comparability between studies is difficult, and the analyzed data sets often are limited. Simultaneously, a well- resolved image of the stress drop distribution in space and time could help greatly to understand the nucleation and rupture processes of megathrust earthquakes.Stress drop measurements are usually derived from corner frequencies of recorded displacement spectra. They involve large uncertainties due to measurement errors and assumptions about earthquake dynamics. To improve the accuracy, I plan to develop a refined methodology which combines three different techniques: a spectral ratio method, a spectral stacking method, and the lower bound approach. The first two approaches are spectra techniques, the third approach is based on the magnitude frequency distribution and earthquake locations. By exploiting the synergies of these techniques, I hypothesize that it will be possible to significantly enhance the robustness and accuracy of the measurements.A particularly interesting study region is the northern Chilean subduction zone which is considered as 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. Important underlying works such as the compilation of a high resolution seismicity catalog with over 100,000 earthquakes including for- and aftershock series and the detection of long-term repeating earthquake sequences have already been carried out. Additionally, detailed GPS-based studies exist which independently constrain the co-seismic slip and after-slip distribution. Therefore, this data set provides the great possibility analyze thousand of events in a self-consistent manner and to compare the derived stress drop patterns with geodetic results in great detail.The major contribution of the here proposed study will be an advanced method for stress drop estimation. I expect that its application to northern Chile will provide an unprecedentedly detailed image of the stress drop distribution in a subduction zone. Furthermore, it will help to improve our still insufficient knowledge of the relation between stress drop, frictional behavior, and applied stress.

• DFG Programme: Research Grants
• International Connection: USA
• Cooperation Partners: Professorin Dr. Rachel Abercrombie; Professor Dr. Thomas Goebel
• Co-Investigator: Dr. Jonathan Bedford