Disentangling roles of stress, pore pressure and shaking from wavefields recorded during the 2014 Northern Chile earthquake sequence

• Applicants: Dr. Jörn Kummerow; Dr. Christoph Sens-Schönfelder; Professor Dr. Serge A. Shapiro; Professor Dr. Frederik Tilmann
• Subject Area: Geophysics
• Term: from 2015 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 281499449

Despite our general understanding of the macroscopic circumstances that generate large earthquakes, significant uncertainties exist about the internal processes in the material that hosts the rupture. However, these local processes are the crucial component that govern the evolution of a rupture into a large earthquake.The earthquake sequence in northern Chile that culminated in the April 1st 2014 Iquique earthquake (Mw 8.1) represents an exceptional opportunity for the investigation of such deformation and damage processes in a subduction zone because of its extended foreshock sequence, which was captured alongside the main shock by the Integrated Plate boundary Observatory of Chile (IPOC). Well monitored plentiful seismicity in the preparation phase of the large event is interesting in itself as it provides a unique opportunity to study the preparatory phase of an imminent great earthquake. In addition, as the foreshock and aftershock sequences partially overlap, the fault zone is illuminated in a similar way before and after the earthquake, easing both the study of the static structure as well as its variability. Such a possibility is lacking in most of the sequences previously investigated with the methods proposed here.To constrain the dominant factors influencing seismogenesis during the Iquique earthquake sequence we use seismic interferometry and waveform processing in three directions: (A) high precision seismicity mapping, (B) tomographic structural imaging, and (C) detection of temporal material changes. A joint analysis will interpret the results in terms of stress, pore pressure variations and impact of shaking. High precision waveform-based event relocation will delineate areas of activity and identify clusters of repeating events in order to understand the distribution of asperities and their possible variability through time. Waveform analysis will be used to better constrain the depth of the predominantly offshore seismicity, crucial for understanding the partition of deformation between the overriding plate, the plate interface and the downgoing plate. Also, a catalogue of repeating events forms the basis for the application of coda wave interferometry and determination of time-dependencies in double-difference S minus P travel times. Finally, ambient noise interferometry will be used to infer the static shear velocity structure from surface wave tomography but also to infer time-dependent changes.This project is part of a research consortium and a rationale for the whole project bundle is provided in a summary paper attached to this application.

• DFG Programme: Research Grants