Observing seismic and silent faulting related to a megathrust earthquake cycle: Joint application of InSAR and creepmeter ground displacement measurements
Final Report Abstract
We explored a combination of methods from quantitative tectonic geomorphology and geodesy to investigate the interaction of the upper crustal Atacama Fault System in N-Chile and the subduction zone seismic cycle of the underlying megathrust. The Atacama Fault System (AFS) is an active trench-parallel fault that ruptured at least three times in M≤7 Earthquakes in the past 10 ky, documented in the paleoseismological record demonstrating the potential of large events in the future. To investigate the current surface creep rate and to deduce the mode of strain accumulation, we applied InSAR for the investigation of the total fault length and millimeter to centimeter scale displacement and installed creepmeters for very local scale observations with micron precision and high temporal resolution. To investigate the long-term rupture history and the recurrence of large earthquakes along the different segments of the AFS we tested the applicability of two geomorphic markers, in order to 1) discriminate and quantify individual surface-breaking events; 2) extract cumulative and incremental vertical displacements from topographic data and investigate the displacement pattern along strike; 3) deduce reliable estimates of paleomagnitudes. One of the results was unexpected and is a unique observation along subduction zones so far. From the investigation of fault displacement in the 3.5 years prior and 1.5 years after the Mw=7.7 Tocopilla earthquake, we determined a reversal in the fault kinematics along one of the upper crustal faults overlying the Tocopilla rupture. This observation though surprising can be confirmed by field observations showing surface faults with opposing senses of displacement in the same outcrop. Additionally creepmeter observations starting in the early postseismic period also confirm the postseismic sense of displacement derived from InSAR data analysis and modeling and suggests the continuation of the postseismic transient signal until at least 2015. This finding indicates that transients in displacement accumulation take place on very short time scales and need to be taken into consideration in the interpretation of very short time scale observations. Nevertheless it is the permanent deformation that leads to the long-term deformation signals that are preserved in the fault scarp morphology. The testing of the geomorphic markers successfully lead to a new methodology that enables us to detect subtle gradient changes in high-resolution topographic profiles representing individual, potentially seismogenic surfacebreaking events at the analyzed fault segments. This new method developed in this study is a well-suited approach to assess the multiple rupture history of a complex fault system and is applicable to all types of fault scarps including composite and multiple scarps. This study following an approach combining geomorphological and geodetic techniques may lead to a better understanding of complex and transient faulting processes.
Publications
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(2011), Subduction Earthquake Segment Boundary Expressed in Surface Deformation of Mejillones Peninsula, N-Chile, J. Geophys. Res., 116, B02402
Victor, P., M. Sobiesiak, S. N. Nielsen, J. Glodny, and O. Oncken
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(2011): ~5cm ground resolution DEMs and Ortho-Imagery for the Atacama Fault System (AFS) in northern Chile, acquired with the Modular Airborne Camera System (MACS), Abstract G13A-0865. 2011 Fall Meeting, AGU, San Francisco, USA
Zielke, O., Victor, P., Oncken, O., Bucher, T., Lehmann, M.
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(2012), Response of forearc crustal faults to the megathrust earthquake cycle: InSAR evidence from Mejillones Peninsula, Northern Chile, Earth Planet. Sci. Lett., 333-334, 157-164
Shirzaei, M., R. Bürgmann, O. Oncken, T. R. Walter, P. Victor, and O. Ewiak
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(2012): Investigating the strain accumulation of upper plate faults at the N-Chilean convergent plate boundary at different spatial and temporal scale, Abstract T43A-2638. 2012 Fall Meeting, AGU, San Francisco, USA
Ewiak, O., Victor, P., Ziegenhagen, T. and O. Oncken
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(2012): The contribution of remotely triggered displacement events to the long-term strain accumulation along the Atacama Fault System, N-Chile, Abstract T22C-04. 2012 Fall Meeting, AGU, San Francisco, USA
Victor P., Schurr B., Sobiesiak M., Ewiak O. and Oncken O.
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(2014): Interaction of trench-parallel fault systems and the subduction zone earthquake cycle investigated with the IPOC Creepmeter array in N-Chile. Abstract. 2014 SSA Annual Meeting, Anchorage, Alasca. Seismological Research Letters, Volume 85, 2, p. 446
Victor P., Sobiesiak M., Schurr B., Ewiak O., Gonzalez G. and Oncken O.
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(2014): The IPOC Creepmeter Array in N-Chile: Monitoring Slip Accumulation Triggered by Local or Remote Earthquakes, Abstract T13C-4673, 2014 Fall Meeting, AGU, San Francisco, USA
Victor P., Schurr B., Oncken O., Sobiesiak M. and Gonzalez G.
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(2015), Investigating multiple fault rupture at the Salar del Carmen segment of the Atacama Fault System (northern Chile): Fault scarp morphology and knickpoint analysis, Tectonics, 34(2), 187-212
Ewiak, O., P. Victor, and O. Oncken
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Dynamic triggering of shallow slip on forearc faults constrained by monitoring surface displacement with the IPOC Creepmeter Array. Earth and Planetary Science Letters, Volume 502, 15 November 2018, Pages 57-73
Victor P., M. Sobiesiak, G. Gonzalez, M. Kempter, T. Ziegenhagen, and O. Oncken
