Abstract
AbstractUnderstanding the mechanisms by which earthquake cycles produce folding and accommodate shortening is essential to quantify the seismic potential of active faults and integrate aseismic slip within our understanding of the physical mechanisms of the long‐term deformation. However, measuring such small deformation signals in mountainous areas is challenging with current space‐geodesy techniques, due to the low rates of motion relative to the amplitude of the noise. Here we successfully carry out a multitemporal Interferometric Synthetic Aperture Radar analysis over the North Qaidam fold‐thrust system in NE Tibet, where eight Mw> 5.2 earthquakes occurred between 2003 and 2009. We report various cases of aseismic slip uplifting the thickened crust at short wavelengths. We provide a rare example of a steep, shallow, 13‐km‐long and 6‐km‐wide afterslip signal that coincides spatially with an anticline and that continues into 2011 in response to a Mw 6.3 event in 2003. We suggest that a buried seismic slip during the 2003 earthquake has triggered both plastic an‐elastic folding and aseismic slip on the shallow thrusts. We produce a first‐order two‐dimensional model of the postseismic surface displacements due to the 2003 earthquake and highlight a segmented slip on three fault patches that steepen approaching the surface. This study emphasizes the fundamental role of shallow aseismic slip in the long‐term and permanent deformation of thrusts and folds and the potential of Interferometric Synthetic Aperture Radar for detecting and characterizing the spatiotemporal behavior of aseismic slip over large mountainous regions.
Highlights
Recent developments in space geodetic monitoring and in fault rupture inversions have highlighted the variability in fault deformation style in term of where and when slip is accommodated on such structures
We suggest that a buried seismic slip during the 2003 earthquake has triggered both plastic an-elastic folding and aseismic slip on the shallow thrusts
We present a multitemporal Interferometric Synthetic Aperture Radar (InSAR) processing method to assist the unwrapping of interferograms affected by high-fringe rates, as well as an approach to decompose time series of surface displacement into functional basis functions
Summary
Recent developments in space geodetic monitoring and in fault rupture inversions have highlighted the variability in fault deformation style in term of where and when slip is accommodated on such structures. As aseismic stress release affects the slip budget and may potentially trigger large earthquakes (Obara & Kato, 2016; Socquet et al, 2017; Vallée et al, 2013) or halt seismic ruptures (Jolivet et al, 2013), the identification of creeping fault regions and the characterization of their temporal evolution, or their relation with earthquakes, are essential for seismic hazard assessments. Another reason for studying aseismic slip is to constrain the time period within the seismic cycle during which geomorphological structures are formed.
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