Interseismic and Postseismic Shallow Creep of the North Qaidam Thrust Faults Detected with a Multitemporal InSAR Analysis

Abstract

Understanding 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 M w > 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 M w 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.

Post‐Earthquake Fold Growth Imaged in the Qaidam Basin, China, With Interferometric Synthetic Aperture Radar

“…As reported by the authors (Daout, Sudhaus, Kausch, et al, 2019), shallow creep is in agreement with a rate-strengthening fault behavior of the uppermost part of the crust, but the duration, the amplitude, and the spatial extent of the observed surface displacements following the 2003 earthquake, during the 2003-2011 Envisat period, is a notable particularity, despite the low strain rate of the area. The 10 November 2008 and the 28 August 2009 Haixi earthquakes occurred in close proximity to each other within the Olongbulak Shan, to the west of the Delingha rupture ( Figure 1), and were followed by a period of an increased rate of seismicity in the region and aseismic slip (Daout, Steinberg, Isken, et al, 2020;Daout, Sudhaus, Kausch, et al, 2019;Elliott, Parsons, et al, 2011;Feng, 2015;Guihua et al, 2013;Liu, Xu, Wen, & Fok, 2015;. Daout, Steinberg, Isken, et al (2020) modeled the 2008 earthquake with a ∼32° north-dipping fault that roots under the Olongbulak pop-up structure at ∼12 km depth (top edge of the fault) ( Figure 1b), as well as down-dip aferslip along a coplanar north-dipping plane.…”

“…The structural cross-section across the Delingha anticline shown in Figure 4c is inferred from the observed signal, our own geomorphological mapping, and available models from Yin, Dang, Wang, et al (2008), Fang et al (2007), and Daout, Sudhaus, Kausch, et al (2019) (Figure S13). The Delingha fold shows sharp contacts between the truncated Pleistocene units on the southern sides of the fold and the Holocene deposits within the Delingha basin, in the footwall (Figure 4b, (Yin, Dang, Wang, et al, 2008)).…”

“…In addition, although simplified models are valuable in many ways, modeling shortening and the associated uplift across a fold‐and‐thrust belt system with one or two elastic dislocations is an arguable simplification of the complicated history and geometry of a thrusting morphology, which may involve several interconnected faults and folds that interact with each other, multiple bends, and anelastic deformation as in the upper plate around the bends (e.g., Daout, Barbot, Peltzer, Doin, et al., 2016; Davis et al., 1983; Medwedeff & Suppe, 1997; Sathiakumar et al., 2020; Tapponnier, Meyer, et al., 1990; Whipple et al., 2016). Some other geodetic observations have recently documented or/and modeled episodic aseismic ground deformations (e.g., Mariniere et al., 2020) or long‐periods of afterslip that correlate with the present‐day geomorphology (e.g., Barnhart, Lohman, & Mellors, 2013; Copley, 2014; Daout, Sudhaus, Kausch, et al., 2019; Elliott, Bergman, et al., 2015; Fielding et al., 2004; Mackenzie et al., 2016; Wimpenny et al., 2017; Zhou et al., 2018). These measurements suggest that the permanent deformation in fold‐and‐thrust belts might be sometimes created by distributed off‐fault deformation (i.e., anelastic buckling of the medium), or aseismic slip on secondary faults branching from the main earthquake fault or around it, and which occur during stages of the earthquake cycle other than the seismic event.…”

“…In this study, we conduct a Multi-Temporal Interferometric Synthetic Aperture Radar analysis across this northeastern part of the Tibetan Plateau using both C-band Envisat (2003C-band Envisat ( -2011 data derived from Daout, Sudhaus, Kausch, et al (2019), and C-band Sentinel-1 (2014-2019) data (Figures 1 and S2). We processed the Sentinel-1 data set and corrected both Envisat and Sentinel-1 data sets for tropospheric path delays using the newly ERA-5 atmospheric model provided by the European Center for Medium-Range Weather Forecasts (ECMWF).…”

Localized Afterslip at Geometrical Complexities Revealed by InSAR After the 2016 Central Italy Seismic Sequence

“…Unwrapping was performed in 2‐D with the NSBAS chain (Doin et al, 2015; Grandin et al, 2012). After unwrapping, to account for errors associated with stratified troposphere, we removed a quadratic cross‐function of elevation (z) and azimuth to ramps in azimuth (y) and in range (x) estimation following the function ax + by + c + ez + fz * az + g * (z * az) 2 using a least squares approach (Daout et al, 2019). Time series were then calculated following the NSBAS method (Daout et al, 2016; Doin et al, 2011) using an approach based on the Small Baseline Subset time series Analysis of López‐Quiroz et al's (2009) algorithm.…”