Time-Dependent Afterslip of the 2009 Mw 6.3 Dachaidan Earthquake (China) and Viscosity beneath the Qaidam Basin Inferred from Postseismic Deformation Observations

Abstract

Abstract:The 28 August 2009 Mw 6.3 Dachaidan (DCD) earthquake occurred at the Qaidam Basin's northern side. To explain its postseismic deformation time series, the method of modeling them with a combination model of afterslip and viscoelastic relaxation is improved to simultaneously assess the time-dependent afterslip and the viscosity. The coseismic slip model in the layered model is first inverted, showing a slip pattern close to that in the elastic half-space. The postseismic deformation time series can be explained by the combination model, with a total root mean square (RMS) misfit of 0.37 cm. The preferred time-dependent afterslip mainly occurs at a depth from the surface to about 9.1 km underground and increases with time, indicating that afterslip will continue after 28 July 2010. By 334 days after the main shock, the moment released by the afterslip is 0.91ˆ10 18 N¨m (Mw 5.94), approximately 24.3% of that released by the coseismic slip. The preferred lower bound of the viscosity beneath the Qaidam Basin's northern side is 1ˆ10 19 Pa¨s, close to that beneath its southern side. This result also indicates that the viscosity structure beneath the Tibet Plateau may vary laterally.

Blind Thrusting, Surface Folding, and the Development of Geological Structure in the Mw 6.3 2015 Pishan (China) Earthquake

“…Afterslip distributed around and slightly overlapping the coseismic slip patch is in line with theoretical models including but not limited to the case where a velocity-weakening patch is surrounded by velocitystrengthening fault plane (Avouac, 2015;Helmstetter & Shaw, 2009;Marone et al, 1991) and has already been observed in some cases (e.g., Liu et al, 2016;Miyazaki et al, 2004;Thomas et al, 2014). In this case our interpretation is limited by the similarity of surface displacement patterns produced by different models.…”

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

“…The 10 November 2008 earthquake occurred south of the Olongbulak Shan with a depth of ∼12 km and produced short‐term and low‐amplitude down‐dip afterslip (Daout, Steinberg, Isken, et al., 2020). Conversely, the 28 August 2009 shallow event occurred at a depth of ∼5 km and produced afterslip around the co‐seismic area (Daout, Steinberg, Isken, et al., 2020; Elliott, Parsons, et al., 2011; Liu, Xu, Li, et al., 2016) (Figure 1b). Despite the deep origin of the 2008 post‐seismic, it is important to note that the short‐term post‐seismic observed in the Envisat data during the 2009–2011 period, might be a combination of the post‐seismic surface displacements from both Haxi earthquakes.…”

“…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, Li, et al., 2016; Liu, Xu, Wen, & Fok, 2015; Liu, Xu, Wen, & Li, 2016). Daout, Steinberg, Isken, et al.…”

Modeling Orbital Error in InSAR Interferogram Using Frequency and Spatial Domain Based Methods

“…The theoretical accuracy can be as high as a centimeter to as low as a millimeter. This technique has been widely used to identify many geophysical processes that usually cause long-wavelength crustal deformation, including strain accumulation along locked continental faults, coseismic deformation caused by the occurrence of faulting in the lithosphere, and postseismic deformation caused by afterslip and viscoelastic relaxation [4][5][6].…”