The postseismic response to the 2002M7.9 Denali Fault earthquake: constraints from InSAR 2003-2005

Abstract

S U M M A R YInSAR is particularly sensitive to vertical displacements, which can be important in distinguishing between mechanisms responsible for the postseismic response to large earthquakes (afterslip, viscoelastic relaxation). We produce maps of the surface displacements resulting from the postseismic response to the 2002 Denali Fault earthquake, using data from the Canadian Radarsat-1 satellite from the periods summer 2003, summer 2004 and summer 2005. A peak-to-trough signal of amplitude 4 cm in the satellite line of sight was observed between summer 2003 and summer 2004. By the period between summer 2004 and summer 2005, the displacement rate had dropped below the threshold required for observation with InSAR over a single year. The InSAR observations show that the principal postseismic relaxation process acted at a depth of ∼50 km, equivalent to the top of the mantle. However, the observations are still incapable of distinguishing between distributed (viscoelastic relaxation) and localized (afterslip) deformation. The imposed coseismic stresses are highest in the lower crust and, assuming a Maxwell rheology, a viscosity ratio of at least 5 between lower crust and upper mantle is required to explain the contrast in behaviour. The lowest misfits are produced by mixed models of viscoelastic relaxation in the mantle and shallow afterslip in the upper crust. Profiles perpendicular to the fault show significant asymmetry, which is consistent with differences in rheological structure across the fault.

A Review of Interferometric Synthetic Aperture RADAR (InSAR) Multi-Track Approaches for the Retrieval of Earth’s Surface Displacements

“…It is straightforward to note that the pdf distribution of the multi-look phase (see Equation (20)) is symmetrical with respect to its mean value (i.e., ϕx). This is in agreement with the additive model of Equation (19). It is worth noting that the validity of the model (19) is restricted to the [ϕx − π, ϕx + π] interval.…”

“…This is in agreement with the additive model of Equation (19). It is worth noting that the validity of the model (19) is restricted to the [ϕx − π, ϕx + π] interval. A closed-form for the standard deviation of the interferometric phase is hard to investigate, unless in the limit of Cramer-Rao, which is valid for high values of the spatial coherence k, where it assumes the asymptotic value [60]: Figure 5 plots the standard deviation of the multi-looked phase vs. the spatial coherence for different values of n. For example, if we consider a SAR pixel with given spatial coherence k = 0.35 and we assume n = 80, we obtain the height estimate has a standard deviation of about 1.5 m (by assuming a perpendicular baseline of the interferogram of 200 m).…”

“…Among these techniques, the SAR interferometry [13][14][15][16] plays a major role in the study of the dynamic of Earth's crust, thus permitting the monitoring of the surface movements. Deformations can be induced by several geophysical phenomena, such as the extensive fractures due to big earthquakes [17][18][19], pre-seismic deformations [20], slow-moving landslides [21][22][23][24], the eruptions of active volcanoes [25][26][27][28]. Human beings also severely contribute to the changes in the environment.…”

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

“…Three postseismic deformation mechanisms, alone or mixed, have been proposed to interpret the observed movements after an earthquake event, including poroelastic rebound, afterslip, and viscoelastic relaxation. InSAR observations have been successfully used to constrain the possible geophysical mechanisms of some earthquake cases [15,16,[25][26][27][28][29][30][31][32]. The mechanism of poroelastic rebound usually influences the postseismic deformation within a few kilometers to fault ruptures in a short period of time, whereas the other two mechanisms can generate postseismic deformation with a similar spatial pattern in the first few years [11,33].…”

“…The nearest station is approximately 40 km far away from the epicenter, making it unavailable to use GPS observation to do the following modeling. Meanwhile, InSAR data has also been confirmed as an alternative observation to investigate the postseismic process due to its high vertical precision and spatial resolution [15,16,[25][26][27][28][29][30][31][32]. Feng [22] and Liu et al [23] have derived the postseismic deformation time series.…”