We report Global Positioning System (GPS) measurements of postseismic deformation following the 2015 M w 7.8 Gorkha (Nepal) earthquake, including previously unpublished data from 13 continuous GPS stations installed in southern Tibet shortly after the earthquake. We use variational Bayesian Independent Component Analysis (vbICA) to extract the signal of postseismic deformation from the GPS time series, revealing a broad displacement field extending >150 km northward from the rupture. Kinematic inversions and dynamic forward models show that these displacements could have been produced solely by afterslip on the Main Himalayan Thrust (MHT) but would require a broad distribution of afterslip extending similarly far north. This would require the constitutive parameter (a − b)σ to decrease northward on the MHT to ≤0.05 MPa (an extreme sensitivity of creep rate to stress change) and seems unlikely in light of the low interseismic coupling and high midcrustal temperatures beneath southern Tibet. We conclude that the northward reach of postseismic deformation more likely results from distributed viscoelastic relaxation, possibly in a midcrustal shear zone extending northward from the seismogenic MHT. Assuming a shear zone 5-20 km thick, we estimate an effective shear-zone viscosity of 3•10 16-3•10 17 Pa•s over the first 1.12 postseismic years. Near-field deformation can be more plausibly explained by afterslip itself and implies (a − b)σ~0.5-1 MPa, consistent with other afterslip studies. This near-field afterslip by itself would have re-increased the Coulomb stress by ≥0.05 MPa over >30% of the Gorkha rupture zone in the first postseismic year, and deformation further north would have compounded this reloading. However, the data used in previous studies of post-Gorkha deformation provided limited resolution of this key region north of the rupture: Global Positioning System (GPS) data (Figures 1a and 1b, open squares) were either confined to Nepal (
On 1 May 2017, two MW6.2 earthquakes occurred near the border of northwestern British Columbia and Alaska separated by about 2 hr in time. Despite their close distance (~10 km), the two events have different focal mechanisms, with the first featuring a reverse focal mechanism and the second strike slip. Both focal plane solutions are inconsistent with the nearby southeastern Denali fault system. To resolve their ruptured fault planes, we invert for the earthquake point source parameters and analyze rupture directivity via regional and teleseismic waveforms. We also model the near‐field GPS data and relocate the aftershocks to determine the fault planes. The results indicate that the first event ruptured updip along a steep SW‐dipping fault and the second event ruptured to the ESE along a left‐lateral fault. We infer that the earthquake doublet was related to the regional stress field and slip on the active Duke River fault. The involved faults are associated with transpression caused by the oblique collision of the Yakutat block.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.