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Postseismic Deformation Following the 2015 M_w7.8 Gorkha (Nepal) Earthquake: New GPS Data, Kinematic and Dynamic Models, and the Roles of Afterslip and Viscoelastic Relaxation

Liu-Zeng, J. and Zhang, Z. and Rollins, C. and Gualandi, A. and Avouac, J.-P. and Shi, H. and Wang, P. and Chen, W. and Zhang, R. and Zhang, P. and Wang, W. and Li, Y. and Wang, T. and Li, Z. (2020) Postseismic Deformation Following the 2015 M_w7.8 Gorkha (Nepal) Earthquake: New GPS Data, Kinematic and Dynamic Models, and the Roles of Afterslip and Viscoelastic Relaxation. Journal of Geophysical Research. Solid Earth, 125 (9). Art. No. e2020JB019852. ISSN 2169-9313. https://resolver.caltech.edu/CaltechAUTHORS:20200819-162804555

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Abstract

We report Global Positioning System (GPS) measurements of postseismic deformation following the 2015 M_w7.8 Gorkha (Nepal) earthquake, including previously unpublished data from 13 continuous GPS stations installed in southern Tibet shortly after the earthquake.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 ~3·10¹⁶–3·10¹⁷ 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.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1029/2020jb019852DOIArticle
http://tectonics.caltech.edu/resources/gorkha.htmlRelated ItemData
ORCID:
AuthorORCID
Rollins, C.0000-0002-5291-6956
Gualandi, A.0000-0002-3100-8932
Avouac, J.-P.0000-0002-3060-8442
Additional Information:© 2020 American Geophysical Union. Issue Online: 03 September 2020; Version of Record online: 03 September 2020; Accepted manuscript online: 08 July 2020; Manuscript accepted: 29 June 2020; Manuscript revised: 22 June 2020; Manuscript received: 25 March 2020. We are indebted to Sylvain Barbot and an anonymous reviewer for providing suggestions and feedback that greatly improved the manuscript. We thank Lisa Christiansen and Naveed Near‐Ansari for technical assistance. J. L.‐Z. was supported by the National Natural Science Foundation of China (NSFC) (41761144065 and U1839203) and Basic Research Fund for Central Scientific Institutes (IGCEA 1206 and 1812). J.‐P. A. was supported by National Science Foundation (NSF) Award EAR‐1821853. Data Availability Statement: The data are published in the repository http://tectonics.caltech.edu/resources/gorkha.html as follows: ITRF2008_midday_ODRENGL.zip are the time series at 171 stations in ITRF2008 (light gray in Figures 3 and 4). Indiafixed_midday_detrended_deseasonal_rmoffsets_rmaftershock_errpropagation_ODRENGL.zip are the post‐Gorkha portions of the time series at 94 stations with trends, seasonal signals, and post‐Gorkha offsets removed (blue in Figures 3 and 4). Liuetal_2020_postseismicIC1.zip are the time series of the first postseismic Independent Component at the 67 stations that have data over ≥20% of the postseismic period (black in Figures 3 and 4). Liu_etal_ITRF2008ts_UNRcomparison.zip contains plots comparing our time series in ITRF2008 (Figures 3 and 4, light gray) with those from the Nevada Geodetic Laboratory (NGL). vel_interp_ODRENGL.txt gives the estimated India‐relative linear velocities at all stations (main text section 2; Figures 3 and 4, orange; Figures 5 and 7, red arrows). vel_Indiafixed_literatureunified.txt gives India‐relative velocities from literature (section 2; Figures 5 and 7, gray arrows). offsets_estimated_Indiafixed_ODRENGL.txt specifies offsets estimated and removed from the India‐relative time series. The 13 new stations are bolded in Figures 1, 6, and 8.
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
National Natural Science Foundation of China41761144065
National Natural Science Foundation of ChinaU1839203
Basic Research Fund for Central Scientific InstitutesIGCEA 1206
Basic Research Fund for Central Scientific InstitutesIGCEA 1812
NSFEAR-1821853
Issue or Number:9
Record Number:CaltechAUTHORS:20200819-162804555
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200819-162804555
Official Citation:Liu‐Zeng, J., Zhang, Z., Rollins, C., Gualandi, A., Avouac, J.‐P., & Shi, H., et al. (2020). Postseismic deformation following the 2015 Mw7.8 Gorkha (Nepal) earthquake: New GPS data, kinematic and dynamic models, and the roles of afterslip and viscoelastic relaxation. Journal of Geophysical Research: Solid Earth, 125, e2020JB019852. https://doi.org/10.1029/2020JB019852
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105040
Collection:CaltechAUTHORS
Deposited By: George Porter
Deposited On:20 Aug 2020 14:15
Last Modified:18 Sep 2020 20:56

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