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‘Two go together’: Near-simultaneous moment release of two asperities during the 2016 Mw 6.6 Muji, China earthquake

‘Two go together’: Near-simultaneous moment release of two asperities during the 2016 Mw 6.6 Muji, China earthquake
‘Two go together’: Near-simultaneous moment release of two asperities during the 2016 Mw 6.6 Muji, China earthquake
On 25 November 2016, a Mw 6.6 earthquake ruptured the Muji fault in western Xinjiang, China. We investigate the earthquake rupture independently using geodetic observations from Interferometric Synthetic Aperture Radar (InSAR) and regional seismic recordings. To constrain the fault geometry and slip distribution, we test different combinations of fault dip and slip direction to reproduce InSAR observations. Both InSAR observations and optimal distributed slip model suggest buried rupture of two asperities separated by a gap of greater than 5 km. Additional seismic gaps exist at the end of both asperities that failed in the 2016 earthquake. To reveal the dynamic history of asperity failure, we inverted regional seismic waveforms for multiple centroid moment tensors and construct a moment rate function. The results show a small centroid time gap of 2.6 s between the two sub-events. Considering the >5 km gap between the two asperities and short time interval, we propose that the two asperities failed near-simultaneously, rather than in a cascading rupture propagation style. The second sub-event locates ∼39 km to the east of the epicenter and the centroid time is at 10.7 s. It leads to an estimate of average velocity of 3.7 km/s as an upper bound, consistent with upper crust shear wave velocity in this region. We interpret that the rupture front is propagating at sub-shear wave velocities, but that the second sub-event has a reduced or asymmetric rupture time, leading to the apparent near-simultaneous moment release of the two asperities.
0012-821X
34-42
Bie, Lidong
c86a2fa9-3fd4-4efd-b606-04b27ecc2c92
Hicks, Stephen
036d1b3b-bb7a-4a22-b2ce-71618a1723a3
Garth, Thomas
06c5b0c6-d7a3-4050-9009-50addc6e6fbc
Gonzalez, Pablo
1069108c-49be-4815-81ed-6cf5b832d10a
Rietbrock, Andreas
9fbc63af-9a9a-4dfe-a389-83d92b5f4cc2
Bie, Lidong
c86a2fa9-3fd4-4efd-b606-04b27ecc2c92
Hicks, Stephen
036d1b3b-bb7a-4a22-b2ce-71618a1723a3
Garth, Thomas
06c5b0c6-d7a3-4050-9009-50addc6e6fbc
Gonzalez, Pablo
1069108c-49be-4815-81ed-6cf5b832d10a
Rietbrock, Andreas
9fbc63af-9a9a-4dfe-a389-83d92b5f4cc2

Bie, Lidong, Hicks, Stephen, Garth, Thomas, Gonzalez, Pablo and Rietbrock, Andreas (2018) ‘Two go together’: Near-simultaneous moment release of two asperities during the 2016 Mw 6.6 Muji, China earthquake. Earth and Planetary Science Letters, 491, 34-42. (doi:10.1016/j.epsl.2018.03.033).

Record type: Article

Abstract

On 25 November 2016, a Mw 6.6 earthquake ruptured the Muji fault in western Xinjiang, China. We investigate the earthquake rupture independently using geodetic observations from Interferometric Synthetic Aperture Radar (InSAR) and regional seismic recordings. To constrain the fault geometry and slip distribution, we test different combinations of fault dip and slip direction to reproduce InSAR observations. Both InSAR observations and optimal distributed slip model suggest buried rupture of two asperities separated by a gap of greater than 5 km. Additional seismic gaps exist at the end of both asperities that failed in the 2016 earthquake. To reveal the dynamic history of asperity failure, we inverted regional seismic waveforms for multiple centroid moment tensors and construct a moment rate function. The results show a small centroid time gap of 2.6 s between the two sub-events. Considering the >5 km gap between the two asperities and short time interval, we propose that the two asperities failed near-simultaneously, rather than in a cascading rupture propagation style. The second sub-event locates ∼39 km to the east of the epicenter and the centroid time is at 10.7 s. It leads to an estimate of average velocity of 3.7 km/s as an upper bound, consistent with upper crust shear wave velocity in this region. We interpret that the rupture front is propagating at sub-shear wave velocities, but that the second sub-event has a reduced or asymmetric rupture time, leading to the apparent near-simultaneous moment release of the two asperities.

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Accepted/In Press date: 16 March 2018
e-pub ahead of print date: 27 March 2018
Published date: 1 June 2018

Identifiers

Local EPrints ID: 419208
URI: https://eprints.soton.ac.uk/id/eprint/419208
ISSN: 0012-821X
PURE UUID: 521258e0-d59a-490c-b610-248e1eda88e1
ORCID for Stephen Hicks: ORCID iD orcid.org/0000-0002-7476-3284

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Date deposited: 09 Apr 2018 16:30
Last modified: 14 Mar 2019 01:26

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Contributors

Author: Lidong Bie
Author: Stephen Hicks ORCID iD
Author: Thomas Garth
Author: Pablo Gonzalez
Author: Andreas Rietbrock

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