Slip model of the 2008 M w 7.9 Wenchuan (China) earthquake derived from co-seismic GPS data

Abstract

Near-field co-seismic GPS data were used to derive the slip distribution of the 12 May 2008 Wenchuan earthquake. Based on field measurements and geological observations, the earthquake is represented by ruptures on the Beichuan fault and a neighboring fault from Pengxian to Guanxian, both dipping with a decreasing angle with depth. Using a layered elastic crust model, we obtained a slip model that not only best fits the co-seismic GPS data but which also shows general consistency with the surface ruptures observed from the field survey. The slip maxima are dominant at a very shallow depth near Beichuan and Jiangyou, although the exact peak value of the slip distribution is not well constrained due to the inhomogeneous data coverage in the near-fault area. The maximum slip in our inversion is thus limited to about 9 m, as estimated from the field measurement, but no strict restriction is applied to the slip direction, i.e., the rake angle. The slip model yields a moment magnitude that is very close to M w = 7.9, which is the estimate based on teleseismic observations. Near the hypocenter, the slip exhibits reverse behavior. The major rupture near Beichuan involves both right-lateral strike-slip and reverse components. Slip on the secondary fault is dominated by the reverse component with a maximum of approximately 2-3 m.

Deep coseismic slip of the 2008 Wenchuan earthquake inferred from joint inversion of fault stress changes and GPS surface displacements

“…The spatial distribution of fault slip from the GPS-only inversion agrees well with the geodetic data obtained in previous studies, including GPS and/or InSAR observations (Hao et al, 2009;Shen et al, 2009;Diao et al, 2010;Tong et al, 2010;Wang et al, 2011. The coseismic slips on fault planes are with varying characteristics along the strike direction.…”

“…The total geodetic moment estimated from our preferred slip model is 9.4 × 10 20 Nm (equivalent to a moment magnitude of 7.96), which is slightly greater than the 9.2 × 10 20 Nm (equivalent to a moment magnitude of 7.91) derived from the GPSonly inversion slip model. The moment magnitude of our preferred slip model is close to the existing results from the geodetic inversion using GPS and/or InSAR data but also larger than the seismic moment magnitude of 7.8 from Zhao et al (2010), which may result from the additional surface displacements caused by the few aftershocks in the period of used data (Shen et al, 2009;Diao et al, 2010;Tong et al, 2010;Wang et al, 2011;Zhao et al, 2010).…”

“…12. The mean GPS misfits from the joint inversion reach 1.6 cm and 1.8 cm for the north and east components, respectively, which is significantly less than the results from the inversion using only GPS and/or InSAR data (Hao et al, 2009;Shen et al, 2009;Diao et al, 2010;Tong et al, 2010;Wang et al, 2011). Most model misfits are less than 1.0 cm, and more than 98% of the GPS displacements can be well explained in the joint inversion slip model.…”

“…However, coseismic faulting below 15 km is not recognized in the previous studies using only geodetic data (Hao et al, 2009;Shen et al, 2009;Diao et al, 2010;Tong et al, 2010;Wang et al, 2011, while the inversions based on seismic data indicate deeper slip (Ji and Hayes, 2008;Zhao et al, 2010).…”

Rapid afterslip and short-term viscoelastic relaxation following the 2008 MW7.9 Wenchuan earthquake

“…Layer Using the constrained least squares method (Diao et al, 2010), Xu et al (2010) derived the coseismic slip distribution of the five sub-faults. The data they used include the 158 horizontal and 46 vertical GPS displacements as mentioned above and 3 801 re-sampled InSAR LOS displacements derived from six high precision Lband SAR (PALSAR) data (Hashimoto et al, 2009).…”