Relocation of the M8.0 Wenchuan earthquake and its aftershock sequence

S U M M A R YSince centroid moment tensor (CMT) solution is not enough to describe the mechanism variations of large earthquakes, multiple CMTs were investigated in recent years by inverting seismic waveforms to retrieve the mechanism complexities. However, a problem in these waveform inversions is the trade-off between spatial mechanism variation and temporal rupture process, which may lead to ambiguous results. In this work, we propose a simple but practical approach to invert geodetic coseismic data for spatial mechanism variation. Because there is no need to solve for rupture velocity, geodetic inversion is generally more efficient and robust than waveform inversion. This approach was used to investigate the mechanism variation of the 2008 Wenchuan earthquake. In the case study, a line fault, whose position had been optimized through a 3-D grid search, was used to approximate the rupture fault, aiming to determine the mechanism variations along the strike direction. From the inversion results, there are thrustslips and strike-slips in the southwest and northeast, respectively. The mechanism change appears at 160-200 km to the northeast of the epicentre, where compensated linear vector dipoles (CLVDs) have a local maximum and also support a significant mechanism change. By testing eight line faults with different positions, it is found that the inversion results do not strongly depend on the fault position, suggesting that the mechanism and its variations are robustly constrained in coseismic data inversion with our approach. Compared to waveform inversions, this work provides a more effective way to explore the mechanism complexities, and lays a foundation for future joint inversion of seismic and geodetic data sets.

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“…The location and orientation of the line fault is in good agreement with the aftershock distribution (Huang et al 2008; Fig. 1).…”

Section: A P P L I C At I O N T O T H E 2 0 0 8 M W 7 9 W E N C H Usupporting

confidence: 74%

Geodetic inversion for source mechanism variations with application to the 2008 Mw7.9 Wenchuan earthquake

Zhang

Wang

2015

Geophysical Journal International

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“…(b) Three-dimensional geometry of the main fault and discrete slip on patches. The white dots show aftershocks up to 22 July 2008 (Huang et al, 2008).…”

Section: Data Compilationmentioning

confidence: 99%

“…The parameters are taken from CRUST2.0 (Mooney et al, 1998) (see Table 1). Based on the aftershock distribution (Huang et al, 2008) and the mapped surface ruptures identified in the field survey (Liu et al, 2008;Zhang et al, 2008), we then design a double-fault source model. The main Beichuan fault is divided into two segments: the NE segment is 120 km, striking N228.5…”

Section: Parameter Settingmentioning

confidence: 99%

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

et al. 2010

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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.

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“…The earthquake propagated unilaterally to the northeast, leaving the southern segments of the LMSF (hereafter refered to as the southern LMSF) unbroken [9,10] (Figure 1). In addition, the southern LMSF accommodated few aftershocks [11]. On 20 April 2013, the Mw 6.6 Lushan earthquake ruptured the southern LMSF and filled part of the rupture deficit along the southern LMSF [12].…”

Section: Introductionmentioning

confidence: 99%

“…In addition, the southern LMSF accommodated few aftershocks [11]. On 20 April 2013, the Mw 6.6 Lushan earthquake ruptured the southern LMSF and filled part of the rupture deficit along the southern LMSF [12].…”

Section: Introductionmentioning

confidence: 99%

GPS-Derived Fault Coupling of the Longmenshan Fault Associated with the 2008 Mw Wenchuan 7.9 Earthquake and Its Tectonic Implications

Zhang

Shan

et al. 2018

Remote Sensing

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Abstract:Investigating relationships between temporally-and spatially-related continental earthquakes is important for a better understanding of the crustal deformation, the mechanism of earthquake nucleation and occurrence, and the triggering effect between earthquakes. Here we utilize Global Positioning System (GPS) velocities before and after the 2008 Mw 7.9 Wenchuan earthquake to invert the fault coupling of the Longmenshan Fault (LMSF) and investigate the impact of the 2008 Mw 7.9 Wenchuan earthquake on the 2013 Mw 6.6 Lushan earthquake. The results indicate that, before the 2008 Mw 7.9 Wenchuan earthquake, fault segments were strongly coupled and locked at a depth of~18 km along the central and northern LMSF. The seismic gap between the two earthquake rupture zones was only locked at a depth < 5 km. The southern LMSF was coupled at a depth of~10 km. However, regions around the hypocenter of the 2013 Mw 6.6 Lushan earthquake were not coupled, with an average coupling coefficient~0.3. After the 2008 Mw 7.9 Wenchuan earthquake, the central and northern LMSF, including part of the seismic gap, were decoupled, with an average coupling coefficient smaller than 0.2. The southern LMSF, however, was coupled to~20 km depth. Regions around the hypocenter of the 2013 Mw 6.6 Lushan earthquake were also coupled. Moreover, by interpreting changes of the GPS velocities before and after the 2008 Mw 7.9 Wenchuan earthquake, we find that the upper crust of the eastern Tibet (i.e., the Bayan Har block), which was driven by the postseismic relaxation of the 2008 Mw 7.9 Wenchuan earthquake, thrust at an accelerating pace to the Sichuan block and result in enhanced compression and shear stress on the LMSF.

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Relocation of the M8.0 Wenchuan earthquake and its aftershock sequence

Cited by 158 publications

References 13 publications

Geodetic inversion for source mechanism variations with application to the 2008 Mw7.9 Wenchuan earthquake

Geodetic inversion for source mechanism variations with application to the 2008 Mw7.9 Wenchuan earthquake

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

GPS-Derived Fault Coupling of the Longmenshan Fault Associated with the 2008 Mw Wenchuan 7.9 Earthquake and Its Tectonic Implications

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