Geometric Control on Seismic Rupture and Earthquake Sequence Along the Yingxiu-Beichuan Fault With Implications for the 2008 Wenchuan Earthquake

Zhang, Lei; Liu, Yajing; Li, Duo; Yu, Hongyu und He, Changrong (2022): Geometric Control on Seismic Rupture and Earthquake Sequence Along the Yingxiu-Beichuan Fault With Implications for the 2008 Wenchuan Earthquake. In: Journal of Geophysical Research - Solid Earth, Bd. 127, Nr. 12, e2022JB024113

Abstract

The 2008 M-w 7.9 Wenchuan earthquake is the most disastrous seismic event in China since 1976. Both field and seismological investigations suggest a multi-stage coseismic rupture with most damage associated with the Yingxiu-Beichuan Fault (YBF) of spatially variable fault strike and dip angles. To investigate the effect of fault geometric complexity on coseismic rupture and paleoseismic pattern on the YBF, we perform earthquake sequence modeling on 3D fault geometry in the framework of rate-and-state friction law. Our model produces a long-term earthquake sequence with quasi-regular recurrences of whole-fault ruptures and segmented ruptures. The along-strike rupture segmentation, earthquake propagation speed, and slip rate are mainly controlled by along-strike variations of fault dip and strike angles. Particularly, the YBF can be divided into two segments: the southern segment featured by large events (M-w > 8.0) and the northern segment with smaller events (M-w < 7.5), with recurrence intervals primarily determined by the tectonic loading rate. In a whole-rupture event, the rupture speed mainly correlates with the fault dip angle;a smaller dip angle results in a wider seismogenic zone and higher rupture speeds, whereas the small-scale variation in rupture speed is regulated by the fault strike angle. The effect of strike variation on the total coseismic slip amount is more pronounced due to the large strike angle gradient along the YBF. After varying the slip vector to reflect the northward transition from the dominant thrust-slip to strike-slip faulting during the Wenchuan coseismic rupture, we obtain reasonably good agreement of model simulated coseismic surface displacements with GPS observations. Plain Language Summary The Yingxiu-Beichuan Fault (YBF) hosting the 2008 M-w 7.9 Wenchuan earthquake has a complex nonplanar interface. Seismic studies after the Wenchuan earthquake have unveiled a complex rupture process. Field trenching studies find a complex recurrence interval and rupture pattern of paleoseismic events. Here, we conduct a numerical simulation of earthquake sequences on the 3D YBF to study the effect of fault geometry on the coseismic rupture and paleoseismic behaviors. Our modeling results are quantitatively comparable with most field observations. Both whole-fault ruptures and partial rupture events are produced. The larger events (magnitude >8.0) initiate near the southern end of the YBF. The smaller events (magnitude <7.5) initiates near the northern end of the YBF. Their repeating time is mainly controlled by the background tectonic loading rate. In the partial rupture events, coseismic rupture stops near Nanba area when encountering a geometrical barrier due to a sharp change of fault dip. While the lateral rupture propagation speed is controlled by variation of both fault dip and strike angles, coseismic slip distribution is more controlled by the variation of fault strike (lateral fault orientation) than dip. We find that the orientation of slip vector is important in coseismic rupture modeling of Wenchuan-type event.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Geowissenschaften > Department für Geo- und Umweltwissenschaften
• Themengebiete: 500 Naturwissenschaften und Mathematik > 550 Geowissenschaften, Geologie
• ISSN: 2169-9313
• Sprache: Englisch