Semiannual velocity variations around the 2008 Mw 7.9 Wenchuan Earthquake fault zone revealed by ambient noise and ACROSS active source data

Abstract

We continuously monitor the long-term seismic velocity variation of one of the major ruptured faults of the devastating 2008 M w 7.using accurately controlled routinely operated signal system active source and seismic noise-based monitoring technique. Our measurements show that the temporal velocity change is not homogeneous and highly localized in the damaged fault zone and the adjacent areas. Velocity variations from the active and passive methods are quite consistent, which both are characterized by ±0.2 % seasonal variation, with peak and trough at winter and summer, respectively. The periodic velocity variation within fault zone exhibits remarkably positive correlation with barometric pressure with stress sensitivity in the order of 10 -6 Pa -1 , suggesting that the plausible mechanism might be the crack density variation of the shallow subsurface medium of the damaged fault zone in response to the cyclic barometric pressure loading.

Active source monitoring at the Wenchuan fault zone: coseismic velocity change associated with aftershock event and its implication

“…A *2.0 % velocity change at stress drop of 0.0077-0.0125 MPa corresponds to a stress sensitivity of *10 -6 Pa -1 . Stress sensitivity of *10 -6 Pa -1 is little bit larger than the previous results from laboratory and field measurements (e.g., Simmons 1964;Niu et al 2008), but consistent with the stress sensitivity of velocity perturbation from the passive and active source data in this region (Chen et al 2014) and the sensitivity of fractured zone or surface sediments in others (e.g., Silver et al 2007;Wang et al 2008). Coring samples from the WSFD No.…”

Strong Seasonal Variations of Seismic Velocity in Eastern Margin of Tibetan Plateau and Sichuan Basin From Ambient Noise Interferometry

“…In addition, although there is the same level of loading, the local heterogeneities (e.g., directions of the cracks) (kilometer scale, Figure 6) contribute to the rapid spatial variations of the seasonality, which is similar to the conclusion of Chen et al. (2014). The phases of different depths are mostly synchronized (Figure 8c), indicating the same mechanism for the velocity change.…”

“…Thermal‐elastic effect tends to be regional and decays rapidly with depth (Ben‐Zion & Leary, 1986), so that it is inconsistent with the rapid spatial variations of our observed seasonality at the period of 2–10 s (Figures 5 and 6). In contrast, the effect of precipitation, through direct loading or pore pressure, depends on complex structures of cracks and materials in the crust (Chen et al., 2014) and can extend to much greater depths (Tsai, 2011).…”

Recent advances in imaging crustal fault zones: a review

“…Many observations have been reported on temporal velocity changes in fault zones and volcanic areas from the ANCC results (e.g., Chen et al 2014;Liu et al 2014). However, the resolution of the ANCC results is often limited by the frequency of extracted signals.…”