Seismic noise correlations to image structural and mechanical changes associated with the Mw 7.9 2008 Wenchuan earthquake

Abstract

We locate temporal changes of seismic wave speed and scattering properties of the crust associated with the 2008 Mw7.9 Wenchuan earthquake. To that end, we analyze ambient seismic noise records from 2007 until the end of 2008 in the 1–3 s period band and in the 12–20 s period band measured in a region that covers the southern two thirds of the fault activated during the earthquake. To locate the changes, we use a refined imaging procedure based on the sensitivity of scattered waves to weak perturbations. This inverse method uses the radiative transfer approximation to describe the intensity of the noise correlation coda. Our results show that the largest structural changes are observed northeast of the Wenchuan epicenter, around the fault zone where aftershocks are distributed. The spatial and temporal characteristics of the behavior of the crust at depth around the Wenchuan earthquake suggest a postseismic and geology‐dependent signature of the middle crust. We also observe a clear seasonal signature within the Sichuan basin at depth that we relate to the heavy rainfalls during the monsoon season. This seasonality can also be observed at the surface in form of a waveform decoherence. Our study highlights that seismic velocity changes, and waveform decoherence are independent measurements that are sensitive to different parameters and can thus give complementary information. In our study we also point out the value of studying the evolution of the changes at different times in the coda.

The time dependence of rock healing as a universal relaxation process, a tutorial

“…Relaxation of the seismic velocity after perturbing rocks has been observed in laboratory studies (Ten Cate & Shankland 1996;Zaitsev et al 2003;Vakhnenko et al 2004;Ten Cate 2011) and field observations (Poupinet et al 1984;Schaff & Beroza 2004;Wegler & Sens-Schönfelder 2007;Brenguier et al 2008;Wu et al 2009;Nakata & Snieder 2011Wu & Peng 2012;Brenguier et al 2014;Obermann et al 2014;Richter et al 2014), and is thus an observable property under the right conditions. These observations usually show a recovery similar to the relaxation shown in Fig.…”

“…Laboratory studies (Ten Cate & Shankland 1996;Zaitsev et al 2003;Vakhnenko et al 2004;Ten Cate 2011) and seismological field observations (Poupinet et al 1984;Schaff & Beroza 2004;Wegler & SensSchönfelder 2007;Brenguier et al 2008;Wu et al 2009;Nakata & Snieder 2011;Hobiger et al 2012;Nakata & Snieder 2012;Wu & Peng 2012;Brenguier et al 2014;Obermann et al 2014;Richter et al 2014;Gassenmeier et al 2016) show that the seismic velocity of rocks is often reduced during shaking, and recovers afterwards. Gassenmeier et al (2016) demonstrated that, at least in some cases, these changes are caused by the shaking of the subsurface that damages the material.…”

Application of seismic interferometry by multidimensional deconvolution to ambient seismic noise recorded in Malargüe, Argentina

“…Seismic monitoring has been applied successfully on various scales (e.g. Obermann et al 2014;Salvermoser et al 2015).…”

Towards monitoring the englacial fracture state using virtual-reflector seismology

“…This may allow monitoring of subsurface velocity changes smaller than half a per cent and with a daily resolution (Sens-Schönfelder & Wegler 2006;Obermann et al 2014). Usually, the measurement of velocity changes relies on later arriving coda waves of ambientfield derived medium responses, which have followed an indirect and thus longer path through the medium.…”