Ambient Noise Monitoring of Seismic Speed

Ambient Noise Monitoring of Seismic Speed An example of the seasonal variation of the sources of secondary microseisms obtained from teleseismic body waves (see Landes et al. 2010 for details).
With the availability of continuous recordings from numerous seismological networks, it is now possible to use the ambient seismic noise to monitor the temporal evolution of mechanical properties of the Earth’s crust. As an example, we show the detection of co-seismic and post seismic change of seismic speeds associated with the 2004 Parkfield earthquake based on correlations of seismic noise recorded by stations of the High Resolution Seismic Network [Brenguier et al., 2008]. The velocity drops at the time of the earthquake, and recovers slowly during the next years. The similarity of the time evolution of the velocity anomaly with the strain measured by GPS suggests that the velocity change can be associated to both the well-documented response of shallow layers to strong motions, and the strain at depth. Changes of velocity are small and a high precision of measurement is required. Specifically, we must separate the effect of changes at depth and the apparent changes due to the temporal migration of the sources of noise. The latter can be also studies from the analysis of long continuous seismic recordings available at international data centers such as IRIS DMC [e.g. Landes et al., 2010].
</p><p>Brenguier F., M. Campillo,C. Hadziioannou, N.M. Shapiro, R.M. Nadeau, E. Larose (2008), Postseismic relaxation along the San Andreas fault in the Parkfield area investigated with continuous seismological observations SCIENCE, 321 (5895), 1478-1481.
</p><p>Landes M, Hubans F, Shapiro NM, Paul A., and M. Campillo Origin of deep ocean microseisms by using teleseismic body waves J. Geophysical Res. 115: B05302,2010
</p><p>Acknowledgements: This work is supported by the European Research Council Advanced Grant WHISPER</p>


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