Retrieving robust noise-based seismic velocity changes from sparse data sets: synthetic tests and application to Klyuchevskoy volcanic group (Kamchatka)

• Published in: Geophysical Journal International
• Main Authors: Gómez-García, C, Brenguier, F., Boue, P., Shapiro, N. M., Droznin, D, Droznina, S. Ya., Senyukov, S. L., Gordeev, E. I.
• Other Authors: Institute of Earth Sciences Jaume Almera, Consejo Superior de Investigaciones Científicas Madrid (CSIC), Institut de Physique du Globe de Paris (IPGP), Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Université Paris Diderot - Paris 7 (UPD7)-IPG PARIS-Institut national des sciences de l'Univers (INSU - CNRS), Union Nationale des Coopératives Agricoles d'Elevage et d'Insémination Animale pour l'Espèce Caprine (CAPRI-IA), Kamchatka Branch of the Geophysical Service, Russian Academy of Sciences Moscow (RAS), Kamchatka Branch of the Geophysical Survey RAS, Institute of Volcanology and Seismology of the RAS, Far Eastern Branch of the Russian Academy of Sciences (FEB RAS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2018
• Subjects: Coda waves; Time series analysis; Time-series analysis; Seismic interferometry; Seismic noise; Volcano monitoring; [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]; Kamchatka
• Online Access: https://hal.univ-grenoble-alpes.fr/hal-02928326; https://hal.univ-grenoble-alpes.fr/hal-02928326/document; https://hal.univ-grenoble-alpes.fr/hal-02928326/file/Clara_draft_last_ver%20%281%29.pdf; https://doi.org/10.1093/gji/ggy190

International audience Continuous noise-based monitoring of seismic velocity changes provides insights into volcanic unrest, earthquake mechanisms and fluid injection in the subsurface. The standard monitoring approach relies on measuring traveltime changes of late coda arrivals between daily and reference noise cross-correlations, usually chosen as stacks of daily cross-correlations. The main assumption of this method is that the shape of the noise correlations does not change over time or, in other terms, that the ambient-noise sources are stationary through time. These conditions are not fulfilled when a strong episodic source of noise, such as a volcanic tremor, for example, perturbs the reconstructed Green's function. In this paper, we propose a general formulation for retrieving continuous time-series of noise-based seismic velocity changes without the requirement of any arbitrary reference cross-correlation function (CCF). Instead, we measure the changes between all possible pairs of daily cross-correlations and invert them using different smoothing parameters to obtain the final velocity change curve. We perform synthetic tests in order to establish a general framework for future applications of this technique. In particular, we study the reliability of velocity change measurements versus the stability of noise CCFs. We apply this approach to a complex data set of noise cross-correlations at Klyuchevskoy volcanic group (Kamchatka), hampered by loss of data and the presence of highly non-stationary seismic tremors.