Response of hydrothermal system to stress transients at Lassen Volcanic Center, California, inferred from seismic interferometry with ambient noise

Abstract

Abstract:Time-lapse monitoring of seismic velocity at volcanic areas can provide unique insight into the property of hydrothermal and magmatic fluids and their temporal variability. We established a quasi real-time velocity monitoring system by using seismic interferometry with ambient noise to explore the temporal evolution of velocity in the Lassen Volcanic Center, Northern California. Our monitoring system finds temporal variability of seismic velocity in response to stress changes imparted by an earthquake and by seasonal environmental changes. Dynamic stress changes from a magnitude 5.7 local earthquake induced a 0.1 % velocity reduction at a depth of about 1 km. The seismic velocity susceptibility defined as ratio of seismic velocity change to dynamic stress change is estimated to be about 0.006 MPa −1 , which suggests the Lassen hydrothermal system is marked by high-pressurized hydrothermal fluid. By combining geodetic measurements, our observation shows that the long-term seismic velocity fluctuation closely tracks snowinduced vertical deformation without time delay, which is most consistent with an hydrological load model (either elastic or poroelastic response) in which surface loading drives hydrothermal fluid diffusion that leads to an increase of opening of cracks and subsequently reductions of seismic velocity. We infer that heated-hydrothermal fluid in a vapor-dominated zone at a depth of 2-4 km range is responsible for the long-term variation in seismic velocity

Monitoring reservoir response to earthquakes and fluid extraction, Salton Sea geothermal field, California

“…We attribute decreases in seismic velocities to increases in crack opening induced by stress transients. Under this assumption, the sensitivity of velocity changes to external stress transients (η) was evaluated through the ratio of relative seismic velocity change (Δ v = dv / v ) and external stress transient (Δσ), η = (Δ v /Δσ) ( 15 , 35 , 36 ). If crack density (ρ c ) governs the velocity reduction, this stress sensitivity can be decomposed into two terms expressed as η = (Δ v /Δρ c )(Δρ c /Δσ) ( 37 ).…”

Coherence‐Based Approaches for Estimating the Composition of the Seismic Wavefield

“…Particular attention has been paid to understand the effect that the inhomogeneous distribution of noise sources would have on the coherence or cross‐correlation measured between stations, with the goal of determining whether measurements can be reliably used for the study of seismic velocities or attenuation (e.g., Cupillard & Capdeville, ; Harmon et al, ; Lawrence & Prieto, ; Tsai, , ; Weaver, ; Yang & Ritzwoller, ), with additional studies exploring the extent to which signal preprocessing can reduce the effect of inhomogeneous noise sources (e.g., Bensen et al, ; Viens et al, ). Some of these velocity or attenuation measurements require a great amount of precision and stability over time (Froment et al, ), such as for the observation of material velocity changes; velocity variations on a daily or monthly time scale may be as small as a couple percent but have been shown to yield valuable information regarding temperature or pore pressure changes (i.e., Brenguier et al, ; Lecocq et al, ; Taira & Brenguier, ). This paper explores two aspects of such cross‐correlation or coherence‐based observations that affect the final precision with which measurements may be reliably made.…”

Evidence of Changes of Seismic Properties in the Entire Crust Beneath Japan After the Mw 9.0, 2011 Tohoku‐oki Earthquake

“…The continuous monitoring of seismic velocities offers a new tool to capture the physical processes that take place after large earthquakes. This can provide insights not only into the tectonic and volcanic processes (Brenguier, Campillo, et al, ; Brenguier, Shapiro, et al, ; Brenguier et al, ; Chen et al, ; Froment et al, ; Obermann et al, ; Taira & Brenguier, ; Wegler et al, ) but also into some transient fluctuations that are derived from external environmental perturbations (Sens‐Schönfelder & Wegler, ; Meier et al, ; Hillers et al, ; Hillers, Ben‐Zion, et al, ; Wang et al, ). The characteristic depth at which such changes can be monitored varies from meters (Hillers, Retailleau, et al, ; Mao et al, ; Sens‐Schönfelder & Wegler, ) down to dozens of kilometers into the crust (Froment et al, ; Obermann et al, ; Rivet et al, ), through measurements at various periods.…”