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

Taka’Aki Taira,Florent Brenguier

doi:10.1186/s40623-016-0538-6

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 snow-induced 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

Highlights

The Lassen Volcanic Center (LVC) is one of the southernmost active volcanoes in the Cascades Volcanic Arc and has experienced at least 14 eruptions in the last 100,000 years (Clynne and Muffler 2010)
Brenguier et al (2014) identifies the zones of high velocity susceptibility (>0.0005 MPa−1) that are spatially correlated with hydrothermal and volcanic fields. They suggest that an effective confining pressure will be reduced due to highly pressurized hydrothermal and magmatic fluid, proposing that a reduction of the confining pressure will be responsible for the high values of velocity susceptibility. We find that this velocity susceptibility obtained at the LVC is higher than or comparable to those obtained in Mt Fuji and other hydrothermal areas in Japan by Brenguier et al (2014), which would indicate that there would be an existence of high-pressurized hydrothermal fluid at the LVC
A quasi real-time monitoring system for seismic velocity at the LVC is established by making use of seismic interferometry approach with the continuous data archived at Northern California Earthquake Data Center (NCEDC)

Summary

Introduction

The Lassen Volcanic Center (LVC) is one of the southernmost active volcanoes in the Cascades Volcanic Arc and has experienced at least 14 eruptions in the last 100,000 years (Clynne and Muffler 2010). The Lassen hydrothermal system is the most extensive active hydrothermal system of the Cascade arc and is characterized by a shallow vapor-dominated reservoir underlain by ~240 °C hot waters (Muffler et al 1982; Ingebritsen and Sorey 1985; Ingebritsen et al 2016). Taira and Brenguier Earth, Planets and Space (2016) 68:162 hydrothermal system has been suggested to be driven by heat from cooling mafic magma reservoirs beneath the LVC (Clynne et al 2012). The extensively active Lassen hydrothermal system may pose potential hazards to the Lassen region including emissions of gases and hydrothermal explosions

Results

Discussion

Conclusion