Seismic Noise Interferometry Research Articles

Shallow volcanic reservoirs and pathways beneath Aso caldera revealed using ambient seismic noise tomography

Imaging the shallow velocity structures beneath Aso caldera is necessary to further understand volcanism at the volcano and in the region. The network for monitoring Aso volcano has been progressively renewed and upgraded with denser and more modern instruments. We used approximately 4 years of seismic data recorded by a network of 25 seismic stations to image S-wave velocity (Vs) structures beneath Aso caldera with seismic noise interferometry. We calculated daily cross-correlation functions (CCFs) of broadband and short-period station pairs separately and then stacked CCFs monthly, to obtain the time-domain empirical Green’s functions and corresponding Rayleigh-wave phase-velocity dispersion curves. Finally, we constructed 1–5-s phase-velocity maps interpolated from nodes spaced 0.05° grid. The maps allow investigating crustal Vs structures between the surface and a depth of 6 km, likely related to shallow volcanic reservoirs and pathways. High velocities are found within the first kilometer of the crust beneath post-caldera central cones. Low velocities in the center of the post-caldera central cones extend from the surface to a depth of 1–2.5 km; we infer that the anomalies mark shallow hydrothermal reservoirs likely replenished by precipitation and hydrographic networks. The prevalence of high velocities below 3 km can be considered as consolidated igneous rock. Low-velocity anomalies identified at depths of 5–6 km beneath the post-caldera central cones could be a manifestation of magma accumulation. The low-velocity belts situated at 2.5–5 km depths are likely pathways for the transfer of hydrothermal fluids, volcanic gases, or melting magma to the surface. The northern part of the caldera shows relevant lateral velocity variations, with low velocities and high velocities predominant in the east and west, respectively. Other low-Vs anomalies appear near the surface to the west and northwest of Aso caldera.

Ambient noise Love wave tomography at a gold mine tailings storage facility

Tailings storage facilities (TSFs) are some of the most challenging structures to operate in the mining industry. Some of these structures are susceptible to liquefaction and piping failure, and need to be monitored carefully. In this study, ambient seismic noise interferometry is applied to image the internal structure of a tailings storage facility (TSF) that showed signs of increased seepage. Twenty geophones were deployed along a roughly 100 m section of the TSF and recorded continuous seismic data. The ambient noise was used to create Love wave dispersion curves between sensor pairs, which were in turn inverted to estimate the shear wave velocity of the dam wall as a function of depth. The velocity profile indicated the phreatic surface roughly 10 m below the surface, with regions near the centre of the array showing the phreatic surface as close as 3 m below the surface. These areas are spatially well correlated with the area where increased seepage was identified and the results were comparable with cone penetration tests that were performed in the area. The study showed that the analysis of ambient seismic noise can be a cost-effective, fast and non-invasive method to image the internal structure of TSFs.

Multipathing Rayleigh Waves From Long‐Distance Noise Cross Correlation Along an Ocean‐Continent Boundary (Alaska to California)

AbstractSeismic interferometry can reliably extract interstation surface waves in homogeneous or smooth media. We test the validity of this technique in the case of sharp lateral heterogeneity, by examining paths along the western edge of continental North America. After cross correlating several years of time series of ambient seismic noise, we extract interstation Rayleigh waves with different arrivals in the frequency of 0.04 to 0.06 Hz (periods 17 to 25 s). Using beamforming and seismic wavefield simulations, we show that the different Rayleigh wave arrivals are related to the oceanic and continental paths, respectively. This multipathing of Rayleigh waves that is identified from ambient noise is also identified from earthquakes. Our results demonstrate that seismic noise interferometry is capable of extracting realistic surface waves for complex structural paths such as along the continental margin of North America. Additional studies from other regions may demonstrate the potential for using multipathing surface waves within full waveform inversion.

Seismic and experimental insights into eruption precursors at Volcán de Colima.

We combine geophysical and experimental observations to interpret preeruptive unrest at Volcán de Colima in 1998. 17,893 volcanic earthquakes were detected between 1 October and 31 December 1998, including 504 clusters. Using seismic ambient noise interferometry, we observe a drop in velocity prior to the eruption linked to damage accumulation during magma ascent. This is supported by experimental observations where static stress causes a velocity decrease prior to failure. Furthermore, we observe acoustic emission clusters during the experiments, with lower porosity samples producing higher numbers of repeaters. This behavior introduces tensile failure as an additional viable mechanism for clusters during magma ascent. The findings suggest that preeruptive magma ascent may be monitored to variable degrees of accuracy via descriptions of damage accumulation and associated seismic velocity changes.

Monitoring crustal changes at volcanoes by seismic noise interferometry: Mt. Etna case of study

In this work, we analysed the seismic noise recorded at Mt. Etna by 18 stations during the interval 2007–2015 in the frequency band 0.1–0.3Hz, chosen to avoid contamination from volcanic tremor. Variations in time of medium seismic velocity in the range −0.8 to 0.8% were found, mostly affecting the stations located on the volcano summit and flanks. Based on the investigated frequency content, the Δv/v changes took place from the surface to a depth of ~4.5–6.5km. To identify the source mechanism of the observed medium changes, the variations were quantitatively compared by wavelet transform coherence with volcano-tectonic and meteorological parameters. A significant relationship with meteorological parameters with seasonal periodicity (especially air temperature and snow loading) was found, probably caused by thermo-elastic strain and increasing-decreasing surface loading cycles. Moreover, a sharp medium velocity decrease, taking place in mid-December 2009 and clearly time-related to the largest volcano-tectonic strain release phenomenon of the investigated period, was also found. Such a velocity decrease was interpreted as resulting from ascent of fluids and gas exsolution taking place at the same time as the volcano-tectonic swarm.

Temporal velocity variations retrieved by seismic noise in Changbaishan volcano, NE China

We present the current status of seismic noise interferometry to reconstruct the seismic velocity and discuss the four phases from single-station data preparation to quality control of data processing procedures. Each phase of the processing procedure has been discussed in detail with salient examples using seismic data acquired in Changbaishan volcano region. In the end, we use continuous recordings in Jilin, China to track the temporal change of the seismic velocity variations with the method promoted in this paper. We filter the data between the frequency band 0.02 and 0.1 Hz, which the Rayleigh waves are most sensitive to the shear wave velocities in the crust and uppermost mantle. The long-term seismic variations present strong seasonal influence which may be caused by precipitation. We find clear evidence that the seismic velocity drops by up to ∼0.8% which may be caused by the dilatation of the volcanic edifice before the Mar. 11 2011 Japan earthquake.

Ambient seismic noise interferometry in Hawai'i reveals long-range observability of volcanic tremor

Ambient seismic noise interferometry in Hawai'i reveals long-range observability of volcanic tremor