Seismic Noise Interferometry Research Articles

Matrix imaging as a tool for high-resolution monitoring of deep volcanic plumbing systems with seismic noise

Volcanic eruptions necessitate precise monitoring of magma pressure and inflation for improved forecasting. Understanding deep magma storage is crucial for hazard assessment, yet imaging these systems is challenging due to complex heterogeneities that disrupt standard seismic migration techniques. Here we map the magmatic and hydrothermal system of the La Soufrière volcano in Guadeloupe by analyzing seismic noise data from a sparse geophone array under a matrix formalism. Seismic noise interferometry provides a reflection matrix containing the signature of echoes from deep heterogeneities. Using wave correlations resistant to disorder, matrix imaging successfully unscrambles wave distortions, revealing La Soufrière’s internal structure down to 10 km with 100 m resolution. This method surpasses the diffraction limit imposed by geophone array aperture, providing crucial data for modeling and high-resolution monitoring. We see matrix imaging as a revolutionary tool for understanding volcanic systems and enhancing observatories’ abilities to monitor dynamics and forecast eruptions.

Corrigendum: Insights into fluid migration during the 2021 La Palma eruption using seismic noise interferometry

Corrigendum: Insights into fluid migration during the 2021 La Palma eruption using seismic noise interferometry

Insights into fluid migration during the 2021 La Palma eruption using seismic noise interferometry

Ambient noise correlation analyses are largely used to monitor temporal medium changes generally associated with stress field variations and/or fluid movement. Here, we analyze the 2021 eruption of La Palma, the most active island in the Canary archipelago, to study its effects on the structure in a post-eruptive stage. To date, most of the studies, whether in volcanic environments or other geological systems, focus on determining seismic velocity changes that can be associated with precursory signals. In our study, we are interested in localizing the medium changes that permit constraining the depth of the most affected structure and suggesting possible mechanisms capable of inducing such alterations. The auto- and cross-correlation functions were computed using the phase cross-correlation strategy. The correlations were linearly stacked using a 3-day sliding window. The combination of these two approaches proved to render the best results. The analysis of 3 years of data resulted in the detection of occasional decorrelation before the eruption, followed by a well-defined decoherence period after the eruption. In addition, the relationship between the waveform correlation and lag time, using autocorrelations from before and after the eruption, permits identifying phase shifts and waveform distortion, which are sensitive to different parameters and, thus, have great importance in inferring the possible mechanism. Phase shifts occur when there is only velocity change without changing the structure, whereas waveform distortion is caused by a structural (geological) change. We also inferred the depths at which the most significant medium alterations occur. We observed that the decorrelation occurs at lag times corresponding to changes localized in depth. The surface structure appears to not have undergone significant medium changes for depths until approximately 8 km, either before or after the eruption.

Using time-lapse seismic velocity changes to monitor the Domo de San Pedro Geothermal field, Mexico

The Domo de San Pedro Geothermal field, located in the westernmost part of the trans-Mexican volcanic belt, is part of a silicic volcanic complex. Geothermal energy is produced since 2015 from 9 wells as deep as 3 km. We monitor geothermal operations using a continuous seismic dataset from a temporary network of 20 broadband stations from March 2021 to January 2022. The well logs describing the geothermal operations allow us to investigate the seismic response of the geothermal field to fluid extraction and re-injection across the geothermal wells. We produced a catalog of 217 local earthquakes and derive an optimized 1D velocity model for the geothermal field between 1.2 m above the sea level (masl) and 12 km depth. Apparent velocity changes (dv/v) are measured using seismic ambient noise interferometry from the coda of noise cross-correlations. Next, we identify and locate subsurface velocity anomalies, combining the methods of station collapse sensitivity and ambient noise imaging applied to the continuous seismic noise records. We distinguish three periods of seismic activity where prominent changes in velocity coincide with the re-injection of fluids and significant variation in the production rate of the geothermal wells. We determine the distribution of these velocity transients inside the geothermal field and propose that they are associated with variations in reservoir fluid content and effective stress changes beneath the volcanic system and are responsible for induced microseismicity. Our study shows that implementing dv/v quantification as an additional tool for geothermal seismic monitoring can lead to an improved understanding of the behavior of the geothermal system over time and ultimately de-risk geothermal operations.

Steam caps in geothermal reservoirs can be monitored using seismic noise interferometry

Harvesting geothermal energy often leads to a pressure drop in reservoirs, decreasing their profitability and promoting the formation of steam caps. While steam caps are valuable energy resources, they also alter the reservoir thermodynamics. Accurately measuring the steam fraction in reservoirs is essential for both operational and economic perspectives. However, steam content estimations are very limited both in space and time since current methods rely on direct measurements within production wells. Besides, these estimations normally present large uncertainties. Here, we present a pioneering method for indirectly sampling the steam content in the subsurface using the ever-present seismic background noise. We observe a consistent annual velocity drop in the Hengill geothermal field (Iceland) and establish a correlation between the velocity drop and steam buildup using in-situ borehole data. This application opens new avenues to track the evolution of any gas reservoir in the crust with a surface-based and cost-effective method.

Spatiotemporal evaluation of Rayleigh surface wave estimated from roadside dark fiber DAS array and traffic noise

Seismic imaging and monitoring of the near-surface structure are crucial for the sustainable development of urban areas. However, standard seismic surveys based on cabled or autonomous geophone arrays are expensive and hard to adapt to noisy metropolitan environments. Distributed acoustic sensing (DAS) with pre-existing telecom fiber optic cables, together with seismic ambient noise interferometry, have the potential to fulfill this gap. However, a detailed noise wavefield characterization is needed before retrievingcoherent waves from chaotic noise sources. We analyze local seismic ambient noise by tracking five-month changes in signal-to-noise ratio (SNR) of Rayleigh surface wave estimated from traffic noise recorded by DAS along the straight university campus busy road. We apply the seismic interferometry method to the 800 m long part of the Penn State Fiber-Optic For Environment Sensing (FORESEE) array. We evaluate the 160 virtual shot gathers (VSGs) by determining the SNR using the slant-stack technique. We observe strong SNR variations in time and space. We notice higher SNR for virtual source points close to road obstacles. The spatial noise distribution confirms that noise energy focuses mainly on bumps and utility holes. We also see the destructive impact of precipitation, pedestrian traffic, and traffic along main intersections on VSGs. A similar processing workflow can be applied to various straight roadside fiber optic arrays in metropolitan areas.

Seismic Noise Interferometry and Distributed Acoustic Sensing (DAS): Inverting for the Firn Layer S‐Velocity Structure on Rutford Ice Stream, Antarctica

AbstractFirn densification profiles are an important parameter for ice‐sheet mass balance and palaeoclimate studies. One conventional method of investigating firn profiles is using seismic refraction surveys, but these are difficult to upscale to large‐area measurements. Distributed acoustic sensing (DAS) presents an opportunity for large‐scale seismic measurements of firn with dense spatial sampling and easy deployment, especially when seismic noise is used. We study the feasibility of seismic noise interferometry (SI) on DAS data for characterizing the firn layer at the Rutford Ice Stream, West Antarctica. Dominant seismic energy appears to come from anthropogenic noise and shear‐margin crevasses. The DAS cross‐correlation interferometry yields noisy Rayleigh wave signals. To overcome this, we present two strategies for cross‐correlations: (a) hybrid instruments—correlating a geophone with DAS, and (b) stacking of selected cross‐correlation panels picked in the tau‐p domain. These approaches are validated with results derived from an active survey. Using the retrieved Rayleigh wave dispersion curve, we inverted for a high‐resolution 1D S‐wave velocity profile down to a depth of 100 m. The profile shows a “kink” (velocity gradient inflection) at ∼12 m depth, resulting from a change of compaction mechanism. A triangular DAS array is used to investigate directional variation in velocity, which shows no evident variations thus suggesting a lack of azimuthal anisotropy in the firn. Our results demonstrate the potential of using DAS and SI to image the near‐surface and present a new approach to derive S‐velocity profiles from surface wave inversion in firn studies.

In-situ monitoring of rock slope destabilization with ambient seismic noise interferometry in southwest China

The damage evolving on rock slopes, including unstable mass failure events, is expected to be associated with a rigidity loss of geomaterials. Therefore, velocity changes (dv/v) inferred from ambient noise interferometry allow remotely assessing the damage state of the slope. However, the time scale and amplitude of the dv/v evolution associated with the slope destabilizations are not well known, and their detection and characterization require both high precision and high temporal resolution in dv/v. We herein report an in-situ one-year monitoring of the dv/v on the slow-moving Pubugou rock slope with a high temporal resolution up to 20-min by using two seismic stations in the mountainous region of Sichuan, China, where the slope is affected by both earthquakes and rainfall. The results confirm the feasibility of (1) detecting a possible precursor dv/v drop (−0.5%) ∼40 min before a slope destabilization; (2) characterizing the dv/v caused by the superimposed effects of moderate earthquakes and rainfall; and (3) quantifying the daily dv/v fluctuations of the slope caused by the environmental thermal forcing through thermoelastic effects. In addition, the measurement error and the detectable depth resolution of the dv/v are also addressed in this study. Finally, we suggest the high-resolution technique as a complementary means to be used for operational rock slope damage surveillance in the future.

Estimating Cross-Coupling in Site Response by Seismic Noise Interferometry: An Example from an Alpine Valley (Northeastern Italy)

Abstract The assessment of site response is an important task for improved seismic hazard estimation. The standard tools and approaches, however, generally neglect the cross-coupling effect among the three components of motion due to heterogeneities in the underground structure. In this study, we propose a means to estimate cross-coupling effects by the inversion of the deconvolved wavefield derived from seismic noise analysis. These functions are obtained by deconvolving the three components of the ground motion recorded at a site with those recorded at a reference site. The proposed procedure is applied to a set of recordings collected in the Sarca Valley (northeastern Italy) by a temporary seismometric network. The results show that the cross-coupling components are not negligible, and are related to lateral variations in the bedrock surface and heterogeneities within the sedimentary cover.

Construction and use of real-time seismic velocity change detection system to monitor the temporal and spatial changes of crustal stress and fault activity in Taiwan

Taiwan is a hotbed of seismic and orogeny activity and this is the basis of the research of Dr Hsin-Hua Huang, Earth Structures Laboratory, Institute of Earth Sciences, Academia Sinica, Taiwan. He has illuminated detailed crustal and slab structures that have furthered understanding of Taiwan orogeny, incorporated ambient noise data to resolve high-resolution imaging of the volcanic and fault structure in northern Taiwan and conducted research that led to the discovery of multi-layering magma beneath the Yellowstone supervolcano in the US. The ultimate goal of his diverse studies is to achieve an improved imaging of the structure of the Earth and establish better understanding of the orogenic tectonic process and assess and mitigate natural hazards, such as volcanoes and earthquakes. In their latest project, Huang and the team are using the seismic wave interferometry method, combined with Taiwan's existing real-time signal transmission Taiwan Broadband Seismic Network (BATS) and the Central Weather Bureau Seismic Network (CWB24), to develop an automated real-time seismicity change detection system. The idea is that by measuring changes in the transmission velocity of seismic waves in the crust, physical parameters such as the degree of rock compression or changes in porosity can be linked and discussed. The researchers have performed an extensive review of knowledge about the current stage of fault zone failure and healing processes,the advantages of seismic noise interferometry and the need for Taiwan fault zone monitoring and related seismic interferometry research. In order to understand the temporal changes in crustal structure and the behaviour of velocity changes across faults, a long-term and stable real-time seismic velocity change monitoring system is necessary.

Correlations of Seismic Velocities and Elastic Moduli with Temperature in Superhot and Enhanced Geothermal Systems

This paper presents correlations derived by linear regression analysis of seismic velocities VP and VS and elastic moduli EP and ES with temperature in Los Humeros superhot (SHGS) and Acoculco enhanced (EGS) geothermal systems at depths down to 3 km below the surface and temperatures up to approximately 400 °C. In Los Humeros, the seismic velocity models were derived from the inversion of legacy active seismic survey data acquired in 1998, as well as from passive seismic monitoring and ambient seismic noise interferometry carried out during 2017–2019 by the GEMex consortium. In the Acoculco EGS, ambient seismic noise data were used. Steady-state formation temperatures were re-evaluated during and after the end of the GEMex project using measurements provided as a courtesy of the Federal Electricity Commission of Mexico (CFE). The density data needed for the calculation of elastic moduli were provided by the GEMex consortium, as derived from the inversion of regional and local gravity surveys. The analysis indicated that statistically significant correlations of seismic parameters to temperature exist in the vertical direction, namely exponential in Los Humeros superhot and logarithmic in Acoculco EGS, but no correlation was evident in the horizontal direction. This result suggests an indirect relationship among the considered variables due to interdependence on other parameters, such as pressure and vapor saturation. As the analysis was performed using only data obtained from sensing-at-surface methods, without direct geophysical calibration at depth, a distributed fiber-optic seismic and temperature sensing system at both surface and downhole is proposed for active-source and passive seismic monitoring, and seismic-while-drilling by the drill-bit source is considered for reverse vertical seismic profile (RVSP) recording whenever possible for future high-temperature geothermal applications.

A linear algorithm for ambient seismic noise double beamforming without explicit crosscorrelations

Geoscientists and engineers are increasingly using denser arrays for continuous seismic monitoring, and they often turn to ambient seismic noise interferometry for low-cost near-surface imaging. Although ambient noise interferometry greatly reduces acquisition costs, the computational cost of pair-wise comparisons between all sensors can be prohibitively slow or expensive for applications in engineering and environmental geophysics. Double beamforming of noise correlation functions is a powerful technique to extract body waves from ambient noise, but it is typically performed via pair-wise comparisons between all sensors in two dense array patches (scaling as the product of the number of sensors in one patch with the number of sensors in the other patch). By rearranging the operations involved in the double beamforming transform, I have developed a new algorithm that scales as the sum of the number of sensors in two array patches. Compared to traditional double beamforming of noise correlation functions, the new method is more scalable, easily parallelized, and it does not require raw data to be exchanged between dense array patches.

Upper-Crustal Seismic Anisotropy in the Cantabrian Mountains (North Spain) from Shear-Wave Splitting and Ambient Noise Interferometry Analysis

AbstractThe upper-crustal anisotropy of the Cantabrian Mountains (North Spain) has been investigated using two independent but complementary methodologies: (a) shear-wave splitting and (b) ambient seismic noise interferometry. For this purpose, we have processed and compared seismic data from two networks with different scales and recording periods. The shear-wave splitting results show delay times between 0.06 and 0.23 s and spatially variable fast-polarization directions. We calculate that the anisotropic layer has a maximum effective thickness of around 7.5 km and an average anisotropy magnitude of between 4% and 8%. Consistently, our ambient noise observations point to an anisotropy magnitude between 4% and 9% in the first 10 km of the crust. Our results show a clear correlation between the fast directions from both methods and the orientations of the local faults, suggesting that the anisotropy is mainly controlled by the structures. Furthermore, in the west of the study area, fast-polarization directions tend to align parallel to the Variscan fabric in the crust, whereas to the east, in which the Alpine imprint is stronger, many fast directions are aligned parallel to east–west-oriented Alpine features.

Finite‐Frequency Sensitivity Kernels for Seismic Noise Interferometry Based on Differential Time Measurements

AbstractFull waveform adjoint tomography has achieved great success in applications from global Earth structure using earthquakes to exploration seismology using active sources. When combined with ambient seismic noise data, however, the ambient noise cross correlations are subject to strong variability and bias due to nonstationary and unevenly distributed noise sources. As a result, the shape of the structure sensitivity kernel can deviate significantly from the classic banana‐doughnut kernel of a point source, which has been used in previous studies as an inference from empirical Green's function and contains bias. In this study I calculate the sensitivity kernel for ambient noise cross correlation by introducing an additional station to the classic two‐station setting. I compute sensitivity kernels for differential traveltime measurements. These differential sensitivity kernels show promise for canceling the overlapping part of the original source and structure kernels for pairs of stations in interferometry, thus significantly reducing the effect of nonisotropically distributed and nonstationary noise sources. I apply the ambient noise differential sensitivity kernel to synthetic data examples based on 2‐D membrane waves, though the approach will apply for 3‐D as well. Our results for multiple station pairs show promise for velocity tomography based on seismic noise interferometry when perfect information on noise source distribution is not available.

Noise-based ballistic wave passive seismic monitoring – Part 2: surface waves

SUMMARYWe develop a new method to monitor and locate seismic velocity changes in the subsurface using seismic noise interferometry. Contrary to most ambient noise monitoring techniques, we use the ballistic Rayleigh waves computed from 30 d records on a dense nodal array located above the Groningen gas field (the Netherlands), instead of their coda waves. We infer the daily relative phase velocity dispersion changes as a function of frequency and propagation distance with a cross-wavelet transform processing. Assuming a 1-D velocity change within the medium, the induced ballistic Rayleigh wave phase shift exhibits a linear trend as a function of the propagation distance. Measuring this trend for the fundamental mode and the first overtone of the Rayleigh waves for frequencies between 0.5 and 1.1 Hz enables us to invert for shear wave daily velocity changes in the first 1.5 km of the subsurface. The observed deep velocity changes (±1.5 per cent) are difficult to interpret given the environmental factors information available. Most of the observed shallow changes seem associated with effective pressure variations. We observe a reduction of shear wave velocity (–0.2 per cent) at the time of a large rain event accompanied by a strong decrease in atmospheric pressure loading, followed by a migration at depth of the velocity decrease. Combined with P-wave velocity changes observations from a companion paper, we interpret the changes as caused by the diffusion of effective pressure variations at depth. As a new method, noise-based ballistic wave passive monitoring could be used on several dynamic (hydro-)geological targets and in particular, it could be used to estimate hydrological parameters such as the hydraulic conductivity and diffusivity.

Quantifying the Effects of Nondiffuse Noise on Ballistic and Coda Wave Amplitude From Variances of Seismic Noise Interferometry in Southern California

AbstractWe develop a new approach based on the variance of noise cross‐correlation to characterize the noise source and wave propagation under the influence of a nondiffuse noise field. Based on the standard errors for the Fourier spectra of stacked noise cross‐correlation and the assumption of a diffuse field, we derive an analytical expression for the variance of every time point in the stacked cross‐correlation and validate the theory using synthetic diffuse noise data. The ambient seismic noise field in Southern California is, however, not fully diffuse. The observed correlated neighboring frequencies in the noise data—a definitive character of the nondiffuse field, map into the noise cross‐correlation, biasing its variances from theoretical predictions under fully diffuse field assumption. For the secondary ocean microseism, we find strong positive correlation between the correlated neighboring frequencies and the deviations from diffuse field theory‐predicted variances. The ballistic arrivals on average contain more significant bias than the coda segments of the noise cross‐correlation, which agrees with previous time‐lapse monitoring studies based on ambient seismic noise. In addition, the station pairs having significant bias between actual and diffuse field theory‐predicted variances are aligned with the strongest source direction and exhibit significant beamforming source fluctuation.

Evidence of reactivation of a hydrothermal system from seismic anisotropy changes

Seismic velocity measurements have revealed that the Tohoku-Oki earthquake affected velocity structures of volcanic zones far from the epicenter. Using a seismological method based on ambient seismic noise interferometry, we monitored the anisotropy in the Mount Fuji area during the year 2011, in which the Tohoku-Oki earthquake occurred (Mw = 9.0). Here we show that even at 400 km from the epicenter, temporal variations of seismic anisotropy were observed. These variations can be explained by changes in the alignment of cracks or fluid inclusions beneath the volcanic area due to stress perturbations and the propagation of a hydrothermal fluid surge beneath the Hakone hydrothermal volcanic area. Our results demonstrate how a better understanding of the origin of anisotropy and its temporal changes beneath volcanoes and in the crust can provide insight into active processes, and can be used as part of a suite of volcanic monitoring and forecasting tools.

Crustal seismic velocity responds to a magmatic intrusion and seasonal loading in Iceland's Northern Volcanic Zone.

Seismic noise interferometry is an exciting technique for studying volcanoes, providing a continuous measurement of seismic velocity changes (dv/v), which are sensitive to magmatic processes that affect the surrounding crust. However, understanding the exact mechanisms causing changes in dv/v is often difficult. We present dv/v measurements over 10 years in central Iceland, measured using single-station cross-component correlation functions from 51 instruments across a range of frequency bands. We observe a linear correlation between changes in dv/v and volumetric strain at stations in regions of both compression and dilatation associated with the 2014 Bárðarbunga-Holuhraun dike intrusion. Furthermore, a clear seasonal cycle in dv/v is modeled as resulting from elastic and poroelastic responses to changing snow thickness, atmospheric pressure, and groundwater level. This study comprehensively explains variations in dv/v arising from diverse crustal stresses and highlights the importance of deformation modeling when interpreting dv/v, with implications for volcano and environmental monitoring worldwide.

Short‐ and Long‐Term Variations in the Reykjanes Geothermal Reservoir From Seismic Noise Interferometry

AbstractThe Reykjanes Geothermal System (RGS) is a high‐temperature geothermal system located on the Reykjanes peninsula, a transtensional plate‐boundary zone located on the southwestern tip of Iceland. The area is characterized by high seismicity, recent volcanism, and high‐temperature geothermal fields. We use seismic noise records from April 2014 to August 2015 to study stress changes and potential deformation of the subsurface caused by injection and production operations at RGS through seismic interferometry. We retrieve continuous time series of waveform similarity values and seismic velocity changes during this period. The S‐transform of the similarity values allows us to clearly identify three variations in the mechanical properties of the Reykjanes peninsula related to rapid changes of RGS production. In addition, we observe a slow seismic velocity decrease of 0.36%/year in the reservoir due to the water deficit and seasonal variations associated with the energy production demand.

Decrease in Seismic Velocity Observed Prior to the 2018 Eruption of Kīlauea Volcano With Ambient Seismic Noise Interferometry

AbstractThe 2018 Kīlauea eruption was a complex event that included deformation and eruption at the summit and along the East Rift Zone. We use ambient seismic noise interferometry to measure time‐lapse changes in seismic velocity of the volcanic edifice prior to the lower East Rift Zone eruption. Our results show that seismic velocities increase in relation to gradual inflation of the edifice between 1 March and 20 April. In the 10 days prior to the 3rd of May eruption onset, a rapid seismic velocity decrease occurs even though the summit is still inflating. We confirm that intereruptive velocity change is correlated with surface deformation, while the velocity decrease prior to eruption is likely due to accumulating damage induced by the pressure exerted by the magma reservoir on the edifice. The accumulating damage and subsequent decrease in bulk edifice strength may have facilitated increased transport of magma from the summit reservoir to the Middle East Rift Zone.