Ocean Microseisms Research Articles

Detection of a CO2 plume by time-lapse analysis of Rayleigh-wave amplitudes extracted from downhole DAS recordings of ocean microseisms

Amplitudes of Rayleigh waves are known to decrease exponentially away from the surface. If elastic properties of the solid are stratified on a scale much smaller than the wavelength, the Rayleigh-wave amplitude at a given depth should also be affected by the formation properties at that depth: the softer the medium, the larger the amplitude. An increasingly widespread deployment of fiber-optic cables in wells makes it possible to record this depth variation of Rayleigh-wave strain amplitudes and their variations over time (due to changes of formation properties) using distributed acoustic sensing (DAS). To investigate this opportunity, we have explored temporal variations of downhole DAS amplitudes of ocean-generated Rayleigh waves during injection of CO2 into a water-saturated thin porous layer. Analysis of these data clearly shows changes of these amplitudes related to the CO2 injection. To understand these amplitude variations, we perform a theoretical analysis and numerical simulations, which explain our field observations. In particular, analysis of downhole DAS data and theoretical modeling show that Rayleigh-wave amplitudes measured with vertical fiber-optic cables can be used to detect thin layers in the subsurface. Furthermore, time-lapse analysis of these amplitudes indicates temporal changes of stiffness of these layers, such as changes in saturation or pressure of the fluid in a porous layer in the vicinity of the borehole. In particular, Rayleigh-wave amplitudes are sensitive to the presence in the vicinity of the wellbore of a CO2 plume created as a result of a small injection into a thin porous reservoir layer. Our analysis also shows that the effect of a thin layer on Rayleigh-wave amplitudes strongly depends on frequency so that at different frequencies the amplitude is affected by different combinations of elastic properties. This opens an opportunity to use amplitude variations with depth at different frequencies to separately estimate changes in bulk and shear moduli.

Continuous isolated noise sources induce repeating waves in the coda of ambient noise correlations


 Continuous excitation of isolated noise sources leads to repeating wave arrivals in cross correlations of ambient seismic noise, including throughout their coda. These waves propagate from the isolated sources. We observe this effect on correlation wavefields computed from two years of field data recorded at the Gräfenberg array in Germany and two master stations in Europe. Beamforming the correlation functions in the secondary microseism frequency band reveals repeating waves incoming from distinct directions to the West, which correspond to well-known dominant microseism source locations in the Northeastern Atlantic Ocean. These emerge in addition to the expected acausal and causal correlation wavefield contributions by boundary sources, which are converging onto and diverging from the master station, respectively. Numerical simulations reproduce this observation. We first model a source repeatedly exciting a wavelet, which helps illustrate the fundamental mechanism behind repeated wave generation. Second, we model continuously acting secondary microseism sources and find good agreement with our observations. Our observations and modelling have potentially significant implications for the understanding of correlation wavefields and monitoring of relative velocity changes in particular. Velocity monitoring commonly assumes that only multiply scattered waves, originating from the master station, are present in the coda of the correlation wavefield. We show that repeating waves propagating from isolated noise sources may dominate instead, including the very late coda. Our results imply that in the presence of continously acting noise sources, which we show is the case for ordinary recordings of ocean microseisms, velocity monitoring assuming scattered waves may be adversely affected with regard to measurement technique, spatial resolution, as well as temporal resolution. We further demonstrate that the very late coda of correlation functions contains useful signal, contrary to the common sentiment that it is dominated by instrument noise.

Seismic ambient noise imaging above an underground mine: An example from Boliden Tara Mines, Ireland

We use a passive seismic data set recorded from June 2017 to July 2018 by twenty-one stations deployed in a five by five km grid to the south-west of the Boliden Tara Mines orebody (Eastern Ireland) to image the shallower part of the Carboniferous rock units. We cross-correlate one year of ambient noise between all station pairs to generate cross-correlation functions that are rich in surface waves. Then we investigate the locations of the noise sources by applying f-k cross-correlation beamforming. We find two persistent noise sources associated with oceanic microseisms and a cluster of anthropogenic activities, respectively. We undertake dispersion analysis to extract group velocity measurements in the 1–9 Hz band that we invert using the fast marching method to create Rayleigh wave velocity maps. This is followed by a wavelet-based sparsity constrained tomographic method to produce a 3-D shear wave velocity model down to 800 metres. The results highlight low and high-velocity anomalies related to the structural and stratigraphic heterogeneity within the Upper Dark limestone formation. In addition, the velocity gradient of our model agrees with the sonic log velocity profile available adjacent to the study area, suggesting that this sparse network can be used to obtain reliable broad-scale information and could also guide the design phase of more expensive and involved experiments, such as active seismic reflection imaging.

Bayesian regional moment tensor from ocean bottom seismograms recorded in the Lesser Antilles: implications for regional stress field

SUMMARY Seismic activity in the Lesser Antilles (LA) is characterized by strong regional variability along the arc reflecting the complex subduction setting and history. Although routine seismicity monitoring can rely on an increasing number of island stations, the island-arc setting means that high-resolution monitoring and detailed studies of fault structures require a network of ocean bottom seismometers (OBS). As part of the 2016–2017 Volatile recycling at the Lesser Antilles arc (VoiLA) project, we deployed 34 OBS stations in the forearc and backarc. During the deployment time, 381 events were recorded within the subduction zone. In this paper, we perform full-waveform regional moment tensor (RMT) inversions, to gain insight into the stress distribution along the arc and at depth. We developed a novel inversion approach, AmΦB—‘Amphibious Bayesian’, taking into account uncertainties associated with OBS deployments. Particularly, the orientation of horizontal components (alignment uncertainty) and the high noise level on them due to ocean microseisms are accounted for using AmΦB. The inversion is conducted using a direct, uniform importance sampling of the fault parameters within a multidimensional tree structure: the uniXtree-sampling algorithm. We show that the alignment of the horizontal OBS components, particularly in high noise level marine environments, influences the obtained source mechanism when using standard least-squares (L2) RMT inversion schemes, resulting in systematic errors in the recovered focal mechanisms including high artificial compensated linear vector dipole (CLVD) contributions. Our Bayesian formulation in AmΦB reduces these CLVD components by nearly 60 per cent and the aberration of the focal geometry as measured by the Kagan angle by around 40 per cent relative to a standard L2 inversion. Subsequently, we use AmΦB-RMT to obtain 45 (Mw > 3.8) regional MT solutions, out of which 39 are new to any existing database. Combining our new results with existing solutions, we subsequently analyse a total of 151 solutions in a focal mechanism classification (FMC) diagram and map them to the regional tectonic setting. We also use our newly compiled RMT database to perform stress tensor inversions along the LA subduction zone. On the plate interface, we observe the typical compressional stress regime of a subduction zone and find evidence for upper-plate strike slip and normal fault behaviour in the north that becomes a near arc-perpendicular extensional stress regime towards the south. A dominant slab perpendicular extensional stress regime is found in the slab at 100–200 km beneath the central part of the arc. We interpret this stress condition to be a result of slab pull varying along the arc due to partial slab detachment along previously hypothesized lateral slab tear near Grenada, at the southern end of the LA arc, leading to reactivation of pre-existing structures around the subducted Proto-Caribbean ridge.

Investigating Short-Period Lake-Generated Microseisms Using a Broadband Array of Onshore and Lake-Bottom Seismometers

Abstract Recent analyses of ambient seismic noise proximal to large lakes identify excitations between periods of 0.5 and 5 s as lake-generated microseisms, though the mechanisms producing them remain unclear in the absence of distinct spectral peaks. We present a unique data set combining onshore and offshore seismometers to investigate the dominant parameters controlling water-to-solid-earth seismic coupling in a lacustrine environment. Using a set of broadband observations that include six lake-bottom seismometers, we compare signals collected both within and around Lake Malawi (Nyasa) in southeastern Africa, the fifth largest freshwater lake in the world. We document clear evidence for two peaks within the lake microseism band, with pervasive diurnal excitations between periods of ∼0.6–1.3 and ∼1.3–3 s. Variations in spectral behavior as a function of recording depth and proximity to both steep lake-floor slopes and the shoreline suggest that the spectral bands may correspond to single- and double-frequency generation processes, akin to primary and secondary ocean microseisms generated by the shoaling of wind-driven gravity waves along shorelines and wave interactions within the open body of water, respectively. However, both the absolute amplitudes and temporal evolution we observe in these two bands are complex and often inconsistent with traditional microseism theory. Therefore, these spectral bands may alternatively result from complex wave–wave interaction at the lake surface within the enclosed northern end of the lake. The diurnal behavior of lake microseisms, as well as their polarizations, suggest that the wave energy is driven by a combination of seasonally varying nighttime winds funneled by lakeshore topography and waveguide effects. This work also provides a glimpse into seasonal variation in lacustrine ambient seismic noise and thus also into lake processes.

Distributed fiber-optic sensing transforms an abandoned well into a permanent geophysical monitoring array: A case study from Australian South West

Distributed temperature sensing (DTS) and distributed acoustic sensing (DAS) data recorded by a fiber-optic array installed during the decommissioning operations of the 1550 m Harvey 3 well in Western Australia reveal an abundance of valuable information about the course of the decommissioning process and the quality of the cement job. The DAS monitoring has detected vibrational disturbances during the cement's setting up, while DTS was used to assess setting up of the cement and curing times as well as uniformity of cementation from the distribution of temperature along the borehole. A weeklong trial acquisition of passive seismic data with the same array a year later shows an abundance of seismic events in a wide frequency range from below 1 mHz to above 200 Hz. The downhole DAS array provides traveltimes and amplitudes of these events, which include earthquakes, mine blasts, ocean microseisms, and local human activity. The amplitudes of waves from distant seismic events can be used to estimate and monitor physical properties of the media along the extent of the well. When used in combination with information from active vertical seismic profiling, these events can help obtain independent estimates of velocities and densities. Spectral analysis of low-frequency microseisms shows a strong correlation between passively recorded DAS and local weather observations. This shows that the ability to continuously record oceanic microseisms at low frequencies opens opportunities to employ such arrays for wave climate studies. In addition, the data contain peculiar in-hole reverberations likely caused by crossflow of groundwater behind the intermediate casing, which may indicate imperfections of the cement job. The results demonstrate that a downhole fiber-optic array installed in an abandoned well represents an opportunity to establish a permanent facility for continuous recording of passive and active geophysical data and for exploring various applications.

The Widespread Influence of Great Lakes Microseisms Across the Midwestern United States Revealed by the 2014 Polar Vortex

AbstractDuring the winter of 2014, a weak polar vortex brought record cold temperatures to the north‐central (“Midwest”) United States, and the Great Lakes reached the highest extent of ice coverage (92.5%) since 1979. This event shut down the generation of seismic signals caused by wind‐driven wave action within the lakes (termed “lake microseisms”), giving an unprecedented opportunity to isolate and characterize these novel signals through comparison with nonfrozen time periods. Using seismic records at 72 broadband stations, we observe Great Lakes microseism signals at distances >300 km from the lakes. In contrast to conventional oceanic microseisms, there is no clear relationship between the frequency content of the seismic signals (observed from ~0.5–5‐s period) and the dominant swell period or resonance periods of the lakes based on their bathymetric profiles. Thus, the exact generation mechanism is not readily explained by conventional microseism theory and warrants further investigation.

Lakes as a Source of Short‐Period (0.5–2 s) Microseisms

AbstractWe identify and document microseisms produced by wave action in six lakes: The Great Slave Lake, Lake Ontario, Yellowstone Lake, Dianchi Lake, Fuxian Lake, and Erhai Lake. The lakes span more than 2 orders of magnitude in size (areas of 210–27,000 km2) and sample a range of climatic and tectonic regimes in Canada, the U.S., and China. Lake‐generated microseisms create spectral peaks at periods near 1 s and are often polarized as Rayleigh waves propagating away from the lake. In contrast to ocean‐generated microseisms, lake‐generated microseisms are only observed within about 25–30 km of the shoreline. This is consistent with the well‐known high attenuation of short‐period Rayleigh waves (Rg). It is unclear if lake‐generated microseisms are produced by a linear shoaling process, analogous to primary ocean microseisms, or a nonlinear wave‐wave interaction process, analogous to secondary ocean microseisms. If they are mainly produced by shoaling, lake‐generated microseisms might provide a spatially integrated measure of shoreline erosion. Regardless of the source mechanism, lake‐generated microseisms appear to provide a record of ice phenology for lakes that freeze in the winter. Such data could contribute to assessing the effects of climate change on high‐latitude lakes in remote areas. Finally, it is likely that lake‐generated microseisms are useful for imaging the geological structure of the shallow crust, information that is important for quantifying seismic hazard and can be difficult to obtain in urban areas where active source imaging is not feasible.

Detection of long-duration tremors at Deception Island volcano, Antarctica

We analyze seismic data from permanent seismic stations located on Deception Island volcano, Livingston Island, and Cierva Cove, Antarctica, and identify a type of signal named Deception long-duration signals (DLDS). They are characterized by low amplitudes, long durations (several hours to days), frequency content limited to the 0.5–5Hz band, and are detected only at Deception Island. We develop a semi-automated method to systematically detect the occurrence of DLDS during February 2008–January 2015. We identify 276 DLDS episodes with amplitudes in the range of 0.5–2μm/s and durations from 3h to 13days. The temporal distribution shows an annual modulation, suggesting a seasonal effect. DLDS activity generally increases during the austral winter, although the annual distributions display two different behaviors. Some of them have a single maximum in the winter, while others are bimodal and show a second maximum during spring. Several mechanisms can explain the occurrence of long-duration signals. However, the only mechanism that explains the spectral content, duration, temporal distribution, and station coverage of the DLDS is the occurrence of volcanic tremors. Tremor generation at Deception Island has been explained by the resonance of fluid-filled conduits within the hydrothermal and/or shallow volcanic conduits. However, the long durations of the DLDS require a triggering mechanism that could be active for a long time span. The seasonal modulation of the DLDS suggests the influence of external effects. Most DLDS episodes can be related to periods with high-amplitude oceanic microseisms, which can induce an external forcing and introduce pressure variations in the volcanic/hydrothermal fluids. However, in some cases DLDS occur independently from oceanic noise amplitude. These cases precede summer surveys with large numbers of seismic events, indicating an increasingly restless state of the volcano. They can be produced by triggering mechanisms of internal, volcanic origin, such as the occurrence of changes in the stress distribution in the volcano edifice induced by magma dynamics, or fluctuations in the rate of volcanic gas supply.

Implications of Sea Ice on Southern Ocean Microseisms Detected by a Seismic Array in West Antarctica

Implications of Sea Ice on Southern Ocean Microseisms Detected by a Seismic Array in West Antarctica

Spatial coherence of the seismic wavefield continuously recorded by the USArray

AbstractWe use a method based on the array covariance matrix eigenvalues to study the level of spatial coherence and of isotropy of the seismic wavefield continuously recorded during 2010 by the USArray. First, we observe that the raw data are often dominated by local sources. To remove their influence, we apply spectral and temporal normalizations to the input signals. We notice that this widely used preprocessing in ambient‐noise seismology does not fully homogenize the seismic wavefield and that some strongly coherent arrivals persist. Among these persistent signals generated by teleseismic sources we detect (1) seismic waves emitted by strong earthquakes, (2) a nearly continuous quasi‐monochromatic signal at 26 s period, and (3) multiday coherent wave trends in the spectral band of oceanic microseisms (0.07–0.2 Hz). For the latter, beamforming analysis shows that while most of the signals are composed of surface waves, some are dominated by body waves likely generated in the deep ocean.

Interpreting cross-correlations of one-bit filtered seismic noise

Seismic noise, generated by oceanic microseisms and other sources, illuminates the crust in a manner different from tectonic sources, and therefore provides independent information. The primary measurable is the two-point cross-correlation, evaluated using traces recorded at a pair of seismometers over a finite-time interval. However, raw seismic traces contain intermittent large-amplitude perturbations arising from tectonic activity and instrumental errors, which may corrupt the estimated cross-correlations of microseismic fluctuations. In order to diminish the impact of these perturbations, the recorded traces are filtered using the nonlinear one-bit digitizer, which replaces the measurement by its sign. Previous theory shows that for stationary Gaussian-distributed seismic noise fluctuations one-bit and raw correlation functions are related by a simple invertible transformation. Here we extend this to show that the simple correspondence between these two correlation techniques remains valid for {\it non-stationary} Gaussian and a very broad range of {\it non-Gaussian} processes as well. For a limited range of stationary and non-stationary Gaussian fluctuations, we find that one-bit filtering performs at least as well as spectral whitening. We therefore recommend using one-bit filtering when processing terrestrial seismic noise, with the substantial benefit that the measurements are fully compatible with current theoretical interpretation (e.g., adjoint theory). Given that seismic records are non-stationary and comprise small-amplitude fluctuations and intermittent, large-amplitude tectonic/other perturbations, we outline an algorithm to accurately retrieve the correlation function of the small-amplitude signals.

Source distribution of ocean microseisms and implications for time-dependent noise tomography

A qualitative analysis of ocean microseism source distribution observed in North America during fall and winter months was carried out. I review the theory of the origin of ocean microseisms and show that it can be used in conjunction with wave-wave interaction maps to quantify the source distribution anisotropy. It is demonstrated that microseisms generation in the North Atlantic and in the North Pacific Oceans are inherently different. North Atlantic microseisms are generated predominantly in the deep ocean, while North Pacific microseisms are dominated by coastal reflections. In spite of these differences both result from repeated ocean wave patterns that give rise to an anisotropic noise pattern, which cannot be randomized by time averaging. Considering time-varying ambient noise imaging, which aims to resolve a fraction of a percent changes in the crust over short distances, the source anisotropy would introduce a relatively significant error that needs to be accounted for.

High-frequency ambient noise tomography of southeast Australia: New constraints on Tasmania's tectonic past

[1] The island of Tasmania, at the southeast tip of Australia, is an ideal natural laboratory for ambient noise tomography, as the surrounding oceans provide an energetic and relatively even distribution of noise sources. We extract Rayleigh wave dispersion curves from the continuous records of 104 stations with ∼15 km separation. Unlike most passive experiments of this type, which observe very little coherent noise below a 5 s period, we clearly detect energy at periods as short as 1 s, thanks largely to the close proximity of oceanic microseisms on all sides. The main structural elements of the eastern and northern Tasmanian crust are revealed by inverting the dispersion curves (between 1 and 12 s period) for both group and phase velocity maps. Of particular significance is a pronounced band of low velocity, observed across all periods, that underlies the Tamar River Valley and continues south until dissipating in southeast Tasmania. Together with evidence from combined active source and teleseismic tomography and heat flow data, we interpret this region as a diffuse zone of strong deformation associated with the mid-Paleozoic accretion of oceanic crust along the eastern margin of Proterozoic Tasmania, which has important implications for the evolution of the Tasman Orogen of eastern Australia. In the northwest, a narrower low-velocity anomaly is seen in the vicinity of the Arthur Lineament, which may be attributed to local sediments and strong deformation and folding associated with the final phases of the Tyennan Orogeny.

Adaptive interferometry for ground-roll suppression

Generally, seismic interferometry refers to a method of extracting the wavefield responses between two receivers as if we had replaced one of those receivers by a source (van Manen et al., 2005; Wapenaar and Fokkema, 2006). This is done by a process of cross-correlation and summation of wavefields observed at those receivers. These recorded wavefields can be excited by active sources (earthquakes, dynamite, air guns, vibroseis, and others) or passive sources (oceanic microseisms, traffic on roads, industrial machinery, and others). When applying seismic interferometry using surface sources and surface receivers, the recovered inter-receiver response is dominated by surface waves. This phenomenon is observed in both global and regional seismology where passive seismic energy is used, and in exploration seismology, where active sources are used.

Directionality analysis and Rayleigh wave tomography of ambient seismic noise in southern Norway

SUMMARY We process seismic broad-band data from southern Norway by cross correlation of ambient seismic noise in view of getting a better image of the crustal structure in the area. The main data set sterns from the temporary MAGNUS network which operated continuously from 2006 September to 2008 June. Additionally, data from permanent stations of the National Norwegian Seismic Network, the NORSAR array and GSN stations in the region are used. We compute vertical component cross-correlation functions using 41 receivers for 3-month time windows. Evaluation of the azimuthal and temporal variation of signal-to-noise ratios (SNRs) and f–k analysis of data from NORSAR array between 3 and 25 s period shows that the dominant source areas of seismic noise are located to the west and north of the network during most of the measurement time, which corresponds well to the Norwegian coast line. During summer months, the SNRs decrease but the azimuthal distribution becomes more uniform between 7 and 12 s period, suggesting a more diffuse character of the wavefield. Primary ocean microseisms above 12 s show different dominant source azimuths during this time period compared to the winter months. Time–frequency analysis is applied to measure Rayleigh wave group velocity dispersion curves between each station pair for each 3-month correlation stack and the mean and variance of all dispersion curves is computed for each path. After rejection of low-quality data, a careful analysis shows that the group velocities are not biased by noise directionality. We invert the data for group velocity maps at period bands between 3 and 25 s. At short periods, we find an average Rayleigh wave group speed of about 3 km s−1 and velocity anomalies that correlate very well with local surface geology. While higher velocities (+5 per cent) can be associated with the Caledonian nappes in the central part of southern Norway, the Oslo Graben is reflected by negative velocity anomalies (−3 to −5 per cent). At longer periods, group velocities correlate well with the variation of Moho depths beneath southern Norway.

Characterization of the seismic environment at the Sanford Underground Laboratory, South Dakota

An array of seismometers is being developed at the Sanford Underground Laboratory, the former Homestake mine, in South Dakota to study the properties of underground seismic fields and Newtonian noise, and to investigate the possible advantages of constructing a third-generation gravitational-wave detector underground. Seismic data were analyzed to characterize seismic noise and disturbances. External databases were used to identify sources of seismic waves: ocean-wave data to identify sources of oceanic microseisms and surface wind-speed data to investigate correlations with seismic motion as a function of depth. In addition, sources of events contributing to the spectrum at higher frequencies are characterized by studying the variation of event rates over the course of a day. Long-term observations of spectral variations provide further insight into the nature of seismic sources. Seismic spectra at three different depths are compared, establishing the 4100 ft level as a world-class low seismic-noise environment.

Origin of deep ocean microseisms by using teleseismic body waves

Recent studies of oceanic microseisms have concentrated on fundamental mode surface waves. Extraction of fundamental mode Rayleigh and Love wave Green functions from station‐station correlations of ambient seismic noise has recently been demonstrated to be a very powerful tool for imaging of the Earth's crust and uppermost mantle. In this study we concentrate on energetic arrivals in two frequency bands around the primary (14 s) and the secondary (7 s) microseismic peaks that appear at near‐zero times in noise cross correlations. Thanks to a polarization analysis of data from the Eastern Turkey Seismic Experiment network, we identify this “near‐zero time” signal as an upcoming P wave in the secondary microseismic frequency band (5–10 s). In a second step, analyzing noise cross correlations from three different arrays (in Yellowstone, in Turkey, and in Kyrgyzstan), we determine the origin of these signals by means of beam‐forming analysis and its projection on the Earth. Our results show that in the 0.1–0.3 Hz frequency band, the energetic “near‐zero” time arrivals in seismic noise cross correlations are mainly formed by teleseismic P, PP, and PKP waves. Generation of this ambient body waves in the secondary microseismic band presents a marked seasonal behavior with sources located in southern and northern oceans during summer and winter, respectively. Moreover, body wave array analysis is accurate enough to confirm that significant amount of the microseism energy is generated far from the coast in deep oceans.

Global climate imprint on seismic noise

In the absence of earthquakes, oceanic microseisms are the strongest signals recorded by seismic stations. Using the GEOSCOPE global seismic network, we show that the secondary microseism spectra have global characteristics that depend on the station latitude and on the season. In both hemispheres, noise amplitude is larger during local winter, and close to the equator, noise amplitude is stable over the year. There is an excellent correlation between microseism amplitude variations over the year and changes in the highest wave areas. Considering the polarization of the secondary microseisms, we show that stations in the Northern Hemisphere and close to the equator record significant changes of the secondary microseism source azimuth over the year. During Northern Hemisphere summer, part or all of the sources are systematically located farther toward the south than during winter. Stations in French Guyana (MPG) and in Algeria (TAM) record microseisms generated several thousand kilometers away in the South Pacific Ocean and in the Indian Ocean, respectively. Thus, secondary microseism sources generated by ocean waves which originate in the Southern Hemisphere can be recorded by Northern Hemisphere stations when local sources are weak. We also show, considering a station close to Antarctica, that primary and secondary microseism noise amplitudes are strongly affected by changes of the sea ice floe and that sources of these microseisms are in different areas. Microseism recording can therefore be used to monitor climate changes.

BLIND SOURCE SEPARATION: AN APPLICATION TO THE MT. MERAPI VOLCANO, INDONESIA

Independent Component Analysis (ICA) is an emerging new technique in the blind identification of signals recorded in a variety of different fields. ICA tries to find the most statistically independent sources from an observable random vector, with the only restriction that all sources but at most one are non-Gaussian; no other a priori information on sources and mixing dynamic system are needed. The applications of these techniques to the analysis of volcanic time series are relatively few to date. In this paper we show that ICA is a suitable technique to separate a volcanic source component from ocean microseisms background noise in a seismic dataset recorded at the Mt. Merapi volcano, Indonesia. The encouraging results obtained with this methodology in the presented case study support their wider applicability in volcano seismology.