Development of a low cost method to estimate the seismic signature of a geothermal field form ambient noise analysis.

Anomalies in seismic ambient noise, defined as strong spectral amplification of the vertical components at frequencies of several Hertz, are currently observed on sites located above hydrocarbon reservoirs. If properly understood, these anomalies could have a potential for applications such as geothermal reservoir exploration or underground gas storage monitoring. Under purely elastic modeling, the nature of these anomalies was mainly explained by the geological structure more than the fluid reservoir itself. &#160;The main objective of the present work is to explain the exact origin of the anomalies by numerical simulations of the 3D wave propagation using specfem3D code. The simulated spectral anomalies are essentially static and determined by the typical geological reservoir environments. The effect of an anticline structure, which is a common characteristic of hydrocarbon reservoirs, is investigated using different types of sources. Results show that the spectral anomalies caused by the presence of the anticline structure have similarities with the anomalies observed in real data. More work is needed to extract laws linking geometrical characteristics of the anticline to spectral properties. Future works will also include analysis on real gas storage sites, followed by a transposition to the geothermal field applications, for which more complicated parameters appear to participate to the phenomenon.

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Integration of ambient noise and ERT data to investigate the structure of the Yang Jia Gou rock avalanche deposits (Sichuan - China)

10.5194/egusphere-egu21-4578 ◽

2021 ◽

Author(s):

Paola Capone ◽

Vincenzo Del Gaudio ◽

Janusz Wasowski ◽

Wei Hu ◽

Nicola Venisti ◽

...

Keyword(s):

Mechanical Properties ◽

Rayleigh Waves ◽

Ambient Noise ◽

Noise Analysis ◽

Rock Avalanche ◽

Landslide Dam ◽

Mountainous Area ◽

The Tibetan Plateau ◽

Large Variability ◽

Single Station

On 12 May 2008, the mountainous area of Longmenshan, which separates the Tibetan Plateau from the Sichuan Basin, was hit by the 8.0 Ms Wenchuan earthquake which triggered about 200,000 landslides, some of which caused river damming with the formation of temporary lakes. Failures of the landslide dams can induce severe flooding downstream, therefore, it is important to study their structure and mechanical properties in order to evaluate their stability conditions.The present study investigates the landslide dam deposits of a rock avalanche triggered in Yang Jia Gou, in Sichuan Province, using single-station three component recordings of ambient noise, with the aim of obtaining information about thickness and mechanical properties of the deposits from their resonance properties. Three noise measurement campaigns and two ERT surveys were conducted to support data interpretation. The data were analyzed using the traditional Nakamura&#8217;s technique, HVNR, and the innovative technique HVIP, both based on the calculation of ratios between horizontal and vertical amplitude of ground motion. Both methods revealed the presence &#160;of resonance peaks, a major one at lower frequency, and a minor one at higher frequencies, representative of the deposit layering. HVNR showed a considerable instability in terms of amplitude of H/V, likely because this technique analyzes the entire noise wave field recorded, so to be subject to a large variability related to a variable composition of the noise field. This problem does not affect the HVIP method, which is based on the analysis of the ellipticity of Rayleigh waves, isolated from the recording.Rayleigh wave ellipticity curves were used as targets in the inversion phase to obtain the velocity profile of the site. The subsoil model was &#160;constrained by the data derived from the resistivity profiles. The results revealed: &#160;different velocity layers inside the deposit; lateral variations in thickness, in accordance with the higher frequency peak, and in mechanical properties, with an increase of stiffness, probably due to a major portion of rocky blocks; an increase in thickness of the entire deposit, probably because of the irregularities of the substrate.Further investigations are in progress through other kinds of noise analysis exploiting the synchronization of simultaneous recordings. This can provide additional constraints (to be derived from the dispersion of group velocity of Rayleigh waves) and aid resolving interpretation ambiguities.

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Spectral probability density as a tool for ambient noise analysis

The Journal of the Acoustical Society of America ◽

10.1121/1.4794934 ◽

2013 ◽

Vol 133 (4) ◽

pp. EL262-EL267 ◽

Cited By ~ 39

Author(s):

Nathan D. Merchant ◽

Tim R. Barton ◽

Paul M. Thompson ◽

Enrico Pirotta ◽

D. Tom Dakin ◽

...

Keyword(s):

Probability Density ◽

Ambient Noise ◽

Noise Analysis

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Directional variations of site response in a landslide area using ambient noise analysis via Nakamura’s and polarization-based method

Soil Dynamics and Earthquake Engineering ◽

10.1016/j.soildyn.2020.106492 ◽

2021 ◽

Vol 141 ◽

pp. 106492

Author(s):

Mohsen Kazemnia Kakhki ◽

Vincenzo Del Gaudio ◽

Sadegh Rezaei ◽

Webe João Mansur

Keyword(s):

Ambient Noise ◽

Site Response ◽

Noise Analysis ◽

Landslide Area

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Estimating bedrock depth in the case of regolith sites using ambient noise analysis

Engineering Geology ◽

10.1016/j.enggeo.2018.06.022 ◽

2018 ◽

Vol 243 ◽

pp. 145-159 ◽

Cited By ~ 9

Author(s):

Bambang Setiawan ◽

Mark Jaksa ◽

Michael Griffith ◽

David Love

Keyword(s):

Ambient Noise ◽

Noise Analysis ◽

Bedrock Depth

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Ambient Noise Analysis of Deep-Ocean Measurements in the Northeast Pacific

IEEE Journal of Oceanic Engineering ◽

10.1109/joe.2007.891885 ◽

2007 ◽

Vol 32 (2) ◽

pp. 497-512 ◽

Cited By ~ 40

Author(s):

Roy D. Gaul ◽

David P. Knobles ◽

Jack A. Shooter ◽

August F. Wittenborn

Keyword(s):

Ambient Noise ◽

Noise Analysis ◽

Deep Ocean ◽

Northeast Pacific ◽

Ocean Measurements

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Accurate Indoor Sound Level Measurement on a Low-Power and Low-Cost Wireless Sensor Node

Sensors ◽

10.3390/s18072351 ◽

2018 ◽

Vol 18 (7) ◽

pp. 2351 ◽

Cited By ~ 9

Author(s):

Vladimir Risojević ◽

Robert Rozman ◽

Ratko Pilipović ◽

Rok Češnovar ◽

Patricio Bulić

Keyword(s):

Low Power ◽

Sensor Node ◽

Ambient Noise ◽

Ieee 802.15.4 ◽

Low Cost ◽

Sound Level ◽

Wireless Sensor ◽

Sound Level Meter ◽

Hardware Platform ◽

Level Meter

Wireless sensor networks can provide a cheap and flexible infrastructure to support the measurement of noise pollution. However, the processing of the gathered data is challenging to implement on resource-constrained nodes, because each node has its own limited power supply, low-performance and low-power micro-controller unit and other limited processing resources, as well as limited amount of memory. We propose a sensor node for monitoring of indoor ambient noise. The sensor node is based on a hardware platform with limited computational resources and utilizes several simplifications to approximate more complex and costly signal processing stage. Furthermore, to reduce the communication between the sensor node and a sink node, as well as the power consumed by the IEEE 802.15.4 (ZigBee) transceiver, we perform digital A-weighting filtering and non-calibrated calculation of the sound pressure level on the node. According to experimental results, the proposed sound level meter can accurately measure the noise levels of up to 100 dB, with the mean difference of less than 2 dB compared to Class 1 sound level meter. The proposed device can continuously monitor indoor noise for several days. Despite the limitations of the used hardware platform, the presented node is a promising low-cost and low-power solution for indoor ambient noise monitoring.

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Determining seismic shear-velocity from ambient noise sources at regional and local scales

10.26686/wgtn.17067788.v1 ◽

2021 ◽

Author(s):

◽

Francesco Civilini

Keyword(s):

Surface Wave ◽

Ambient Noise ◽

Shear Velocity ◽

Volcanic Field ◽

Geothermal Field ◽

Near Surface ◽

Velocity Models ◽

Geothermal Fields ◽

Cross Correlations ◽

Velocity Changes

We present three projects that use different bandwidths of the ambient noise spectrum to solve geophysical problems. Specifically, we use signals within the noise field to determine surface and shear wave velocities, image the shallow and deep crust, and monitor time-dependent deformation resulting from geothermal fluid injection and extraction. Harrat Al-Madinah, a Cenozoic bimodal alkaline volcanic field in west-central Saudi Arabia, is imaged using shear-velocities obtained from natural ambient seismic noise. To our knowledge, this project is the first analysis of Saudi Arabia structure using ambient noise methods. Surface wave arrivals are extracted from a year's worth of station-pair cross-correlations, which are approximations of the empirical Green's function of the interstation path. We determine group and phase velocity surface wave dispersion maps with a 0.1 decimal degree resolution and resolve a zone of slow surface wave velocity south-east of the city of Medina, which is spatially correlated with the most recent historical eruption (the 1256 CE Medina eruption). Dispersion curves are calculated at each grid-point of the surface-wave velocity maps and inverted to obtain measurements of shear-velocity with depth. The 1D velocity models are then used to produce average shear-velocity models for the volcanic field. A shear-velocity increase ranging from 0.5 to 1.0 km/s, suggesting a layer interface, is detected at approximately 20 km depth and compared to P-wave measurement from a previous refraction study. We compute cross-section profiles by interpolating the inversions into a pseudo-3D model and resolve a zone of slow shear-velocity below the 1256 CE eruption location. These areas are also spatially correlated with low values of Bouguer gravity. We hypothesize that the low shear-velocity and gravity measurements are caused by fluids and fractures created from prior volcanic eruptions. We use the coda of cross-correlations extracted from ambient noise to determine shear-velocity changes at Rotokawa and Ngatamariki, two electricity producing geothermal fields located in the North Island of New Zealand. Stacks of cross correlations between stations prior to the onset of production are compared to cross correlations of moving stacks in time periods of well stimulation and the onset of electricity production using the Moving Window Cross Spectral technique. An increase between 0.05% to 0.1% of shear-velocity is detected at Rotokawa coinciding with an increase of injection. The shear-velocity subsequently decreases by approximately 0.1% when the rate of production surpasses the rate of injection. A similar amplitude shear-velocity increase is detected at Ngatamariki during the beginning of injection. After the initial increase, the shear-velocity at Ngatamariki fluctuates in response to differences in injection and production rates. A straight-ray pseudo-tomography analysis is conducted at the geothermal fields, which reveals that localized positive velocity changes are co-located with injection wells. Lastly, we use ambient noise and active sources at the Ngatamariki geothermal field to determine the structure of the top 200 meters using the Refraction Microtremor technique. We deployed a linear 72-channel array of vertical geophones with ten meter spacing at two locations of the geothermal field and determine average 1D and 2D shear-velocity profiles. We were able to image depths between 57 to 93 meters for 2D profiles and up to 165 meters for 1D profiles. A shear-velocity anomaly was detected across one of the lines that coincided with the inferred location of a fault determined from nearby well logs. This suggests that the method can be used to cheaply and quickly constrain near-surface geology at geothermal fields, where ambient noise is abundant and typical reflection and refraction surveys require large inputs of energy and are hindered by attenuation and scattering in near-surface layers.

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