Seismic Sensors Research Articles

Сейсмический датчик для систем мониторинга. Разработка и результаты

The short-period seismic sensor IGES-006 developed at the NAS RA Institute of Geophysics and Engineering Seismology after A. Nazarov is presented. The IGES-006 sensor can be used both as part of various seismic monitoring systems and for solving special engineering problems. The sensor prototype has successfully passed laboratory and field tests, including the seismic monitoring mode. A comparative analysis of seismic signals recorded using IGES-006 and sensors in the time and frequency domains have been carried out.

Peculiarities of the HVSR Method Application to Seismic Records Obtained by Ocean-Bottom Seismographs in the Arctic

The application of the horizontal-to-vertical spectral ratio (HVSR) modeling and inversion techniques is becoming more and more widespread for assessing the seismic response and velocity model of soil deposits due to their effectiveness, environmental friendliness, relative simplicity and low cost. Nevertheless, a number of issues related to the use of these techniques in difficult natural conditions, such as in the shelf areas of the Arctic seas, where the critical structures are also designed, remain poorly understood. In this paper, we describe the features of applying the HVSR modeling and inversion techniques to seismic records obtained by ocean-bottom seismographs (OBS) on the outer shelf of the Laptev Sea. This region is characterized by high seismotectonic activity, as well as sparse submarine permafrost distribution and the massive release of bubble methane from bottom sediments. The seismic stations were installed for one year and their period of operation included periods of time when the sea was covered with ice and when the sea was ice-free. The results of processing of the recorded ambient seismic noise, as well as the wave recorder data and ERA5 and EUMETSAT reanalysis data, showed a strong dependence of seafloor seismic noise on the presence of sea ice cover, as well as weather conditions, wind speed in particular. Wind-generated gravity waves, as well as infragravity waves, are responsible for the increase in the level of ambient seismic noise. The high-frequency range of 5 Hz and above is strongly affected by the coupling effect, which in turn also depends on wind-generated gravity waves and infragravity waves. The described seafloor seismic noise features must be taken into account during HVSR modeling and interpretation. The obtained HVSR curves plotted from the records of one of the OBSs revealed a resonant peak corresponding to 3 Hz, while the curves plotted from the records of another OBS did not show clear resonance peaks in the representative frequency range. Since both OBSs were located in the area of sparse distribution of submarine permafrost, the presence of a resonance peak may be an indicator of the presence of a contrasting boundary of the upper permafrost surface under the location of the OBS. The absence of a clear resonant peak in the HVSR curve may indicate that the permafrost boundary is either absent at this site or its depth is beyond the values corresponding to representative seismic sensor frequency band. Thus, HVSR modeling and inversion techniques can be effective for studying the position of submarine permafrost.

A Ground Moving Target Detection Method for Seismic and Sound Sensor Based on Evolutionary Neural Networks

The accurate identification of moving target types in alert areas is a fundamental task for unattended ground sensors. Considering that the seismic and sound signals generated by ground moving targets in urban areas are easily affected by environmental noise and the power consumption of unattended ground sensors needs to be reduced to achieve low-power consumption, this paper proposes a ground moving target detection method based on evolutionary neural networks. The technique achieves the selection of feature extraction methods and the design of evolving neural network structures. The experimental results show that the improved model can achieve high recognition accuracy with a smaller feature vector and lower network complexity.

Восстановление данных о разности времен прихода продольной и поперечной сейсмических волн на сейсмических датчиках

We developed a method for seismic sensor data recovery and simulated seismic sensor operation using artificial neural networks. We selected two parameters to train the artificial neural network on: the time between seismograph recordings of longitudinal (primary) and transverse (secondary) seismic waves, as well as the time between primary seismic wave recordings by two seismographs located at a certain distance from each other. We used data on 2636 earthquakes that occurred in 2020 in the Republic of Dagestan for our seismograph data recovery. The existing 19 seismic stations recorded less than 60 % of the total number of earthquakes. To recover seismic data, we trained the neural network twice for each seismic sensor, the first time involving zero time differences regarding seismic wave arrival at seismographs that did not record the time, and the second time involving time differences recovered from the results of training the neural network for the first time. Times between seismic wave recordings with known data were used as inputs to train the artificial neural network, while time differences to be determined were designated as outputs. The trained neural network displays a correlation coefficient related to real time intervals between seismograph recordings of seismic waves that exceeds 0.99919. The paper provides root-mean-square error plots of the neural network operation by epochs of its training, plots demonstrating how training results calculated by the neural network matchthe initial data, and histograms of neural network operation errors

Sensitive seismic sensors based on microwave frequency fiber interferometry in commercially deployed cables

The use of fiber infrastructures for environmental sensing is attracting global interest, as optical fibers emerge as low cost and easily accessible platforms exhibiting a large terrestrial deployment. Moreover, optical fiber networks offer the unique advantage of providing observations of submarine areas, where the sparse existence of permanent seismic instrumentation due to cost and difficulties in deployment limits the availability of high-resolution subsea information on natural hazards in both time and space. The use of optical techniques that leverage pre-existing fiber infrastructure can efficiently provide higher resolution coverage and pave the way for the identification of the detailed structure of the Earth especially on seismogenic submarine faults. The prevailing optical technique for use in earthquake detection and structural analysis is distributed acoustic sensing (DAS) which offers high spatial resolution and sensitivity, however is limited in range (< 100 km). In this work, we present a novel technique which relies on the dissemination of a stable microwave frequency along optical fibers in a closed loop configuration, thereby forming an interferometer that is sensitive to deformation. We call the proposed technique Microwave Frequency Fiber Interferometer (MFFI) and demonstrate its sensitivity to deformation induced by moderate-to-large earthquakes from either local or regional epicenters. MFFI signals are compared to signals recorded by accelerometers of the National Observatory of Athens, Institute of Geodynamics National Seismic Network and by a commercially available DAS interrogator operating in parallel at the same location. Remarkable agreement in dynamical behavior and strain rate estimation is achieved and demonstrated. Thus, MFFI emerges as a novel technique in the field of fiber seismometers offering critical advantages with respect to implementation cost, maximum range and simplicity.

High-resolution TENGS for earthquakes ground motion detection

Towards a deeper consciousness of the human being in preserving the natural environment of our planet, huge effort is nowadays being exerted by scientists all over the world to use green and free energy. The main motivation for this effort is to protect humanity, today and in the future, from the big natural disasters that often affect the poorest areas of the globe. In this work, TENGs (triboelectric nanogenerators) with an inertial mass on their surface are proposed to be used as self-powered seismic sensors (SEIS-TENGs) in the detection of seismic waves with global connectivity to the Internet of Things (IoT). For this purpose, various TENGs with several characteristics such as low cost, flame retardancy, and frequency-dependent sensitivity were fabricated with different materials such as Paper, Polyvinylalcohol (PVA), Polyvinyledenefluoride (PVDF) and PDMS. The TENGs based on PVA10PPA-PEI/PVDF exhibited the highest sensitivity of 280 Hz and the ones based on Paper/PDMS were very low cost and easy to manufacture. Pulses, artificially generated with an electro-mechanical machine operating in fatigue mode, were remotely transmitted by using LoRA communication protocol and could be monitored in the TTS (The Thing of Stack) platform. Finally, a realistic application of SEIS-TENG was carried out by simulating earthquakes with a triaxial shaking table and the seimsic waves were measured using SEIS-TENGs. Interestingly, they exhibited a similar response to the acceleration, velocity, and displacement, and with today’s commercial accelerometers such as micromechanical systems (MEMS). Furthermore, the number of quakes detected by SEIS-TENG was very similar to that of the MEMS. The results obtained demonstrate that the SEIS-TENGs are very promising to be employed in a global IoT seismic network. They will allow measuring ground oscillations to prevent the catastrophes caused by earthquakes.

DAS signature of reservoir pressure changes caused by a CO2 injection: Experience from the CO2CRC Otway Project

Distributed Acoustic Sensing (DAS) is a fast-developing technology and is being actively used in geophysical monitoring applications. DAS technology is based on continuous measurements along a fibre-optic cable and can record seismic waves/signals that induce axial strain in the cable. Most DAS systems are designed to measure signals higher than 1 Hz; however some DAS systems are sensitive to low-frequency (< 1 Hz) signals such as reservoir pressure variations.At the time of CO2 injection within the CO2CRC Otway Project, pressure related strain-rate DAS signals were observed in two monitoring wells. These signals are highly correlated with the pressure signals measured by borehole pressure gauges above the perforations in monitoring wells.Comparison of DAS measurements and pressure measurements shows a linear relationship between the two datasets. Analysis of data shows that DAS is able to detect reservoir pressure variations higher than 10−4 psi/s. Analysis of pressure variations and strain calculated from DAS strain rate values allows estimation of the elastic modulus of the reservoir formation.Obtained results show that DAS systems can be utilised not only as seismic sensors, but also as continuous pressure sensors that can help track possible CO2 leakages into the overburden. In contrast to traditional pressure gauges, DAS is also capable of tracking the pressure profile along the entire well. DAS pressure sensing capabilities open up many new applications to complement subsurface reservoir pressure monitoring, CCUS and hydrogeological studies.

The Near Fault Observatory community in Europe: a new resource for faulting and hazard studies

The Near Fault Observatories (NFOs) community is one of the European Plate Observing System (EPOS, http://www.epos-eu.org) Thematic Communities, today consisting of six research infrastructures that operate in regions characterised by high seismic hazard originating from different tectonic regimes. Earthquakes respond to complex natural systems whose mechanical properties evolve over time. Thus, in order to understand the multi-scale, physical/chemical processes responsible for the faulting that earthquakes occur on, it is required to consider phenomena that intersect different research fields, i.e., to put in place multidisciplinary monitoring. Hence, NFOs are grounded on modern and multidisciplinary infrastructures, collecting near fault high resolution raw data that allows generation of innovative scientific products. The NFOs usually complement regional backbone networks with a higher density distribution of seismic, geodetic, geochemical and other geophysical sensors, at surface and sometimes below grade. These dense and modern networks of multi-parametric sensors are sited at and around active faults, where moderate to large earthquakes have occurred in the past and are expected in the future. They continuously monitor the underlying Earth instability processes over a broad time interval. Data collected at each NFO results in an exceptionally high degree of knowledge of the geometry and parameters characterizing the local geological faults and their deformation pattern. The novel data produced by the NFO community is aggregated in EPOS and is made available to a diverse set of stakeholders through the NFO Federated Specific Data Gateway (FRIDGE). In the broader domain of the Solid Earth sciences, NFOs meet the growing expectations of the learning and communication sectors by hosting a large variety of scientific information about earthquakes as a natural phenomenon and a societal issue. It represents the EPOS concept and objective of aggregating and harmonising the European research infrastructures capabilities to facilitate broader scientific opportunity. The NFOs are at the cutting edge of network monitoring. They conduct multidisciplinary experiments for testing multi-sensor stations, as well as realise robust and ultra-low latency, transmission systems that can routinely accommodate temporary monitoring densification. The effort to continuously upgrade the technological efficiency of monitoring systems positions the NFO at the centre of marketing opportunities for the European enterprises devoted to new sensor technology. The NFOs constitute ideal test beds for generating expertise on data integration, creating tools for the next generation of multidisciplinary research, routine data analysis and data visualization. In particular focus is often on near-real time tools and triggering alarms at different levels are tested and implemented, strengthening the cooperation with the Agencies for risk management. NFOs have developed innovative operational actions such as the Testing Centre for Earthquake Early Warning and Source Characterisation (CREW) and detailed fast ground shaking and damage characterization. Complementing the recent growth of modern laboratory and computational models, the NFOs can provide interdisciplinary observations of comparable high resolution to describe the behaviour of fault slip over a vast range of spatial and temporal scales and aiding to provide more accurate earthquake hazard characterizations.

Seismic monitoring of CO2 geosequestration using multi-well 4D DAS VSP: Stage 3 of the CO2CRC Otway project

An important part of any CO2 geosequestration project is to ensure CO2 containment and conformance in the subsurface. This is generally done by implementing a comprehensive, risk-based Measurement, Monitoring and Verification plan, a key element of which is active time-lapse seismic monitoring. However, high cost and environmental impact of the standard surface seismic monitoring dictate the need for a cost-effective and environmentally friendly alternative. An opportunity to develop such method emerges with advances in distributed acoustic sensing (DAS) technology, which turns an optical fibre into a seismic sensor with dense spatial sampling. DAS can be permanently deployed in multiple wells across the geosequestration site providing a robust and non-intrusive network of seismic receivers. This approach was developed and tested in the CO2CRC Otway project, where injection of 15 kt of CO2 at 1.5 km depth was monitored with a 4D vertical seismic profiling (VSP) using five borehole DAS arrays and mobile vibroseis sources. The 4D DAS VSP in each of the five wells provides broadly consistent images of the CO2 plume with some differences due to different illumination of the target horizon, lateral variation of velocities, and seismic anisotropy. When the newly injected CO2 reaches a CO2 plume created as a result of an earlier injection into the same formation ∼600 m updip, 4D DAS VSP shows a change in reflectivity in that area and beyond. This shows a potential of 4D DAS VSP for monitoring gas injection into gas-saturated reservoirs.

Ultralow-frequency seismic sounding of railway subgrade state by passing trains

The degradation of the railway subgrade is a common cause for train accidents in Russia because of the extensive railway system and large areas of weak soils. We present a seismic monitoring technique that utilizes moving trains as signal sources to probe the properties of the subgrade. The broadband (periods up to 100 s) seismic sensors recorded signals over several weeks during a nonstop monitoring experiment. The large statistic allows us to identify the signals properties, and thus these signals are processed by an automated system. We defined the parameters of the low-frequency signal generated by a passing train that are sensitive to changes in the subgrade state. These are the ratio of amplitudes of horizontal components, and the time interval between the end of the train passage and the maximum amplitude surge in the component transversal to rails. We propose an analytical model to describe the interaction between a moving train and the subgrade that takes into consideration the viscosity of a substrate layer. The application of this model produces a consistent explanation of processes in the media and enables an “in situ” estimation of soil elasticity and viscosity, caused by seasonal thawing.

Can DAS be used to monitor mining induced seismicity?

Distributed acoustic sensing (DAS) is being applied in an increasing number of geoscientific fields. We present herein preliminary results of applying DAS to monitor microseismicity in underground mines. We installed 275 m of fiber optic cable approximately 1500 m below the surface in an operational mine and recorded mine seismicity for two weeks during November of 2018. The first approximately 50 m was tied to the sidewall safety mesh and a further 225 m was grouted into a down-dipping borehole alongside four three-component geophone sensors with 14 Hz high-sensitivity elements. The geophone sensors are located 132 m, 154 m, 176 m and 198 m down the borehole. We show that, for the larger seismic events (MW > −0.1), there is relatively good agreement in the data collected with DAS compared to the geophone data. There is some amplitude variation, especially at higher frequencies, but the phase of the recordings match well. We were able to include the DAS data in processing select events using PhaseNet, a machine-learning based algorithm, to pick phase arrivals and then locate these events using a recently developed interferometric method. In our comparison of the background noise of the DAS and that of the geophones, we found that the DAS as installed in our experiment has a noise floor orders of magnitude higher than the seismic background of the mine. Furthermore we compared the recordings in the different fiber sections (tied to the safety mesh and grouted, respectively) to analyze the feasibility of using existing mining communication infrastructure as sufficiently accurate seismic sensors. Fiber optic communication cables are typically tied to the sidewall mesh in the absence of dedicated conduits, and thus our mesh-coupled section was a suitable proxy for this scenario. We found extremely limited utility in the recordings of the mesh coupled fiber.

The Experimental Validation of a Digital Filter Mathematical Modelling for Nuclear Fuel Vibration Monitoring System

Aiming at vehicles will produce shocks and vibrations for various reasons in the process of transportation and handling, any shock and vibration that exceeds the regulations would cause damage to the nuclear fuel being transported. In order to monitor and analyze the shock and vibration data scientifically, a monitoring system based on MEMS acceleration sensor technology is developed to measure shocks and vibrations. The measured result involves some noise caused by the sensitivity of the sensor and the electrical noise, and a digital filter mathematical modelling is introduced to reduce noise and improve the measured result accuracy. In order to verify the effectiveness of the device designed in this paper, the device and the high-precision seismic acceleration sensor AC73 are, respectively, used for field tests; the results show that the test precision of the designed device can meet the requirements, and also, the designed shock and vibration monitoring system can record and store the three-axis acceleration, temperature, humidity, pressure, time, and other parameters that exceed the set threshold during nuclear fuel transportation in real time and complete the fuel assembly transportation status assessment and promptly remind the transportation personnel to take safety precautions and treatment measures. Therefore, it can be widely used in the monitoring, recording, and postevent data analysis of the transportation process of important products such as nuclear fuel.

Moment magnitude (Mw) from hydrophone records of low energy volcanic quakes

Earthquake magnitude calibration using hydrophone records has been carried out at Campi Flegrei caldera, an active area close to the highly populated area of Naples city, partly undersea. Definite integrals of the hydrophone records amplitude spectra, between the limits of 1 and 20 Hz, were calculated on a set of small volcano-tectonic earthquakes with moment magnitudes ranging from 1 to 3.3. The coefficients of a linear relationship between the logarithm of these integrals and the magnitude were obtained by linear optimization, thus defining a useful equation to calculate the moment magnitude from the hydrophone record spectra. This method could be easily exported to other volcanic areas, where submerged volcanoes are monitored by networks of hydrophones and seismic sensors on land. The proposed approach allows indeed magnitude measurements of small magnitude earthquakes occurring at sea, thus adding useful information to the seismicity of these volcanoes.

Determining the coordinates of the earthquake hypocenter with the simultaneous determination of seismic wave velocities

Objective. The purpose of the study is to determine the coordinates of the earthquake hypocenter with the simultaneous determination of the seismic wave velocity.Method. The study is based on the use of figures of the fourth and second order - the Cassini oval and hyperbola, figures of the second order - ellipse and hyperbola and combined methods that allow, at given seismic wave velocities, according to three seismic sensors, to determine the coordinates of the earthquake hypocenter. In this case, the velocities are assumed to be known a priori. According to the readings of the fourth seismic sensor, and for given seismic wave velocities, the distance from the fourth seismic sensor to the hypocenter is determined. Again, according to the coordinates of the fourth seismic sensor and the hypocenter coordinates calculated from the three seismic sensors, the distance between them is calculated. If the seismic wave velocities do not correspond to the true ones, a discrepancy will appear between the two calculated values of the distances from the hypocenter to the fourth seismic sensor. By varying the velocities of seismic waves when calculating the coordinates of the hypocenter, we achieve a minimum discrepancy.Result. The problem of determining the coordinates of the earthquake hypocenter with the simultaneous determination of seismic wave velocities is solved. The error distribution densities in determining the coordinates of the earthquake hypocenter and seismic wave velocities are obtained.Conclusion. The proposed method makes it possible to increase the accuracy of determining the coordinates of the earthquake source, as well as to refine the values of seismic wave velocities.

System design and laboratory tests of an autonomous seismic station for space applications

We introduce a reference concept for a small and lightweight instrument carrier system for operation in isolated areas on Earth (or even on other celestial bodies) that autonomously records data after deployment at a site remote from the main station, thus called Remote Unit (RU). In particular, we present here concepts for realizing an autonomously operating seismometer, including support functions provided by encapsulating the actual instrument into the RU carrier. The conceptualization of the RU is based on the design of MASCOT, and intended for evolving into an instrument carrier for lunar exploration. Still in this paper we focus on the functionality needed for realizing the remote and autonomous aspects of the concept. Evolutionary steps needed for the system design to survive on a planetary body are briefly discussed, but not intensively covered in this paper, but elsewhere.We developed two prototypes of this RU including three seismic sensors each, either fixed, the other one with a built-in self-leveling mechanism. We used standard seismic sensors, which were integrated into a lightweight instrument carrier equipped with all required support structures for remote terrestrial operation, including power, thermal control, and data acquisition (total mass of prototypes not exceeding 3 ​kg and 10 ​kg, respectively). We have carried out laboratory tests and evaluated seismic data from these two types of RU to evaluate noise levels, spectral response, and overall performance of the systems. We demonstrate that the systems provide reproducible data at high signal levels, which warrant comfortable scientific interpretation of seismic data from active and passive experiments. Noise level and detected spectral anomalies (due to mechanical structure and associated Eigenfrequencies) are well within expectations.

A field experiment of a temperature-tolerant distributed acoustic sensor in deep geothermal reservoir prospecting

Seismic exploration technologies with distributed acoustic sensing (DAS) are investigated to acquire seismic waves in high-temperature environments and locate supercritical geothermal reservoirs deeper than the brittle-ductile transition boundary in Japan. We conducted a seismic reflection survey in the Mori-Nigorikawa geothermal field in the Nigorikawa caldera basin. An optical fiber system and an array of geophones were installed to 2100 m depth in F-01, a little-deviated high-temperature geothermal production well, and along a road for about 1.2 km on the surface. Numerous reflectors appear to gather at a depth between 2000 and 3000 m, corresponding to the production zone of the well. Although the production zone is located mainly within the Nigorikawa volcanic conduit estimated in the past geothermal analysis, the reflectors are also distributed outside the conduit. The DAS waveforms show distinct traveltime discontinuity at 1060 m depth. Our traveltime tomography and forward-simulated synthetic DAS waveforms could indicate the existence of a water layer 250 m long and 50 m thick at 1060 m depth. The Mori Geothermal Power Plant reinjects wastewater at this depth through a reducing well. The use of high-temperature-tolerant fiber enables the deployment of seismic sensors much closer to the deep target and may investigate effective fluid circulation through production and reducing wells.

ANALISIS SINYAL SEISMIK DAN SELF POTENTIAL (SP) DARI FENOMENA SEIMOELEKTRIK DI GUNUNG LUMPUR BLEDUG KUWU JAWA TENGAH

Abstarct Bledug Kuwu is one of the mud volcano (gunung lumpur) in Java. Bledug Kuwu eruption periodically occured with a frequency of more than five times in one minute, pointed by the release of gas bubbles and mud. This study aims to observe the signals of the seismic and self potential (SP) from seismoelectric phenomenon generated by Bledug Kuwu eruption. Measurements were performed by placed seismic sensor around the main crater point of Bledug Kuwu mud volcano, while the SP sensor placed in the vertical, the radial and tangential direction from the point of the main crater of a Bledug Kuwu mud volcano.. The result of analysis shows that the dominant frequency of seismic events is 0,2 Hz, while dominant frequency of SP signals is 48,0 Hz. The arrival time difference between seismic and SP signals predominantly in the range of time (0,0 to 1,5 second) which indicates that the appears of the seismic signal causes the appearance of the signal SP as a result of the transfer fluid as described in the seismoelectric phenomenon.The average value of the amplitude of seismic events for Z, NS and EW component is 0,6694, 0,4848 and 0,5158 Count/Volt. The average value of the amplitude of SP events for Z, NS and EW component is 1,338, 1,249 and 0,909 mVolt. SP events will appear if amplitude of seismic events more than 0,2 Count value. Amplitude of sesmic events proportional to the amplitude of the SP event with value of the correlation coefficient between the both is more than 80.0%, the seismic events caused the material in its path have excessive pressure that pore fluid in the material move and cause the separation of charge is the source of the appear of SP signal, the greater the amplitude of the seismic event the pressure exerted on the material so that the larger the amplitude of the SP events formed also getting bigger, this is in accordance with the theory of the seismoelectric phenomenon by electrokinetic effect mechanismKeyword: Bledug Kuwu, Self Potential (SP), seismic, dominant frequency, different arrival time, amplitude and seismoelectric effect.

Continuous monitoring of the depth of the water-mud interface using distributed acoustic sensing

PurposeCurrent surveying techniques used by port authorities to estimate the nautical depth are limited in depth resolution and temporal resolution. Because of this, certain heavily occupied quay walls cannot be optimised in terms of utilisation. Therefore, a permanent continuous measuring system with a higher depth resolution is needed to optimise the occupation at these quay walls. We show how this could be achieved with distributed acoustic sensing (DAS) using fibre-optical cables.MaterialsWe analyse recordings from a dual-frequency echo-sounder source along a standard communication optical fibre coiled vertically around a PVC pipe to represent vertical seismic profiling. This PVC pipe is placed inside a transparent plastic cylindrical tank which is partly filled with water and mud. This allows us to track the water-mud interface visually. We use a Silixa iDAS v2 and a Febus A1 DAS interrogator to convert the optical fibre into a seismic sensor. We use a wave generator to select the source frequency and an amplifier to amplify the output of the wave generator to a SIMRAD 38/200 COMBI C dual-frequency echo-sounder.ResultsWe identify standing waves and use them to make accurate depth estimates of the water-mud interface inside the column we measure. Due to the high apparent velocity, the standing waves are easy to identify in the time domain. Due to the constructive interference, standing waves also show the water-mud interface in a power spectral density plot. We demonstrate that these standing waves could be used with an on-demand permanent continuous measuring system using ambient noise sources.ConclusionOur laboratory experiment showed that DAS could be used to estimate the water-mud interface. In addition, we showed the potential for on-demand monitoring in ports and waterways using DAS. Furthermore, due to the low cost of optical fibres, and the possibility of utilising ambient noise sources, DAS could be used for continuous depth monitoring purposes in ports and waterways.

Characteristics, relationships and precision of direct acoustic-to-seismic coupling measurements from local explosions

SUMMARY Acoustic energy originating from explosions, sonic booms, bolides and thunderclaps have been recorded on seismometers since the 1950s. Direct pressure loading from the passing acoustic wave has been modelled and consistently observed to produce ground deformations of the near surface that have retrograde elliptical particle motions. In the past decade, increased deployments of colocated seismometers and infrasound sensors have driven efforts to use the transfer function between direct acoustic-to-seismic coupling to infer near-surface material properties including seismic velocity structure and elastic moduli. In this study, we use a small aperture (≈600 m) array of broadband seismometers installed in different manners and depths in both granite and sedimentary overburden to understand the fundamental nature and repeatability of seismic excitation from 1 to 15 Hz using horizontally propagating acoustic waves generated by 97 local (2–10 km) explosions. In agreement with modelling, we find that the ground motions induced by acoustic-to-seismic coupling attenuate rapidly with depth. We confirm the modelled relation between acoustic and ground motion amplitudes, but show that within one acoustic wavelength, the uncertainty in the transfer coefficient between seismic and acoustic energy at a given seismic station increases linearly with separation distance between the seismic and acoustic sensor. We attribute this observation to the rapid decorrelation of the infrasonic wavefield across small spatial scales and recommend colocating seismic and infrasound sensors for use in studies seeking to invert for near-surface material properties. Additionally, contrary to acoustic-to-seismic coupling theory and prior observations, we find that seismometers emplaced in granite do not record retrograde elliptical particle motions in response to direct pressure loading. We rule out seismometer tilt effects as a likely source of this observations and suggest that existing models of acoustic-to-seismic excitation may be too simplistic for seismometers placed in high rigidity materials.

A Fingerprinting Based Audio-Seismic Systems for Human Target Localization in an Outdoor Environment Using Regression

Human target localization has a plethora of ubiquitous applications, including healthcare and security. Reliable location estimation is challenging in outdoor settings because most targets do not carry, wear, or attach a sensor to their bodies to provide motion information. Seismic and audio sensors can be used extensively to monitor targets in an unobtrusive manner. This paper proposes regression-based methods to localize a human target in an outdoor environment using seismic and audio signatures. The approaches fall into two groups. The first group of approaches applies a late fusion on the audio and seismic modality for target localization. First, a regression algorithm on the seismic signals is applied to estimate the distance of the target from each sensor; then, the target distance information is combined with the audio direction to infer the target location. In contrast to the first group of approaches, the second group of approaches applies an early fusion of audio and seismic modality to directly predict the target location. We compare the proposed methods with multiple state-of-the-arts on different evaluation measures. On 5-fold cross-validation, we achieve a root-mean-localization error of 0.735 and 0.907 meters in an area of 324 meter <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , for dataset-1 and dataset-2, respectively. The best results with proposed approaches show an improvement of 4.68 and 4.57 meters over the best performing state-of-the-art approach for dataset-1 and dataset-2, respectively. We also analyzed the generalization capabilities of the proposed methods. Further, a detailed ablation study on the number of sensors required for localization, feature selection, training data requirement, etc., has been carried out.