Repeat well logging using earthquake wave amplitudes measured by distributed acoustic sensors

2020 ◽  
Vol 39 (7) ◽  
pp. 513-517
Author(s):  
Roman Pevzner ◽  
Boris Gurevich ◽  
Anastasia Pirogova ◽  
Konstantin Tertyshnikov ◽  
Stanislav Glubokovskikh
Keyword(s):  
Seismic Waves ◽  
Fiber Optic ◽  
Synthetic Data ◽  
Seismic Source ◽  
Small Scale ◽  
Acoustic Sensors ◽  
Linear Strain ◽  
Subsurface Characterization ◽  
Distributed Acoustic Sensing ◽  
Subsurface Monitoring

Well-based technologies for seismic subsurface monitoring increasingly utilize fiber-optic cables installed in boreholes as distributed acoustic sensing (DAS) systems. A DAS cable allows measuring linear strain of the fiber and can serve as an array of densely spaced seismic receivers. The strain amplitudes recorded by the DAS cable depend on the near-well formation properties (the softer the medium, the larger the strain). Thus, these properties can be estimated by measuring relative variations of the amplitudes of seismic waves propagating along the well. An advantage of such an approach to subsurface characterization and monitoring is that no active seismic source is required. Passive sources such as earthquakes can be utilized. A synthetic data example demonstrates viability of the approach for monitoring of small-scale CO2 injection into an aquifer. Two field DAS data examples based on signal recordings from several distant earthquakes show that the relevant properties of the near-well formation can be estimated with an accuracy of approximately 5%.

Distributed Acoustic Sensing Turns Fiber‐Optic Cables into Sensitive Seismic Antennas

2019 ◽  
Vol 91 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Zhongwen Zhan
Keyword(s):  
Seismic Waves ◽  
Fiber Optic ◽  
Glass Fibers ◽  
Ocean Bottom ◽  
Thin Glass ◽  
Acoustic Sensing ◽  
Wide Range ◽  
Solar System Bodies ◽  
Distributed Acoustic Sensing ◽  
Seismic Networks

Abstract Distributed acoustic sensing (DAS) is a new, relatively inexpensive technology that is rapidly demonstrating its promise for recording earthquake waves and other seismic signals in a wide range of research and public safety arenas. It should significantly augment present seismic networks. For several important applications, it should be superior. It employs ordinary fiber‐optic cables, but not as channels for data among separate sophisticated instruments. With DAS, the hair‐thin glass fibers themselves are the sensors. Internal natural flaws serve as seismic strainmeters, kinds of seismic detector. Unused or dark fibers are common in fiber cables widespread around the globe, or in dedicated cables designed for special application, are appropriate for DAS. They can sample passing seismic waves at locations every few meters or closer along paths stretching for tens of kilometers. DAS arrays should enrich the three major areas of local and regional seismology: earthquake monitoring, imaging of faults and many other geologic formations, and hazard assessment. Recent laboratory and field results from DAS tests underscore its broad bandwidth and high‐waveform fidelity. Thus, while still in its infancy, DAS already has shown itself as the working heart—or perhaps ear drums—of a valuable new seismic listening tool. My colleagues and I expect rapid growth of applications. We further expect it to spread into such frontiers as ocean‐bottom seismology, glacial and related cryoseismology, and seismology on other solar system bodies.

scholarly journals Pulsed-laser source characterization in laboratory seismic experiments

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
C. Shen ◽  
D. Brito ◽  
J. Diaz ◽  
F. Sanjuan ◽  
C. Bordes ◽  
...  
Keyword(s):  
Seismic Waves ◽  
Ultrasonic Transducer ◽  
Pulsed Laser ◽  
Seismic Source ◽  
Laser Source ◽  
Small Scale ◽  
Attractive Alternative ◽  
Source Characterization ◽  
Incident Laser Power ◽  
Theoretical Predictions

AbstractThe present study aimed to characterize the properties of a laser-generated seismic source for laboratory-scale geophysical experiments. This consisted of generating seismic waves in aluminum blocks and a carbonate core via pulsed-laser impacts and measuring the wave-field displacement via laser vibrometry. The experimental data were quantitatively compared to both theoretical predictions and 2D/3D numerical simulations using a finite element method. Two well-known and distinct physical mechanisms of seismic wave generation via pulsed-laser were identified and characterized accordingly: a thermoelastic regime for which the incident laser power was relatively weak, and an ablation regime at higher incident powers. The radiation patterns of the pulsed-laser seismic source in both regimes were experimentally measured and compared with that of a typical ultrasonic transducer. This study showed that this point-like, contact-free, reproducible, simple-to-use laser-generated seismic source was an attractive alternative to piezoelectric sources for laboratory seismic experiments, especially those concerning small scale, sub-meter measurements.

Turning a Telecom Fiber-Optic Cable into an Ultradense Seismic Array for Rapid Postearthquake Response in an Urban Area

2021 ◽  
Author(s):  
Xiangfang Zeng ◽  
Feng Bao ◽  
Clifford H. Thurber ◽  
Rongbing Lin ◽  
Shuofan Wang ◽  
...  
Keyword(s):  
Ground Motion ◽  
Early Warning ◽  
Fiber Optic ◽  
Small Scale ◽  
Monitoring Networks ◽  
Motion Pattern ◽  
Fiber Optic Cable ◽  
Epicentral Area ◽  
Distributed Acoustic Sensing ◽  
Deployment Time

Abstract Aftershock-monitoring networks deployed in the epicentral area of a damaging earthquake play important roles in earthquake early warning and ShakeMap estimation, which contribute to hazard mitigation. Using distributed acoustic sensing (DAS) technology with dark fiber can significantly reduce deployment time and cost, and improve spatial sampling, both of which help capture more aftershocks. In this study, we used a 7.6 km dark fiber in Tangshan, China, to monitor seismicity after the 12 July 2020 Ms 5.1 earthquake. The DAS array detected dozens of earthquakes missed by the local permanent network that doubled the number of aftershocks. The relocated aftershocks are distributed mainly north of the DAS array, and the ground-motion pattern changes also hint small-scale features. Our successful results demonstrate the feasibility of using DAS and dark fiber for rapid postearthquake response.

Effect of complex topography on the wavefield recorded by DAS and buried fiber optic cable at Azuma volcano, Northeast Japan

2020 ◽  
Author(s):  
Kentaro Emoto ◽  
Takeshi Nishimura ◽  
Hisashi Nakahara ◽  
Satoshi Miura ◽  
Mare Yamamoto ◽  
...  
Keyword(s):  
Seismic Waves ◽  
Fiber Optic ◽  
Velocity Structure ◽  
Incident Angle ◽  
Gaussian Function ◽  
Separation Distance ◽  
P Wave ◽  
Small Scale ◽  
Fiber Optic Cable ◽  
Access Road

<p>First DAS observation at Mt. Azuma, Japan was conducted in July 2019 using buried fiber optic cable along the road access to the volcano. Mt. Azuma is an active volcano located in the Tohoku region. Different from non-volcanic regions, wavefields in the volcano is more complex due to its topography and the strong heterogeneities beneath the volcanic edifice. The strength of the scattering of seismic waves due to small-scale velocity heterogeneities in the volcano is reported to be more than one order higher than that in the non-volcanic region. To estimate small-scale heterogeneities, a dense observation network is necessary. The high spatial resolution is one of the advantages of the DAS observation. Therefore, DAS observation in the volcano might be a good chance for the estimation of the small-scale heterogeneity.</p><p> </p><p>We used 14km length of the fiber optic cable buried along to the access road to the observatory near the summit installed by the Ministry of Land, Infrastructure, Transport and Tourism to monitor the volcanic activities. The spatial and temporal samplings were 10m and 1000Hz, respectively. The observation period was for 3 weeks. In addition to regional and teleseismic earthquakes, volcanic earthquakes were also observed. A teleseismic P-wave was analyzed to investigate the effect of small-scale heterogeneities. Because the incident angle of the teleseismic P-wave is almost vertical to the portion of the fiber optic cable used for the DAS observation, a simple model can be used. We calculate the cross-correlation coefficient (CCC) of waveforms between channels and analyze its dependence on the distances between channel pairs. The recorded wavefield was fluctuated by scattering due to the small-scale heterogeneities and different waveforms were recorded even though the propagation distances are the same. Therefore, the spatial variation of the waveforms of teleseismic P-wave recorded at surface stations would be related to the small-scale heterogeneities beneath of the array.</p><p> </p><p>The CCC decreases with increasing separation distance and converges to a constant value. This shape can be modeled by the Gaussian function and we defined the spatial scale of CCC by fitting the Gaussian function. The scale decreases with increasing frequency. The finite difference simulation of the wave propagation was performed by changing the velocity structure and compare the synthetic and observed CCCs. We found that the effect of the topography is most significant on the CCC. Because analyzed waveforms mainly consist of the converted surface wave from the teleseismic P-wave, the effect of subsurface small-scale heterogeneities is not significant. Our result shows that it is necessary to consider the effect of the topography in analyses of DAS data recorded in volcanoes.</p>

Capturing Glacier-Wide Cryoseismicity With Distributed Acoustic Sensing

2021 ◽  
Author(s):  
Fabian Walter ◽  
Patrick Paitz ◽  
Andreas Fichtner ◽  
Pascal Edme ◽  
Wojciech Gajek ◽  
...  
Keyword(s):  
Fiber Optic ◽  
Flow Line ◽  
Ground Deformation ◽  
Sensor Coverage ◽  
Mountain Glacier ◽  
Acoustic Sensing ◽  
Alpine Glacier ◽  
Glacier Ice ◽  
Distributed Acoustic Sensing ◽  
Ice Sheet Dynamics

<p>Over the past 1-2 decades, seismological measurements have provided new and unique insights into glacier and ice sheet dynamics. At the same time, sensor coverage is typically limited in harsh glacial environments with littile or no access. Turning kilometer-long fiber optic cables placed on the Earth’s surface into thousands of seismic sensors, Distributed Acoustic Sensing (DAS) may overcome the limitation of sensor coverage in the cryosphere.</p><p>First DAS applications on the Greenland and Antarctic ice sheets and on Alpine glacier ice have highlighted the technique’s superiority. Signals of natural and man-made seismic sources can be resolved with an unrivaled level of detail. This offers glaciologists new perspectives to interpret their seismograms in terms of ice structure, basal boundary conditions and source locations. However, previous studies employed only relatively small network scales with a point-like borehole deployment or < 1 km cable aperture at the ice surface.</p><p>Here we present a DAS installation, which aims to cover the majority of an Alpine glacier catchment: For one month in summer 2020 we deployed a 9 km long fiber optic cable on Rhonegletscher, Switzerland, and gathered continuous DAS data. The cable followed the glacier’s central flow line starting in the lowest kilometer of the ablation zone and extending well into the accumulation area. Even for a relatively small mountain glacier such as Rhonegletscher, cable deployment was a considerable logistical challenge. However, initial data analysis illustrates the benefit compared to conventional cryoseismological instrumentation: DAS measurements capture ground deformation over many octaves, including typical high-frequency englacial sources (10s to 100s of Hz) related to crevasse formation and basal sliding as well as long period signals (10s to 100s of seconds) of ice deformation. Depending on the presence of a snow cover, DAS records contain strong environmental noise (wind, meltwater flow, precipitation) and thus exhibit lower signal-to-noise ratios compared to conventional on-ice seismic installations. This is nevertheless outweighed by the advantage of monitoring ground unrest and ice deformation of nearly an entire glacier. We present a first compilation of signal and noise records and discuss future directions to leverage DAS data sets in glaciological research.</p><p> </p><p> </p><p> </p>

Seismic Observations of Four Thunderstorms Using an Underground Fiber-Optic Array

2021 ◽  
Author(s):  
Samuel Hone ◽  
Tieyuan Zhu
Keyword(s):  
Fiber Optic ◽  
Seismic Velocity ◽  
Ground Surface ◽  
State College ◽  
Full Waveform ◽  
Penn State ◽  
Distributed Acoustic Sensing ◽  
Back Azimuth ◽  
Optic Array ◽  
The Waves

Abstract Thunderstorms are a common atmospheric phenomenon that cause abundant acoustic disturbances, which can interact with the ground surface, creating a link between atmospheric and solid Earth processes. This article reports seismological observations of four thunderstorms through the spring and summer of 2019, as recorded by the distributed acoustic sensing fiber-optic array (4.9 km) on the Penn State campus in State College, Pennsylvania. With a dense sensor array in the local region, we are able to construct the seismic full waveform response of the thunderstorm events (hereafter referred to as thunderquakes) and track the wave propagation across the array. We use a time-domain grid search to obtain the back azimuth and slowness of the waves, and a modified Geiger’s method to pinpoint source locations of the thunderquakes. Correlated with the time of the recorded signal, this data allows reconstruction of thunderstorm movement as well as offering measurements of the seismic velocity.

Phase-modulated fiber optic acoustic sensors

1989 ◽  
Vol 28 (2) ◽  
pp. 1-6 ◽  
Author(s):  
N. Lagakos ◽  
J. Bucaro
Keyword(s):  
Fiber Optic ◽  
Acoustic Sensors

scholarly journals Fractional integration of seismic wavelets in anelastic media to recover multiscale properties of impedance discontinuities

Geophysics ◽  
2018 ◽  
Vol 83 (2) ◽  
pp. V61-V71 ◽  
Author(s):  
Stephan Ker ◽  
Yves Le Gonidec
Keyword(s):  
Wavelet Transform ◽  
Fractional Integration ◽  
Synthetic Data ◽  
Seismic Source ◽  
Seismic Attributes ◽  
Data Set ◽  
Shaping Filter ◽  
Gaussian Derivative ◽  
Intrinsic Attenuation ◽  
Seismic Wavelet

Multiscale seismic attributes based on wavelet transform properties have recently been introduced and successfully applied to identify the geometry of a complex seismic reflector in an elastic medium. We extend this quantitative approach to anelastic media where intrinsic attenuation modifies the seismic attributes and thus requires a specific processing to retrieve them properly. The method assumes an attenuation linearly dependent with the seismic wave frequency and a seismic source wavelet approximated with a Gaussian derivative function (GDF). We highlight a quasi-conservation of the Gaussian character of the wavelet during its propagation. We found that this shape can be accurately modeled by a GDF characterized by a fractional integration and a frequency shift of the seismic source, and we establish the relationship between these wavelet parameters and [Formula: see text]. Based on this seismic wavelet modeling, we design a time-varying shaping filter that enables making constant the shape of the wavelet allowing retrieval of the wavelet transform properties. Introduced with a homogeneous step-like reflector, the method is first applied on a thin-bed reflector and then on a more realistic synthetic data set based on an in situ acoustic impedance sequence and a high-resolution seismic source. The results clearly highlight the efficiency of the method in accurately restoring the multiscale seismic attributes of complex seismic reflectors in anelastic media by the use of broadband seismic sources.

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