Influencing factors of seismic signals generated by un-tuned large volume airgun array in a land reservoir

Chen, Meng; Yang, Wei; Wang, Weitao; Wang, Baoshan; Ge, Hongkui; Chen, Li; Ding, Yansheng; Qiao, Jiyan; Chen, Yong

doi:10.1007/s11589-014-0073-0

Cited by 3 publications

(1 citation statement)

References 30 publications

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“…The source repeatability is of key importance in measuring the subtle subsurface velocity changes (e.g., Zhan et al, ). The airgun signals are affected by several dominant factors, such as water level, towing depth, and working pressure (Chen et al, ). During the experiment, the water level was continuously monitored with a precision of 0.1 cm and exhibited no discernable change.…”

Section: Field Experimentsmentioning

confidence: 99%

Diurnal and Semidiurnal P‐ and S‐Wave Velocity Changes Measured Using an Airgun Source

et al. 2020

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Monitoring the subtle seismic velocity changes provides a promising tool to study the Earth's dynamic processes. However, the precise monitoring of seismic velocity with high temporal resolution is still challenging especially at large distances. Here, we continuously monitor P-wave and S-wave velocities with a precision of up to 10 −5 using an airgun source. During a 1-week experiment conducted in the Yunnan Province, Southwestern China, unambiguous diurnal and semidiurnal velocity changes with amplitudes of~10 −4 -10 −3 were observed for both P-and S-waves at distances up to 21 km. The amplitudes of P-wave velocity (Vp) change are 1.2 to 3.8 times the amplitudes of S-wave velocity (Vs) changes. The velocity variation decreases with the increase in distance and is larger in the basin region than that in the mountainous region. Seismic velocity change shows less correlation with volumetric tide strain but strong correlation with changes of air temperature and air pressure. We propose that the thermal strains from air temperature changes are the primary cause of the observed diurnal and semidiurnal seismic velocity changes. The stronger Vp than Vs change is explained by the higher Vp sensitivity to the saturation rate. The velocity changes in mountainous area are ascribed mainly to the crack density changes, while both crack density change and saturation change are required to account for the velocity changes in the basin. Key Points:• Diurnal and semidiurnal P-and Swave velocity changes of 10 −3 -10 −4 are observed with a precision of 10 −5 using an airgun source • The change in Vp is larger than that in Vs, and velocity changes in basin are stronger than in mountainous area • The thermal strain-induced crack density or/and saturation ratio changes are likely responsible for the observed velocity changes Supporting Information:• Supporting Information S1 . (2020). Diurnal and semidiurnal P-and S-wave velocity changes measured using an airgun source.

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Section: Field Experimentsmentioning

confidence: 99%

Diurnal and Semidiurnal P‐ and S‐Wave Velocity Changes Measured Using an Airgun Source

et al. 2020

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Time-Lapse Monitoring of Daily Velocity Changes in Binchuan, Southwestern China, Using Large-Volume Air-Gun Source Array Data

Luan

Yang

Wang

et al. 2022

Seismological Research Letters

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Temporal changes of seismic velocities in the Earth’s crust can be induced by stress perturbations or material damage from reasons such as strong ground motion, volcanic activities, and atmospheric effects. However, monitoring the temporal changes remains challenging, because most of them generally exist in small travel-time differences of seismic data. Here, we present an excellent case of daily variations of the subsurface structure detected using a large-volume air-gun source array of one-month experiment in Binchuan, Yunnan, southwestern China. The seismic data were recorded by 12 stations within ∼10 km away from the source and used to detect velocity change in the crust using the deconvolution method and sliding window cross-correlation method, which can eliminate the “intercept” error when cutting the air-gun signals and get the real subsurface variations. Furthermore, the multichannel singular spectral analysis method is used to separate the daily change (∼1 cycle per day) from the “long-period” change (<1 cycle per day) or noise. The result suggests that the daily velocity changes at the two nearest stations, 53277 (offset ∼700 m) and 53278 (offset ∼2.3 km), are well correlated with air temperature variation with a time lag of 5.0 ± 1.5 hr, which reflects that the velocity variations at the subsurface are likely attributed to thermoelastic strain. In contrast, both daily and long-period velocity changes at distant stations correlate better with the varying air pressure than the temperature, indicating that the velocity variations at deeper depth are dominated by the elastic loading of air pressure. Our results demonstrate that the air-gun source is a powerful tool to detect the velocity variation of the shallow crust media.

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Seasonal Variations of Seismic Travel-Time Changes in Binchuan, Southwestern China, Inferred from Large Volume Air-Gun Source Array Data

Luan

Yang

Wang

et al. 2023

Seismological Research Letters

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Active sources, especially air-gun sources in the water reservoir, have proven to be powerful tools for detecting regional scale velocity changes. However, the water level change affects the repeatability of the air-gun waveform and, thus, affects the stability of the detection of the velocity changes. This article explores how to make full use of the air-gun signals excited at different water levels from analyzing three years of air-gun data recorded by 20 stations deployed from ∼50 m to ∼25 km from the source. At the same time, by utilizing the poroelastic model, we quantify both vertical and horizontal distances affected by the water level change. More important, supported by the strain data from one borehole strainmeter station, the influence mechanisms of the seasonal variation derived from the three years of air-gun data are also discussed. Results indicate the water level affects the main frequency of the air gun and has a strong influence on the coda wave. When the water level of the reservoir changes abruptly, the dominant effect on the derived delay time change is from the water level change. In this case, the deconvolution method can hardly eliminate the influence of the abrupt water level change. However, when the reservoir's water level changes gently, the delay time varies accordingly rather than inversely with the water level. Other reasons affect the material properties and, thus, influence the derived delay time. The modeled vertical component of poroelastic strain caused by the reservoir water level change is 1×10−7. The observed strain (4×10−7) from the strainmeter is likely associated with thermoelastic strain induced by temperature change. Our results show that although the long-term air-gun signal is affected by water level, there is still much information about changes in the subsurface that is worth mining.

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Influencing factors of seismic signals generated by un-tuned large volume airgun array in a land reservoir

Cited by 3 publications

References 30 publications

Diurnal and Semidiurnal P‐ and S‐Wave Velocity Changes Measured Using an Airgun Source

Diurnal and Semidiurnal P‐ and S‐Wave Velocity Changes Measured Using an Airgun Source

Time-Lapse Monitoring of Daily Velocity Changes in Binchuan, Southwestern China, Using Large-Volume Air-Gun Source Array Data

Seasonal Variations of Seismic Travel-Time Changes in Binchuan, Southwestern China, Inferred from Large Volume Air-Gun Source Array Data

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