Identification of and Favorable Conditions for a New Long-Offset Seismic Phase from Offshore–Onshore Seismic Surveys

Abstract Offshore–onshore seismic survey is one of the main methods to study crustal structures in offshore–onshore transitional zones. At present, the seismic waves commonly used in imaging are the crustal refraction (Pg), the crustal reflection from the Moho (PmP), and the upper-mantle refraction (Pn) waves. The propagation distances of Pg and PmP are commonly less than 210 km, and Pn propagates with an apparent velocity of ∼8 km/s. In 2015, two offshore–onshore wide-angle seismic lines with a length of ∼350 km were acquired in the Pearl River Estuary. In addition to Pg, PmP, and Pn, a new seismic phase was observed, which has a long propagation distance (offset of ∼170–290 km), low apparent velocity (∼5.85 km/s), and low frequency (∼4–7 Hz). Similar seismic phases have been widely reported in previous offshore–onshore and reservoir seismic surveys, but the understanding of these phases is still limited. Herein, we used both raytracing and waveform modeling methods to identify the new seismic phase as the secondary Pg phase, which reflects from the surface (named Pg2Pg). We also discuss favorable conditions for Pg2Pg, including (1) a thin sedimentary layer with low velocity at the surface in which the reflection of Pg occurs, which can reduce the incidence angles and hence increase the energy of the reflected waves; (2) a sedimentary basement dipping toward the sea at the positions of the air gun shots, which focuses seismic waves; (3) relatively smooth interfaces of the medium, which can reduce the scattering of Pg2Pg; and (4) air guns that can excite low-frequency signals, which can reduce the attenuation of seismic waves. Checkerboard tests and practical applications show that Pg2Pg can significantly improve upper-crustal resolution, especially for onshore areas. Our research promotes the data mining of offshore–onshore seismic surveys, which is important for obtaining more detailed crustal structures.

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Cetacean behavioral responses to noise exposure generated by seismic surveys: how to mitigate better?

Annals of Geophysics ◽

10.4401/ag-7089 ◽

2016 ◽

Vol 59 (4) ◽

Author(s):

Clara Monaco ◽

Jesús M. Ibáñez ◽

Francisco Carrión ◽

L. Mario Tringali

Keyword(s):

Noise Exposure ◽

Behavioral Responses ◽

Seismic Survey ◽

Seismic Exploration ◽

Mitigation Measures ◽

Seismic Surveys ◽

Reflection Seismic ◽

Joint Nature Conservation Committee ◽

Air Gun ◽

Southern Mediterranean

Cetaceans use sound in many contexts, such as in social interactions, as well as to forage and to react in dangerous situations. Little information exists to describe how they respond physically and behaviorally to intense and long-term noise levels. Effects on cetaceans from seismic survey activities need to be understood in order to determine detailed acoustic exposure guidelines and to apply appropriated mitigation measures. This study examines direct behavioral responses of cetaceans in the southern Mediterranean Sea during seismic surveys with large airgun arrays (volume up to 5200 ci) used in the TOMO-ETNA active seismic experiment of summer 2014. Wide Angle Seismic and Multi-Channel Seismic surveys had carried out with refraction and reflection seismic methods, producing about 25,800 air-gun shots. Visual monitoring undertaken in the 26 daylights of seismic exploration adopted the protocol of the Joint Nature Conservation Committee. Data recorded were analyzed to examine effects on cetaceans. Sighting rates, distance and orientation from the airguns were compared for different volume categories of the airgun arrays. Results show that cetaceans can be disturbed by seismic survey activities, especially during particularly events. Here we propose many integrated actions to further mitigate this exposure and implications for management.

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Occurrence of sea turtles during seismic surveys in Northeastern Brazil

Biota Neotropica ◽

10.1590/s1676-06032006000100004 ◽

2006 ◽

Vol 6 (1) ◽

Cited By ~ 5

Author(s):

Cristiano Leite Parente ◽

Juliana Doyle Lontra ◽

Maria Elisabeth de Araújo

Keyword(s):

Sea Turtles ◽

Low Frequency ◽

Chelonia Mydas ◽

Sea Turtle ◽

Reproductive Period ◽

Northeastern Brazil ◽

Seismic Survey ◽

Shallow Waters ◽

Seismic Surveys ◽

Lepidochelys Olivacea

There are seven species of sea turtles around the world. Among these, five visit the northeast coast of Brazil to reproduce and feed. These sea turtles are impacted by human activity and need conservation measures. The seismic survey is one of these activities due to its high intensity and low frequency sound emissions in the marine environment. Records of sea turtles during seismic surveys in shallow waters of the northeast of Brazil between 2002 and 2003 are presented in this study with some discussion about the effectiveness of the monitoring procedures. Three species of sea turtle were recorded within the seismic survey areas. The Chelonia mydas species was the most commonly sighted turtle. There was only one record of Caretta caretta and Lepidochelys olivacea. The presence of sea turtles in Sergipe state was linked to the reproductive period while this pattern was not observed in Ceará state. The absence of information about distribution and abundance of sea turtles in the surveyed areas previous to and after the seismic surveys, as well as numerous incomplete data make it hard to identify the effect of seismic surveys on those factors and also sea turtle behaviors.

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SEISMIC SIGNATURES OF LARGE AIR GUNS

Geophysics ◽

10.1190/1.1440237 ◽

1971 ◽

Vol 36 (6) ◽

pp. 1162-1173 ◽

Cited By ~ 9

Author(s):

W. Harry Mayne ◽

Roy G. Quay

Keyword(s):

Energy Levels ◽

Low Frequency ◽

Experimental Tests ◽

Frequency Spectra ◽

Seismic Surveys ◽

Air Gun ◽

Absolute Energy ◽

Overall Performance ◽

Marine Seismic ◽

Effective Source

Large chamber air guns are a reliable and effective source of energy for marine seismic surveys. Air guns with chamber volumes of 300 and 1000 cubic inches demonstrate desirable low‐frequency responses and high absolute energy levels. Overall performance has been compromised, however, by the bubble effect. Previous attempts at minimizing the bubble response have resulted in loss of reliability, reduced power, or incomplete bubble suppression, or a combination thereof. In this paper, we present the results of experimental tests on air guns with 300 and 1000 cubic inch chambers and describe a divided‐chamber gun which greatly attenuates the bubble effect. Significant improvements in the width and flatness of the frequency spectra are demonstrated by analysis of the actual signatures obtained in deep water and with record sections comparing the results obtained with the standard and improved guns along an identical traverse. The bubble‐attenuating air gun simultaneously provides improved resolution, high absolute‐energy levels, and excellent reliability.

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A comparative study of multi-scaled high-resolution seismic surveys in shallow marine environments: examples from three sites, offshore Korea

10.5194/egusphere-egu2020-12869 ◽

2020 ◽

Author(s):

Young Jun Kim ◽

Snons Cheong ◽

Deniz Cukur ◽

Dong-Geun Yoo

Keyword(s):

High Resolution ◽

Data Processing ◽

Seismic Data ◽

Single Channel ◽

Seismic Source ◽

Seismic Survey ◽

Minimum Length ◽

Seismic Surveys ◽

Air Gun ◽

Target Depth

In marine seismic surveys, various acquisition systems are used depending on the survey purpose, target depth, survey environment, and conditions. A 3D survey of oil and/or gas exploration, for instance, require large-capacity air-gun arrays and six or more streamers with a minimum length of 6 km. In contrast, a high-resolution seismic survey for the shallow-water geological research and engineering needs a small capacity source such as air-gun, sparker, and boomer, deployed with a single-channel or multi-channel (24-channel) streamers. The main purpose of our seismic survey was to investigate the Quaternary geology and stratigraphy of offshore, Korea. Because the Quaternary is the most recent geological period, our target depth was very shallow at about 50 m below the sea-bottom. We used a high-frequency seismic source including a sparker of 2,000 J capacity or a 60 in3 mini GI-gun and an eight-channel streamer with a 3.125 m group interval or a single-channel streamer that included 96 elements. To compare the resolution of seismic data according to the seismic source, a boomer or sparker systems were used with the single-channel streamer on a small survey ship. The seismic data processing was performed at the Korea Institute of Geoscience and Mineral Resources (KIGAM) with ProMAX, and the data processing and resolution of each survey were compared based on their acquisition systems.

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UNDERWATER CHARACTER AND HORIZONTAL PROPAGATION OF AIR-GUN SIGNALS

The APPEA Journal ◽

10.1071/aj97046 ◽

1998 ◽

Vol 38 (1) ◽

pp. 708

Author(s):

J.D. Penrose ◽

R.D. McCauley

Keyword(s):

Shallow Water ◽

Sound Propagation ◽

Model Performance ◽

Low Frequency ◽

Propagation Model ◽

Seismic Survey ◽

Biological Research ◽

Water Characteristics ◽

Air Gun ◽

Development Paths

This paper describes work carried out as part of an APPEA/ERDC supported project, Investigation of the Environmental Effects of Offshore Seismic Survey Activities. In this project biological research concerning the interaction of acoustic signals with marine organisms is linked to sound propagation studies focussed on frequencies, water characteristics and seabed types of relevance to offshore exploration practice. A key feature of the propagation component of the project concerns the extent to which lateral propagation of airgun signals in the water column may be adequately predicted.The study of acoustic propagation in the sea is an integral part of both scientific and defence enquiry. In recent years, the comparatively complex issue of propagation in shallow water, here considered as involving depths of 200 m or less, has received increasing attention. The literature concerning low frequency propagation in shallow water has features in common with seismic literature. Different emphases, however, notably concerning applications, the role of shear waves in solids and the geometry of the propagation environment have largely resulted in separate development paths being adopted by these two related fields. This paper summarises the range of modelling approaches available to predict shallow water propagation, some key issues influencing propagation and the influence of water and seabed parameters on model performance.An illustration of propagation model performance is provided in this paper by comparing the output from a normal mode model KRAKEN, with experimental data obtained using a mono-frequency source in shallow water in Cleveland Bay, Queensland. This offers an opportunity to assess propagation in a complex and, in acoustic terms, poorly classified environment. These results will be complemented in the conference presentation by airgun data obtained in Exmouth Gulf, Western Australia.

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Exposure to seismic air gun signals causes physiological harm and alters behavior in the scallop Pecten fumatus

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1700564114 ◽

2017 ◽

Vol 114 (40) ◽

pp. E8537-E8546 ◽

Cited By ~ 12

Author(s):

Ryan D. Day ◽

Robert D. McCauley ◽

Quinn P. Fitzgibbon ◽

Klaas Hartmann ◽

Jayson M. Semmens

Keyword(s):

Blood Cell ◽

Sublethal Effects ◽

Low Frequency ◽

Repeated Exposure ◽

Seismic Signals ◽

Seismic Surveys ◽

Naturally Occurring ◽

Air Gun ◽

Behavioral Parameters ◽

The Impact

Seismic surveys map the seabed using intense, low-frequency sound signals that penetrate kilometers into the Earth’s crust. Little is known regarding how invertebrates, including economically and ecologically important bivalves, are affected by exposure to seismic signals. In a series of field-based experiments, we investigate the impact of exposure to seismic surveys on scallops, using measurements of physiological and behavioral parameters to determine whether exposure may cause mass mortality or result in other sublethal effects. Exposure to seismic signals was found to significantly increase mortality, particularly over a chronic (months postexposure) time scale, though not beyond naturally occurring rates of mortality. Exposure did not elicit energetically expensive behaviors, but scallops showed significant changes in behavioral patterns during exposure, through a reduction in classic behaviors and demonstration of a nonclassic “flinch” response to air gun signals. Furthermore, scallops showed persistent alterations in recessing reflex behavior following exposure, with the rate of recessing increasing with repeated exposure. Hemolymph (blood analog) physiology showed a compromised capacity for homeostasis and potential immunodeficiency, as a range of hemolymph biochemistry parameters were altered and the density of circulating hemocytes (blood cell analog) was significantly reduced, with effects observed over acute (hours to days) and chronic (months) scales. The size of the air gun had no effect, but repeated exposure intensified responses. We postulate that the observed impacts resulted from high seabed ground accelerations driven by the air gun signal. Given the scope of physiological disruption, we conclude that seismic exposure can harm scallops.

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Low Frequency Broad Band Acoustic Propagation in Andaman Sea

Defence Science Journal ◽

10.14429/dsj.69.14224 ◽

2019 ◽

Vol 69 (2) ◽

pp. 127-130

Author(s):

Nimmi R. Nair ◽

R. Suganthbalaji ◽

Elizabeth Shani N. X. ◽

P. V. Nair

Keyword(s):

Broad Band ◽

Low Frequency ◽

Acoustic Propagation ◽

Andaman Sea ◽

Seismic Survey ◽

Deep Waters ◽

Sound Levels ◽

Air Gun ◽

Power Spectral ◽

Different Depths

During November 2017, an active source seismic survey was performed in Andaman sea to study the acoustic propagation characteristics. High power low frequency acoustic signals generated by 20-air gun array onboard ORV Samudra Ratnagar were recorded from INS Sagardhwani at four different depths within 8 km ranges in shallow and deep waters. Low frequency sound levels were estimated using root mean square and power spectral values. Amplitude levels were analysed with respect to arrival time variation with frequency and is presented.

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Polytetrafluoroethylene Films in Rigid Polyurethane Foams’ Dielectric Permittivity Measurements with a One-Side Access Capacitive Sensor

Polymers ◽

10.3390/polym13071173 ◽

2021 ◽

Vol 13 (7) ◽

pp. 1173

Author(s):

Ilze Beverte ◽

Ugis Cabulis ◽

Sergejs Gaidukovs

Keyword(s):

Dielectric Properties ◽

Dielectric Permittivity ◽

Low Frequency ◽

Capacitive Sensor ◽

Polyurethane Foams ◽

Active Area ◽

Ptfe Film ◽

Practical Applications ◽

Permittivity Measurements ◽

The Impact

As a non-metallic composite material, widely applied in industry, rigid polyurethane (PUR) foams require knowledge of their dielectric properties. In experimental determination of PUR foams’ dielectric properties protection of one-side capacitive sensor’s active area from adverse effects caused by the PUR foams’ test objects has to be ensured. In the given study, the impact of polytetrafluoroethylene (PTFE) films, thickness 0.20 mm and 0.04 mm, in covering or simulated coating the active area of one-side access capacitive sensor’ electrodes on the experimentally determined true dielectric permittivity spectra of rigid PUR foams is estimated. Penetration depth of the low frequency excitation field into PTFE and PUR foams is determined experimentally. Experiments are made in order to evaluate the difference between measurements on single PUR foams’ samples and on complex samples “PUR foams + PTFE film” with two calibration modes. A modification factor and a small modification criterion are defined and values of modifications are estimated in numerical calculations. Conclusions about possible practical applications of PTFE films in dielectric permittivity measurements of rigid PUR foams with one-side access capacitive sensor are made.

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A periodic seismic isolation foundation with an extremely broad low-frequency attenuation zone: Theoretical analysis and experimental verification

Advances in Structural Engineering ◽

10.1177/13694332211064665 ◽

2021 ◽

pp. 136943322110646

Author(s):

Peng Zhou ◽

Shui Wan ◽

Xiao Wang ◽

Yingbo Zhu ◽

Muyun Huang

Keyword(s):

Seismic Isolation ◽

Seismic Waves ◽

Periodic Structures ◽

Finite Size ◽

Low Frequency ◽

Bridge Structure ◽

Engineering Structures ◽

P Waves ◽

New Type ◽

Dominant Frequencies

The attenuation zones (AZs) of periodic structures can be used for seismic isolation design. To cover the dominant frequencies of more seismic waves, this paper proposes a new type of periodic isolation foundation (PIF) with an extremely wide low-frequency AZ of 3.31 Hz–17.01 Hz composed of optimized unit A with a wide AZ and optimized unit B with a low-frequency AZ. The two kinds of optimized units are obtained by topology optimization on the smallest periodic unit with the coupled finite element-genetic algorithm (GA) methodology. The transmission spectra of shear waves and P-waves through the proposed PIF of finite size are calculated, and the results show that the AZ of the PIF is approximately the superposition of the AZs of the two kinds of optimized units. Additionally, shake tests on a scale PIF specimen are performed to verify the attenuation performance for elastic waves within the designed AZs. Furthermore, numerical simulations show that the acceleration responses of the bridge structure with the proposed PIF are attenuated significantly compared to those with a concrete foundation under the action of different seismic waves. Therefore, the newly proposed PIF is a promising option for the reduction of seismic effects in engineering structures.

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Numerical simulation of seismic waves in porous media components

Eurasian Journal of Mathematical and Computer Applications ◽

10.32523/2306-6172-2021-9-1-4-30 ◽

2021 ◽

Vol 9 (1) ◽

pp. 4-30

Author(s):

M. Azeredo ◽

◽

V. Priimenko ◽

Keyword(s):

Numerical Simulation ◽

Porous Medium ◽

High Frequency ◽

Seismic Waves ◽

Computational Algorithm ◽

Low Frequency ◽

Physical Parameters ◽

Mathematical Algorithm ◽

Biot Equations ◽

Attenuation And Dispersion

This work presents a mathematical algorithm for modeling the propagation of poroelastic waves. We have shown how the classical Biot equations can be put into Ursin’s form in a plane-layered 3D porous medium. Using this form, we have derived explicit for- mulas that can be used as the basis of an efficient computational algorithm. To validate the algorithm, numerical simulations were performed using both the poroelastic and equivalent elastic models. The results obtained confirmed the proposed algorithm’s reliability, identify- ing the main wave events in both low-frequency and high-frequency regimes in the reservoir and laboratory scales, respectively. We have also illustrated the influence of some physical parameters on the attenuation and dispersion of the slow wave.

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