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69-451: The canal is located near the village of Nea Roda in the Athos peninsula. Starting to the east of Nea Roda on the north coast it follows a fairly straight southwesterly direction towards the south coast, ending west of the village Tripiti . The canal is now completely covered by sediments, but its outline is visible from air photos, and has been detected by several surveys. The total length of

138-554: A breakthrough in seismic imaging. These are now the three common types of marine towed streamer seismic surveys. Marine survey acquisition is not just limited to seismic vessels; it is also possible to lay cables of geophones and hydrophones on the sea bed in a similar way to how cables are used in a land seismic survey, and use a separate source vessel. This method was originally developed out of operational necessity in order to enable seismic surveys to be conducted in areas with obstructions, such as production platforms , without having

207-466: A canal from sea to sea, wide enough to float two triremes rowed abreast. The work, led by the two Persians Bubares and Artachaees , lasted three years. It was completed in 480 BC by forcibly recruited locals, as well as Egyptian and Phoenician workers. The length, according to Herodotus, was 12 stadia (about 1,900 metres or 6,200 feet), and it was capped at both ends by dikes to prevent surf from clogging it. The canal soon fell into disrepair as it

276-526: A canal there, but he could not trace all of it. Three separate modern land surveys, led by the Frenchman M. Choiseul-Gouffier in the 18th century, by T. Spratt of England in 1838, and by the German A. Struck in 1901, all found evidence of the canal in the central part of the isthmus. But as late as 1990 the length and width of the canal was in dispute, as was the question of whether the canal reached all

345-426: A carefully designed seismic survey. The Scholte wave is similar to ground roll but occurs at the sea-floor (fluid/solid interface) and it can possibly obscure and mask deep reflections in marine seismic records. The velocity of these waves varies with wavelength, so they are said to be dispersive and the shape of the wavetrain varies with distance. A head wave refracts at an interface, travelling along it, within

414-401: A channel built through the Athos isthmus in order to avoid falling prey to the same catastrophe. Herodotus speculates that pride also was a motivating factor: As far as I can judge by conjecture, Xerxes gave the command for this digging out of pride, wishing to display his power and leave a memorial; with no trouble they could have drawn their ships across the isthmus, yet he ordered them to dig

483-456: A controlled seismic source in a land survey and particularly common choices are Vibroseis and dynamite. Vibroseis is a non-impulsive source that is cheap and efficient but requires flat ground to operate on, making its use more difficult in undeveloped areas. The method comprises one or more heavy, all-terrain vehicles lowering a steel plate onto the ground, which is then vibrated with a specific frequency distribution and amplitude. It produces

552-507: A free surface of a solid, but the elastic constants and density of air are very low compared to those of rocks so the surface of the Earth is approximately a free surface . Low velocity, low frequency and high amplitude Rayleigh waves are frequently present on a seismic record and can obscure signal, degrading overall data quality. They are known within the industry as ‘Ground Roll’ and are an example of coherent noise that can be attenuated with

621-458: A long time, it was the only seismic source available until weight dropping was introduced around 1954, allowing geophysicists to make a trade-off between image quality and environmental damage. Compared to Vibroseis, dynamite is also operationally inefficient because each source point needs to be drilled and the dynamite placed in the hole. Unlike in marine seismic surveys, land geometries are not limited to narrow paths of acquisition, meaning that

690-409: A low energy density, allowing it to be used in cities and other built-up areas where dynamite would cause significant damage, though the large weight attached to a Vibroseis truck can cause its own environmental damage. Dynamite is an impulsive source that is regarded as the ideal geophysical source due to it producing an almost perfect impulse function but it has obvious environmental drawbacks. For

759-514: A number of streamers to be towed out wide to the port and starboard side of a vessel. Current streamer towing technology such as seen on the PGS operated Ramform series of vessels built between 2013 and 2017 has pushed the number of streamers up to 24 in total on these vessels. For vessels of this type of capacity, it is not uncommon for a streamer spread across the stern from 'door to door' to be in excess on one nautical mile. The precise configuration of

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828-463: A reflection from a particular boundary to arrive at the geophone is called the travel time . If the seismic wave velocity in the rock is known, then the travel time may be used to estimate the depth to the reflector. For a simple vertically traveling wave, the travel time t {\displaystyle t} from the surface to the reflector and back is called the Two-Way Time (TWT) and

897-439: A set of 8 streamers and 2 separate vessels towing seismic sources that were located at the start and end of the last receiver line (see diagram). This configuration was "tiled" 4 times, with the receiver vessel moving further away from the source vessels each time and eventually creating the effect of a survey with 4 times the number of streamers. The end result was a seismic dataset with a larger range of wider azimuths, delivering

966-431: A smaller depth of penetration, is known as Ground-penetrating radar or GPR. Reflection seismology, more commonly referred to as "seismic reflection" or abbreviated to "seismic" within the hydrocarbon industry, is used by petroleum geologists and geophysicists to map and interpret potential petroleum reservoirs . The size and scale of seismic surveys has increased alongside the significant increases in computer power since

1035-420: A two-dimensional vertical profile through the crust, now referred to as 2D data. This approach worked well with areas of relatively simple geological structure where dips are low. However, in areas of more complex structure, the 2D technique failed to properly image the subsurface due to out of plane reflections and other artefacts. Spatial aliasing is also an issue with 2D data due to the lack of resolution between

1104-399: A type of inverse problem . That is, given a set of data collected by experimentation and the physical laws that apply to the experiment, the experimenter wishes to develop an abstract model of the physical system being studied. In the case of reflection seismology, the experimental data are recorded seismograms, and the desired result is a model of the structure and physical properties of

1173-416: A volume of 2000 cubic inches to 7000 cubic inches, but this will depend upon the specific geology of the survey area. Marine seismic surveys generate a significant quantity of data due to the size of modern towed streamer vessels and their towing capabilities. A seismic vessel with 2 sources and towing a single streamer is known as a Narrow-Azimuth Towed Streamer (or NAZ or NATS). By the early 2000s, it

1242-432: A wide range of offsets and azimuths is usually acquired and the largest challenge is increasing the rate of acquisition. The rate of production is obviously controlled by how fast the source (Vibroseis in this case) can be fired and then move on to the next source location. Attempts have been made to use multiple seismic sources at the same time in order to increase survey efficiency and a successful example of this technique

1311-429: Is Independent Simultaneous Sweeping (ISS). A land seismic survey requires substantial logistical support; in addition to the day-to-day seismic operation itself, there must also be support for the main camp for resupply activities, medical support, camp and equipment maintenance tasks, security, personnel crew changes and waste management. Some operations may also operate smaller 'fly' camps that are set up remotely where

1380-508: Is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth 's subsurface from reflected seismic waves . The method requires a controlled seismic source of energy, such as dynamite or Tovex blast, a specialized air gun or a seismic vibrator. Reflection seismology is similar to sonar and echolocation . Reflections and refractions of seismic waves at geologic interfaces within

1449-422: Is considered to be the area where the land meets the sea, presenting unique challenges because the water is too shallow for large seismic vessels but too deep for the use of traditional methods of acquisition on land. Examples of this environment are river deltas, swamps and marshes, coral reefs, beach tidal areas and the surf zone. Transition zone seismic crews will often work on land, in the transition zone and in

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1518-479: Is described by the Zoeppritz equations . In 1919, Karl Zoeppritz derived 4 equations that determine the amplitudes of reflected and refracted waves at a planar interface for an incident P-wave as a function of the angle of incidence and six independent elastic parameters. These equations have 4 unknowns and can be solved but they do not give an intuitive understanding for how the reflection amplitudes vary with

1587-438: Is given by the formula where d {\displaystyle d} is the depth of the reflector and V {\displaystyle V} is the wave velocity in the rock. A series of apparently related reflections on several seismograms is often referred to as a reflection event . By correlating reflection events, a seismologist can create an estimated cross-section of the geologic structure that generated

1656-652: Is known as the "Shuey approximation", is valid for angles of incidence less than 30 degrees (usually the case in seismic surveys) and is given below: where R ( 0 ) {\displaystyle R(0)} = reflection coefficient at zero-offset (normal incidence); G {\displaystyle G} = AVO gradient, describing reflection behaviour at intermediate offsets and ( θ ) {\displaystyle (\theta )} = angle of incidence. This equation reduces to that of normal incidence at ( θ ) {\displaystyle (\theta )} =0. The time it takes for

1725-564: Is populated by the descendants of immigrants from Roda (now Narlı), and people from various other villages who were forced to leave during the population exchange between Greece and Turkey . It is considered, by many, to be the largest settlement of refugees coming to North Halkidiki after the Greek Genocide . Nea Roda is named after the original village called Roda (now the Turkish village of Narlı). Rodi (Ρόδι) meaning pomegranate,

1794-412: Is repeated. Typically, the recorded signals are subjected to significant amounts of signal processing . When a seismic P-wave encounters a boundary between two materials with different acoustic impedances, some of the energy in the wave will be reflected at the boundary, while some of the energy will be transmitted through the boundary. The amplitude of the reflected wave is predicted by multiplying

1863-421: Is the first of the three distinct stages of seismic exploration, the other two being seismic data processing and seismic interpretation. Seismic surveys are typically designed by National oil companies and International oil companies who hire service companies such as CGG , Petroleum Geo-Services and WesternGeco to acquire them. Another company is then hired to process the data, although this can often be

1932-550: Is the root of the word Roda which means "many pomegranates"; and "Nea" (Νέα) meaning new is the meaning of the first word. This due to an abundance pomegranate trees in the original village. This can be seen even today in the new village, where many people still have pomegranate trees in their backyard. Roda/Narli is a coastal village in the western part of the Cyzicus Peninsula, 12 km northwest of Artaki (today called Erdek ) and 28 km west of Michaniona. The Greek name of

2001-420: Is to send elastic waves (using an energy source such as dynamite explosion or Vibroseis ) into the Earth, where each layer within the Earth reflects a portion of the wave's energy back and allows the rest to refract through. These reflected energy waves are recorded over a predetermined time period (called the record length) by receivers that detect the motion of the ground in which they are placed. On land,

2070-770: The Histories of the ancient Greek historian Herodotus , which recounts the events of the Greco-Persian Wars , the Persian commander Mardonios , in 492 BC, lost a great part of his fleet, 300 ships and 20,000 men, in a storm going around the cliffs of the Athos peninsula , during the First Persian invasion of Greece . Xerxes, in preparation for the Second Persian invasion of Greece , in 483 BC ordered

2139-510: The Zoeppritz equations and by advances in computer processing capacity. AVO studies attempt with some success to predict the fluid content (oil, gas, or water) of potential reservoirs, to lower the risk of drilling unproductive wells and to identify new petroleum reservoirs. The 3-term simplification of the Zoeppritz equations that is most commonly used was developed in 1985 and is known as the "Shuey equation". A further 2-term simplification

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2208-474: The Earth were first observed on recordings of earthquake-generated seismic waves. The basic model of the Earth's deep interior is based on observations of earthquake-generated seismic waves transmitted through the Earth's interior (e.g., Mohorovičić, 1910). The use of human-generated seismic waves to map in detail the geology of the upper few kilometers of the Earth's crust followed shortly thereafter and has developed mainly due to commercial enterprise, particularly

2277-432: The Earth's crust. In common with other types of inverse problems, the results obtained from reflection seismology are usually not unique (more than one model adequately fits the data) and may be sensitive to relatively small errors in data collection, processing, or analysis. For these reasons, great care must be taken when interpreting the results of a reflection seismic survey. The general principle of seismic reflection

2346-550: The Persians to conquer the Greek cities-states had failed. The canal needed several years to be built and hundreds of residents of the area (mainly Acanthians, since Acanthus , modern Ierissos , is situated only 5 km away, but also residents of Sani and Ouranoupolis ) were used by Xerxes as slaves for the completion of the canal. It is commonly regarded as the site of the world's first offshore wind farm. The village today

2415-455: The amplitude of the incident wave by the seismic reflection coefficient R {\displaystyle R} , determined by the impedance contrast between the two materials. For a wave that hits a boundary at normal incidence (head-on), the expression for the reflection coefficient is simply where Z 1 {\displaystyle Z_{1}} and Z 2 {\displaystyle Z_{2}} are

2484-611: The bottom of a body of water and the air-water interface are common in marine seismic data, and are suppressed by seismic processing . Cultural noise includes noise from weather effects, planes, helicopters, electrical pylons, and ships (in the case of marine surveys), all of which can be detected by the receivers. Particularly important in urban environments (i.e. power lines), it is hardly removable. Some particular sensor as microelectromechanical systems (MEMs) are used to decrease these interference when in such environments. The original seismic reflection method involved acquisition along

2553-547: The canal made by the Persian King and extends into the peninsula; it ends in Athos, a high mountain projecting into the Aegean sea . The veracity of Herodotus' claims was doubted already in ancient times, but land surveys and geophysical investigations of the peninsula have confirmed the existence of the canal. In the second century BC, Demetrius of Scepsis stated based on first-hand information that there had, indeed, been

2622-494: The canal was 2 kilometres (1.2 mi), its width was 30 metres (100 ft), and it was 3 metres (10 ft) deep, enough for a trireme to pass. One end is at 40°22′52.8″N 23°55′43.2″E  /  40.381333°N 23.928667°E  / 40.381333; 23.928667  ( Northern end ) , the other at 40°21′54.2″N 23°54′53.9″E  /  40.365056°N 23.914972°E  / 40.365056; 23.914972  ( Southern end ) . According to

2691-436: The compromise the resultant image quality. Ocean bottom cables (OBC) are also extensively used in other areas that a seismic vessel cannot be used, for example in shallow marine (water depth <300m) and transition zone environments, and can be deployed by remotely operated underwater vehicles (ROVs) in deep water when repeatability is valued (see 4D, below). Conventional OBC surveys use dual-component receivers, combining

2760-463: The create a tuned energy pulse into the seabed from which the reflected energy waves are recorded on the streamer receiver groups. Gun arrays are tuned, that is the frequency response of the resulting air bubble from the array when fired can be changed depending upon the combination and number of guns in a specific array and their individual volumes. Guns can be located individual on an array or can be combined to form clusters. Typically, source arrays have

2829-537: The development of commercial applications of seismic waves included Mintrop, Reginald Fessenden , John Clarence Karcher , E. A. Eckhardt, William P. Haseman, and Burton McCollum. In 1920, Haseman, Karcher, Eckhardt and McCollum founded the Geological Engineering Company. In June 1921, Karcher, Haseman, I. Perrine and W. C. Kite recorded the first exploration reflection seismograph near Oklahoma City, Oklahoma . Early reflection seismology

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2898-608: The distance is too far to travel back to the main camp on a daily basis and these will also need logistical support on a frequent basis. Towed streamer marine seismic surveys are conducted using specialist seismic vessels that tow one or more cables known as streamers just below the surface typically between 5 and 15 metres depending upon the project specification that contain groups of hydrophones (or receiver groups) along their length (see diagram). Modern streamer vessels normally tow multiple streamers astern which can be secured to underwater wings, commonly known as doors or vanes that allow

2967-487: The energy of the incident wave, it is easy to show that By observing changes in the strength of reflections, seismologists can infer changes in the seismic impedances. In turn, they use this information to infer changes in the properties of the rocks at the interface, such as density and wave velocity , by means of seismic inversion . The situation becomes much more complicated in the case of non-normal incidence, due to mode conversion between P-waves and S-waves , and

3036-458: The equation: where v is the seismic wave velocity and ρ ( Greek rho ) is the density of the rock. When a seismic wave travelling through the Earth encounters an interface between two materials with different acoustic impedances, some of the wave energy will reflect off the interface and some will refract through the interface. At its most basic, the seismic reflection technique consists of generating seismic waves and measuring

3105-427: The impedance of the first and second medium, respectively. Similarly, the amplitude of the incident wave is multiplied by the transmission coefficient T {\displaystyle T} to predict the amplitude of the wave transmitted through the boundary. The formula for the normal-incidence transmission coefficient is As the sum of the energies of the reflected and transmitted wave has to be equal to

3174-713: The late 20th century. This led the seismic industry from laboriously – and therefore rarely – acquiring small 3D surveys in the 1980s to routinely acquiring large-scale high resolution 3D surveys. The goals and basic principles have remained the same, but the methods have slightly changed over the years. The primary environments for seismic hydrocarbon exploration are land, the transition zone and marine: Land – The land environment covers almost every type of terrain that exists on Earth, each bringing its own logistical problems. Examples of this environment are jungle, desert, arctic tundra, forest, urban settings, mountain regions and savannah. Transition Zone (TZ) – The transition zone

3243-560: The lines. Beginning with initial experiments in the 1960s, the seismic technique explored the possibility of full three-dimensional acquisition and processing. In the late 1970s the first large 3D datasets were acquired and by the 1980s and 1990s this method became widely used. Reflection seismology is used extensively in a number of fields and its applications can be categorised into three groups, each defined by their depth of investigation: A method similar to reflection seismology which uses electromagnetic instead of elastic waves, and has

3312-471: The lower medium and produces oscillatory motion parallel to the interface. This motion causes a disturbance in the upper medium that is detected on the surface. The same phenomenon is utilised in seismic refraction . An event on the seismic record that has incurred more than one reflection is called a multiple . Multiples can be either short-path (peg-leg) or long-path, depending upon whether they interfere with primary reflections or not. Multiples from

3381-447: The method was first invented. Major service companies in recent years have included CGG , ION Geophysical , Petroleum Geo-Services , Polarcus , TGS and WesternGeco , but since the oil price crash of 2015, providers of seismic services have continued to struggle financially such as Polarcus, whilst companies that were seismic acquisition industry leaders just ten years ago such as CGG and WesternGeco have now removed themselves from

3450-417: The narrowest point of the Athos peninsula in the municipality of Stagira-Akanthos , Chalkidiki , Greece . In 480 BC, Xerxes , King of Persia , opened a canal for his fleet to pass through. He did this in order to avoid rounding the edge of Athos peninsula, where Mardonius saw his fleet being destroyed ten years earlier due to extreme weather conditions. This is the place where the first attempt of

3519-476: The petroleum industry. Seismic reflection exploration grew out of the seismic refraction exploration method, which was used to find oil associated with salt domes . Ludger Mintrop, a German mine surveyor, devised a mechanical seismograph in 1914 that he successfully used to detect salt domes in Germany. He applied for a German patent in 1919 that was issued in 1926. In 1921 he founded the company Seismos, which

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3588-442: The reflections. In addition to reflections off interfaces within the subsurface, there are a number of other seismic responses detected by receivers and are either unwanted or unneeded: The airwave travels directly from the source to the receiver and is an example of coherent noise . It is easily recognizable because it travels at a speed of 330 m/s, the speed of sound in air. A Rayleigh wave typically propagates along

3657-428: The rock properties involved. The reflection and transmission coefficients, which govern the amplitude of each reflection, vary with angle of incidence and can be used to obtain information about (among many other things) the fluid content of the rock. Practical use of non-normal incidence phenomena, known as AVO (see amplitude versus offset ) has been facilitated by theoretical work to derive workable approximations to

3726-401: The same company that acquired the survey. Finally the finished seismic volume is delivered to the oil company so that it can be geologically interpreted. Land seismic surveys tend to be large entities, requiring hundreds of tons of equipment and employing anywhere from a few hundred to a few thousand people, deployed over vast areas for many months. There are a number of options available for

3795-402: The seismic acquisition environment entirely and restructured to focus upon their existing seismic data libraries, seismic data management and non-seismic related oilfield services. Seismic waves are mechanical perturbations that travel in the Earth at a speed governed by the acoustic impedance of the medium in which they are travelling. The acoustic (or seismic) impedance, Z , is defined by

3864-443: The settlement was Roda (registered in the book of the metropolis) and the Turkish (presented in official Ottoman documents) was Rutya. In the early 20th century, the village had almost 200 houses, 150 of which were christian and 50 of which were muslim. The village inhabitants spoke the Greek language but on the contrary, the only ones knowing the Turkish language were those occupied in shipping. Millennia of Greek habitation and history

3933-477: The shallow water marine environment on a single project in order to obtain a complete map of the subsurface. Marine – The marine zone is either in shallow water areas (water depths of less than 30 to 40 metres would normally be considered shallow water areas for 3D marine seismic operations) or in the deep water areas normally associated with the seas and oceans (such as the Gulf of Mexico). Seismic data acquisition

4002-428: The streamers on any project in terms of streamer length, streamer separation, hydrophone group length and the offset or distance between the source centre and the receivers will be dependent upon the geological area of interest below the sea floor that the client is trying to get data from. Streamer vessels also tow high energy sources, principally high pressure air gun arrays that operate at 2000psi that fire together to

4071-552: The subsurface and a better signal to noise ratio. The seismic properties of salt poses an additional problem for marine seismic surveys, it attenuates seismic waves and its structure contains overhangs that are difficult to image. This led to another variation on the NATS survey type, the wide-azimuth towed streamer (or WAZ or WATS) and was first tested on the Mad Dog field in 2004. This type of survey involved 1 vessel solely towing

4140-475: The time taken for the waves to travel from the source, reflect off an interface and be detected by an array of receivers (as geophones or hydrophones ) at the surface. Knowing the travel times from the source to various receivers, and the velocity of the seismic waves, a geophysicist then attempts to reconstruct the pathways of the waves in order to build up an image of the subsurface. In common with other geophysical methods, reflection seismology may be seen as

4209-404: The typical receiver used is a small, portable instrument known as a geophone , which converts ground motion into an analogue electrical signal. In water, hydrophones are used, which convert pressure changes into electrical signals. Each receiver's response to a single shot is known as a “trace” and is recorded onto a data storage device , then the shot location is moved along and the process

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4278-429: The way across the isthmus or if ships were dragged through parts of it. A British and Greek collaborative geophysical investigation launched in the 1990s found, using seismic survey and sediment analysis, that the canal had crossed the whole isthmus. Herodotus' account was vindicated, as they also confirmed that the canal was constructed rapidly and that it was only used for a short period of time. Some studies suggest

4347-409: The workers were both regular Achaemenid soldiers and recruited local Balkan people (Thracians and Greeks) with the legal status of kurtaš , who were paid for and fed from the Persian treasury. 40°22′24″N 23°55′28″E  /  40.3732°N 23.9245°E  / 40.3732; 23.9245 Nea Roda Nea Roda is a village 115 km (71 mi) southeast of Thessaloniki , on

4416-554: Was accepted that this type of acquisition was useful for initial exploration but inadequate for development and production, in which wells had to be accurately positioned. This led to the development of the Multi-Azimuth Towed Streamer (MAZ) which tried to break the limitations of the linear acquisition pattern of a NATS survey by acquiring a combination of NATS surveys at different azimuths (see diagram). This successfully delivered increased illumination of

4485-440: Was erased in a few short years in order to rid the region of the indigenous Greek Orthodox Christian peoples of Turkey. Today, Nea Roda is a modern village with 1,192 residents (2011 census), making it the second biggest town of the municipal unit of Stagira-Akanthos after Ierissos . Fishing , tourism and agriculture are the people's main occupations. Seismic survey Reflection seismology (or seismic reflection )

4554-614: Was hired to conduct seismic exploration in Texas and Mexico, resulting in the first commercial discovery of oil using the refraction seismic method in 1924. The 1924 discovery of the Orchard salt dome in Texas led to a boom in seismic refraction exploration along the Gulf Coast, but by 1930 the method had led to the discovery of most of the shallow Louann Salt domes, and the refraction seismic method faded. After WWI , those involved in

4623-558: Was not used after the Persian fleet had passed through on their way first to the battle of Artemisium and then on to that of Salamis . The canal still formed part of the landscape 80 years later as it is mentioned in passing by Thucidydes in The History of the Peloponnesian War from around 400 BC: After the taking of Amphipolis, Brasidas and his allies marched to the so-called Actè, or coastland, which runs out from

4692-443: Was one of the most successful seismic contracting companies for over 50 years and was the parent of an even more successful company, Texas Instruments . Early GSI employee Henry Salvatori left that company in 1933 to found another major seismic contractor, Western Geophysical . Many other companies using reflection seismology in hydrocarbon exploration, hydrology , engineering studies, and other applications have been formed since

4761-410: Was viewed with skepticism by many in the oil industry. An early advocate of the method commented: The Geological Engineering Company folded due to a drop in the price of oil. In 1925, oil prices had rebounded, and Karcher helped to form Geophysical Research Corporation (GRC) as part of the oil company Amerada . In 1930, Karcher left GRC and helped to found Geophysical Service Incorporated (GSI). GSI

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