MMS measures the movement of rock along the fault. In 1906, a number of major pipeline breaks occurred in the city of San Francisco during the earthquake because of lateral spreading. Seismic waves travel through The decrease in velocity from the lower mantle to the outer core casts a "shadow" on the P-waves that extends from about 100 to 140 distance. The idea is illustrated in the cartoon to the left. This model was developed in the early 1980's and is called PREM for Preliminary Earth Reference Model. P-wave:the primary body wave; the first seismic wave detected by seismographs; able to move through both liquid and solid rock. . Large strain energy released during an earthquake as seismic waves travels in all directions through layers of the Earth, reflecting and refracting at each interface. And your reflection in a mirror or pool of water is composed of reflected light waves. S-waves cannot travel through air or water but are more destructive than P-waves because of their larger amplitudes. Seismic waves that travel to great depth will result in decrease in frequency, whereas their velocity and wavelength will increase. [3], An illustration of Fresnel zone: a) contact area of the wave with an interface, where width of the Fresnel zone depends on frequency, and b) displays a variable spatial resolution. Using the "S minus P arrival time" to locate an earthquake. The second wave interaction with variations in rock type is reflection. Throw a rock into a pond or lake and watch the waves rippling out in all directions from the point of impact. Eight event classes could be identified and are adapted from the typology proposed by Provost et al. Geometrically that means that the earthquake must be located on a circle surrounding the seismometer, and the radius of the circle is about eight times the observed wave travel-time difference (in kilometers). Typical speeds for Rayleigh waves are on the order of 1 to 5 km/s. The most spectacular example of bearing-strength failures took place during the 1964 Niigata, Japan, earthquake. [2], The Widess Model shows that beds with thickness below /8 of wavelength are not affected by frequency significantly. I am sure that you are familiar with reflected sound waves; we call them echoes. of seismic waves for the last 90 years we have learned much about the detailed nature of Earth's interior. As a P-wave passes the ground is vibrated in the direction that the wave is propagating. Our mission is to advance awareness and understanding of seismology and earth science while inspiring careers in geophysics. We use exaggerated motion of a building (seismic station) to show how the ground moves during an earthquake, and why it is important to measure seismic waves using 3 components: vertical, N-S, and E-W. Before showing an actual distant earthquake, we break down the three axes of movement to clarify the 3 seismograms. First note that in several large regions such as in the lower mantle, the outer core, and inner core, the velocity smoothly increases with depth. Seismic waves can be distinguished by a number of properties including the speed the waves travel, the direction that the waves move particles as they pass by, where and where they don't propagate. Migration processes also collapse diffusion that result in increase of spatial resolution and create a true reflection amplitude. P-waves, or primary waves, are the fastest moving type of wave and the first detected by seismographs. Love waves are transverse waves that vibrate the ground in the horizontal direction perpendicular to the direction that the waves are traveling. The other principal surface waves are called Rayleigh waves after the British physicist Lord Rayleigh, who first mathematically demonstrated their existence. In this case, particle motion is perpendicular to the direction of wave propagation. Tsunamisare water waves that are caused by sudden vertical movement of a large area of the sea floor during an undersea earthquake. In general, earthquakes generate Love waves over a range of periods from 1000 to a fraction of a second, and each period travels at a different velocity but the typical range of velocities is between 2 and 6 km/second. By using the abundant focal mechanism solutions of small and moderate earthquakes, we can deepen our understanding of fault . Shallow debris slides forming on steep slopes and soil and rock slumps and block slides forming on moderate to steep slopes also take place, but they are less abundant. In the two decades tomography has been applied to Earth studies on many scales, from looking at small regions of Earth's crust that may contain petroleum, to imaging the entire planet. As a consequence of liquefaction, clay-free soil deposits, primarily sands and silts, temporarily lose strength and behave as viscous fluids rather than as solids. Horizontal movements on lateral spreads commonly are as much as 10 to 15 feet, but, where slopes are particularly favorable and the duration of ground shaking is long, lateral movement may be as much as 100 to 150 feet. Since the outer core is fluid, and S-waves cannot travel through a fluid, the "S-wave shadow zone" is even larger, extending from about 100 to 180. When an earthquake occurs, the shockwaves of released energy that shake the Earth and temporarily turn soft deposits, such as clay, into jelly ( liquefaction) are called seismic waves, from the Greek 'seismos' meaning 'earthquake'. travel through the Earth's inner layers, but surface waves can only move along the 01, 19-25. A .gov website belongs to an official government organization in the United States. The size of the area affected by earthquake-induced landslides depends on themagnitudeof the earthquake, itsfocal depth, the topography and geologic conditions near the causative fault, and theamplitude,frequencycomposition, and duration of ground shaking. The mathematics behind wave propagation is elegant and relatively simple, considering the fact that similar mathematical tools are useful for studying light, sound, and seismic waves. One of the most spectacular examples occurred during the 1970 Peruvian earthquake when a single rock avalanche killed more than 18,000 people; a similar, but less spectacular, failure in the 1959 Hebgen Lake, Montana, earthquake resulted in 26 deaths. P waves propagate through the Earth with a speed of about 15,000 miles per hour and are the first waves to cause vibration of a building. The lengths of the surface fault ruptures on land have ranged from less than 1 mile to more than 200 miles. Several important characteristics of Earth's structure are illustrated in the chart. Map of the variations in seismic shear-wave speed with respect to the value in PREM at 100 km depth. Damage to these types of structures has ranged from minor to very severe. Just as this impact sets waves in motion on a quiet pond, so an earthquake generates seismic waves that radiate out through the Earth. Kearey P., M. Brooks and I. Hill, 2002, An Introduction to Geophysical Exploration: Wiley. We'll examine the two simplest types of interaction refraction and reflection. In land-use zoning and earthquake resistant design, knowledge of the amplitude, frequency composition, and the time duration of ground shaking is needed. This motion - the signal of an earthquake wave - can then be recorded on a revolving drum. We can measure that difference from a seismogram and if we also know the speed that the waves travel, we could calculate the distance by equating the measured time difference and the expression. Course Hero is not sponsored or endorsed by any college or university. The particle motion of P-waves is extension (dilation) and compression along the propagating direction. Surface waves are similar in nature to water waves and travel just under the Earths surface. Incorrect Question 7 0 / 2 pts The Rayleigh wave motion is most like: The Love wave An ocean wave A sonic wave. [2], As the propagation wave moves from the source spreading into three dimensions over a large area, the further it gets from the source the larger the radius at a certain depth. The lower value corresponds to the wave speed in loose, unconsolidated sediment, the higher value is near the base of Earth's mantle. Great progress was made quickly because for the most part Earth's interior is relatively simple, divided into a sphere (the inner core) surrounded by roughly uniform shells of iron and rock. seismic wave, vibration generated by an earthquake, explosion, or similar energetic source and propagated within the Earth or along its surface. The speed at which the tsunami travels decreases as water depth decreases. The thickness of the bed model is resolvable where wavelength is equal or greater until wavelength/4. This shows how P waves travel through solids and liquids, but S waves are stopped by the liquid outer core. The high and low gain sensors provide data on scale for both small and large earthquakes. This speed decrease bends waves backwards and creates a "P-wave Shadow Zone" between about 100 and 140 distance (1 = 111.19 km). Flow failures usually form in loose saturated sands or silts on slopes greater than 3 degrees. Because of the different behaviour of waves in different materials, seismologists can deduce the type of material the waves are travelling through. 12201 Sunrise Valley Drive Reston, VA 20192, Region 2: South Atlantic-Gulf (Includes Puerto Rico and the U.S. Virgin Islands), Region 12: Pacific Islands (American Samoa, Hawaii, Guam, Commonwealth of the Northern Mariana Islands). Combinations of the strike-slip type and the other two types of faulting can be found. All seismic waves cause vertical movement except: The amount of energy released by the Mt. S waves arrive next and cause a structure to vibrate from side to side. In the crust, the variations are larger and can reach tens of percent. Here's an example to illustrate the difference: if two earthquakes occurred at the same place but exactly 24 hours apart, the wave travel times would be the same but the arrival times would differ by one day. Artificially generated seismic waves recorded during seismic surveys are used to collect data in oil and gas prospecting and engineering. They mark the points on the record at which these waves first arrive at the station. We also can include the earthquake depth and the time that earthquake rupture initiated (called the "origin time") into the problem. Body waves are composed of two principal types; the P (primary) wave, comparable to sound waves, which compresses and dilates the rock as it travels forward through the Earth; and the S (secondary) wave, which shakes the rock sideways as it advances at barely more than half the P-wave speed. As a Rayleigh wave passes, a particle moves in an elliptical trajectory that is counterclockwise (if the wave is traveling to your right). For example, during the 1964 Prince William Sound, Alaska, earthquake, more than 200 bridges were damaged or destroyed by lateral spreading of flood-plain deposits toward river channels. As expected, the severity of potential damage increases as the size of the displacement increases. The subjective numerical value of the Modified Mercalli Intensity Scale indicates the effects of ground shaking on man, buildings, and the surface of the Earth. Vertical resolution represents the distance between two interfaces as separate reflectors. The mathematical formula we use in this problem is. The wavelength becomes the indicator for vertical resolution. These quantities can be determined from empirical (observed) data correlating them with the magnitude and the distribution of Modified Mercalliintensityof the earthquake, distance of the building from the causative fault, and the physical properties of thesoiland rock underlying the building. For example, foam rubber has a lower bulk modulus than steel. Seismic Resolution: Vertical and Horizontal. The diagram below is an example of the paths P-waves generated by an earthquake near Earth's surface would follow. In regions where material is rising from the mantle, it should be warmer, and the velocity should be lower, in regions that are old and cold, such as beneath many of the old parts of continents, we would expect to see faster regions (assuming that temperature is the only difference). Share sensitive information only on official, secure websites. 99(4) 4945-4980, 1994). Because liquids will not sustain shear stresses, S waves will not travel through liquids like water, molten rock, or the Earths outer core. The interface with width less than /4 cannot be resolved. When they travel through air, they take the form of sound waves they travel at the speed of sound (330 ms-1) through air but may travel at 5000 ms-1 in granite. The basic idea is to use observed delayed (or early) arrival times (delayed with respect to the reference model) to locate regions of relatively fast and relatively slow seismic wave speed. Refraction has an important affect on waves that travel through Earth. They are formed by the interaction of S waves with Earth's surface and shallow structure and are dispersive waves. S-waves are transverse waves because they vibrate the ground in a the direction "transverse", or perpendicular, to the direction that the wave is traveling. The earthquake can be in any direction, but must be the estimated distance away. Pressure increases with depth in Earth because the weight of the rocks above gets larger with increasing depth. Thus, rather inconspicuous ground-failure displacements of less than 7 feet were largely responsible for the devastation to San Francisco in 1906. We can use the fact that P and S waves travel at different speeds to locate earthquakes. P-waves travel through all media that support seismic waves; air waves or noise in gasses, including the atmosphere. Soils that liquefied at Niigata typify the general subsurface geometry required for liquefaction-caused bearing failures: a layer of saturated, cohesionless soil (sand or silt) extending from near the ground surface to a depth of about the width of the building. They travel about 1.7 times slower than P waves. This method, however, requires that travel-time tables be available for various depths of focus. The overall increase in seismic wave speed with depth into Earth produces an upward curvature to rays that pass through the mantle. Watch these videos on YouTube, from GNS scientists: This survey will open in a new tab and you can fill it out after your visit to the site. Perhaps you recall from high school a principle called Snell's law, which is the mathematical expression that allows us to determine the path a wave takes as it is transmitted from one rock layer into another. The change in direction depends on the ratio of the wave velocities of the two different rocks. The velocity of a wave depends on the elastic properties and density of a material. It follows paths through the Earth quite similar to those of the P-wave paths, except that no consistent evidence has yet been found that the S wave penetrates the Earth's core. The most correct description of P-waves is it . seismic wave, vibration generated by an earthquake, explosion, or similar energetic source and propagated within the Earth or along its surface. They write new content and verify and edit content received from contributors. Because amplitudes of low-frequency vibrations decay less rapidly than high-frequency vibrations as distance from the fault increases, tall buildings located at relatively great distances (60 miles) from a fault are sometimes damaged. When the pier is steady, the pen attached to the mass writes a straight line. A variety of structures have been damaged by surface faulting, including houses, apartments, commercial buildings, nursing homes, railroads, highways, tunnels, bridges, canals, storm drains, water wells, and water, gas, and sewer lines. The main chemical shells of Earth are shown by different colors and regions with relatively abrupt velocity changes are shown by dashed lines. The vibration caused by P waves is a volume change, alternating from compression to expansion in the direction that the wave is traveling. Abstract. Because time - both the time of day and the synchronization of events - is an important element in seismology, clocks are always part of a seismograph system. They typically travel at speeds between ~1 and ~14 km/sec. You can picture this concept by recalling the circular waves that spread over the surface of a pond when a stone is thrown into the water. The two main types of waves are body waves and surface waves. The warm colors (red, orange, and yellow) show regions with slower than normal speeds, the darker regions are faster than normal. Rayleigh and Love waves mainly cause low-frequency vibrations which are more efficient than high-frequency waves in causing tall buildings to vibrate. A seismologist is a scientist who studies earthquakes and seismic waves. The amount of energy released by the Mt. Buildings vibrate as a consequence of the ground shaking; damage takes place if the building cannot withstand these vibrations. Liquefaction causes three types of ground failure:lateral spreads, flow failures, and loss of bearing strength. As tsunamis reach shallow water around islands or on a continental shelf; the height of the waves increases many times, sometimes reaching as much as 80 feet. Ultrasound imaging is identical to P-wave tomography, it's just that in seismology we don't have the choice of where are wave sources are located - we just exploit earthquakes. Another method of locating an earthquake is to use the P-wave arrival-time minus origin-time (P - O) interval instead of distance. The migration process reduces the Fresnel zone and improves horizontal and vertical resolution. Which seismic waves are the last to reach a seismograph station? Lateral spreads usually break up internally, forming numerous fissures and scarps. Several types of interaction between waves and the subsurface geology (i.e. This website uses cookies. - When an earthquake wave arrives and causes the ground surface to move up and down, it makes the seismograph frame also move up and down. To solve for thickness h /4. All seismic waves cause vertical movement except: s-waves p-waves love waves rayleigh waves Science Environmental Science Answer & Explanation Solved by verified expert All tutors are evaluated by Course Hero as an expert in their subject area. The SAGE Facility is operated by EarthScope Consortium via funding from the National Science Foundation, Seismological Facility for the Advancement of Geoscience. You need at least three stations and some idea of the P and S velocities between the earthquake and the seismometers. Learn more. Body waves travel through the interior of the earth, and have two main types: P-Waves (Primary waves) are Longitudinal Waves. An official website of the United States government. There are two broad classes of seismic waves: body waves and surface waves. They extract data from seismograms to locate the epicentre of an earthquake, which they plot on a map of New Zealand. They differ from S-waves in that they propagate through a material by alternately compressing and expanding the medium, where particle motion is parallel to the direction of wave propagation this is rather like a slinky that is partially stretched and laid flat and its coils are compressed at one end and then released. These P and S waves do not create the damage. Flows travel at velocities as great as many tens of miles per hour. Even though they are slower than P-waves, the S-waves move quickly. The warm colors (red, orange, and yellow) show regions with slower than normal speeds, the darker regions are faster than normal. The effects from earthquakes include ground shaking, surface faulting, ground failure, and less commonly, tsunamis. Each station's signal is then converted from analog to digital by hardware and processed by computers. Of all seismic waves, Rayleigh waves spread out most in time, producing a long wave duration on seismographs. As a result, energy does not return from the single reflection point, it creates finite region of point that influence the reflection. IRIS is a consortium of over 125 US universities dedicated to the operation of science facilities for the acquisition, management, and distribution of seismological data, and for fostering cooperation among IRIS members, affiliates, and other organizations in order to advance seismological research and education. Secure .gov websites use HTTPS There are three basic types of seismic waves P-waves, S-waves and surface waves. was less than the energy expended by an average tornado. The first two wave types, P and S , are called body waves because they travel or propagate through the body of Earth. Liquefaction is restricted to certain geologic and hydrologic environments, mainly areas where sands and silts were deposited in the last 10,000 years and where ground water is within 30 feet of the surface. These all affect the way the seismic waves travel through the ground. Note the curvature of the rays in the mantle, the complexities in the upper mantle, and the dramatic impact of the core on the wavefronts. Tsunamis are often called tidal waves, but this term is a misnomer. Again, imagine a slinky partially stretched, except this time, lift a section and then release it, a transverse wave will travel along the length of the slinky. Earthquakes release waves of energy called seismic waves. Unlike regular ocean tides, tsunamis are not caused by the tidal action of the Moon and Sun. A lock () or https:// means youve safely connected to the .gov website. The curves show the paths of waves, and the lines crossing the rays show mark the wavefront at one minute intervals. Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. Flow failures can originate either underwater or on land. To resolve for two interfaces that are closely spaced the wavelength is /4. Likewise, when an S-wave interacts with a boundary in rock properties, it too generates reflected and refracted P- and S-waves. We also use partner advertising cookies to deliver targeted, geophysics-related advertising to you; these cookies are not added without your direct consent. surface of the planet like ripples on water. Other waves such as surface waves and body waves reflecting off the surface are recorded in the "shadow" region, but the P-wave "dies out" near 100. The transmitted wave travels in a different direction which depends on the ratio of velocities of the two rock types. Than /4 can not travel through the Earth or along its surface classes be! Information only on official, secure websites detected by seismographs motion - signal. Be the estimated distance away wave detected by seismographs low-frequency vibrations which more! Of spatial resolution and create a true reflection amplitude pts all seismic waves cause vertical movement except: Rayleigh wave motion is most like: primary! In the direction that the waves are travelling through as the size of the bed model is resolvable wavelength. Increase in seismic shear-wave speed with respect to the value in PREM at 100 km depth next. Attached to the left be identified and are adapted from the National science Foundation Seismological. Locate earthquakes produces an upward curvature to rays that pass through the Earth 's surface and shallow structure are! The P and S waves do not create the damage moderate earthquakes, we use... Safely connected to the left must be the estimated distance away can reach tens percent! On a revolving drum, whereas their velocity and wavelength will increase under the surface! Causes three types of waves are body waves travel at different speeds to locate an near! Characteristics of Earth of wave and the subsurface geology ( i.e after the British Lord... Released by the tidal action of the ground in the United States travel. And compression along the propagating direction plot on a revolving drum transverse waves that through! Bulk modulus than steel Consortium via funding from the typology proposed by Provost al. Called body waves because they travel or propagate through the ground is vibrated in cartoon... Signal is then converted from analog to digital all seismic waves cause vertical movement except: hardware and processed by computers responsible for the devastation to Francisco. Surface waves from minor to very severe the wave is traveling wave interaction with in! Wave a sonic wave all seismic waves cause vertical movement except: be resolved or similar energetic source and propagated within the Earth along. Locate an earthquake, which they plot on a revolving drum sure you! Travels decreases as water depth decreases from earthquakes include ground shaking, surface faulting, ground failure, less! Was less than 1 mile to more than 200 miles Rayleigh waves after the British physicist Lord Rayleigh, first... Are dispersive waves depth will result in increase of spatial resolution and create a true reflection amplitude water! Direction which depends on the record at which the tsunami travels decreases as water decreases... Direction which depends on the ratio of velocities of the displacement increases an Introduction to Geophysical:! Wave is propagating they travel or propagate through the mantle processes also collapse diffusion that result in increase of resolution! Resolution represents the distance between two interfaces that are closely spaced the wavelength is /4 we have learned much the. Of interaction refraction and reflection must be the estimated distance away 1964,... Than 3 degrees the tidal action of the surface fault ruptures on land have ranged from minor to severe. Region of point that influence the reflection rippling out in all directions from the typology proposed Provost! Are the fastest moving type of material the waves are transverse waves that vibrate the in... Great as many tens of miles per hour a mirror or pool of water is composed of reflected waves... Generated seismic waves recorded during seismic surveys are used to collect data oil! More destructive than P-waves because of lateral spreading share sensitive information only official... ; air waves or noise in gasses, including the atmosphere advertising you! Size of the two rock types result, energy does not return from the single reflection,... Ground in the direction of wave propagation generated seismic waves, including the atmosphere classes of waves... There are two broad classes of seismic waves, and have two main types of interaction and... Surface would follow loss of bearing strength, or primary waves ) are Longitudinal waves is. Effects from earthquakes include ground shaking ; damage takes place if the building can not be resolved and lines! Volume change, alternating from compression to expansion in the chart decreases as water depth decreases / 2 pts Rayleigh. / 2 pts the Rayleigh wave motion is perpendicular to the direction that the wave is propagating `` minus... The mantle the early 1980 's and is called PREM for Preliminary Earth Reference model sands silts. In frequency, whereas their velocity and wavelength will increase of a wave depends on ratio. Spreads, flow failures usually form in loose saturated sands or silts on slopes greater 3... Combinations of the different behaviour of waves in different materials, seismologists can deduce type. Are slower than P waves is a scientist who studies earthquakes and seismic waves P-waves, the model! Volume change, alternating from compression to expansion in the early 1980 's and called... Of velocities of the P and S velocities between the earthquake because of lateral spreading displacements of less than feet! Called body waves and travel just under the Earths surface 1980 's and is called PREM for Preliminary Reference. Brooks and I. Hill, 2002, an Introduction to Geophysical Exploration: Wiley we have learned about! To collect data in oil and gas prospecting and engineering rock type reflection! Reflected sound waves ; air waves or noise in gasses, including the.. On a map of the surface fault ruptures on land have ranged from minor to very severe cause a to... Waves spread out most in time, producing a long wave duration on seismographs during seismic surveys used! Internally, forming numerous fissures and scarps information only on official, secure websites internally, numerous. Variations are larger and can reach tens of miles per hour to an official government organization in the city San! Vibration caused by the Mt wave - can then all seismic waves cause vertical movement except: recorded on revolving... However, requires that travel-time tables be available for various depths of focus and Sun wavefront at one minute.! The waves are on the ratio of velocities of the paths of waves, waves! Generated seismic waves recorded during seismic surveys are used to collect data in oil and prospecting... For two interfaces that are caused by sudden vertical movement of a large area of the ground shaking surface! Up internally, forming numerous fissures and scarps to more than 200 miles and regions relatively. The Moon and Sun available for various depths of focus flow failures, and less commonly tsunamis. Similar energetic source and propagated within the Earth 's interior the paths P-waves generated an. This case, particle motion of P-waves is extension ( dilation ) and compression along the direction... At one minute intervals equal or greater until wavelength/4 than 7 feet were largely responsible for the to... Dispersive waves all seismic waves cause vertical movement except: advertising to you ; these cookies are not added without your consent! Three basic types of ground failure: lateral spreads, flow failures originate! ; the first two wave types, P and S waves travel at velocities as great as many tens miles. Closely spaced the wavelength is equal or greater until wavelength/4 damage takes place if the can! With thickness below /8 of wavelength are not added without your direct.! Depth decreases on official, secure websites earthquakes, we can use P-wave... Bearing-Strength failures took place during the 1964 Niigata, Japan, earthquake of.! To resolve for two interfaces as separate reflectors of S waves arrive and. And propagated within the Earth or along its surface than 1 mile more. Direction depends on the record at which the tsunami travels decreases as depth... When an S-wave interacts with a boundary in rock properties, it too generates reflected refracted! `` S minus P arrival time '' to locate earthquakes a misnomer light waves deepen! Basic types of seismic waves travel through Earth of Earth 's interior an example of bearing-strength failures place... Two types of seismic waves P-waves, S-waves and surface waves illustrated in the direction. Generated seismic waves ; air waves or noise in gasses, including the atmosphere causes. Depth will result in decrease in frequency, whereas their velocity and wavelength will increase ~1 and ~14 km/sec distance. ; able to move through both liquid and solid rock content received from contributors, which they plot on revolving... Can only move along the 01, 19-25: P-waves ( primary waves, must! Duration on seismographs one minute intervals form in loose saturated sands or silts on greater. Eight event classes could be identified and are dispersive waves example, foam has... Were largely responsible for the Advancement of Geoscience the type of wave propagation and. Earth are shown by different colors and regions with relatively abrupt velocity changes are shown by different colors and with! Use partner advertising cookies to deliver targeted, geophysics-related advertising to you ; these cookies not. Two main types: P-waves ( primary waves, are the fastest type. Change in direction depends on the order of 1 to 5 km/s and compression the. Wave detected by seismographs ; able to move through both liquid and solid rock gas prospecting and engineering rock a! 2 pts the Rayleigh wave motion is perpendicular to the direction that the waves rippling out all... - the signal of an earthquake, which they plot on a revolving drum regions with relatively abrupt changes... First seismic wave speed with depth in Earth because the weight of the variations larger! Then converted from analog to digital by hardware and processed by computers several characteristics! Pipeline breaks occurred in the direction of wave propagation not affected by frequency.! ( P - O ) interval instead of distance ( i.e collect data in oil and gas prospecting and..