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87-589: According to some seismologists the 1892 Laguna Salada earthquake ranks among the largest earthquakes in California and Baja California in historic times. It occurred on 23 February 1892, and was centered near Laguna Salada in Baja California. The Laguna Salada Fault is thought to be the origin of the 2010 Baja California earthquake. Prior to this, the fault had not produced a major earthquake for over 100 years, since 1892. The Laguna Salada Fault

174-458: A feedback circuit. The amount of force necessary to achieve this is then recorded. In most designs the electronics holds a mass motionless relative to the frame. This device is called a "force balance accelerometer". It measures acceleration instead of velocity of ground movement. Basically, the distance between the mass and some part of the frame is measured very precisely, by a linear variable differential transformer . Some instruments use

261-408: A geo-sismometro , possibly the first use of a similar word to seismometer . Naturalist Nicolo Zupo devised an instrument to detect electrical disturbances and earthquakes at the same time (1784). The first moderately successful device for detecting the time of an earthquake was devised by Ascanio Filomarino in 1796, who improved upon Salsano's pendulum instrument, using a pencil to mark, and using

348-431: A linear variable differential capacitor . That measurement is then amplified by electronic amplifiers attached to parts of an electronic negative feedback loop . One of the amplified currents from the negative feedback loop drives a coil very like a loudspeaker . The result is that the mass stays nearly motionless. Most instruments measure directly the ground motion using the distance sensor. The voltage generated in

435-402: A coil attached to the mass which voltage moves through the magnetic field of a magnet attached to the frame. This design is often used in a geophone , which is used in exploration for oil and gas. Seismic observatories usually have instruments measuring three axes: north-south (y-axis), east–west (x-axis), and vertical (z-axis). If only one axis is measured, it is usually the vertical because it

522-554: A copy of which can be found at the University Library in Bologna, and a further mercury seismoscope was constructed by Niccolò Cacciatore in 1818. James Lind also built a seismological tool of unknown design or efficacy (known as an earthquake machine) in the late 1790s. Pendulum devices were developing at the same time. Neapolitan naturalist Nicola Cirillo set up a network of pendulum earthquake detectors following

609-406: A digital seismograph can be simply input to a computer. It presents the data in a standard digital format (often "SE2" over Ethernet ). The modern broadband seismograph can record a very broad range of frequencies . It consists of a small "proof mass", confined by electrical forces, driven by sophisticated electronics . As the earth moves, the electronics attempt to hold the mass steady through

696-527: A given quake. Luigi Palmieri , influenced by Mallet's 1848 paper, invented a seismometer in 1856 that could record the time of an earthquake. This device used metallic pendulums which closed an electric circuit with vibration, which then powered an electromagnet to stop a clock. Palmieri seismometers were widely distributed and used for a long time. By 1872, a committee in the United Kingdom led by James Bryce expressed their dissatisfaction with

783-433: A hair attached to the mechanism to inhibit the motion of a clock's balance wheel. This meant that the clock would only start once an earthquake took place, allowing determination of the time of incidence. After an earthquake taking place on October 4, 1834, Luigi Pagani observed that the mercury seismoscope held at Bologna University had completely spilled over, and did not provide useful information. He therefore devised

870-414: A low-budget way to get some of the performance of the closed-loop wide-band geologic seismographs. Strain-beam accelerometers constructed as integrated circuits are too insensitive for geologic seismographs (2002), but are widely used in geophones. Some other sensitive designs measure the current generated by the flow of a non-corrosive ionic fluid through an electret sponge or a conductive fluid through

957-505: A mantle of silicates, surrounding a core of iron. In 1906 Richard Dixon Oldham identified the separate arrival of P waves , S-waves and surface waves on seismograms and found the first clear evidence that the Earth has a central core. In 1909, Andrija Mohorovičić , one of the founders of modern seismology, discovered and defined the Mohorovičić discontinuity . Usually referred to as

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1044-399: A month after the event. The first observations of normal modes were made in the 1960s as the advent of higher fidelity instruments coincided with two of the largest earthquakes of the 20th century the 1960 Valdivia earthquake and the 1964 Alaska earthquake . Since then, the normal modes of the Earth have given us some of the strongest constraints on the deep structure of the Earth. One of

1131-412: A near-surface explosion, and are much weaker for deep earthquake sources. Both body and surface waves are traveling waves; however, large earthquakes can also make the entire Earth "ring" like a resonant bell. This ringing is a mixture of normal modes with discrete frequencies and periods of approximately an hour or shorter. Normal mode motion caused by a very large earthquake can be observed for up to

1218-453: A particular location within a particular time-span, and they are routinely used in earthquake engineering . Public controversy over earthquake prediction erupted after Italian authorities indicted six seismologists and one government official for manslaughter in connection with a magnitude 6.3 earthquake in L'Aquila, Italy on April 5, 2009 . A report in Nature stated that the indictment

1305-552: A portable device that used lead shot to detect the direction of an earthquake, where the lead fell into four bins arranged in a circle, to determine the quadrant of earthquake incidence. He completed the instrument in 1841. In response to a series of earthquakes near Comrie in Scotland in 1839, a committee was formed in the United Kingdom in order to produce better detection devices for earthquakes. The outcome of this

1392-487: A seismometer was deployed on the planet Mars by the InSight lander, the first time a seismometer was placed onto the surface of another planet. In Ancient Egypt , Amenhotep, son of Hapu invented a precursor of seismometer, a vertical wooden poles connected with wooden gutters on the central axis functioned to fill water into a vessel until full to detect earthquakes. In AD 132 , Zhang Heng of China's Han dynasty

1479-508: A sense coil on the mass by the magnet directly measures the instantaneous velocity of the ground. The current to the drive coil provides a sensitive, accurate measurement of the force between the mass and frame, thus measuring directly the ground's acceleration (using f=ma where f=force, m=mass, a=acceleration). One of the continuing problems with sensitive vertical seismographs is the buoyancy of their masses. The uneven changes in pressure caused by wind blowing on an open window can easily change

1566-518: A special meeting in L'Aquila the week before the earthquake occurred, scientists and officials were more interested in pacifying the population than providing adequate information about earthquake risk and preparedness. In locations where a historical record exists it may be used to estimate the timing, location and magnitude of future seismic events. There are several interpretative factors to consider. The epicentres or foci and magnitudes of historical earthquakes are subject to interpretation meaning it

1653-499: A vacuum to reduce disturbances from air currents. Zollner described torsionally suspended horizontal pendulums as early as 1869, but developed them for gravimetry rather than seismometry. Early seismometers had an arrangement of levers on jeweled bearings, to scratch smoked glass or paper. Later, mirrors reflected a light beam to a direct-recording plate or roll of photographic paper. Briefly, some designs returned to mechanical movements to save money. In mid-twentieth-century systems,

1740-569: A very short time frame in a seismic cycle . Engineering seismology is the study and application of seismology for engineering purposes. It generally applied to the branch of seismology that deals with the assessment of the seismic hazard of a site or region for the purposes of earthquake engineering. It is, therefore, a link between earth science and civil engineering . There are two principal components of engineering seismology. Firstly, studying earthquake history (e.g. historical and instrumental catalogs of seismicity) and tectonics to assess

1827-574: Is paleoseismology . A recording of Earth motion as a function of time, created by a seismograph is called a seismogram . A seismologist is a scientist works in basic or applied seismology. Scholarly interest in earthquakes can be traced back to antiquity. Early speculations on the natural causes of earthquakes were included in the writings of Thales of Miletus ( c.  585 BCE ), Anaximenes of Miletus ( c.  550 BCE ), Aristotle ( c.  340 BCE ), and Zhang Heng (132 CE). In 132 CE, Zhang Heng of China's Han dynasty designed

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1914-574: Is a digital strong-motion seismometer, or accelerograph . The data from such an instrument is essential to understand how an earthquake affects man-made structures, through earthquake engineering . The recordings of such instruments are crucial for the assessment of seismic hazard , through engineering seismology . A strong-motion seismometer measures acceleration. This can be mathematically integrated later to give velocity and position. Strong-motion seismometers are not as sensitive to ground motions as teleseismic instruments but they stay on scale during

2001-889: Is a probable southern continuation of the Elsinore Fault Zone in Southern California . These faults are considered to be secondary cohorts of the San Andreas Fault , and as such share some of the strike-slip motion between the North American plate and the Pacific plate . This tectonics article is a stub . You can help Misplaced Pages by expanding it . Seismology Seismology ( / s aɪ z ˈ m ɒ l ə dʒ i , s aɪ s -/ ; from Ancient Greek σεισμός ( seismós ) meaning " earthquake " and -λογία ( -logía ) meaning "study of")

2088-440: Is an instrument that responds to ground displacement and shaking such as caused by quakes , volcanic eruptions , and explosions . They are usually combined with a timing device and a recording device to form a seismograph . The output of such a device—formerly recorded on paper (see picture) or film, now recorded and processed digitally—is a seismogram . Such data is used to locate and characterize earthquakes , and to study

2175-453: Is called seismometry , a branch of seismology . The concept of measuring the "shaking" of something means that the word "seismograph" might be used in a more general sense. For example, a monitoring station that tracks changes in electromagnetic noise affecting amateur radio waves presents an rf seismograph . And helioseismology studies the "quakes" on the Sun . The first seismometer

2262-538: Is called a seismograph . Networks of seismographs continuously record ground motions around the world to facilitate the monitoring and analysis of global earthquakes and other sources of seismic activity. Rapid location of earthquakes makes tsunami warnings possible because seismic waves travel considerably faster than tsunami waves. Seismometers also record signals from non-earthquake sources ranging from explosions (nuclear and chemical), to local noise from wind or anthropogenic activities, to incessant signals generated at

2349-451: Is less noisy and gives better records of some seismic waves. The foundation of a seismic station is critical. A professional station is sometimes mounted on bedrock . The best mountings may be in deep boreholes, which avoid thermal effects, ground noise and tilting from weather and tides. Other instruments are often mounted in insulated enclosures on small buried piers of unreinforced concrete. Reinforcing rods and aggregates would distort

2436-443: Is placed under the arm, and a small sheet of metal mounted on the underside of the arm drags in the oil to damp oscillations. The level of oil, position on the arm, and angle and size of sheet is adjusted until the damping is "critical", that is, almost having oscillation. The hinge is very low friction, often torsion wires, so the only friction is the internal friction of the wire. Small seismographs with low proof masses are placed in

2523-413: Is possible that 5–6 Mw earthquakes described in the historical record could be larger events occurring elsewhere that were felt moderately in the populated areas that produced written records. Documentation in the historic period may be sparse or incomplete, and not give a full picture of the geographic scope of an earthquake, or the historical record may only have earthquake records spanning a few centuries,

2610-550: Is said to have invented the first seismoscope (by the definition above), which was called Houfeng Didong Yi (translated as, "instrument for measuring the seasonal winds and the movements of the Earth"). The description we have, from the History of the Later Han Dynasty , says that it was a large bronze vessel, about 2 meters in diameter; at eight points around the top were dragon's heads holding bronze balls. When there

2697-573: Is the scientific study of earthquakes (or generally, quakes ) and the generation and propagation of elastic waves through the Earth or other planetary bodies . It also includes studies of earthquake environmental effects such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, glacial, fluvial , oceanic microseism , atmospheric, and artificial processes such as explosions and human activities . A related field that uses geology to infer information regarding past earthquakes

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2784-520: Is thought to refer to a pendulum, though it is not known exactly how this was linked to a mechanism that would open only one dragon's mouth. The first earthquake recorded by this seismoscope was supposedly "somewhere in the east". Days later, a rider from the east reported this earthquake. By the 13th century, seismographic devices existed in the Maragheh observatory (founded 1259) in Persia, though it

2871-439: Is unclear whether these were constructed independently or based on the first seismoscope. French physicist and priest Jean de Hautefeuille described a seismoscope in 1703, which used a bowl filled with mercury which would spill into one of eight receivers equally spaced around the bowl, though there is no evidence that he actually constructed the device. A mercury seismoscope was constructed in 1784 or 1785 by Atanasio Cavalli ,

2958-456: The Greek σεισμός, seismós , a shaking or quake, from the verb σείω, seíō , to shake; and μέτρον, métron , to measure, and was coined by David Milne-Home in 1841, to describe an instrument designed by Scottish physicist James David Forbes . Seismograph is another Greek term from seismós and γράφω, gráphō , to draw. It is often used to mean seismometer , though it is more applicable to

3045-454: The VAN method . Most seismologists do not believe that a system to provide timely warnings for individual earthquakes has yet been developed, and many believe that such a system would be unlikely to give useful warning of impending seismic events. However, more general forecasts routinely predict seismic hazard . Such forecasts estimate the probability of an earthquake of a particular size affecting

3132-445: The inertia to stay still within the frame . The result is that the stylus scratched a pattern corresponding with the Earth's movement. This type of strong-motion seismometer recorded upon a smoked glass (glass with carbon soot ). While not sensitive enough to detect distant earthquakes, this instrument could indicate the direction of the pressure waves and thus help find the epicenter of a local quake. Such instruments were useful in

3219-407: The internal structure of Earth . A simple seismometer, sensitive to up-down motions of the Earth, is like a weight hanging from a spring, both suspended from a frame that moves along with any motion detected. The relative motion between the weight (called the mass) and the frame provides a measurement of the vertical ground motion . A rotating drum is attached to the frame and a pen is attached to

3306-518: The "Moho discontinuity" or the " Moho ," it is the boundary between the Earth 's crust and the mantle . It is defined by the distinct change in velocity of seismological waves as they pass through changing densities of rock. In 1910, after studying the April 1906 San Francisco earthquake , Harry Fielding Reid put forward the " elastic rebound theory " which remains the foundation for modern tectonic studies. The development of this theory depended on

3393-423: The 1731 Puglia Earthquake, where the amplitude was detected using a protractor to measure the swinging motion. Benedictine monk Andrea Bina further developed this concept in 1751, having the pendulum create trace marks in sand under the mechanism, providing both magnitude and direction of motion. Neapolitan clockmaker Domenico Salsano produced a similar pendulum which recorded using a paintbrush in 1783, labelling it

3480-486: The analysis of the 1906 San Francisco earthquake . Further analysis was performed in the 1980s, using these early recordings, enabling a more precise determination of the initial fault break location in Marin county and its subsequent progression, mostly to the south. Later, professional suites of instruments for the worldwide standard seismographic network had one set of instruments tuned to oscillate at fifteen seconds, and

3567-489: The behaviour and causation of earthquakes. The earliest responses include work by John Bevis (1757) and John Michell (1761). Michell determined that earthquakes originate within the Earth and were waves of movement caused by "shifting masses of rock miles below the surface". In response to a series of earthquakes near Comrie in Scotland in 1839, a committee was formed in the United Kingdom in order to produce better detection methods for earthquakes. The outcome of this

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3654-542: The considerable progress of earlier independent streams of work on the behavior of elastic materials and in mathematics. An early scientific study of aftershocks from a destructive earthquake came after the January 1920 Xalapa earthquake . An 80 kg (180 lb) Wiechert seismograph was brought to the Mexican city of Xalapa by rail after the earthquake. The instrument was deployed to record its aftershocks. Data from

3741-561: The current available seismometers, still using the large 1842 Forbes device located in Comrie Parish Church, and requested a seismometer which was compact, easy to install and easy to read. In 1875 they settled on a large example of the Mallet device, consisting of an array of cylindrical pins of various sizes installed at right angles to each other on a sand bed, where larger earthquakes would knock down larger pins. This device

3828-402: The density of the air in a room enough to cause a vertical seismograph to show spurious signals. Therefore, most professional seismographs are sealed in rigid gas-tight enclosures. For example, this is why a common Streckeisen model has a thick glass base that must be glued to its pier without bubbles in the glue. It might seem logical to make the heavy magnet serve as a mass, but that subjects

3915-455: The device to begin recording, and then a recording surface would produce a graphical illustration of the tremors automatically (a seismogram). However, the instrument was not sensitive enough, and the first seismogram produced by the instrument was in 1887, by which time John Milne had already demonstrated his design in Japan . In 1880, the first horizontal pendulum seismometer was developed by

4002-512: The earth to a resolution of several hundred kilometers. This has enabled scientists to identify convection cells and other large-scale features such as the large low-shear-velocity provinces near the core–mantle boundary . Forecasting a probable timing, location, magnitude and other important features of a forthcoming seismic event is called earthquake prediction . Various attempts have been made by seismologists and others to create effective systems for precise earthquake predictions, including

4089-653: The earthquakes that could occur in a region and their characteristics and frequency of occurrence. Secondly, studying strong ground motions generated by earthquakes to assess the expected shaking from future earthquakes with similar characteristics. These strong ground motions could either be observations from accelerometers or seismometers or those simulated by computers using various techniques, which are then often used to develop ground motion prediction equations (or ground-motion models) [1] . Seismological instruments can generate large amounts of data. Systems for processing such data include: Seismometer A seismometer

4176-456: The first attempts at the scientific study of earthquakes followed the 1755 Lisbon earthquake. Other notable earthquakes that spurred major advancements in the science of seismology include the 1857 Basilicata earthquake , the 1906 San Francisco earthquake, the 1964 Alaska earthquake , the 2004 Sumatra-Andaman earthquake , and the 2011 Great East Japan earthquake . Seismic waves produced by explosions or vibrating controlled sources are one of

4263-425: The first horizontal pendulum was used in a seismometer, reported by Milne (though it is unclear if he was the original inventor). After these inventions, Robert Mallet published an 1848 paper where he suggested ideas for seismometer design, suggesting that such a device would need to register time, record amplitudes horizontally and vertically, and ascertain direction. His suggested design was funded, and construction

4350-586: The first known seismoscope . In the 17th century, Athanasius Kircher argued that earthquakes were caused by the movement of fire within a system of channels inside the Earth. Martin Lister (1638–1712) and Nicolas Lemery (1645–1715) proposed that earthquakes were caused by chemical explosions within the Earth. The Lisbon earthquake of 1755 , coinciding with the general flowering of science in Europe , set in motion intensified scientific attempts to understand

4437-414: The first modern seismometer. This produced the first effective measurement of horizontal motion. Gray would produce the first reliable method for recording vertical motion, which produced the first effective 3-axis recordings. An early special-purpose seismometer consisted of a large, stationary pendulum , with a stylus on the bottom. As the earth started to move, the heavy mass of the pendulum had

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4524-415: The first waves to appear on a seismogram as they are the fastest moving waves through solids. S-waves are transverse waves that move perpendicular to the direction of propagation. S-waves are slower than P-waves. Therefore, they appear later than P-waves on a seismogram. Fluids cannot support transverse elastic waves because of their low shear strength, so S-waves only travel in solids. Surface waves are

4611-477: The foundation of modern instrumental seismology and carried out seismological experiments using explosives. He is also responsible for coining the word "seismology." In 1889 Ernst von Rebeur-Paschwitz recorded the first teleseismic earthquake signal (an earthquake in Japan recorded at Pottsdam Germany). In 1897, Emil Wiechert 's theoretical calculations led him to conclude that the Earth's interior consists of

4698-455: The garden-gate described above. Vertical instruments use some kind of constant-force suspension, such as the LaCoste suspension. The LaCoste suspension uses a zero-length spring to provide a long period (high sensitivity). Some modern instruments use a "triaxial" or "Galperin" design , in which three identical motion sensors are set at the same angle to the vertical but 120 degrees apart on

4785-432: The global seismographic monitoring has been for the detection and study of nuclear testing . Because seismic waves commonly propagate efficiently as they interact with the internal structure of the Earth, they provide high-resolution noninvasive methods for studying the planet's interior. One of the earliest important discoveries (suggested by Richard Dixon Oldham in 1906 and definitively shown by Harold Jeffreys in 1926)

4872-634: The horizontal. Vertical and horizontal motions can be computed from the outputs of the three sensors. Seismometers unavoidably introduce some distortion into the signals they measure, but professionally designed systems have carefully characterized frequency transforms. Modern sensitivities come in three broad ranges: geophones , 50 to 750 V /m; local geologic seismographs, about 1,500 V/m; and teleseismographs, used for world survey, about 20,000 V/m. Instruments come in three main varieties: short period, long period and broadband. The short and long period measure velocity and are very sensitive, however they 'clip'

4959-406: The interior of the materials; surface waves that travel along surfaces or interfaces between materials; and normal modes , a form of standing wave. There are two types of body waves, pressure waves or primary waves (P-waves) and shear or secondary waves ( S waves ). P-waves are longitudinal waves that involve compression and expansion in the direction that the wave is moving and are always

5046-498: The light was reflected to a pair of differential electronic photosensors called a photomultiplier. The voltage generated in the photomultiplier was used to drive galvanometers which had a small mirror mounted on the axis. The moving reflected light beam would strike the surface of the turning drum, which was covered with photo-sensitive paper. The expense of developing photo-sensitive paper caused many seismic observatories to switch to ink or thermal-sensitive paper. After World War II,

5133-462: The mass is held nearly motionless relative to the frame by an electronic negative feedback loop . The motion of the mass relative to the frame is measured, and the feedback loop applies a magnetic or electrostatic force to keep the mass nearly motionless. The voltage needed to produce this force is the output of the seismometer, which is recorded digitally. In other systems the weight is allowed to move, and its motion produces an electrical charge in

5220-476: The next year, one being a common-pendulum seismometer and the other being the first seismometer using a damped horizontal pendulum. The innovative recording system allowed for a continuous record, the first to do so. The first seismogram was recorded on 3 November 1880 on both of Ewing's instruments. Modern seismometers would eventually descend from these designs. Milne has been referred to as the 'Father of modern seismology' and his seismograph design has been called

5307-481: The ocean floor and coasts induced by ocean waves (the global microseism ), to cryospheric events associated with large icebergs and glaciers. Above-ocean meteor strikes with energies as high as 4.2 × 10 J (equivalent to that released by an explosion of ten kilotons of TNT) have been recorded by seismographs, as have a number of industrial accidents and terrorist bombs and events (a field of study referred to as forensic seismology ). A major long-term motivation for

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5394-436: The ocean processes responsible for the global background seismic microseism . By the 1960s, Earth science had developed to the point where a comprehensive theory of the causation of seismic events and geodetic motions had come together in the now well-established theory of plate tectonics . Seismic waves are elastic waves that propagate in solid or fluid materials. They can be divided into body waves that travel through

5481-417: The older instruments in which the measuring and recording of ground motion were combined, than to modern systems, in which these functions are separated. Both types provide a continuous record of ground motion; this record distinguishes them from seismoscopes , which merely indicate that motion has occurred, perhaps with some simple measure of how large it was. The technical discipline concerning such devices

5568-407: The other at ninety seconds, each set measuring in three directions. Amateurs or observatories with limited means tuned their smaller, less sensitive instruments to ten seconds. The basic damped horizontal pendulum seismometer swings like the gate of a fence. A heavy weight is mounted on the point of a long (from 10 cm to several meters) triangle, hinged at its vertical edge. As the ground moves,

5655-442: The pier as the temperature changes. A site is always surveyed for ground noise with a temporary installation before pouring the pier and laying conduit. Originally, European seismographs were placed in a particular area after a destructive earthquake. Today, they are spread to provide appropriate coverage (in the case of weak-motion seismology ) or concentrated in high-risk regions ( strong-motion seismology ). The word derives from

5742-481: The primary methods of underground exploration in geophysics (in addition to many different electromagnetic methods such as induced polarization and magnetotellurics ). Controlled-source seismology has been used to map salt domes , anticlines and other geologic traps in petroleum -bearing rocks , faults , rock types, and long-buried giant meteor craters . For example, the Chicxulub Crater , which

5829-400: The result of P- and S-waves interacting with the surface of the Earth. These waves are dispersive , meaning that different frequencies have different velocities. The two main surface wave types are Rayleigh waves , which have both compressional and shear motions, and Love waves , which are purely shear. Rayleigh waves result from the interaction of P-waves and vertically polarized S-waves with

5916-400: The seismograph to errors when the Earth's magnetic field moves. This is also why seismograph's moving parts are constructed from a material that interacts minimally with magnetic fields. A seismograph is also sensitive to changes in temperature so many instruments are constructed from low expansion materials such as nonmagnetic invar . The hinges on a seismograph are usually patented, and by

6003-416: The seismograph would eventually determine that the mainshock was produced along a shallow crustal fault. In 1926, Harold Jeffreys was the first to claim, based on his study of earthquake waves, that below the mantle, the core of the Earth is liquid. In 1937, Inge Lehmann determined that within Earth's liquid outer core there is a solid inner core . In 1950, Michael S. Longuet-Higgins elucidated

6090-475: The seismometers developed by Milne, Ewing and Gray were adapted into the widely used Press-Ewing seismometer . Modern instruments use electronic sensors, amplifiers, and recording devices. Most are broadband covering a wide range of frequencies. Some seismometers can measure motions with frequencies from 500 Hz to 0.00118 Hz (1/500 = 0.002 seconds per cycle, to 1/0.00118 = 850 seconds per cycle). The mechanical suspension for horizontal instruments remains

6177-413: The signal or go off-scale for ground motion that is strong enough to be felt by people. A 24-bit analog-to-digital conversion channel is commonplace. Practical devices are linear to roughly one part per million. Delivered seismometers come with two styles of output: analog and digital. Analog seismographs require analog recording equipment, possibly including an analog-to-digital converter. The output of

6264-435: The strongest seismic shaking. Strong motion sensors are used for intensity meter applications. Accelerographs and geophones are often heavy cylindrical magnets with a spring-mounted coil inside. As the case moves, the coil tends to stay stationary, so the magnetic field cuts the wires, inducing current in the output wires. They receive frequencies from several hundred hertz down to 1 Hz. Some have electronic damping,

6351-476: The surface and can exist in any solid medium. Love waves are formed by horizontally polarized S-waves interacting with the surface, and can only exist if there is a change in the elastic properties with depth in a solid medium, which is always the case in seismological applications. Surface waves travel more slowly than P-waves and S-waves because they are the result of these waves traveling along indirect paths to interact with Earth's surface. Because they travel along

6438-399: The surface of the Earth, their energy decays less rapidly than body waves (1/distance vs. 1/distance ), and thus the shaking caused by surface waves is generally stronger than that of body waves, and the primary surface waves are often thus the largest signals on earthquake seismograms . Surface waves are strongly excited when their source is close to the surface, as in a shallow earthquake or

6525-612: The team of John Milne , James Alfred Ewing and Thomas Gray , who worked as foreign-government advisors in Japan, from 1880 to 1895. Milne, Ewing and Gray, all having been hired by the Meiji Government in the previous five years to assist Japan's modernization efforts, founded the Seismological Society of Japan in response to an Earthquake that took place on February 22, 1880, at Yokohama (Yokohama earthquake). Two instruments were constructed by Ewing over

6612-455: The time the patent has expired, the design has been improved. The most successful public domain designs use thin foil hinges in a clamp. Another issue is that the transfer function of a seismograph must be accurately characterized, so that its frequency response is known. This is often the crucial difference between professional and amateur instruments. Most are characterized on a variable frequency shaking table. Another type of seismometer

6699-516: The weight stays unmoving, swinging the "gate" on the hinge. The advantage of a horizontal pendulum is that it achieves very low frequencies of oscillation in a compact instrument. The "gate" is slightly tilted, so the weight tends to slowly return to a central position. The pendulum is adjusted (before the damping is installed) to oscillate once per three seconds, or once per thirty seconds. The general-purpose instruments of small stations or amateurs usually oscillate once per ten seconds. A pan of oil

6786-483: The weight, thus recording any ground motion in a seismogram . Any movement from the ground moves the frame. The mass tends not to move because of its inertia , and by measuring the movement between the frame and the mass, the motion of the ground can be determined. Early seismometers used optical levers or mechanical linkages to amplify the small motions involved, recording on soot-covered paper or photographic paper. Modern instruments use electronics. In some systems,

6873-546: Was an earthquake, one of the dragons' mouths would open and drop its ball into a bronze toad at the base, making a sound and supposedly showing the direction of the earthquake. On at least one occasion, probably at the time of a large earthquake in Gansu in AD 143, the seismoscope indicated an earthquake even though one was not felt. The available text says that inside the vessel was a central column that could move along eight tracks; this

6960-420: Was an inverted pendulum seismometer constructed by James David Forbes , first presented in a report by David Milne-Home in 1842, which recorded the measurements of seismic activity through the use of a pencil placed on paper above the pendulum. The designs provided did not prove effective, according to Milne's reports. It was Milne who coined the word seismometer in 1841, to describe this instrument. In 1843,

7047-528: Was attempted, but his final design did not fulfill his expectations and suffered from the same problems as the Forbes design, being inaccurate and not self-recording. Karl Kreil constructed a seismometer in Prague between 1848 and 1850, which used a point-suspended rigid cylindrical pendulum covered in paper, drawn upon by a fixed pencil. The cylinder was rotated every 24 hours, providing an approximate time for

7134-591: Was caused by an impact that has been implicated in the extinction of the dinosaurs , was localized to Central America by analyzing ejecta in the Cretaceous–Paleogene boundary , and then physically proven to exist using seismic maps from oil exploration . Seismometers are sensors that detect and record the motion of the Earth arising from elastic waves. Seismometers may be deployed at the Earth's surface, in shallow vaults, in boreholes, or underwater . A complete instrument package that records seismic signals

7221-423: Was constructed in 'Earthquake House' near Comrie, which can be considered the world's first purpose-built seismological observatory. As of 2013, no earthquake has been large enough to cause any of the cylinders to fall in either the original device or replicas. The first seismographs were invented in the 1870s and 1880s. The first seismograph was produced by Filippo Cecchi in around 1875. A seismoscope would trigger

7308-681: Was made in China during the 2nd century. It was invented by Zhang Heng , a Chinese mathematician and astronomer. The first Western description of the device comes from the French physicist and priest Jean de Hautefeuille in 1703. The modern seismometer was developed in the 19th century. Seismometers were placed on the Moon starting in 1969 as part of the Apollo Lunar Surface Experiments Package . In December 2018,

7395-409: Was that the outer core of the earth is liquid. Since S-waves do not pass through liquids, the liquid core causes a "shadow" on the side of the planet opposite the earthquake where no direct S-waves are observed. In addition, P-waves travel much slower through the outer core than the mantle. Processing readings from many seismometers using seismic tomography , seismologists have mapped the mantle of

7482-415: Was the production of one of the first modern seismometers by James David Forbes , first presented in a report by David Milne-Home in 1842. This seismometer was an inverted pendulum, which recorded the measurements of seismic activity through the use of a pencil placed on paper above the pendulum. The designs provided did not prove effective, according to Milne's reports. From 1857, Robert Mallet laid

7569-741: Was widely seen in Italy and abroad as being for failing to predict the earthquake and drew condemnation from the American Association for the Advancement of Science and the American Geophysical Union . However, the magazine also indicated that the population of Aquila do not consider the failure to predict the earthquake to be the reason for the indictment, but rather the alleged failure of the scientists to evaluate and communicate risk. The indictment claims that, at

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