[8], The first seismometer was made in China during the 2nd century. The voltage generated in a sense coil on the mass by the magnet directly measures the instantaneous velocity of the ground. Fact Check: What Power Does the President Really Have Over State Governors? Briefly, some designs returned to mechanical movements to save money. Seismograph, instrument that makes a record of seismic waves caused by an earthquake, explosion, or other Earth-shaking phenomenon. A modern seismograph includes five basic parts: a clock, a sensor called a seismometer that measures intensity of shaking at the instrument's location, a recorder that traces a chart, or seismogram, of the seismic arrivals, an electronic amplifier, and a data recorder that stores the information for later analysis. The most successful public domain designs use thin foil hinges in a clamp. 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). Analog seismographs require analog recording equipment, possibly including an analog-to-digital converter. Be on the lookout for your Britannica newsletter to get trusted stories delivered right to your inbox. [2] A professional station is sometimes mounted on bedrock.
A new technique for detecting earthquakes has been found, using fiber optic cables.
The rotating drum shifted slightly with each revolution so that recorded lines were not superimposed on each other. A 24-bit analog-to-digital conversion channel is commonplace. A heavy weight is mounted on the point of a long (from 10 cm to several meters) triangle, hinged at its vertical edge. The Cecchi seismograph also used pendulums, but it was the first to record the relative motion of the pendulums with respect to Earth’s ground motions as a function of time. Analog seismographs require analog recording equipment, possibly including an analog-to-digital converter.
The short and long period measure velocity and are very sensitive, however they 'clip' the signal or go off-scale for ground motion that is strong enough to be felt by people. A pan of oil 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. Most instruments are characterized on a variable frequency shaking table. He was given the nickname Earthquake Milne and was considered the father of seismology. [9] The first Western description of the device comes from the French physicist and priest Jean de Hautefeuille in 1703. Seismograph, instrument that makes a record of seismic waves caused by an earthquake, explosion, or other Earth-shaking phenomenon.
This was found to match seismological observations of an Mw6.0 earthquake in Italy, ~1400 km away. Disclaimer 9. The word derives from 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. Seismic waves are detectable because they cause micrometer-scale changes in the length of the cable. In general, then, the seismograph is an instrument in which the relative motion of pendulum and ground is recorded. The seismograph has developed from being a heavy metal container which consisted of dragons, frogs and balls to show the direction of earthquakes to a seismograph which we have in the modern day on mobile phones as apps. Thus, there is no friction to affect the pendulum.
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.[5]. A "Develocorder" was a machine that record data from up to 20 channels into a 16-mm film. One is a seismometer, a device (like the seismoscope) that detects earth movements. By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. Schematic diagram of a strain seismograph. [9] The first Western description of the device comes from the French physicist and priest Jean de Hautefeuille in 1703. A single seismograph pendulum works in only one direction, and cannot give a complete picture of wave motions from other directions. Instruments come in three main varieties: short period, long period and broadband. Basically, the distance between the mass and some part of the frame is measured very precisely, by a linear variable differential transformer. Originally, European seismographs were placed in a particular area after a destructive earthquake. Briefly, some designs returned to mechanical movements to save money. The point of the cable first disturbed by an earthquake's p-wave (essentially a sound wave in rock) can be determined by sending packets in both directions in the looped pair of optical fibers; the difference in the arrival times of the first pair of perturbed packets indicates the distance along the cable. Networks of accelerographs are now operative in several earthquake regions (e.g., California, Japan, Taiwan, Mexico), offering continuous direct recording linked to computers and the Internet. The horizontal pendulum seismograph was improved greatly after World War II.
Exotic cross or two-dimensional arrays of geophones are sometimes used to perform three-dimensional reflective imaging of subsurface features. 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. ", Earthquake Locations Determined by the Southern Alaska Seismograph Network for October 1971 through May 1989, The Lehman amateur seismograph, from Scientific American, Sean Morrisey's professional design of an amateur teleseismograph, The Development Of Very-Broad-Band Seismography: Quanterra And The Iris Collaboration, https://en.wikipedia.org/w/index.php?title=Seismometer&oldid=987614782, Articles needing additional references from July 2014, All articles needing additional references, Articles with unsourced statements from November 2017, Articles with unsourced statements from July 2014, Creative Commons Attribution-ShareAlike License, This page was last edited on 8 November 2020, at 05:22.
Basically, the distance between the mass and some part of the frame is measured very precisely, by a linear variable differential transformer. The basic problem in measuring ground motions is to attain a steady point that remains fixed when the ground moves. 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. Seismometers unavoidably introduce some distortion into the signals they measure, but professionally designed systems have carefully characterized frequency transforms.
The recorded film can be viewed by a machine. This can be mathematically integrated later to give velocity and position. A rotating drum is attached to the frame and a pen is attached to the weight, thus recording any ground motion in a seismogram. Content Filtrations 6. The first true seismograph, according to Italian seismologists, was created in 1875 by Italian physicist Filippo Cecchi.
The paper drum anchored to the ground records the vibration as a stationary pen affixed to the weight traces the path of the relative motion. The difference between the p-wave/s-wave arrival times provides a distance (under ideal conditions), constraining the epicenter to a circle. Delivered seismometers come with two styles of output: analog and digital. The concept of measuring the "shaking" of something means that the word "seismograph" might be used in a more general sense.
The data from such an instrument is essential to understand how an earthquake affects man-made structures, through earthquake engineering. The recorded film can be viewed by a machine. Early seismometers had an arrangement of levers on jeweled bearings, to scratch smoked glass or paper. Seismometers spaced in a seismic array can also be used to precisely locate, in three dimensions, the source of an earthquake, using the time it takes for seismic waves to propagate away from the hypocenter, the initiating point of fault rupture (See also Earthquake location).
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