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Jan 1, 2021 · Seismogram interpretation, described in this article, is essentially devoted to the art of identification of various seismic “arrivals” or wave types visible on seismograms.
Mar 22, 2018 · ‘Seismology and the Earth’s internal structure’ explains compressional and shear elastic deformation and the four types of seismic waves caused by earthquakes: P-waves and S-waves that travel through the body of the Earth, and Rayleigh and Love waves that spread out at and near the Earth’s surface.
- Overview
- Applications of the seismograph
A seismograph records oscillation of the ground caused by seismic waves that travel from their point of origin through Earth or along its surface. The seismogram of a nearby small earthquake has a simple pattern, showing the arrival of P waves (longitudinal waves, which vibrate in the direction of propagation), S waves (transverse waves—that is, waves that vibrate at right angles to the direction of propagation), and surface waves (compression waves with no vertical or longitudinal components). In the case of distant earthquakes or of nearby very large earthquakes, the seismogram pattern is more complicated because it shows various sorts of seismic waves that originate from one or many points but then may be reflected or refracted within Earth’s crust before reaching the seismograph. The relation between the arrival time of the P and S waves and the epicentral distance—i.e., the distance from the point of origin—is expressed by a time-distance curve, in which the arrival time is read on the vertical axis and the epicentral distance on the horizontal axis. If the arrival times of various seismic waves are read on the seismogram at a station and compared with the standard time-distance curves, the epicentral distance from that station (the distance of the centre of the earthquake from the recording station) can be determined. If the epicentral distance from at least three stations is known, the origin of the earthquake can be calculated by simple trigonometric methods.
The eruption of a volcano is commonly accompanied by many small earthquakes, especially when a volcano resumes activity after a long dormant period. Observation with sensitive seismographs therefore plays an important role in predicting volcanic activity.
Often a strong earthquake is preceded by small earthquakes. Observation of very small tremors with sensitive seismographs is helpful in predicting disastrous earthquakes.
Seismographs sometimes detect small and long-continuing oscillations of the ground, called microseisms, that do not originate as earthquakes. The occurrence of some microseisms is related to storms at sea.
Britannica Quiz
The Solid Earth Quiz
A seismograph records oscillation of the ground caused by seismic waves that travel from their point of origin through Earth or along its surface. The seismogram of a nearby small earthquake has a simple pattern, showing the arrival of P waves (longitudinal waves, which vibrate in the direction of propagation), S waves (transverse waves—that is, waves that vibrate at right angles to the direction of propagation), and surface waves (compression waves with no vertical or longitudinal components). In the case of distant earthquakes or of nearby very large earthquakes, the seismogram pattern is more complicated because it shows various sorts of seismic waves that originate from one or many points but then may be reflected or refracted within Earth’s crust before reaching the seismograph. The relation between the arrival time of the P and S waves and the epicentral distance—i.e., the distance from the point of origin—is expressed by a time-distance curve, in which the arrival time is read on the vertical axis and the epicentral distance on the horizontal axis. If the arrival times of various seismic waves are read on the seismogram at a station and compared with the standard time-distance curves, the epicentral distance from that station (the distance of the centre of the earthquake from the recording station) can be determined. If the epicentral distance from at least three stations is known, the origin of the earthquake can be calculated by simple trigonometric methods.
The eruption of a volcano is commonly accompanied by many small earthquakes, especially when a volcano resumes activity after a long dormant period. Observation with sensitive seismographs therefore plays an important role in predicting volcanic activity.
Often a strong earthquake is preceded by small earthquakes. Observation of very small tremors with sensitive seismographs is helpful in predicting disastrous earthquakes.
Seismographs sometimes detect small and long-continuing oscillations of the ground, called microseisms, that do not originate as earthquakes. The occurrence of some microseisms is related to storms at sea.
Britannica Quiz
The Solid Earth Quiz
- The Editors of Encyclopaedia Britannica
A seismograph is a device for measuring the movement of the earth, and consists of a ground-motion detection sensor, called a seismometer, coupled with a recording system. A simple seismometer that is sensitive to up-down motions of the earth can be understood by visualizing a weight hanging on a spring.
Aug 14, 2024 · seismograph, instrument that makes a record of seismic waves caused by an earthquake, explosion, or other Earth -shaking phenomenon. Seismographs are equipped with electromagnetic sensors that translate ground motions into electrical changes, which are processed and recorded by the instruments’ analog or digital circuits.
- The Editors of Encyclopaedia Britannica
Jan 1, 1995 · Seismograms are a complicated mixture of source radiation effects, such as the spectral content and relative amplitude of the primary- and secondary-wave energy that is generated at the source, propagation phenomena, such as multiple arrivals produced by reflection and transmission at seismic impedance boundaries or at the surface, and frequency...
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Mar 5, 2013 · An hypothesis about some feature of a seismogram could be tested by setting up the appropriate model and comparing the synthetic seismogram with the observed one. Synthesizing seismograms can also be used to explore the effects of variation in source and Earth models to answer the question ‘What would be the effect of…?’.
