[Physics Class Notes] on Seismograph Pdf for Exam

The Seismograph

A seismograph, or seismometer is known as an instrument which is used to record and detect earthquakes. Generally we can say that it consists of a mass which is attached to a fixed base. Now during an earthquake the base moves and the mass does not. The motion of the base which is with respect to the mass is commonly said to be transformed into an electrical voltage. The electrical voltage which we are talking about is recorded on paper, and magnetic tape, or another recording medium. This record is said to be proportional to the motion of the seismometer mass relative to the earth.

But it can be mathematically also converted to a record of the absolute of the motion of the ground. The term or device seismograph generally refers to the seismometer and its recording device as a single unit.

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What is Seismograph

A seismometer is known as an instrument that responds to ground motions.

 Such as which is caused by earthquakes and the volcanic eruptions and explosions. The device that is seismometers are usually combined with a timing device and a recording device to form a seismograph. The output of such a device that is formally recorded on paper or we can say film.

Now recorded and processed digitally this is a seismogram. Such data which we have seen just above is used to locate and characterize earthquakes and to study the Earth’s internal structure as well.

The term seismograph is an instrument that generally makes a record of waves which is seismic and is caused by an explosion of the earthquake or other Earth-shaking phenomenon. The seismographs are said to be equipped with the electromagnetic sensors that generally translate the ground motions into charges which are electrical. Which are processed and generally recorded by the instruments’ that are digital or analog circuits. The terms seismograph and seismometer as well are often used interchangeably however we can say that  whereas both devices may detect and measure the waves which are seismic. Here we can say that only a seismograph possesses the capacity to record the phenomena. A record that is produced by a seismograph device on a display screen or the paper printout is known as a seismogram.

Although we can say that originally this was designed to locate natural earthquakes, the seismographs have many other uses as well such as petroleum exploration and investigation of planet earth’s crust and lower layers as well and monitoring of volcanic activity.

What is a Seismometer

An early instrument which was for seismic was known as the seismoscope made no time record of ground oscillations but simply indicated that shaking had occurred. A scholar who was from China named Zhang Heng. He invented such an instrument as early as 132 CE. It was said to be a cylindrical device in shape with eight dragon heads that were arranged around its upper circumference. That too with each ball in its mouth. Around the circumference were eight frogs which were each directly under a dragon head. When an earthquake occurred then at that time the balls were released from a dragon’s mouth which is probably by an internal pendulum that moved back and forth according to the direction of vibration. and along with that these were caught by a frog’s mouth which produced noise.

In 1855 an Italian scientist named Luigi Palmieri designed a seismograph that consisted of several tubes which were U-shaped and they were filled with mercury and oriented toward the different points of the compass. When the ground shook at that time the motion of the mercury made an electrical contact that stopped a clock and simultaneously it started a recording drum on which the motion of a float on the surface of mercury was registered. This device is thus said to indicate time of occurrence and the relative intensity and duration that is of the ground motion.

Seismograph Meaning

The word derives from the Greek which is denoted as: σεισμός, seismós. A shaking or quake that is from the verb σείω, seíō to shake and μέτρον métron that means to measure and was coined by sir David Milne-Home in 1841. This was to describe an instrument which is designed by Scottish physicist James David Forbes.

The instrument that is seismograph is another Greek term from seismós and γράφω, gráphō which means to draw. It is often used to mean seismometer though it is more applicable to the instruments which were older in which the measuring and recording of ground motion were combined. As compared to that of a modern system in which these functions are separated. Both types provide a record which is continuous of ground motion. This record which we are talking about distinguishes them from seismoscopes which merely indicate that motion has occurred. Perhaps we can say that with some simple measure of how large it was.

The technical discipline which is concerning such devices is known as seismometry, or a branch of seismology.

The concept that is of measuring the “shaking” of something means that the word “seismograph” might be used in a more general usage. For example we can say that a monitoring station that tracks changes in electromagnetic noise affecting amateur radio waves presents an rf seismograph. And Helioseismology studies the term “quakes” on the Sun.

The first seismometer was made in the country China during the 2nd century. The first Western description of the device comes from the physicist who was from French and priest Jean de Hautefeuille in 1703. The seismometer which was modern was developed in the late 19th century.

In December 2018, there was a seismometer which was deployed on the planet Mars by the InSight lander. It was the first time a seismometer was placed onto the surface of some other planet.

Today we can see that the most common recorder is a computer with an analog-to-digital converter. That is a disk drive and an internet connection for amateurs purpose of a PC with a sound card and associated software is adequate.