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Quakefinder- A seismologist
What is a seismologist?
A seismologist is a person who's job is to estimate the location of a jerk in the earths surface.He examines the data recorded by scientific instruments and after some calculations he can tell as when and where an earthquake happened on the earth planet and what was the amount of energy released. However, unlike a meteorologist (weather forecaster) he is often unable to predict precisely about an earthquake
A seismologist can also determine through analysis of ground vibration recording what is going on below the earth's surface and what kind of specific structure the crust has at a specific location. He possesses profound knowledge about earth's structure and phenomena going on inside earth.
What device a seismologist uses to record vibrations ?
The device a seismologist uses to record the ground vibrations is called seismometer. In earlier times the seismometer simply used the inertia property of mass to record the ground movements.
A simple seismometer consists of a heavy mass suspended from a spring hinged vertically from the upper side of a frame - wooden or metallic. A pen to drag or line out the motion of ground on a rotating paper role is attached with the heavy mass. As the ground moves, the heavy mass tends to remain at its current position of rest - as per law of inertia or first law of motion. Paper role in the mean while shifts to a new position of transition from under the pen and a sketch is drawn -- which shows the motion of ground relative to the heavy mass. This process goes on to and fro and in this way a pattern - called seismogram - for whole duration of an earthquake is recorded. The seismologist then removes that paper and keep it as record.
A seismologist and modern day technology
Over time, technology has improved. Nowadays, a seismologist uses a seismometer consisting of electric and electronic equipment - Which consists of a sensor, a recording system, and a screen i-e a computer LCD or else. The main component of a modern-day seismometer is an electronic sensor. An electronic sensor, when operational, is very sensitive to the ground's slightest vibrations. It can be imagined that if you walk near an operational sensor, the vibrations produced by your foot steps are recorded by it, which can be observed on the screen of a computer.
Working of electronic seismic sensor
An electronic seismic sensor is generally cylindrically shaped. To put it simply, - it has three sensitive spring coils of some specific elastic constant ( fixed as per requirement) erected in three dimensional arena . An electric current is passed through these three coils in three dimension i-e x, y &z directions, and in this way an electromagnetic field is developed around each of the coils.Three dimensional erection of coils is to record motion of ground in three directions - because when an earthquake happens, the ground motion occurs in three dimensions. So, when sensor lying on the ground is disturbed by ground motion(s), the orientation of electromagnetic field in respective direction is disturbed (changed) as well, which is then recorded by the digitizer and can be observed as wave pattern on the LCD.
Seismologists usually put seismic sensors in a vault- This is because surrounding ambient noise and air pressure can be disturbing and hence can decrease the quality of data being recorded.
How does wave recording looks?
Ambient noise and continuous convectional currents disturbance (present every where almost) is recorded as continuous wave pattern. but when an earthquake happens, the patterns changes to a specific shape -- showing an earthquake (figs 5 & 6)
What does a seismologist do at the time of an earthquake?
As soon as an earthquake happens, the present-day state-of-the-art seismic software records all the parameters (like location co-ordinates for epicenter, depth of epicenter, magnitude of the earthquake etc) automatically in very short time.
But if seismologist is doubtful for any value of a parameter- he may go for manual analysis. Or sometimes a software takes longer time for calculations of parameters - the same can be calculated manually for time saving purpose - without waiting for auto analysis. Generally, seismologist takes P-wave time and S-wave time from the seismogram ( for different stations). Difference of P and S wave time and seismic wave velocity can then be multiplied to estimate the origin distance from the recording station(i-e using S=t*v formula). This process is done for each station where seismic waves are recorded.Graph-drawing for these distances then gives a coinciding point for each distance line--- which is the location of epicenter. But this is usually just in practice. Nowadays, a seismologist picks P and S waves over the software which calculates parameters quickly.
The author is thankful to all the sources used for writing this article.