Earthquake Seismograph
Earthquake Seismograph for Earthquake Instrumentation – This article is a summary of my practical work at BMKG Banda Aceh, Aceh Province, Indonesia.
The practical work I did on February 15 – March 15, 2015, gave me understanding of earthquake measurements. Earthquake Seismograph Writing As an Earthquake Instrumentation, I hope that it can add to our insight into earthquake measurement tools.
Let’s start from the Aceh provincial boundary.
The province of Aceh is an area located between 2º – 6º NL and 95º – 98º East.
The westernmost area of Indonesia is surrounded by territorial boundaries, namely the north bordering the Malacca Strait, the southern part bordering North Sumatra, the east bordering the Malacca Strait, and the west bordering the Indonesian Sea.
Aceh is an area that experienced the worst earthquake in 2004 accompanied by a tsunami. The resulting strength reached 9.3 on the Ricther scale, which killed at least 250,000 people in countries in Asia and Africa.
This happened due to the fault of the Sumatra fault that stretched from the Andaman Sea to South Sumatra. Aceh is located on the Indo-Australian plate and the Eurasian Plate and on the Mediterranean circum (Mulyatno, 2008).
The Indonesian archipelago is located between 6º NL to 11º E and 95º E to 141º E. Indonesia is located between two oceans and continents namely the Pacific Ocean and the Indian Ocean and the Continent of Asia and Australia.
Indonesia is a meeting area of 3 large tectonic plates, namely the Indo-Australian plate, Eurasian plate and the Pacific plate.
The Indo-Australian Plate collides with the Eurasian plate off the coast of Sumatra, Java and Nusatenggara, while with the Pacific in northern Irian and northern Maluku.
Around the location of this plate meeting the accumulation of collision energy is collected to a point where the earth’s layer is no longer able to hold the pile of energy so that it releases in the form of an earthquake (Erstayudha, 2009).
To be able to record and measure ground vibrations due to the earthquake continuously, so that the time of the earthquake, as well as knowing the strength of the earthquake and the location of the earthquake can be used an instrument that is Earthquake Seismograph.
History of BMKG Indonesian
The history of meteorological and geophysical observations in Indonesia began in 1841 beginning with observations made individually by Dr. Onnen, Head of the Hospital in Bogor.
Year by year its activities are developing in accordance with the increasing need for data from weather and geophysical observations.
In 1866, the individual observation activity by the Netherlands Indies Government was formalized as a government agency under the name Magnetisch en Meteorologisch Observatory or the Magnetic and Meteorological Observatory led by Dr. Bergsma.
In 1879 a total of 74 observation stations were built on the rain gauge. In 1902 observations of the earth’s magnetic field were moved from Jakarta to Bogor.
Earthquake observation began in 1908 with the installation of a horizontal component of the Wiechert Earthquake Seismograph in Jakarta, while the installation of a vertical component was carried out in 1928.
In 1912 a reorganization of meteorological observations was made by adding a secondary network. While meteorological services began to be used for lighting in 1930.
During the Japanese occupation between 1942 and 1945, the name of the meteorology and geophysics agency was changed to Kisho Kauso Kusho.
fter the proclamation of Indonesian independence in 1945, the agency was split into two: In Yogyakarta a Meteorological Bureau was formed within the Supreme Headquarters of the Indonesian People’s Army specifically to serve the interests of the Air Force.
In Jakarta the Bureau of Meteorology and Geophysics was formed, under the Ministry of Public Works and Energy. On July 21, 1947 the Meteorology and Geophysics Service was taken over by the Dutch Government and its name was changed to Meteorologisch en Geofisiche Dienst.
Meanwhile, there is also the Meteorology and Geophysics Office maintained by the Government of the Republic of Indonesia, the agency’s position on Jl. Gondangdia, Jakarta.
In 1949, after the surrender of the sovereignty of the Republic of Indonesia from the Netherlands, Meteorologisch en Geofisiche Dienst was changed to the Bureau of Meteorology and Geophysics under the Ministry of Transportation and Public Works.
Furthermore, in 1950 Indonesia officially entered as a member of the World Meteorological Organization (World Meteorological Organization or WMO) and the Head of the Meteorology and Geophysics Office became the Permanent Representative of Indonesia with WMO.
In 1955 the Meteorology and Geophysics Service was renamed the Meteorology and Geophysics Agency under the Department of Transportation, and in 1960 it was renamed the Meteorology and Geophysics Office under the Department of Air Transportation.
In 1965, the name was changed to the Directorate of Meteorology and Geophysics, his position remained under the Department of Air Transportation.
In 1972, the Directorate of Meteorology and Geophysics was renamed the Center for Meteorology and Geophysics, an echelon II institution under the Department of Transportation, and in 1980 its status was upgraded to an echelon I-level agency under the name Meteorology and Geophysics, with a permanent position in the under the Department of Transportation.
In 2002, with Presidential Decree No. 46 and 48 of 2002, the organizational structure was changed to Non-Departmental Government Institutions (LPND) with the permanent name Meteorology and Geophysics Agency.
Finally, through Presidential Regulation No. 61/2008, the Meteorology and Geophysics Agency was renamed the Badan Meteoroloi, Klimatologi and Geofisika (BMKG) with permanent status as Non-Departmental Government Institutions.
On October 1, 2009 Law of the Republic of Indonesia Number 31 of 2009 concerning Meteorology, Climatology and Geophysics was ratified by the President of the Republic of Indonesia, Susilo Bambang Yudhoyono.
History of BMKG Banda Aceh
The Banda Aceh Meteorology, Climatology and Geophysics Agency was established on 1979 which is located in the Mata Ie area, Darul Imarah sub-district, Aceh Besar.
The Mata Ie Banda Aceh Geophysics Station is one of the agencies within the Department of Transportation and is a Technical Implementation Unit (UPT) responsible to the head of the BMG Meteorology and Geophysics Agency which is a government agency whose task is one of which is to monitor earthquake and potential natural events the tsunami.
The geophysical station Mata Ie is located at Latitude 05º 29 ’16.6″ LU with Longitude 95º 17 “44.5” East.
Earthquake Causes
An earthquake is the shake of the earth caused by the sudden release of energy from the earth’s crust.
This energy comes from different sources, such as the breakdown or collision of the earth’s crust, volcanic eruptions, and events created by humans such as explosions or hollow underground debris, such as mining.
Earthquake events can be explained by the theory of tectonic scale enlargement processes, also said tectonic layers.
The layer is in the form of a large sheet of rigid rock that is stable with a thickness of about 100 km that moves together, forming a crust, also called the lithosphere layer and part of the upper mantle of the earth.
The earth’s crust is the outermost part of the earth’s rock layer with a complex internal geological structure and non-uniform thickness of 25-60 km under the continent and 4-6 km below the ocean.
In general, oceanic plates will infiltrate under continental plates, this is due to oceanic plates having a greater density than continental plates.
If the stress has become so great that it exceeds the strength of the earth’s crust, there will be a break in the earth’s crust in the weakest area.
The broken earth skin will release energy or voltage partially or completely to return to its original state. This event of energy release is called an earthquake.
Earthquakes occur along boundaries or associate with tectonic plate boundaries.
In fact the relative movement of the plates goes very slowly, almost equal to the speed of human nail growth (0-20 cm per year).
This results in friction at the plate meeting, which causes energy to accumulate before an earthquake occurs. Earthquake strength varies from place to place as time changes.
In Indonesia, the location of earthquake sources originated from Sumatra, Java, Bali, Nusa Tenggara, some turning north on Sulawesi, then from Nusa Tenggara some continuing east of Maluku and Irian.
Only the island of Kalimantan has relatively no source of earthquake except a little east.
The following figure is the boundary of tectonic plates that pass through Indonesia and are associated with earthquake sources.
a. Earthquake Source
The main cause of earthquakes is the movement of tectonic plates. If the plate moves, then around the plate boundary there will be a collection of energy, and if the rock layer has been unable to hold it, the energy will be released which causes a fault or deformation in the layer of the earth’s crust and there is a tectonic earthquake.
Besides that, due to the movement of the plates there was a fault (fault) in the upper layer of the earth’s crust which is the second generator of tectonic earthquakes.
There are 3 main tectonic plates and 1 small tectonic plate. The three main plates are the Indo-Australian, Eurasian, and Pacific plates, whereas the small plate is the Philippine plate.
b. Earthquake Parameters
To be able to determine the epicenter of an earthquake, there are several parameters used, namely:
- Origin Time:
Origin Time is the time an earthquake occurs at its source in the earth. - Epicenter [Latitude and Longitude]
A point or line on the surface of the earth that is perpendicular to the hypocenter. - Hypocenter [Depth (h)]
The source or place of tectonic, volcanic or ruins causing earthquakes. - Magnitude [Strength]
Magnitude is an earthquake parameter that is measured based on what happened in a certain area, due to earthquake shocks.
- The earthquake was very large with a magnitude greater than 8 SR.
- Large magnitude earthquake between 7 to 8 SR.
- The earthquake damaged the magnitude between 5 and 6 SR.
- The earthquake was magnitude between 4 to 5 SR.
- Small earthquake with a magnitude of 3 to 4 SR.
- Micro magnitude earthquake between 1 to 3 SR.
- An ultra micro earthquake with a magnitude smaller than 1 SR.
The level of damage that is felt at the location. This scale called MMI (Modified Mercalli Intensity) was introduced by Giuseppe Mercalli in 1902.
c. Seismic Waves
Seismic waves are energy propagation from the hypocentric (epicenter) to other places on earth.
There are two waves produced, namely primary wave (P) and secondary wave (S). Primary waves are waves which are the direction of movement or vibration of medium particles in the direction of the wave propagation.
This wave has the greatest propagation speed among other seismic waves. Secondary waves are waves whose direction of vibration is perpendicular to the direction of wave propagation.
These waves can only propagate in solid material only and have a smaller wave velocity than the primary wave.
d. Earthquake Strength Measurement
Measurement of earthquake strength using two methods, namely the Richter Scale and Mercalli Scale.
The Richter scale is a measure of the size of an earthquake’s strength, named after an American earthquake expert and physicist. is defined as the logarithm of the maximum amplitude measured in micrometers (um) from earthquake recordings by Wood-Anderson seismometer, at a distance of 100 km from the epicenter.
The Mercalli scale is a unit for measuring the strength of earthquakes created by volcanologists from Italy named Giuseppe Mercalli in 1902.
e. Earthquake Classification
- Tectonic earthquake
Tekntonik earthquake is an earthquake that occurs from the movement of plates or the earth’s crust. - Volcanic Earthquake
Volcanic earthquake is an earthquake caused by the movement or activity of magma in a volcano. - Earthquake Collapse
The earthquake or the earthquake is an earthquake that occurs because of the collapse of the soil or rocks - Falling Earthquake
A fall earthquake is an earthquake that occurs as a result of a meteor or rock falling to earth. This falling meteor will cause earth vibrations if the meteor mass is large enough. - Artificial Earthquake
An artificial earthquake is an earthquake that occurs due to human activities such as underground or sea nuclear detonation experiments which can cause earth vibrations.
f. Seismograph
What is a Earthquake Seismograph? Seismograph are instruments that can record vibrations from the earth. seismograph equipment a combination of seismometer and seismogram.
Seismometer is a sensitive instrument or also called a sensor that can detect the emission of waves from an earthquake vibration state.
A seismogram is a recording sheet consisting of recording paper or images from a computer in which there is data that is useful for calculating the location and magnitude of an earthquake.
Earthquake Seismograph were first introduced in 132 BC by mathematicians from the Han Dynasty named Zhang Heng, Earthquake seismograph china. This is based on the frequent occurrence of earthquakes in the capital city of Luoyang and the surrounding area. Based on history books, there have been 30 earthquakes in 50 years, from 89 to 140.
g. Seismogram Analysis
Earthquake analysis is carried out on seismogram paper. Measurement is determined by several parameters, namely the determination of primary waves, secondary waves, maximum amplitude, wavelength, magnitude.
Determination of primary waves
Primary waves are the first waves detected.
Secondary wave determination
Secondary waves seen from the end (shrinking) of the P wave and then suddenly increase dramatically. From this drastic increase in the S Wave point measurement point
Determine the maximum amplitude
This maximum amplitude is the height of the wave when measured from the reference point (midpoint).
Determination of wavelength (duration)
Determination of wavelengths starting from the beginning of the vibrations that produce P waves to the end of vibrations that occur in the S wave.
Wave magnitude (earthquake strength)
Showing the magnitude / strength of an earthquake can use the formula used by BMKG stations, is:
Next we wil learn about Principles of Analog earthquake seismograph machine, please read here.
I hope this article is useful.
