See the sources of earthquakes, the wave propagation of earthquakes up to the recording waveform is a process that is learned by people Seismology. Seismology science including science relatively young, new development began in 1660 when Hooke discovered a relationship between the voltage of the strain that will be related to the wave propagation of earthquakes in the earth. California earthquake insurance on this occasion I do not want to discuss about the history of seismology, seismic sources and seismic wave propagation, but I want to say little about the recording process using seismometer wave sensor which has three components.
The development tool seismometer first one started in 1875 when Filippo Cecchi find a way of recording earthquake waves using a pendulum without damping over time. Subsequent developments in 1898 when E. Wiechert seismometer tool wear develop damping viscous and can record the entire duration of the earthquake (Afnimar, 2009). Currently, the development tool truly extraordinary seismometers, all seismometers now using tools and digital systems (Afnimar, 2009).
As I said in writing benefits for the people of earthquake waves and benefits of earthquake waves for tomography . When an earthquake occurs, will appear wave body wave (body wave) wave form P (primary / pressure) and Wave S (secondary / shear) Horizontal Vertical SH and SV. Wave Interference The agency will produce the form of surface waves Love waves and Reyleigh.
Body P wave propagates as a longitudinal wave or pressure wave, the direction of movement of the particles of soil / rock as a result of this wave in the direction of wave propagation gempannya. S Body wave propagates as a transverse wave or waves of string where the direction of movement of particles of soil / rock perpendicular to the direction of propagation of earthquake waves. S wave is divided into two waves S Horizontal (SH) which terletah on the horizontal plane and S wave vertical (SV) located in the vertical plane. SH and SV wave is moving simultaneously but both of these waves are slower than P waves
Love surface waves generated due to the reflected SH wave interference, so the direction of the particle and wave in the horizontal direction perpendicular to the direction of wave propagation (similar to the SH wave). The second surface wave is Reyleigh waves, these waves are formed due to the interference reflected wave P and SV, in the form of an ellipse partikelny motion for a combination between the direction of motion of a particle wave P and SV.
On recording seismometer sensor 3 Components
Seismometer 3 component is a seismometer which has 3 sensors and can record seismic wave waves coming from different directions. Component seismometer sensors on three components include:
- Sensor Components of Vertical Up – Down (Up-down, UD); These sensors record seismic waves which direction the particles move in an upward direction under.
- Sensor Components Horizontal North – South (North-South, NS); These sensors record seismic waves which direction the particles move in the direction of the North – South or its representative in this direction.
- Sensor components Horizontal East – West (East – West, EW); These sensors record seismic waves which direction the particles move in the direction of East – West or its representative in this direction.
When the earthquake wave P, SH, SV, Love and Reyleigh seismometer 3 components, not all components will detect the seismic waves. Detected least earthquake waves depend on the direction (azimuth) of the arrival of seismic waves. Some of the pictures below that I took from the book written by Afnimar Seismology, Ph.D. (lecturer ITB) can help us to understand the process of recording of earthquake waves at seismometers 3 on the sensor components and which components would be recorded earthquake waves when an earthquake happening somewhere.
In addition to all three of these components, known components of radial and transverse components. Radial component is a horizontal component in the direction of wave propagation and the transverse component is a horizontal component perpendicular to the direction of wave propagation. The 3 components seismometer tool installed in earthquake observation stations such as BMKG Stations Mata Ie, Banda Aceh as in the picture on the side.
In Figure 1 above can be seen bottom seismic waves heading to station observers from 45º angle from the north, the angle of the wave of the monitoring stations often also called the angle of back azimuth . P wave particle motion that comes with the “forward-backward” will be recorded at the sensor component – North South, East – West and Top – Bottom. But if the wave is coming out of the corner 90º (east), then the P waves are only recorded on the sensor component the East – West, Up – Down and is not recorded on the sensor component – North South due to the direction of motion of particles as a result of the P wave in the direction of wave propagation.
SV wave has a top particle movement under the direction of propagation as shown in Figure 2, are recorded on the same components as the P wave, which is recorded on the sensor component of the North-South, East-West and Up-Down. If the angle of attack that the earthquake was 90º (east) then recorded also equal to the P wave
SH wave propagation shown in Figure 3, the direction of movement of the particles left-right direction of wave propagation are recorded on the sensor component of the North-South and East-West and is not recorded on the Up-Down sensor components. However, if the direction of the waves coming from the 90º (east) then the SH wave sensor component only recorded on the North-South.
Love surface wave which propagates on the surface has the same direction of motion of a particle with SH wave that is the left-right direction of wave propagation. A wave of love as the image sensor 4 will be recorded on the North-South component and the East-West and is not recorded on the Up-Down sensor components. If gelompang love coming from the east, then it’s just a love wave sensor component recorded on the North-South.
Reyleigh surface wave which is a merging between P waves with wave SV so that the direction of movement of the particles back and forth and up and down and moving elliptic. These waves are recorded on the sensor component of the North-South, East-West and Up-Down. However, if this Reyleigh wave coming from 90º (east) are recorded on the sensor component of the East-West and Up-Down.
Examples of recording results using three component seismometer sensor can be seen in the image below. The picture I took from www.iris.edu but I did not get any information from which direction the arrival of seismic waves.