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A seismometer is an instrument that records ground motion of the Earth’s surface. The ground motion can be described quantitatively as displacement, velocity or acceleration, which is a vector. Modern seismometers include three separate channels, which can record the simultaneous movement in three orthogonal directions. Usually, the three directions are North, East and vertical Upward. In real researches, we usually need to rotate the three-component data into RTZ coordinate system.
NEZ system
NEZ system
NEZ coordinate system is the most commonly used coordinate system
- N: north is positive, south is negative
- E: east is positive, west is negative
- Z: vertical upward is positive, vertical downward is negative
RTZ system
RTZ system
In real researches, we usually rotate the raw three component data from NEZ system to RTZ system. The RTZ system is a coordinate system defined by locations of events and stations, which varies for different event-station pairs.
Definition of RTZ system:
- R: Pointing from the seismic location to the station location
- Z: vertical upward
- T:perpendicular to the plane of Z and R direction. The choice of T direction makes the RTZ coordinate system a left-handed system.
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