Records of Earthquakes

shows some exemplary records of the seismic waves that reached the Saudi Geological Survey from the seismic locations at different distances from the seismograph stations. The three vertical and horizontal components are shown (E, N, Z beside the name of the station). The earthquake may be classified as local, regional, or international, depending on the distance of the epicenter and the seismograph station. When the distance between the epicenter and the station increases, the recorded wavelengths tend to have the lowest frequencies or the longest times of arrivals as the high frequencies become weak and faster in their travel through the crust. The first wave to reach the seismograph is the direct P wave or the compressional wave, followed by the shear or S-waves. The waves may be reflected or refracted in the borders between the different Earth layers, such as the Moho layer, the boundary layer of the mantle and the upper crust. Accordingly, the seismic location can be determined from the time of arrival of these waves. The structures of the crust can also be determined in a more detailed manner by using seismic data from all over the world.

Records of seismic data in the two seismograph stations of the Saudi Geological Survey for a local earthquake in the east of the Kingdom.

Records of seismic data in 7 seismograph stations of the Saudi Geological Survey for a regional earthquake in the south of Iran.

Records of seismic data in 3 seismograph stations of the Saudi Geological Survey for an earthquake in Indonesia.

Recording of a seismograph station for a local earthquake in Harrat Lunayyir. For this 1.8 magnitude earthquake, the first wave to reach the seismograph was the P wave followed by the slower S wave after 6 seconds.