![]() For a given earthquake, the intensity normally decreases with distance from the epicentre. Intensity is a qualitative measure of the strength of shaking caused by an earthquake determined from the observed effects on people, objects and buildings. Measurement of the severity of an earthquake can be expressed in several ways, but the two most common scales used by seismologists are intensity and magnitude. The earthquake occurred at the point where all three circles intersect. Draw a circle around each station with a radius equal to its distance from the earthquake. Once we know the distance to an earthquake from three seismic stations, we can determine the location of the earthquake. Imagine A, B and C are three different seismometer stations at distant locations. Appearance and particle motion are similar to water waves. Rayleigh waves are also dispersive and the amplitudes generally decrease with depth in the Earth. VR 2.0–4.5 km/s in the Earth depending on frequency of the propagating wave. Motion is both in the direction of propagation and perpendicular (in a vertical plane). Depth of penetration of the Love waves is also dependent on frequency, with lower frequencies penetrating to greater depth. Love waves are dispersive, that is, the wave velocity is dependent on frequency, with low frequencies normally propagating at higher velocity. They are largest at the surface and decrease in amplitude with depth. Love waves exist because of the Earth’s surface. VL 2.0–4.5 km/s in the Earth depending on frequency of the propagating wave. Transverse horizontal motion, perpendicular to the direction of propagation and generally parallel to the Earth’s surface. S-waves travel slower than P-waves in a solid and, therefore, arrive after the P-wave. S-waves do not travel through fluids, so do not exist in Earth’s liquid outer core or in air, water or molten rock (magma). P-waves in a liquid or gas are pressure waves, including sound waves.Īlternating transverse motions perpendicular to the direction of propagation.Ĥ.5 km/s in Earth’s mantle 2.5–3.0 km/s in (solid) inner core. Generally smaller and higher frequency than the S and surface waves. P motion travels fastest in materials, so the P-wave is the first energy to arrive on a seismogram. >8 km/s in Earth’s mantle and core 1.5 km/s in water 0.3 km/s in air. ![]() The ground motions from surface waves are often much larger than those motions from body waves.Īlternating compressions (‘pushes’) and dilations (‘pulls’) in the same direction as the wave is propagating. Rayleigh waves are generated by the interaction of P- and S-waves at the surface of the Earth, while Love waves are generated by interference of multiple shear waves. There are two types of surface waves: Rayleigh waves and Love waves. Where a free surface is present (like the Earth/air interface) these two types of motion can combine to form surface waves, which produce a type of shaking that causes buildings to fail and fall down. The S stands for shear or secondary since they are slower than P-waves. S-waves are transverse waves, whose motion is perpendicular to the direction of travel. The P stands for primary because they travel the fastest. P-waves are longitudinal waves that consist of a series of compressions and dilations along the direction of travel. There are two basic types of seismic wave that travel through the body of the Earth: P-waves and S-waves. Z (red) measures up/down motion E (green) measures east/west motion N (blue) measures north/south motion. What are we doing about climate change?Ī three-component seismometer. ![]() Understanding carbon capture and storage.What causes the Earth’s climate to change?.NGR hydrocarbons (well samples) database.Palaeontology and biostratigraphy collections.Donations and loans of materials collections.Engineering and Geotechnical Capability.Integrated resource management in Eastern Africa.Rock Volume Characterisation Laboratory Cluster.Fluid and Rock Processes Laboratory Cluster.Equality, diversity and inclusion at BGS.Environmental policy and sustainability strategy.
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