History of Seismology

  • 1800s: Cauchy, Possion, Stokes, Rayleigh and others developed the theory of elastic wave propagation, and described the existence of body wave (compressional and shear wave) and surface wave in solid materials.
  • 1857: Robert Mallet described the idea that earthquakes radiate seismic waves away from a hypocenter and that they can be located by projecting these waves backward to the source. His work represented the first significant attempt at observational seismology.
  • 1889: First teleseismic observation, made in Potsdam for a Japan event.
  • 1898: E. Wiechert introduced the first seismometer with viscous damping, capable of producing useful records for the entire duration of an earthquake.
  • 1900s: B. B. Galitzen developed the first electromagnetic seismographs.
  • 1900: Richard Oldham reported the identification of P, S, and surface waves on seismograms
  • 1906: Richard Oldham detected Earth’s core from the absence of direct P and S arrivals at source–receiver distances beyond about 100°.
  • 1909: Andrija Mohorovicic found Moho.
  • 1907: the first widely used traveltime tables were produced by Zo ̈ppritz
  • 1914: Beno Gutenberg published traveltime tableswith core phases
  • 1936: Inge Lehmann discovered the solid inner core
  • 1940: Harold Jeffreys and K. E. Bullen published the final version of their travel time tables for a large number of seismic phases, which is called JB table.
  • 1946: an underwater nuclear explosion near Bikini Atoll led to the first detailed seismic recordings of a nuclear bomb.
  • 1949: a Soviet nuclear bomb.
  • 1961: the Worldwide Standardized Seismograph Network (WWSSN) was established

Earth’s structure

  • Crust: 6 km under the oceans, 30–50 km beneath continents.
  • Mantle: 84% of Earth’s volume and 68% of the mass
  • Outer Core
  • Inner Core