Earthquakes

 

      Primary waves

  The primary waves or P waves are one of two types of seismic waves. Their name derives from the fact that they have a greater propagation speed and because this they arrive before. They are longitudinal waves of compression and rarefaction that cause the variation of the volume of the medium in which they travel.

 

  Button enhances the effect of these waves.

 

 

 

 

 

      Secondary waves

  The secondary waves or S waves are one of two types of seismic waves. Their name derives from the fact that they have a lower propagation speed and because of this they arrive later. They are transverse waves that deform the medium in which they travel.

 

  Button enhances the effect of these waves.

 

 

 

 

 

      Love's waves

  Loves waves are seismic waves with a motion tangential to the ground. They attenuate as they go deeper. They are a combination of P waves and S waves.

 

 

 

 

 

      Rayleigh's waves

  Rayleigh's waves are systems of seismic superficial waves obtained with the superimposition of the primary and secondary waves. A particle involved in these waves describes an ellipse.

 

  Button enhances the effect of these waves.

 

 

 

 

 

      Oscillations of the Earth

  Because of its earthquakes the Earth can oscillate in different modes. In fact standing waves are created that make the Earth behave like a bell.

  In the simulation the oscillations have a very large amplitude. In reality they are detected only with very sensitive.

 

  The simulation shows two modes. The choice is made on the tool bar.

  Button allows a simulation with the rotating Earth.

  By clicking the button it is possible to start a new simulation with new features.

 

 

 

 

 

      Epicentre

  The program simulates the survey of the epicentre of an earthquake.

  The method is based on the fact that the primary waves P have a propagation speed about twice as great as that of the secondary waves S.

  Three stations of survey measure the delay with which the S waves arrive in respect to the P waves. For this, by knowing the propagation speed of the two types of waves, it is possible to calculate the distance of the epicentre. It should be on a circumference that has its centre in the station and its radius equal to the calculated distance . With two other stations it is possible to calculate two other circumferences that intersect the first one on the point corresponding to the epicentre.

  At the end of the simulation, in the tool bar, it is possible to see the data regarding the delays .

 

  Click button to have sound.

  With button it is possible to go to the page of the space-time graph at the end of the simulation.

  By clicking on button a segment parallel to the axis of time is drawn, that indicates the delay, that uniting the two curves. It starts from the position T = 0 and moves towards greater values of T. In coincidence with the measured values of , the corresponding distances are marked, so that we obtain the three radii.

  With button it is possible to see in succession the page of the simulation and that of the graphics.

  By clicking on button it is possible to start a new simulation with new features.

 

 

 

 

 

   Standing waves

 

  Standing waves are waves in which the propagation of energy does not occur, but then stand with a maximum in the points called antinodes and with a minimum in the points called nodes.

  Standing waves are obtained by the superimposition of two waves emitted by two sources that vibrate with the same frequency and that move in the opposite direction.

 

 

 

 

 

   Longitudinal waves

 

  It regards waves that vibrate in parallel with the direction of propagation.

 

 

 

 

 

   Transverse waves

 

  It regards waves that vibrate perpendicularly to the direction of propagation.

 

 

 

 

 

   Amplitude

 

  The amplitude of the oscillation represents the maximum displacement of the mobile from the centre of oscillation, i.e. from its equilibrium position.

 

 

 

 

 

   Frequency

 

  The frequency is the number of oscillation in the unit of time. It is measured in Hertz (Hz).