Activity: A study of a seismogram                                                                               K 16-18

 

Subject: data (Analysis of a seismogram)                                                                              

 

Objectives: The amplitude, the frequency, the time and duration of an earthquake, can be determined on a seismogram from the various waves types, which come from ipocenter after the hit of an earthquake.

 

Key words:

Maximum amplitude of soil motion, lenght, frequency and principal phases. Local, regional and teleseismic event.

 

Disciplinary field: Earth Science, Physics

 

Procedure:

Different types of parameters can be exactly calculated from the various waves types recorded on the seismogram. Some examples of these parameters are: amplitude of soil motion, lenght, frequency and principal phases. These parameters allow to characterise the typology of an earthquake. The shape, lenght, maximum amplitude of soil motion and contents of frequency of a seismogram, changes with epicentral distance and magnitude of an earthquake.

 

Phase 1:

On a seismogram of a local earthquake, the students will determine the temporal defference between first arrivals of  P and S phase, maximum amplitude of soil motion, lenght of recording and contents of frequency. The parameters obtained are recorded in a table.

Phase 2:

Comment on the quantity measured

 

Remarks and developments:

To determine the principal phases, the amplitude, the lenght and the contents of frequency on a seismogram of a regional and of a teleseismic event. Remembering the classification of an event on the basis of the epicentral distance, the students can try to acquire the changes of the measured quantities for the three different events.

 

Document 1:

Determination of parameters characterised by a seismogram: principal phases, amplitude, lenght, contents of frequency. Working on a seismogram of a local earthquake.

Earthquake of 2001/03/05, Penisola Sorrentina: 01:09:00.0 GMT, magnitude 2.9 Md.

Considering the recording of  NAPI station which is 32 km from epicentral distance.

 

                                  

Individualisation of P and S phases and maximum amplitude         Lenght of recording

 

 

During every 7 second intervals, the number of cycles is 13 and the frequency is equal to 1.86 Hz.

 

 

The parameters obtained are recorded in a table

 

EARTHQUAKE

Ts-Tp 

FREQUENCY

AMPLITUDE 

LENGHT

Penisola Sorrentina

 5.93 s

 1.86 Hz

 62613.6

 88.05 s

 

Document 2:

The students determine the P and S phases, the lenght, the maximum amplitude of soil motion and contents of frequency for the Egeo and Alaska earthquakes to verify the changes of the parameters with the epicentral distance and magnitude.

The students will comment the results obteined.

Earthquake of 2001/07/26, Egean Sea:00:21:36.9 GMT, magnitude 6.0 mb (epicentral distance

879 km = 8°)

Earthquake of 2002/11/03, Alaska:22:12:41.0 GMT, magnitude 7.9 Mw (epicentral distance

7692 km = 69°)