**GE391 Introduction to Geophysics**

**Homework**

**Due 9/29/2009**

Prof. Alan L. Kafka

Prof. John E. Ebel

1) Read the two
magnitude papers posted at the web site www2.bc.edu/~ebel/GE391.html.

2) Complete the experiment to analyze the amplitudes of
signals recorded on the Devlin BC-ESP instrument. The idea is to measure the
decay of amplitude with distance for jumping near the seismograph, and then to
develop a magnitude scale. You should see a certain amount of amplitude (let's
use maximum amplitude to recreate RichterÕs original magnitude scale idea), and
you know where the disturbance was (i.e., distance from the seismograph). Your goal is to calculate what the
magnitude of the ŌsourceĶ (jumping person) is. Some rough calibration points to
use are as follows: 10 students jumping is about a magnitude -1, and one
student jumping is about a magnitude -2.

3) Do an
analysis of the original data from RichterÕs 1935 (posted on EbelÕs class web
site—see item 1 above). For
each earthquake in Tables III and IV in RichterÕs paper, make a plot of log_{10}(A)
versus log_{10}(D). Then fit a line to the data for each
earthquake. Make a table of the
slopes and intercepts of all of the lines fit. How similar are the slopes for the lines? How well do the intercepts scale to the
average magnitudes for each earthquake in Table V of RichterÕs 1935 paper?

4) Take the
data in the accompanying plot and table and make a plots of log_{10}(A)
versus log_{10}(D). For A, use the maximum amplitudes shown
on the right of the figure for each station. If the last number of the exponent is cut off, assume it is
4. Do separate plots for the BHZ,
EHZ and HHZ data (each is a different kind of seismic instrument). Draw conclusions about whether or not
the amplitude data can be used to calculate a reliable event magnitude.