GE391 Introduction to Geophysics
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 log10(A) versus log10(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 log10(A) versus log10(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.