1. Filename: EarthQuake.xls
2. Problem: Modeling earthquake aftershocks
3. Nature of data:
4. Column Description
A
Date
B
Hrs
C
Minutes
D
Magnitude of earth quake as reported by India meteorology
department (IMD)
E
Magnitude of earth quake at epicentral distance  50 as reported
by United States Geological Survey (USGS) (mb)
F
Magnitude of earth quake at epicentral distance  150 as reported
by National Geophysical Research Institute (NGRI) (Ms)
G
Coda duration (seconds) at 1mm of background noise level
H
Coda duration (seconds) at 2mm of background noise level
I
Coda duration (seconds) at 6mm of background noise level
J
Coda duration (seconds) at 10mm of background noise level
5 Background: Seismology is the study of earthquakes. An earthquake creates
shock waves that travel from epicenter outwards. Like any waveform these waves have
two main features. One is amplitude and the other is period. Amplitude is the maximum
height from the x axis [or alternatively half of the distance between peak and trough]
while period is the distance along x axis between two successive peaks. Traditionally
magnitude of earthquakes is measured on Richter scale. Richter value refers to local
magnitude of energy released by an earthquake. Range of Richter scale is 0-9, highest
recorded so far being 8.9. These values are on a log scale. When the value goes up from 4
to 5 it means the energy released becomes 10 fold. Richter scale 5 means a ground
movement of about 1 mm at a distance of 10 km from the epicenter. The magnitude is
based on amplitude and period information of the seismic waves. These parameters are
difficult to measure because the signal becomes faint on a visible recording device. A
recent alternative method is based on coda duration. For minutes after the violent shaking
of an earthquake, the ground continues to rock imperceptibly. This is called seismic coda.
It shows as a long exponential tail in the output of a seismogram. Coda duration can be as
high as 2 or 3 minutes. This is more useful to estimate the magnitude of local
earthquakes. In an experiment, coda duration is measured at 4 different noise levels.
Large but infrequent earthquakes characterize Kachchh region in Gujrat state, India.
Bhuj area in Rann of Kachchh experienced a large, damaging earthquake on January 26,
2001. Its magnitude was 7.7 on Richter scale. Aftershock activity continued for more
than three years.
The column mb gives Richter magnitude using body wave measurements. The column
Ms gives Richter magnitude using duration of surface waves. The objective is to model
mb /Ms using coda duration as predictors. The specific question is which of the 4 series of
coda duration (at different background noise levels) gives best fitting model. Authors of
original paper use log transformation.
4. Suggested tools: Regression, data transformation.