Stat 120A: Dataset from a real study by On Lei Annie Kwok

Datafile: earthquake

How much acceleration is the ground shaking during an earthquake?

Seismologist and engineers are always interested to know the shaking level
of a site during an earthquake because they need to incorporate the earthquake 
shaking effect in the design of the structure that would be on top of the site.
Peak ground acceleration is often used to quantify this shaking effect. It is 
believed that the peak ground acceleration of a site may depend on the magnitude 
of striking earthquake, how far it is from the epicenter, earthquake 
mechanism (strike slip/reverse fault) and whether the site is soil site or rock
site. 

This dataset contains 907 observations. Each observation contains the information on
the peak ground acceleration (recorded by an accelerometer) of a site in an earthquake event 
(with a certain magnitude and an earthquake mechanism). The distance from the site 
to the epicenter and the site condition,(whether it is soil or rock), are also included.
 
This dataset was from my research group. We compiled these information from the database 
of the Pacific Earthquake Engineering Reserach center, maps and geology reports.

Variables:
"location"		location of the epicenter
"year"			year when earthquake happens
"m"			moment magnitude of the earthquake
"r"			closest distance from the site (accelerometer) to the epicenter, in km
"type"			site condition: r -- rock or s -- soil
"mech"			earthquake mechanism: ss -- strike slip or rev -- reverse
"PGA"			peak horizontal acceleration in unit of g (gravity)

Several seismologist and engineers did actually come up with a relationship that predicts PGA 
for a given m, r, type, mech and some other paramters that are not in this dataset. Their relationships
are different from each other because they have different methods on assigning weights to the data.
But in our study, we may just simply look at how PGA relates to different paramters and come up with
a relationship as what those seismologists and engineers did.