Exploring Earth’s structure using Occam’s Razor
Prepared byMichael Hubenthal, IRIS Consortium
Adapted from Braile, 2000 & DLESE Teaching Boxes, 2008
How do you know what is inside?
What is inside ?
What is inside here?
Think, Write, Pair, Share
How do you know what is inside?
How do you know?
Occam’s Razor - All other things being equal, the simplest solution is the best
Based on your “evidence” what is beneath our feet?
Cal
vin
and
Hob
bes
by B
ill W
atte
rson
Why
are
mod
el im
port
ant i
n sc
ienc
e?
Could this help us test our model?
Theoreticians
Seismologist
Theoreticians
Seismologist
Earth’s surface
Center of the Earth
Scale model of a homogeneous Earth
140°
Seismologists
Theoreticians
Creating a travel-time plot
•Work in teams of ~ 2•Each pair calculates 3 travel times
•Each team makes 1 travel time plot, 0-180 degrees•Discuss results
Use velocity=11 km/sec, distance scale 320 km/cm
103040507080100115130150
Earthquake Wave First Arrivals
Distance From Epicenter (Deg)
Time (Min)
What is the cause of model and observations mismatch?
Shadow zone
Something changes beyond ~110 deg.
Combine results from multiple earthquakes
Assumptions?
?
What has your data established so far?
Have we found any layers?
1st: 1 deg - .5 min2nd: 16 deg - 3.5 min
First Arrivals
http://rev.seis.sc.edu/
Earth’s Interior Structure - Seismic Travel Times in a Constant Velocity Sphere
(L. Braile , December, 2000)
:http// . . . /~web ics purdue edu braile
R = 6371 km
Δ
/ 2
S / 2
Raypath
(chord of length S)
R = 6371 km
Earth’s
Surface
Source
Receiver
Copyright 2000. L. Braile. Permission granted for reproduction for non-commercial uses.
http://rev.seis.sc.edu/ > DLESE Teaching Boxes!
Updated Version
