Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would...
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![Page 1: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/1.jpg)
![Page 2: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/2.jpg)
Modern seismometer
![Page 3: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/3.jpg)
If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder.
east-west
north-south
up-down
Three components of motion can be measured
![Page 4: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/4.jpg)
Station 1
Station 2
Station 4
Station 5
Station 3
![Page 5: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/5.jpg)
Different kinds of waves exist within solid materials
Body waves – propagate throughout a solid medium
![Page 6: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/6.jpg)
![Page 7: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/7.jpg)
![Page 8: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/8.jpg)
Compressional Waves
in one- and two-dimensions
![Page 9: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/9.jpg)
Shear waves
in one- and two- dimensions
![Page 10: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/10.jpg)
€
Vs =μ
ρ
Vp =κ +
4
3μ
ρ
Shear velocity
Compressional velocity
= shear modulus = shear stress / shear strain (restoring force to shear)k = bulk modulus = 1/compressibility (restoring force to compression)
Different types of waves have different speeds
P-waves travel faster than S-waves (and both travel faster than surface waves)
(just like waves on a string)
(a bit like a slinky)
![Page 11: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/11.jpg)
P-waves get there first…
![Page 12: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/12.jpg)
Rayleigh
Love
As well as body waves, there are surface waves that propagate along a surface
![Page 13: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/13.jpg)
![Page 14: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/14.jpg)
![Page 15: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/15.jpg)
Different kinds of damage….
P-wave
S-wave
Sfc-wave
All
![Page 16: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/16.jpg)
P-wavearrival
S-wavearrival
![Page 17: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/17.jpg)
= Hypocenter
Difference between P-wave and S-wave arrival can be used to locatethe location of an earthquake more effectively…
![Page 18: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/18.jpg)
Difference between p- and s-waves can be used to track location
![Page 19: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/19.jpg)
Need 3 stations to isolate location (and the more the better)
![Page 20: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/20.jpg)
The “first-motion” of the earthquake signal has information about the motion on the fault that generated it.
east-west
north-south
up-down
The sense of motion can be used to infer the motion that caused it.
![Page 21: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/21.jpg)
The orientation of faults can be determined from seismic networks
![Page 22: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/22.jpg)
The orientation of faults can be determined from seismic networks
![Page 23: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/23.jpg)
Go to board for Snell’s law
![Page 24: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/24.jpg)
FAST
FAST
SLOW
SLOW
Back to Snell’s LawAny change in wave speed due to composition change with heightwill cause refraction of rays….
This one applies to the crust
![Page 25: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/25.jpg)
![Page 26: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/26.jpg)
![Page 27: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/27.jpg)
![Page 28: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/28.jpg)
![Page 29: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/29.jpg)
![Page 30: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/30.jpg)
Do this on the board
![Page 31: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/31.jpg)
Seismology can be used to infer the structure of the interior of the Earth
![Page 32: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/32.jpg)
First, recall that wave paths are curved within the Earth due to refraction.
![Page 33: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/33.jpg)
If the Earth werehomogenous in composition…
![Page 34: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/34.jpg)
aesthenosphere
crust
coremesosphere
But seismic velocities show great variety of structure
moho
![Page 35: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/35.jpg)
S waves cannot propagate through the core, leading to a huge shadow zone
S waves cannot propagate in a fluid (fluids cannot support shear stresses)
![Page 36: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/36.jpg)
Shadow zones for P-waves existbut less b/c propagation throughthe core
![Page 37: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/37.jpg)
Animation of P wave rays
![Page 38: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/38.jpg)
Animation of P wave fronts
![Page 39: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/39.jpg)
The pathways from any given source are constrained…
![Page 40: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/40.jpg)
Seismic “phases” are named according to their paths
P – P wave only in the mantle
PP – P wave reflected off earths surface so there are two P wave segments in the mantle
pP – P wave that travels upward from a deep earthquake, reflects off the surface and then has a single segment in the mantle
PKP – P wave that has two segments in the mantle separated by a segment in the core
![Page 41: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/41.jpg)
![Page 42: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/42.jpg)
Ray path examples…
![Page 43: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/43.jpg)
Ray path examples…
![Page 44: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/44.jpg)
Can be identified from individual seismograms (just about)
![Page 45: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/45.jpg)
![Page 46: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/46.jpg)
![Page 47: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/47.jpg)
![Page 48: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/48.jpg)
![Page 49: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/49.jpg)
What do we know about the interior composition of the Earth?
![Page 50: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/50.jpg)
What do we know about the interior composition of the Earth?
![Page 51: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/51.jpg)
What do we know about the interior composition of the Earth?
![Page 52: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/52.jpg)
What do we know about the interior composition of the Earth?
![Page 53: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/53.jpg)
![Page 54: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/54.jpg)
![Page 55: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/55.jpg)
How does seismology help?
![Page 56: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/56.jpg)
How does seismology help?
![Page 57: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/57.jpg)
How does seismology help?
![Page 58: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/58.jpg)
How does seismology help?
![Page 59: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/59.jpg)
![Page 60: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/60.jpg)
Velocity beneathHawaii…
![Page 61: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/61.jpg)
Beneath subduction zones
Note the occurrence of deep earthquakes co-located with the down-going slab
![Page 62: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/62.jpg)
Beneath subduction zones
![Page 63: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/63.jpg)
![Page 64: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/64.jpg)
Earthquake number by Richter Scale – variations over time?
![Page 65: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/65.jpg)
Earthquakes are bad for you….
![Page 66: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/66.jpg)
Earthquakes are dangerous
Bam, Iran, 2003
![Page 67: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/67.jpg)
Earthquakes are dangerous
Chi-chi Taiwan, 1999
![Page 68: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/68.jpg)
Earthquakes are dangerous
Olympia, 1965 Seattle, 2001
![Page 69: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/69.jpg)
Earthquakes are dangerous
Sichuan, China, 2008
![Page 70: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/70.jpg)
“Helicorder” record of the Sumatra Earthquake and aftershocks recorded in the Czech Republic
(December 26, 2004)
![Page 71: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/71.jpg)
Earthquakes are dangerous
El Salvador, 2001
![Page 72: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/72.jpg)
Earthquakes are dangerous
Kasmir, 2006
![Page 73: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/73.jpg)
Where, when, and how?
![Page 74: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/74.jpg)
![Page 75: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/75.jpg)
360,000 earthquakes
![Page 76: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/76.jpg)
Black = 0 to 70; green = 70-500km; red = 500 to 700km
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U.S. Earthquakes, 1973-2002
Source, USGS. 28,332 events. Purple dots are earthquakes below 50 km, the green dot is below 100 km.
Earthquakes occur across the US
![Page 78: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/78.jpg)
Earthquakes in California – different frequency in different sections of the fault
creeping
1906 break
1857 break
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USGS shake maps – 2% likelihood of seeing peak ground acceleration equal to given color in the next 50 years
Units of “g”
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USGS shake maps – 2% likelihood of seeing peak ground acceleration equal to given color in the next 50 years
Close to home…
![Page 81: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/81.jpg)
USGS shake maps – 10% likelihood of seeing this level of acceleration inThe next 50 years
![Page 82: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/82.jpg)
USGS shake maps – Shaking depends on what you’re sitting on.
![Page 83: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/83.jpg)
![Page 84: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/84.jpg)
Different ways of measuring Earthquakes – Part 1. By damage
![Page 85: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/85.jpg)
Different ways of measuring Earthquakes – Part 1. By damage
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Different ways of measuring Earthquakes – Part 1. By damage
1966 ParkfieldEarthquake
Notorious for busted forecastof earthquake frequency.
![Page 87: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/87.jpg)
I-80 Freeway collapse (65 deaths)
Different ways of measuring Earthquakes – Part 1. By damage
Loma-PrietaEarthquake 1989
![Page 88: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/88.jpg)
Northridge Earthquake, 1994
Different ways of measuring Earthquakes – Part 1. By damage
-January 17, 1994 at 4:31 AM
-the ground acceleration was one of the highest ever instrumentally recorded in an urban area in North America.
-72 deaths, 9000 injuries, $20billion
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Different ways of measuring Earthquakes – Part 1. By damage
1906 San Francisco vs. 1811 New Madrid
![Page 90: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/90.jpg)
Different ways of measuring Earthquakes – Part 1. By damage
Extent of damage varies widely
Charleston, MOEarthquake
![Page 91: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/91.jpg)
• quantifies the amount of seismic energy released by an earthquake.
• base-10 logarithmic based on the largest displacement, A, from zero on a Wood–Anderson torsion seismometer output.
ML = log10A − log10A0(L)
A0 is an empirical function depending only on the distance of the station from the epicenter, L.
• So an earthquake that measures 5.0 on the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0.
• The effective limit of measurement for local magnitude is about ML = 6.8 (before seismometer breaks).
Different ways of measuring Earthquakes – Part 2. Richter Scale
![Page 92: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/92.jpg)
Wood Anderson seismometer
Uses inertia of copper ball to record accelerations on photo-sensitive paper
Milne seismometerWood Anderson seismometer
![Page 93: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/93.jpg)
Different ways of measuring Earthquakes – Part 2. Richter Scale
Two pieces of information used to calculate size of Earthquake:a)Deflection of seismometer, b)distance from source (based on P & S wave arrivals)
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Equivalency between magnitude and energy
Different ways of measuring Earthquakes – Part 2. Richter Scale
![Page 95: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/95.jpg)
Different ways of measuring Earthquakes – Part 2. Richter Scale
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€
M w =2
3log10
E s
1(N ⋅m = Joule)− 2.9
⎛
⎝ ⎜
⎞
⎠ ⎟
Eseismic = M010 -4.8 = 1.6 M0 · 10-5
‘Moment Magnitude’
AdM 0
= force/unit area · displacement · fault area
= shear modulus · displacement · fault area
= total elastic energy released
Earthquake “moment”
a. Total energy released in an earthquake
b. Only a small fraction released as seismic waves
c. Create logarithmic scale (akin to the others)…
Different ways of measuring Earthquakes – Part 3. By energy released
Empirical formula
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Different ways of measuring Earthquakes – Part 3. By energy released
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Equivalence of seismic moment and rupture length
a) Depends on earthquake sizeb) Depends on fault type
Different ways of measuring Earthquakes – Part 3. By energy released
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Distribution of slipfor various Earthquakes
Different ways of measuring Earthquakes – Part 3. By energy released
Axes are distance along fault& depth.
Colors are slip in m
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Different ways of measuring Earthquakes – Part 3. By energy released
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Different ways of measuring Earthquakes – Part 3. By energy released
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If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder.
This is the sound of the 2004 Parkfield 6.0 Earthquake
More information can come from analyzing Earthquake
![Page 103: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/103.jpg)
Am
plitu
de
Frequency
Narrow band filters
A spectrum what you get when you listen to a signal through a series of narrow band filters
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Amplitude vs. time for different frequency bands
Lower frequencies have larger amplitudes
![Page 105: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/105.jpg)
Theoretical shapes for earthquakes
![Page 106: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/106.jpg)
And the resulting velocity spectrum
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Log10 frequency (hz)
Log
10 M
omen
t (dy
ne-c
m)
1/f (for a box car)
1/f2
(in reality)
But real earthquakes don’t do this
![Page 108: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/108.jpg)
Instead there is a ramp-up time…
The time series of displacement looks very similar
![Page 109: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/109.jpg)
• The theoretical spectrum for a “box car” velocity function decreases as 1/f.
• Observations show a 1/f2 behavior.
• This can be explained as ramping (i.e acceleration) of the velocity at the start and end.
Which fits much better with the velocity spectrum
![Page 110: Modern seismometer If you speeded up any earthquake signal and listened to it with a hi fi, it would sound like thunder. east-west north-south up-down.](https://reader030.fdocuments.us/reader030/viewer/2022032800/56649d4e5503460f94a2dbf3/html5/thumbnails/110.jpg)
1/source duration
Scaled moment
1/ramp time
Get lots of useful information from a velocity spectrum…