Measuring Ground Vibrations Using the S102 Seismometer

1
Measuring Ground Vibrations Using the S102
Seismometer

• A Presentation by
• Dr. Alan ScottDepartment of PhysicsUniversity
  of Wisconsin-Stout

2
Measuring Ground Vibrations Using the S102
Seismometer

• Outline
• S102 Seismometer
• Ground Vibrations
• Earthquakes

3
S102 Seismometer
4
S102 Seismometer
5
Schematic Diagram
6
Schematic Diagram
Up and down movement of magnet induces a voltage
signal in the pick-up coil.
7
Schematic Diagram
But the magnet is actually remaining somewhat
stationary while the ground (which is rigidly
connected to the coil) moves up and down.
8
Damped Harmonic Oscillation
If one displaces the inertial mass then releases
it while keeping the housing stationary, the mass
follows a damped harmonic oscillator behavior.
9
Damped Harmonic Oscillation
S102 Seismometer damping
10
Electromagnetic Induction
After the induced voltage is amplified, the rated
output of the S102 Seismometer is 15 V per
mm/sec, single ended output.
11
Instrument Calibration
A circuit in the meter can displace the inertial
mass in a very uniform way. The signal produced
can be correlated to a specific amount of ground
motion.
12
Instrument Sensitivity
Recording of footsteps taken every 2 seconds at a
distance of about 3 feet away from the
seismometer using a concrete floor.
13
Instrument Sensitivity
If 15V corresponds to a ground motion of 1
mm/sec, the above footsteps have a ground motion
of about 6x10-3 mm/sec. One can estimate the
amplitude of ground motion by assuming a simple
harmonic motion with a frequency of 5 Hz.
14
Instrument Sensitivity
6x10-3 mm/sec -A(2p)(5 Hz)(1) A200 nanometers
15
Ground Motion Produced by an
Earthquake

• P-waves
• Longitudinal waves that expand and compress
  rocks.
• Travel at about 7.3 km/s away from the origin.
• S-waves
• Transverse waves that move rocks perpendicular to
  the waves motion.
• Travel at about 4.6 km/s away from the origin.

16
Ground Motion Produced by an
Earthquake

• L-waves (or Surface-waves)
• Transverse waves that move rocks perpendicular to
  the waves motion.
• Travel along the earths surface.
• Travel at about 2.6 km/s away from the origin.

17
Ground Motion Produced by an
Earthquake
Graph from National Earthquake Information
Service, USGS /neic.usgs.gov/neis/seismology/keepi
ng_track.html
18
Ground Motion Produced by an
Earthquake
2-dimensional animation of wave propagation.
19
Scales to Measure the Strength of
Ground Motion

• Richter Scale
• Mercalli Scale

20
Richter Scale
It is a measure of the amplitude of ground
vibration using a seismometer. With the
seismometer a standard distance of 100 km away
from the epicenter, one gets
Amplitude (mm) 1 10 100
1000 10000
Magnitude 3 4 5
6 7
21
Modified Mercalli Scale
I. Not felt except by a very few under especially
favorable conditions. II. Felt only by a few
persons at rest, especially on upper floors of
buildings. III. Felt quite noticeably by
persons indoors, especially on upper floors of
buildings. Many people do not recognize it as an
earthquake. Standing motor cars may rock
slightly. Vibrations similar to the passing of a
truck. Duration estimated. IV. Felt indoors by
many, outdoors by few during the day. At night,
some awakened. Dishes, windows, doors disturbed
walls make cracking sound. Sensation like heavy
truck striking building. Standing motor cars
rocked noticeably. V. Felt by nearly everyone
many awakened. Some dishes, windows broken.
Unstable objects overturned. Pendulum clocks may
stop.
22
Modified Mercalli Scale
VI. Felt by all, many frightened. Some heavy
furniture moved a few instances of fallen
plaster. Damage slight. VII. Damage negligible
in buildings of good design and construction
slight to moderate in well-built ordinary
structures considerable damage in poorly built
or badly designed structures some chimneys
broken. VIII. Damage slight in specially
designed structures considerable damage in
ordinary substantial buildings with partial
collapse. Damage great in poorly built
structures. Fall of chimneys, factory stacks,
columns, monuments, walls. Heavy furniture
overturned. IX. Damage considerable in
specially designed structures well-designed
frame structures thrown out of plumb. Damage
great in substantial buildings, with partial
collapse. Buildings shifted off foundations. X.
Some well-built wooden structures destroyed most
masonry and frame structures destroyed with
foundations. Rails bent. XI. Few, if any
(masonry) structures remain standing. Bridges
destroyed. Rails bent greatly. XII. Damage
total. Lines of sight and level are distorted.
Objects thrown into the air.
23
Plate Tectonics The Cause of Most Earthquakes
San Andreas fault
Picture from Earthquake On-line Book from USGS,
by Kaye M. Shedlock Louis C. Pakiser,
http//pubs.usgs.gov/gip/earthq1/
24
Plate Tectonics The Cause of Most Earthquakes
Picture from Earthquake On-line Book from USGS,
by Kaye M. Shedlock Louis C. Pakiser,
http//pubs.usgs.gov/gip/earthq1/
25
Plate Tectonics The Cause of Most Earthquakes
Picture from Earthquake On-line Book from USGS,
by Kaye M. Shedlock Louis C. Pakiser,
http//pubs.usgs.gov/gip/earthq1/
26
Seismicity Maps
Graph from National Earthquake Information
Service, USGS http//neic.usgs.gov/neis/general/se
ismicity/us.html
27
Seismicity Maps
Graph from National Earthquake Information
Service, USGS http//neic.usgs.gov/neis/general/se
ismicity/us.html
Alaska
28
Seismicity Maps
Graph from National Earthquake Information
Service, USGS http//neic.usgs.gov/neis/general/se
ismicity/us.html
Central U.S.
29
Earthquakes Are Usually Pre-cursors
To Volcanic Eruptions
Mt. Redoubt
Picture from Earthquake On-line Book from USGS,
by Kaye M. Shedlock Louis C. Pakiser,
http//pubs.usgs.gov/gip/earthq1/
30
Earthquake San Francisco, 1906
Picture from Earthquake On-line Book from USGS,
by Kaye M. Shedlock Louis C. Pakiser,
http//pubs.usgs.gov/gip/earthq1/
31
Earthquake San Francisco, 1906
Picture from Earthquake On-line Book from USGS,
by Kaye M. Shedlock Louis C. Pakiser,
http//pubs.usgs.gov/gip/earthq1/
32
Earthquake Alaska, 1964
Picture from Earthquake On-line Book from USGS,
by Kaye M. Shedlock Louis C. Pakiser,
http//pubs.usgs.gov/gip/earthq1/
33
Earthquake Loma Prieta (Bay Area), 1989
34
Earthquake Loma Prieta (Bay Area), 1989
35
Earthquake Northridge, (Los Angeles), 1994
36
Earthquake Northridge, (Los Angeles), 1994
37
Earthquake Taipei, Taiwan September
20, 1999
Origin Time 174719 GMT LATITUDE
23.78 N LONGITUDE 121.09 E
DEPTH 33 km MAGNITUDE
Ms7.6 (NEIC)
38
Earthquake Taipei, Taiwan
Seismograph readouts in Germany
39
Earthquake Taipei, Taiwan
Epicenter location indicated by the star
40
Monitoring Weapons Proliferation
Source Physics Today, March 1998
41
Monitoring Weapons Proliferation
Source Physics Today, March 1998
42
The End