Portable Broadband Seismology

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Portable Broadband Seismology
Part 8 Seismic Vaults for Temporary Installations

• Jakarta, Indonesia
• May 11-13, 2006
• Bruce Beaudoin
• Marcos Alvarez
• Additional thanks to Pete Davis for use of his
  slides

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Factors controlling the performance of broadband
seismic vaults

• Vault design, siting and construction
• The capacity to detect faint distant earthquakes
  is governed by the signal to noise
  characteristics of the site. The benefit of
  sensitive, high dynamic range, and expensive
  instruments like the STS2 and CMG-3T seismometers
  will be lost if vault design and siting are poor.
• Geology (sedimentary basin vs. batholith)
• Temperature fluctuations (depth of vault)
• Barometric pressure fluctuations
• Ambient noise (ocean proximity, freeways, wells
  etc.)

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Broadband Vault Basic Requirements

• Provide sensor coupling to Earth
• Protect the instruments
• Flooding
• Temperature fluctuations
• Animals
• Secure

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Where is a good place to put a seismic station?

• Far from human-generated noise (roads and
  machinery)
• In a temperature-stable environment
• Far from the ocean
• On solid (competent) rock
• Sky view
• Good Drainage
• Secure

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Components of A Seismic Station

• Data Acquisition System (DAS) to convert electric
  current to numbers (digitize) for a computer to
  process
• Seismometer
• A source of electric power
• Clock to time the data

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Vault Design is Sensor Dependant
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PASSCALBroadband Seismometers
Guralp CMG-3T
Streckeisen STS-2
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Example Regional Station
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Regional Station Construction
Have truck, will travel
Current method custom trailer with water tank,
room for cement bags, and onboard mixer
42 dia. pipe set into 7 deep pit with concrete
on either side of rubber membrane
Flex conduit was replaced with straight sticks
reducing field time significantly. Wires are
pulled during construction phase
Using 3 vehicles, 2 trailers, 1 backhoe, and 3
people, it is feasible to construct 3 sites in 5
days
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Example Regional Station
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Example Portable Station
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Example Portable Station
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Why sand?

• Holcomb et al. IASPEI (Manual of Seim. Obs.
  Practice) Filling empty air space above and
  around the sensor significantly reduces long
  period noise
• John MacMillian, open file report 02-144, sand
  adds to thermal mass around the sensor and will
  prevent thermal air currents
• Guralp manual we recommend the use of fine dry
  sand insulates the instruments from convection
  currents and temperature changes

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Example Portable Station
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Observatory Station
Seismic vault under construction in Madagascar
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Observatory Station
Seismic vault under construction in Madagascar
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Observatory Station
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Observatory Station
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Location Geology Affects Station Noise
Characteristics
Remote Site within the Sierra Nevada Batholith
Site Near University within Rio Grand Rift
Deposits
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Temperature inside the vault vs Surface
Data collected on 1 m deep vault using foam
insulation Socorro, New Mexico
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Temperature inside the vault vs Surface
Conclusion 1 meter deep vault provides good
thermal insulation
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Gallery of Seismic Vaults
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Gallery of Seismic Vaults
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Gallery of Seismic Vaults
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Gallery of Seismic Vaults
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Gallery of Seismic Vaults
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Gallery of Seismic Vaults
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Gallery of Seismic Vaults
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Gallery of Seismic Vaults
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Gallery of Seismic Vaults
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Gallery of Seismic Vaults
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Gallery of Seismic Vaults
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Gallery of Seismic Vaults
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Figi earthquake , M-7.9, 2005347
S-Pier
Q330-STS2
FA-s
R130-CMG3T
FA-c
R130-CMG3T
n-pier
R130-CMG3T
TA.Y22C
Q330-STS2
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close up of verticals
Do the signals look the same?
overlay surface wave
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Power Spectral Density plots comparison between
Y22C TA station FA Test vaults