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Here are some of the articles that have been recently posted to the PASSCAL website:

Broadband Vault Construction


Download Diagram of Vault (jpg)

Construction of the vault for broadband seismometers has a direct impact on data quality. Before construction can begin there are two other important considerations as well; location, and setting. A short discussion of these topics precedes the construction details because you should really pick the right site before going to all the work of building a vault. It takes a long time to find good sites which balance the competing requirements of low noise, access, security, position within the array, power, permission, etc. Finding one site per day is fairly productive.

Station Siting Considerations

April 20th, 2009

These documents address things to consider regarding Station Siting Location/Access, Cultural Noise, and Suggested Materials.

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Seismometers are instruments that measure and record motions of the ground, including those of seismic waves generated by earthquakes, nuclear explosions, and other seismic sources. Records of seismic waves allow seismologists to map the interior of the Earth, and locate and measure the size of these different sources.

Seismograph is another Greek term from Seism - "the shakes" and Grapho - "I draw". It is often used to mean seismometer, though it is more applicable to the older instruments in which the measuring and recording of ground motion were combined than to modern systems, in which these functions are separated. Both types provide a continuous record of ground motion; this distinguishes them from seismoscopes, which merely indicate that motion has occurred, perhaps with some simple measure of how large it was.

The PASSCAL Instrument Center supports the following types of seismometers:

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Installing Broadband Sensors


This manual covers the following tasks related to installing broadband sensors:

Orient sensor Level sensor Connect sensor to DAS (power) Unlock masses (manually or via electronic command, if masses are the type that lock) Center masses (via command) Check waveforms, e.g. stomp test

Note, always handle sensors with care. If you have never worked with sensors or been shown how to install them, you should get help from experienced people, or barring that, carefully read the manufacturer's manual. Never move an unlocked sensor, unless the sensor has no mass locks. Most of the broadband sensors in the PASSCAL fleet are either Streckeisen STS2's or Guralp 3T's; both models have 3 masses and all 3 need to remain locked during transport.

Working with Responses to Get Units of Ground Motion

Necessary information:

Sensor: sensitivity and passband (velocity transducer) or scaling (accelerometer)

For information on sensor sensitivity and passband, see the Sensor Comparison Chart along with the Sensor Response Plot.

Datalogger: Analog-to-Digital (A/D) conversion factor (aka bit weight) and Gain 

Quanterra model Q330: 419,430 counts/volt, or 2.384 uV/count at a Gain of 1 RefTek model RT130: 629,327 counts/volt, or 1.58997 uV/count at a Gain of 1


Example: Counts to Ground Velocity Conversion within the Passband


Seismic Vaults


The construction of the vault for broadband seismometers has a direct impact on the data quality. The principle of broadband sensor vault design is to minimize temperature changes, and to distance the sensor pad from the surficial layer which tilts due to temperature, precipitation, solar insolation, wind, etc.

Nearby sources of ground noise, like footsteps or acoustic noise, are reduced by shallow burial (2-5 ft.) The construction must be adapted to the site and materials available. A decision will have to be made to balance the cost and labor of different vault designs against the length of deployment, resources available, and quality of data expected.

Finding a pre-existing enclosure is a tremendous savings in time and effort. This might include missile silos, power stations, abandoned mines, caves, or root cellars. Consider the details of cables, power, and locating a GPS antenna for timing at these sites.


PASSCAL Accelerometers: Kinemetrics FBA-2 Episensor Features:

Strong-motion sensors are accelerometers, and are designed to measure the large amplitude, high-frequency seismic waves typical of large local earthquakes. These seismic waves result in the strong ground motion we feel during a large earthquake. Strong ground motion is often to blame for the structural damage that occurs during an earthquake. The data seismologists record with strong motion sensors is used to improve the design of earthquake resistant buildings and to understand earthquake-induced geologic hazards like liquefaction and landslides. The range of motions of interest for strong-motion applications includes accelerations from 0.001 to 2 g and frequencies from 0 to 100 Hz or more.

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SiRF Clocks in the Field as of August, 2008

Number of SiRFs Exp. Number Experiment Name 4 200551 Costa Rica Subduction (Nicoya) 2 200559 HLP-lite (aka pre-HLP) 2 200604 Anatahan Volcanoes 1 200609 CAFE 3 200611 CRB-Wallowa 2 200617 PIRE 1 200622 Carpathians 1 200655 Mexico ETS
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Teledyne Geotech S-13 Short Period Sensor

Teledyne Geotech S-13 Short Period Sensor

This passive 1-Hz sensor is seldom used because there are not many in the PASSCAL fleet and they have essentially been replaced by the CMG-40T-1Hz feedback seismometers. Information about S-13's from the old website can be found here.

The S-13's are heavy and awkward. The three components are separate units (about 20lbs each). They have strong magnets (passive seismometers), so they require about 12-inch spacing between each component.

Mark Products L-4C

Mark Products L-4C

 PASSCAL has very few of these 1-Hz passive seismometers, and does not have plans to replace parts that fail. Thus, they are likely to be discontinued, as they are cannabalized for spare parts and lost to attrition. Information from the old website can be found here and the cable drawings can be found here.

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