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

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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Offloading Data

Data that is recorded locally, as opposed to telemetered must be offloaded and stored.  The actual procedures for offloading data depend on type of DAS and the type of media that the data is recorded on.  Offloading should be done as soon as possible after visiting the site in order to secure the data.  If possible offloading and data review should be done close enough to the site so that, if a problem is detected, the site can be revisited.

In general the offload procedure is as follows.

1. Verify that there is the expected amount of data on the media.  If there is not the expected amount of data there may be a problem at the site.

2.  Offload the data.

3.  Verify that the size of the offloaded data corresponds to the amount of data that was on the media.

4.  Review the data for indications of station problems and for data integrity.

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"White Wanderer" Exhibit in Chicago joins Seismology and Art

An exhibit sponsored by the Natural Resources Defense Council has combined the work of University of Chicago seismological scientist Doug MacAyeal of with the art of Luftwerk, to produce an artistic rendition of the seismic "sounds" produced by climate change in the Antarctic. The exhibit opened with a live demonstration of seismic data acquisition, using instruments provided by IRIS/PASSCAL. The project was a collaboration with NRDC, with additional help from the University of Chicago, and was on display at Two Riverside Plaza, Chicago IL from Sept 7th – Oct 1st. 

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TA Installation in Alaska Now Complete

After covering the lower 48 United States from coast to coast with a grid of nearly 1700 sites, the last seismic station of the EarthScope Transportable Array has finally been installed in Alaska. IRIS has commemorated the event with a post titled "EarthScope’s Transportable Array Spans Alaska, the Last Frontier." The IRIS article includes a detailed map of the Alaska TA stations, highlighting the location of the final station A19K.