Components of a typical PNSN Strong Motion Station:

Sensor and Seismograph

Sensor

The ground motion sensor is a 3-component force balance accelerometer. It will be configured to have a 4-g full scale reading. The digitizer is located in the sensor housing. The power supply and Internet communications hardware are enclosed in a separate housing. The sensor will need to be bolted to a level concrete floor or else placed outdoors in a small vault.

Optimal signals are those not affected by the response of structures. Thus, the best locations for the sensors will be either away from buildings or located within low height buildings with only 1 or 2 floors and a footprint of less than 6000 square feet. The sensor should be located in a basement or ground floor. (Diagrams of an indoor installation and an outdoor vault).

Additional considerations are cultural noise. The unit should be located in a "seismically" quiet area. It should not be located near devices with mechanical vibrations such as motors, fans, compressors, and generators. Wind noise can also be a problem so the unit should not be located near tall trees or poles. Indoor installatins will ideally be located in a room that does not have loose items (eg, chairs or desks) that can move around during an earthquake and contaminate the recording of the ground motion.

Digitizer

The analog signal produced by the accelerometer will be digitized by the seismograph. The seismograph will send logical data packets out through it's RS-232 port. A low voltage serial cable connects the digitizer to the Internet communcations hardware, a terminal server, enclosed in the power supply housing.

The sensor/digitizer has 2 external connections:

• GPS receiver
• serial data

The power supply will be installed indoors, near Internet connections, even when the sensor is installed in outdoor vaults. Cabling to vaults is buried in rigid conduit.

The PNSN will be using the CMG-5TD model digital seismograph, manufactured by Guralp.

Below is a photograph of the components Guralp CMG-5TD seismograph system. We also show a photograph of a sensor being installed

Updated August 7, 2002