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<br />b. Between 0.2 and 1.0 g: Transducer should be attached to the ground with a spike <br />or covered with a sand bag. <br />c. Greater than 1.0 g: Transducer should be buried, bonded to the ground or <br />structure with stiff clay or putty, or some other method that should achieve firm <br />attachment. <br />TABLE 1- Acceleration intensity (g's) based on estimated particle velocities and frequencies <br /> Maximum Frequency (Hz or cycles-per-second) <br /> 4 10 15 20 25 30 40 50 100 150 200 <br />PPV (in/s) at <br />Acc. (g)>_ 0.2 <br />3.08 <br />1.23 <br />0.82 <br />0.62 <br />0.49 <br />0.41 <br />0.31 <br />0.25 <br />0.12 <br />0.08 <br />0.06 <br /> <br />PPV (in/s) at <br />Acc. (g) ? 1.0 <br />15.38 <br />6.15 <br />4.10 <br />3.08 <br />2.46 <br />2.05 <br />1.54 <br />1.23 <br />0.62 <br />0.41 <br />0.31 <br /> <br />2. Sensor Burial: When velocity transducers are buried the operator should employ the <br />following methods. <br />a. Excavate a hole that is no less than three times the height of the sensor (ANSI <br />52.47-1990, R1997). <br />b. If possible, spike the sensor to the bottom of the hole. <br />c. Firmly compact soil around and over the sensor. <br />3. Attaching Sensors to bedrock or hard Structural Surfaces: <br />a. Bolt, clamp or use epoxy or putty to firmly couple the sensor to the hard surface. <br />b. The sensor may be attached to the foundation of the structure if it is located <br />within +/- 1-foot of ground level (USBM RI 8969). This should only be used if <br />burial, spiking or and bagging is not practical. <br />4. Other sensor placement methods: Use other methods as described below if disturbance <br />of the ground is not possible. <br />a. Cover transducers with sand bags loosely filled with about 10 pounds of sand. <br />When placed over the sensor the sandbag profile should be as low and wide as <br />possible with a maximum amount of firm contact with the ground. <br />b. A combination of both spiking and sandbagging gives even greater assurance <br />that good coupling is obtained. <br />C. Programming considerations <br />Site conditions dictate certain actions when programming the seismograph. <br />1. Ground motion trigger level: The PPV-trigger-level should be programmed low enough <br />to trigger the unit from blast vibrations and high enough to minimize the occurrence of <br />false events. The level should be slightly above the expected background vibrations for <br />the area. A good starting level is 0.05 in/s.