The Public Seismic Network of San Jose


 Santa Clara County and Santa Cruz County


 Santa Clara County and Santa Cruz County Locating Earthquakes using Earthworm Seismic Network

Aptos PSN Station

Display / AMP Geophones Lehamn Outside Seismic House Lehman Seismograph

Emon Data Collection


Rack mounted amplifier and filter cases

Data Collection


  • Name - EMON by Ted Blank

System: AT1 /2

  • Normal sampling rate: Samples Per Second - 3.949
  • OS - DOS3.3

System: ATE/N/Z

  • Normal sampling rate: Samples Per Second - 63.875
  • OS - DOS3.3


Designer: Pet Rowe

Two gain stages op-27  overall gain

Min - 2,985    1.3DB

Max - 51,740   67.3DB

Filter: Low pass 10Hz   3-poll butterworth



  • Geo Space HS10

Functional Sensitivity         ( 10%)     2.99 V/ips                          Natural Frequency                ( 10%)    1 Hz

Coil Resistance                 ( 10%)    400 ohms

Coil Inductance                     360 mh

Damping Factor         ( 20%)       .031

Damping Constant              1178 2862

Displacement Limit                     0.5 in

Inertial Mass                             33 oz  

Orientation Angle            5


Height                    5.40 in

Diameter                4.38 in

Weight                   9.75 lbs  




  • 10 Sq Ft work area
  • 20 Cu Ft volume
  • Airtight seal
  • 2- Lehman cement mounting pads 2x2x4-feet
  • Full cement floor
  • Interior insulation 2-inch Styrofoam top/sides
  • Exterior 1/2-inch plywood with removable top
  • 2-inch PVC cable pass through to garage interior
  • Outside rain drain to remove standing water
  • Metal roof 4-feet above wooden box to block wind/rain (not shown)

 Lehman boom:

Boom: Aluminum 1-inch sq

Boom length: 30cm

Initial mass: 80 oz

Pre Amp / coax driver gain: 1889

Amp/Coax power supply: +/- 12V steady supply with UPS backup provided from the seismic rack supply via the PVC cable pass through tube.


 Lehman upright support:

Base Plate: Aluminum .75x10x12-inch

Height: 20-inches

Mounting: (3) 3/8-inch 1000 lb cement anchor

Leveling: (2) 2-inch 8-32 hex head machine screw

Upper pivot : #10 machine wire from upright to turnbuckle.

Lower yoke wire: From lower turnbuckle  to boom cross bar .035 steel aircraft cable.

Lower pivot: Hardened point in cupped 8-32 hex head machine screw



 Lehman detail:

Top Photo:

Damping Magnets:   1.5Hx1.75W1.75D-inches

Flag: brass 8x2x.25-inches

Middle Photo:

Manufacturing process: Hand wound

Pickup coil 25mm diameter plastic wire frame x 10mm  x 15mm

Magnet: cow magnet

Magnet Wire size: 52 gauge

Coil Resistance: 12.5K ohms   

Lower Photo:

Manufacturing process: Machine wound

Pickup coil 14mm diameter plastic wire frame x 10mm x 7mm

Magnet: 1.375Wx.75Hx.75D

Magnet Wire size: 38 gauge

Coil Resistance: 71.5 ohms



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Webmaster Public Seismic Network of San Jose   WWW Since August 1997 - BBS Since January 1990 - Last Update Jan 26, 2014 Professor Stephen Hammond