Strong Motion Data on a ADXL05 Sensor

Created: 08/15/98 Update 07/04/09

This page documents the strong motion data I recorded for the magnitude 5.4ML Hollister California event on 8/12/98 at 14:10:25 UTC or 7:10:25am PST.

The event, felt here in Redwood City California and located ~108km (67miles) from me, is the first earthquake recorded by my ADXL05 based strong motion sensor that went online 3/97. Besides the ADXL05 sensor (my *.LC6 event files), I have on loan from the Menlo Park USGS a Kinemetrics three component FBA-23A commercial strong motion sensor. I am currently monitoring the north-south (*.LC5 event files) and vertical (*.LC7 files) channels of the FBA-23A sensor. The single channel ADXL05 based sensor is also oriented north-south so that I could see how this sensor compares to the FBA-23A north-south channel.

Both north-south sensors are set for a maximum acceleration of +- 2 g. The data is collected using one of my 16-Bit A/D Cards so each A/D converter count is the equivalent to ~.0610 mg (4g / 65536 counts). As you can see from the seismograms below, both sensors produced about +- 100 counts, or around +- 6.1 mg, of acceleration. The main difference between the ADXL05 and the FBA-23A is the amount of background noise from the sensor itself. The ADXL05 sensor has about +-3 mg of internal noise and FBA-23A has less than 1 mg. As you can see from the seismograms below, the P wave is buried in the noise of the ADXL05 sensor but can be clearly seen on the FBA-23A sensor.


This is a GIF image of the ADXL05 seismogram:

Download PSN Event File or SAC Binary Event File

This is the FBA-23A Seismogram:

Download PSN Event File or SAC Binary Event File

This WinQuake screen shot shows the S wave part of the event comparing both sensors:

More information about the ADXL05 monolithic accelerometer chip can be found here.

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Larry Cochrane -