Go Down

Topic: Seismograph (Read 8015 times) previous topic - next topic

AWOL

Quote
using very light guage wire

Use a lead-acid battery as the pendulum mass, and use Bluetooth.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

markB

Great discussion guys.
I live on the outskirts of a recent earthquake (well actually two) in Christchurch, New Zealand
In the second quake we experienced a very large vertical component in the order of 2.2 times gravity.

The local Geonet organisation had multiple sensors around the city, and while they were able to read upwards accelerations of 2.2, the downward readings were less, until they worked out the large mass they fixed the sensor to, was freefalling at 1g.

The type (and in our case) location produces two very different effects.
The 7.1 in September and its aftershocks are more horizontal movement and you can hear them coming.
It is further away, and often the shaking intensifies before dying off.

The 6.3 in February and its aftershocks are more vertical, you hear and feel them at the same time, and they generally are almost like someone crashing into the house, and then the shaking dies off.

After the first quake, I do know of one person using a simple accelerometer to measure the quakes, with very good results.

One of the things affecting the drums is sensitivity. By this any local vibrations will reduce the sensitivity to detect new events. I understand that the Geonet devices reset every 24hrs, and they have trouble with a mining operation on the West Coast.

For those that are interested here is a link to the readings and comparison between quakes.
http://db.nzsee.org.nz:8080/documents/43301/43317/GroundMotionComparison+Mw7.1+vs+Mw6.3+-+VERSION+4

You can also see the sources and intensities here http://quake.crowe.co.nz/QuakeMap/Single/

Good luck
Mark

tedcook

Here's an easier way of doing this, perhaps.  Use any graphics editing software to make a black-to-white rectangular gradient and print it out.  Attach the paper to the bottom of a pendulum with a flat bottom.  Below the pendulum have a simple photodetector and LED light source.  As the pendulum swings the reflected light off the paper will change due to the gradient and you'll see a sinusoidal output from the photodetector.  Make two sets of these with the gradients at 90 degrees of each other and you have full x-y information.

A little research into how much ground motion to expect from a typical earthquake will help guide the dimensions of the gradient.  Also keep in mind the resonant frequency of the pendulum.  Ground oscillations faster than the resonant frequency (above resonance) will be much easier to detect than those below resonance.

robtillaart

Quote
Use any graphics editing software to make a black-to-white rectangular gradient and print it out.


If I understand your proposal you could have two colors too, from Red to Green on one axis and from 0-100% saturation on the other, with a color sensor you could detect movements in two  (X and Y) directions as every pixel reflects another color. Thereby detecting directional information about the quake. Correct?
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

tedcook

#19
Jul 04, 2011, 10:38 pm Last Edit: Jul 04, 2011, 10:44 pm by tedcook Reason: 1
Quote
with a color sensor you could detect movements in two  (X and Y) directions as every pixel reflects another color


In principle that works as well.  I'm not familiar with color sensors, but I imagine it has separate output channels for red, green and blue?  Then you could take (R+G) as the saturation axis and (R-G) and the hue axis.

One draw back of my design, which has two orthogonal saturation gradients side-by-side on the pendulum, is that pendulum twist (torsion mode) would mimic a 45o swing.  Having the patterns co-axial as in the hue-saturation design would be immune to this.  One would not expect, however, for an earthquake to induce twisting ground motion - or so I believe.

Go Up