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/