Characterizing earthquakes using accelerometer data Is there a way to use accelerometer data to characterize earthquake intensity, e.g., on Richter scale?
Yes, you can measure seismic energy with accelerometers. Most people do.

There are three ways to measure seismic energy: by displacement $x$, velocity $\dot{x}$, or acceleration $\ddot{x}$. Loose-spring devices like geophones measure velocity; stiff-spring devices like MEMS and relative gravimeters measure acceleration: they are accelerometers. Those used in seismology and exploration geophysics are very precise.

I wrote about the various instruments used to measure seismic energy in a blog post a while back. An excerpt about seismometers:


  Seismometers [are] precision instruments not used in exploration
  seismology because they are usually quite bulky and require careful
  set-up and calibration. [Most modern models] are accelerometers, much
  like relative gravimeters, measuring ground acceleration from the
  force on a proof mass. Seismometers can detect frequencies in a very
  broad band, on the order of 0.001 Hz to 500 Hz: that's 19 octaves!


Short story: When digital seismic receivers arrived on the scene in Calgary in the early 2000s, there was a lot of skepticism. We spent a lot of time comparing them to traditional geophones. The conclusion: they were about the same. Here's one comparison by Michael Hons at CREWES, and here's another; here's yet another from one of the big manufacturers, Sercel (now CGG). Finally, here's a presentation more oriented around earthquake seismology.

Okay, but I was talking about the accelerometers in iPhones!

Oh, sorry. As @Fred points out in his answer, consumer-grade MEMS accelerometers (as you might find in a phone or latop) may not have the sensitivity or calibration that a researcher would want, but one might compensate somewhat for this with multiple measurements, e.g. an array of devices. In other words: quantity, not quality. (This is perfectly legit: we do it in exploration seismics too.)

Dashti et al. (2013) in Earthquake Spectra Journal found you could get useful measurements (e.g. for emergency response) from networks of phones with a few tricks:


The more measurements the better.
Horizontal orientation is best.
Prefer high-friction phone covers.
Don't expect to get great data for small quakes.
Treat small groups of phones as arrays.
Don't use data for phones that fell off a table!