Use iTemblor to explore the relationship between acceleration you impart on your phone and earthquake shaking intensity, based on the Modified Mercalli Intensity (MMI) scale.
While the familiar Richter earthquake magnitude relationship (and others) scale with recorded ground movement, the MMI scale is a qualitative or observational scale of earthquake shaking intensity developed for comparing earthquake effects in locations where there are no seismographs.
The Seismoscope View - The seismoscope is one of the oldest earthquake measurement devices, dating back to ancient China, and records the intensity and direction of shaking in the horizontal plane. In the spirit of the seismoscope, it’s most accurate to use this view by placing your phone on a flat surface (or hold it roughly horizontal) and to shake it horizontally. The movements you impart, plotted in 2D, are measured as acceleration in time which is then converted into MMI values using an empirical relationship between ground acceleration and MMI shaking intensity (Richter, 1958, Western United States).
The Time Series View - The time series view is a traditional seismogram view that plots the accelerations you impart to your phone in 3 dimensions (x, y and z axes). You will see two traces for each axis, orange and green. The orange represents the raw acceleration data with the effects of gravity removed. The green represents the same data after the application of a low pass filter. The low pass filter is used to dampen your input to stay approximately within the frequency bandwidth of large earthquakes. The continuous time series is approximately 10 seconds long and is plotted in units of % gravity (G)
The Data - iTemblor records the accelerations you impart onto your device and subtracts the effect of gravity. Then, a low pass filter is applied to constrain the recordings to stay within the bandwidth of large earthquakes (less than 10 hertz). The seismoscope view displays the fully filtered signal (equivalent to the green trace in the time series view). The time series view displays two traces. Both have gravity removed. The green trace has been low pass filtered (as described) and the orange trace has not.
iTemblor is designed to provide fun and interesting correlations between the accelerations you impart on your iPhone through shaking and earthquake intensity. Efforts have been made to create generalized and realistic representations using published empirical data.
Earthquakes are very complex and variable processes, therefore, iTemblor results should be viewed as approximate at best and be used for educational and entertainment purposes only.