Event times and timespans
Version 4.0 of KML introduced tags that enable data to be introduced to the Google Earth virtual globe in a temporal sequence. Table 6 shows the basic syntax.
Table 6: Timespan Tags for Sequences of Events in Google Earth
<Placemark>
<TimeSpan>
<begin>1979-09-22T07:50:42Z</begin>
<end>1979-09-22T07:55:42Z</end>
</TimeSpan>
<Model>...
</Model>
</Placemark>
Most geophysical applications will involve only an event start time, in which case the <end> tags are omitted. The time format follows standard XML protocols (www.w3.org). Click here for a quicktime movie from De Paor & Williams 2006 [AfterShocks movie] and here for an example from De Paor and Pinan-Llamas 2006 [Andes Timespan movie]
Figure 13. Hawaiian aftershock sequence
Timespan tags enable seismic events to be added to the Google Earth terrain in their correct temporal sequence. Here aftershocks are represented by solid spheres because focal mechanism solutions are not available.
Figure 13 is a still screen shot from a Google Earth timespan showing the sequence of aftershocks for the Kiholo Bay earthquake. Here, the times on the time controller are real dates. However, there are many geophysical and geological applications in which a pre-historic time line would be essential. Experimentation shows that timespan tags accept small negative dates, however, bugs occur when dates exceed a few thousand years, and the program hangs if a start date of negative 4,500 million years is used. At present, the only solution is to scale down the timescale, for example, to let a timespan of 4,500 years, represent the 4.5 b.y. geological record or a timespan of 543 years represent the Phanerozoic.