Data trends Passive seismic file formats continued Passive seismic file formats continue to be the theme of this column, as I explore the files that industry is generating, and what we can do with them. Discussions that were sparked by this column in the last issue of Preview have focused on the two well established formats, SEED and SAC. The general consensus seemed to be that while exporting in the active format of SEG-Y rev 2 is possible, the format is not a natural fit for certain passive seismic data. However, the conversation is continuing around points of specificity and upcoming exchange formats. The most common exploration datasets at the moment are from Tromino devices and those datasets are most easily shared between Tromino users in ASCII time series format. Since the format ticks the time series and ASCII boxes, further deliberations on an acceptable ASCII format for data exchange, akin to other ground surveys, would cater for this large and growing user base. It has also been pointed out that the Adaptive Seismic Data Format (ASDF5), a HDF5 variant, is expected to supersede miniSEED for data exchange in the near future. Rooted in the passive data collection of astronomy, the hierarchical data format is a database-like file that has occasionally been mooted as a rival for increasingly large survey files of all types. The format has wide support in many programming languages and ASDF5 has various open source read/write options available through their website and Github repository ( EDI file format I am also garnering opinions on the EDI (Electrical Data Interchange) file format. Admittedly my personal experience is limited to David E. Wright’s easy to read 1988 SEG presentation on the format, and some minor parsing. I have heard that some geophysicists have their own interpretation of the standard. Have you used EDI and have you found consistency problems? Please send your comments and suggestions/ideas to me at Tim Keeping Associate Editor for geophysical data management and analysis Magnetic pole on the move Alanna Mitchell in her latest book“The Spinning Magnet”(Mitchell 2018), which is reviewed in this issue of Preview (Henderson 2019), said“The north pole is on the run”and also,“each version [of the World Magnetic Model] is out of date by the time the new one is made”. These remarks seem to be particularly apposite, judging by the very latest news about the sudden acceleration of the north pole’s position, and the consequent changes in the shape of the Earth’s magnetic field. The following is extracted from an article by Alexandra Whitze in Nature, 9 January 2019, titled,“Earth’s magnetic field is acting up and geologists don’t know why”. Earth’s north magnetic pole has been skittering away from Canada and towards Siberia (Figure 1), apparently driven by liquid iron sloshing within the planet’s core. The most recent version of the World Magnetic Model came out in 2015, and was supposed to last until 2020 – but the magnetic field is changing so rapidly that researchers will have to fix the model as soon as possible. The problem lies partly with the moving pole, and partly with other shifts deep within the planet. Liquid churning in Earth’s core generates most of the magnetic field, which varies over time as the deep flows change. In 2016, for instance, part of the magnetic field temporarily accelerated deep under northern South America and the eastern Pacific Ocean. Satellites such as the European Space Agency’s Swarm mission tracked the shift. Scientists are working to understand why the magnetic field is changing so dramatically. Geomagnetic pulses, like the one that happened in 2016 beneath South America, might be traced back to “hydromagnetic”waves arising from deep in the core. And the fast motion of the north magnetic pole could be linked to a high-speed jet of liquid iron beneath Canada. References Henderson, R.J. 2019. Book review. Preview 198: 34–35. Mitchell, A. 2018. The spinning magnet. London: Oneworld Publications. 323p. Whitze, A. 2019. Earth’s magnetic field is acting up and geologists don’t know why. Nature 565: 143–44. Roger Henderson Figure 1.  Movement of the magnetic north pole. Source: Whitze (2019). 28 PREVIEW Data trends FEBRUARY 2019