To help researchers explore this data and better understand the Earthquake cycle, we are releasing a new, interactive data visualization which draws geodetic velocity lines on top of a relief map by amplifying position estimates relative to their true positions. Unlike existing approaches, which focus on small time slices or individual stations, our visualization can show all the data for a whole array of stations at once. Open sourced under an Apache 2 license, and available on GitHub, this visualization technique is a collaboration between Harvard’s Department of Earth and Planetary Sciences and Google's Machine Perception and Big Picture teams.
Our approach helps scientists quickly assess deformations across all phases of the earthquake cycle—both during earthquakes (coseismic) and the time between (interseismic). For example, we can see azimuth (direction) reversals of stations as they relate to topographic structures and active faults. Digging into these movements will help scientists vet their models and their data, both of which are crucial for developing accurate computer representations that may help predict future earthquakes.
Classical approaches to visualizing these data have fallen into two general categories: 1) a map view of velocity/displacement vectors over a fixed time interval and 2) time versus position plots of each GNSS component (longitude, latitude and altitude).
|Examples of classical approaches. On the left is a map view showing average velocity vectors over the period from 1997 to 2001. On the right you can see a time versus eastward (longitudinal) position plot for a single station.|
Each of these approaches have proved to be informative ways to understand the spatial distribution of crustal movements and the time evolution of solid earth deformation. However, because geodetic shifts happen in almost imperceptible distances (mm) and over long timescales, both approaches can only show a small subset of the data at any time—a condensed average velocity per station, or a detailed view of a single station, respectively. Our visualization enables a scientist to see all the data at once, then interactively drill down to a specific subset of interest.
Our visualization approach is straightforward; by magnifying the daily longitude and latitude position changes, we show tracks of the evolution of the position of each station. These magnified position tracks are shown as trails on top of a shaded relief topography to provide a sense of position evolution in geographic context.
To see how it works in practice, let’s step through an an example. Consider this tiny set of longitude/latitude pairs for a single GNSS station, with the differing digits shown in bold:
If we were to draw line segments between these points directly on a map, they’d be much too small to see at any reasonable scale. So we take these minute differences and multiply them by a user-controlled scaling factor. By default this factor is 105.5 (about 316,000x).
To help the user identify which end is the start of the line, we give the start and end points different colors and interpolate between them. Blue and red are the default colors, but they’re user-configurable. Although day-to-day movement of stations may seem erratic, by using this method, one can make out a general trend in the relative motion of a station.
|Close-up of a single station’s movement during the three year period from 2003 to 2006.|
We’ve applied our new visualization to the ~20 years of data from the GEONET array in Japan. Through it, we can see small but coherent changes in direction before and after the great 2011 Tohoku earthquake.
|GPS data sets (in .json format) for both the GEONET data in Japan and the Plate Boundary Observatory (PBO) data in the western US are available at earthquake.rc.fas.harvard.edu.|
- Modifying the multiplier adjusts how significantly the movements are magnified.
- We can adjust the time slider nubs to select a particular time range of interest.
- By enabling map markers, we can see information about individual GNSS stations.
|Station designate 960601 of Japan’s GEONET array during the period from 2006 to 2012. Movement magnified 105.1 times (126,000x).|
We’re excited to continue this productive collaboration between Harvard and Google as we explore opportunities for groundbreaking, new earthquake visualizations. If you’d like to try out the visualization yourself, follow the instructions at earthquake.rc.fas.harvard.edu. It will walk you through the setup steps, including how to download the available data sets. If you’d like to report issues, great! Please submit them through the GitHub project page.
We wish to thank Bill Freeman, a researcher on Machine Perception, who hatched the idea and developed the initial prototypes, and Fernanda Viégas and Martin Wattenberg of the Big Picture team for their visualization design guidance.
 Loveless, J. P., and Meade, B. J. (2010). Geodetic imaging of plate motions, slip rates, and partitioning of deformation in Japan, Journal of Geophysical Research.
By Jimbo Wilson, Software Engineer, Big Picture Team and Brendan Meade, Professor, Harvard Department of Earth and Planetary Sciences