Department of Earth and Environmental Sciences
I have begun to explore the use of “data visualizations” to illustrate the results of my research on how patterns of earthquake locations evolve over time. You can go directly to the data visualizations by scrolling to the bottom of this post, but you may want to read the following explanation first.
These data visualizations are based on the concept of “Cellular Seismology” (CS), which I developed to test the hypothesis that past seismicity delineates zones where future earthquakes are likely to occur (Kafka, 2002, 2007). CS studies address one of the fundamental (and as yet unresolved) questions in seismology: To what extent do past earthquake locations delineate zones where future large earthquakes are likely to occur? Many claimed methods of forecasting earthquakes depend on the assumption that past seismicity indicates where future earthquakes are likely to occur. But this assumption, while true in general, is not yet verified at all the levels of detail necessary to directly relate past seismicity to specific future earthquakes and thus to predict exactly where future large earthquakes are likely to occur.
CS is an intentionally simple method of systematically investigating the relationship between locations of past and future earthquakes in a given region. The name “Cellular Seismology” was chosen because it is analogous to a cellular phone system, with past earthquakes acting analogously to a cell phone tower. The cell tower is associated with a circular zone, extending some radius away from the tower, within which cell phones can receive a signal from the tower. Analogously, we envision that some circular zone surrounding the epicenter of a past earthquake is a zone that presumably has the necessary geophysical characteristics to generate future earthquakes.
CS involves analyzing what seismologists refer to as “earthquake catalogs”, which are databases of times, locations and magnitudes of earthquakes in a given region. To implement CS we construct circles of a given radius around each epicenter in an earthquake catalog (which we call the “Pre-CAT”), and investigate the percentage of later-occurring earthquakes (in what we call the “Post-CAT”) that were located within that radius of at least one previous earthquake. These Post-CAT earthquakes that occurred near a Pre-CAT earthquake are referred to as “hits.”
We then systematically analyze the observed percentages of hits, in an attempt to discern the extent to which patterns emerge in the relationship between locations of past and future earthquakes. We have found what seems to be a stable pattern of at least 2/3 to 3/4 of future earthquakes occurring near past earthquakes in most regions, and we are now investigating how the patterns compare and contrast for different regions.
Technical details regarding how the patterns compare and contrast for different regions are described in Kafka (2002), Kafka (2007), and Kafka and Ebel (2011). The data visualizations presented here provide a visual representation of the evolution of locations of earthquakes in Post-CAT relative to CS maps of the locations of earthquakes in the Pre-CAT for the following four regions:
Click on the above links to see the data visualizations of the CS results.
In each of these movies, the Pre-CAT consists of earthquakes occurring from some start date up to 1999, and the Post-CAT is shown for each year from 2000 to 2011. The CS map of the Pre-CAT is shown in grey, and the locations of the Post-CAT earthquakes are color-coded such that they correspond to a spectrum ranging from blue (2000) to red (2011). Also shown for each year is a bar with its height representing the percentage of hits.
As you view these movies, see if you are able to discern any patterns in how the locations of the Post-CAT earthquakes evolve over time relative to the locations of the Pre-CAT earthquakes.
- Kafka, A.L (2002). Statistical analysis of the hypothesis that seismicity delineates areas where future large earthquakes are likely to occur in the central and eastern United States, Seismological Research Letters, 73(6), 990-1001.
- Kafka, A.L. (2007). Does seismicity delineate zones where future large earthquakes will occur in intraplate environments?, In Continental Intraplate Earthquakes: Science, Hazard, and Policy Issues, Geological Society of America Volume, Geological Society of America Special Paper 425, Edited by S. Stein and S. Mazzotti, 35–48, doi: 10.1130/2007.2425(03).
- Kafka, A.L. and J.E. Ebel (2011). Proximity to past earthquakes as a least astonishing hypothesis for forecasting locations of future earthquakes, Bulletin of the Seismological Society of America, 101(4), August 2011, doi: 10.1007/s00024-011-0315-1.