By Robert Morton June 9, 2009
I haven't yet experienced an earthquake since moving to Seattle, but with all the volcanoes in our vicinity I'm definitely curious about this region's plate tectonics. Thanks to data.gov, we were able to download earthquake data since 1973 and take a look at activity across the globe.

First, let’s consider the Cascade Volcanic Arc. This is part of the area known as the Ring of Fire, a ring of volcanoes around the Pacific Ocean which is responsible for about 90% of the world’s earthquakes (Wikipedia). The Cascade Volcanic Arc includes the volcanoes that extend up the Pacific Northwest coast (Mt. St. Helens, Mt. Adams, Mt. Rainier, Mt. Baker to name a few), into the Aleutians in Alaska and the Pacific Ocean. Let’s take a look at the earthquakes in the Cascade Volcanic Arc.

Cascade Volcanic Arc Cascade Volcanic Arc

Many of the largest earthquakes are off the coast, but earthquakes off the coast can cause other problems.
photo credit: tromasbronot

On that note, let’s look at another major earthquake region: the Mariana Trench. The Mariana Trench is the deepest part of the ocean, right off the coast of Japan.

Mariana Trench

image credit: Kmusser

It’s interesting how a mapping of the earthquakes over the years evokes the shape of the Mariana trench: you could almost map it by its seismic activity. The trench is a subduction zone, which is the cause of its high earthquake activity and intensity. While the trench is an impressive 11 km deep, scientists have detected earthquakes at depths of more than 600 km. In contrast, divergent tectonic plate boundaries such as the mid-Atlantic ridge generate fewer, shallower and less violent earthquakes.

Finally, let’s take a look at all this activity in summary. Note that most earthquakes have a magnitude between 4 and 5 on the Richter scale:

Earthquakes near the surface are known as "shallow-focus", and are far more prevalent. The second spike at 33 km in the graph below is consistent with the depth of the upper mantle.

The frequency of "shallow-focus" earthquakes may reflect limitations of our detection technology, which has improved over time as demonstrated in the "Depth vs. Magnitude" view:

For an online, interactive view of this data since 2004, visit the Tableau Public page on earthquakes. Or, download this workbook and explore the data on your own (using the free Tableau Reader, or a free trial of Tableau Desktop). And if you see a big one coming, call us and let us know.

Comments

The workbook demonstrates the power of selection-driven actions on dashboards, which allowed me to control the "zoom level" of the detailed panes by using selection on the coarse-grained panes.

Additionally, I used some hefty calculated fields to bin latitude into visually-square regions. Since the maps are a Mercator projection, simply binning latitude/longitude in even increments will result in skew towards the poles, causing ugly tiling of points on the map. For performance I materialized most of these calculations, but I left "Latitude (bin-3)" and "Longitude (bin-3)" intact for those who are curious.

The magnitude versus Density plot is really interesting. It would be great to see earthquakes laid-out over a time series, or even intensity/time/time, to see if there's another big one coming. Thanks for the great visual!

I just read an AP article on how natural gas drilling has led to earthquakes in north Texas. It only took a brief moment to fact-check the article with Tableau:

It's obvious that this activity is recent, since no earthquakes were detected prior to 2008. The count of events, dates and magnitudes are all consistent with the article.

@nmeyer - that's an interesting idea. I took a brief look at a time-lapse view of San Francisco, and there were more than 100 aftershocks from the magnitude 6.9 quake (Loma Prieta) in Oct. 1989. This makes it more challenging to find extended periods of reduced activity that allow such tremendous pressure to build. You should download the workbook and post your findings!