OK I have been just looking for clusters in the data and I found that over the last little while there has been a cluster of small earthquakes in Mexico, just south of the US border in Chihuahua. Historically, not many earth quakes here, 6 from 1975 to 2000. I haven’t found any before that.
But 2009 and 2010, 2 each year. This year so far? 16! I look at seismic history of the area, and just north east of the cluster, another cluster in New Mexico. This New Mexico cluster is a bit slower, but closely grouped. The new mexico cluster is all in the same area but it has been happening at only 2 between 1974 1998, but from then until now averaging 3 or so a year, 5 in 1999, and most years since then having at least 1 (except 2001 and 2007.) This is a dramatic increase in activity but with data only going back a hundred years or so we can’t tell if this is something new.
The Chihuahua cluster (30.8, 105,8) is on the edge of a zone of faults that roughly runs along the Texas, Mexico border which then seems to turn north into New Mexico at El Paso, away from the New Mexico cluster (32.6, 104.5) so they don’t seem to be connected until you look a bit closer and notice that the fault zone along the border Texas Mexico border is associated with a second fault zone going north from Van Horn Texas toward the Texas, New Mexico border and that the New Mexico cluster is at the edge of this zone if you just extend it 1 degree north. I’m thinking that this proximity and being connected by a fault zone could mean something but what?
Well there are a lot of faults all over the north american plate. Because of tectonics pushing the plate sideways and it running into the Pacific we have the ranges of mountains and the foothills east of those mountains. Considering where these quakes are it would seem that this would be the result of the continuation of mountain building in the western half of North America. My first thought was volcanic, the change in depth from 10 to 5 km seemed to indicate this, but looking at the fault zones I am thinking more folding and bending which while important is not quite so dramatic.
Looking around a little I see a cluster of quakes at Alpine Texas in 1995, April, with the initial quake being a 5.7. This is just east of the same fault zone and south. In 1990 there was a cluster at 34.4, 104.6 with a number of quakes in July then again in November and December that same year. In 1999 a cluster at 32.5, 104.6 (the same spot as the above mentioned New Mexico cluster.)
Looking at even older data, 1906 was a cluster at 34.0, 107.0 which is further north on th same fault. In 1938 a cluster at 33, 108 just west of the fault zone. This data of a series of quakes along one fault zone shows a pattern of clusters of quakes along this fault zone. This activity is increasing and concentrating at the Texas/Mexico border end of the fault. While this hasn’t always been one end to the other the general trend has been and continues to be so I would call this an earthquake storm. So where will the next cluster of quakes be?
Images from USGS.gov
- Earthquake storm in Southwest Pacific? (echlinm.wordpress.com)
- Chihuahua Mexico: 4 earthquakes in 9 hours – Is a major quake on the way? (theextinctionprotocol.wordpress.com)
- Seismologists rumble over quake clusters (sciencenews.org)