Seismicity of Azerbaijan

I'll be away in Azerbaijan the next three weeks or so, working at the Oglanqala archaeological site doing magnetometry.

The Azerbaijani National Academy of Sciences Geology Institute says:

Genetically seismicity of Azerbaijan is associated with activity of seismogenic structures in the Lesser Caucasus and in the Greater Caucasus Ridges. In the most territory of Azerbaijan earthquakes of magnitude M=6-6.5 may take place and in some seismogenic structures one can expect seismic events of a maximum magnitude up to M=7. This indicates that on the whole the territory of Azerbaijan and the adjacent part of the Caspian depression have a moderate seismicity. Though for the recent period in the Caucasus region there have not been recorded any seismic events of magnitude M>7-7.2, from the point of view of their peculiar features this region is characterized by a high engineering-geologic risk. This distinguishes the territory of Azerbaijan from the Pacific mobile belt where intensity of earthquakes by Richter's scale is M=8-8.5. 

The English isn't the best, but try learning Azerbaijani!

Figure from ENVSEC

I'll be in the bottom left area of the map, not far from Ararat.

See you in July.

Jones Geological Services and Dillsburg

Jeri Jones of Jones Geological Services is often mentioned in media accounts of the Dillsburg earthquakes. His company's website has a piece on the Dillsburg series of small events on its web page, mostly focused on the activity last Fall. The isoseismal map contours values of Modified Mercalli intensity from the magnitude 2.1 earthquake of October 19, 2008.

Jones poses the following question:

What makes this swarm of shallow earthquakes interesting to investigate?

1. The number of tremors felt over the last ten weeks
2. The regular “boom” that accompanies many of these tremors
3. A sulfur smell associated with the larger tremors and sometimes within the groundwater

British seismotectonics

Good question posed in the comment after my last entry by Hypo-theses blogger Ian Simpson. Did St. Patrick chase the earthquakes out of Ireland? That would be a nice story indeed, but maybe we can come up with a scientific reason.

I won't claim to be an expert, but a Google search (shhh, don't tell my students) came up with a very nice PowerPoint from Dr. Brian Baptie of the Earthquake Seismology team, Earth Hazards and Systems Programme, British Geological Survey (excellent web site). The paper is on Seismo-tectonics and state of stress of the British Isles, presented at the 8^th International Symposium on Upper Rhine Graben Evolution and Neotectonics. You can find and download the presentation here.

Baptie does indeed note a strong variation in spatial distribution of seismicity throughout the United Kingdom. Earthquakes occur in a north-south band along the length of Britain. But there is an absence of seismicity in northeast Britain, the northwest Atlantic margin and Ireland (as we pointed out yesterday). The rather striking pattern is shown in the figure below.

The figure above (click on it for an enlarged version) shows historical seismicity of the UK (yellow) from 1832 to 1970 for earthquakes of magnitude above 3.0 and instrumental seismicity (red) from 1970 to present for earthquakes with magnitudes > 2.0 (from Earthquakes in the UK).

Baptie concludes that a prevailing stress field due to northwest compression is dominant, suggesting a combination of plate boundary forces plus post-glacial rebound may be controlling re-activation of old faults.

Lancaster earthquakes - how dense are they?

Or, after another entry on the Lancaster earthquake, you might be asking how dense is Rob?

from http://neic.usgs.gov/neis/bulletin/neic_bcah_d.html

The gray color suggests that there is about 0.1 magnitude 5 earthquakes in that region per year, or only 1 every 10 years (which actually seems a bit high to me). But in the Lancaster area, colored white, the frequency is even less. This actually isn't a very interesting diagram here because of the paucity of large earthquakes. We'll have to look at this type of diagram later for a larger earthquake, presumably in some other part of the world near a plate boundary.

Lancaster - Historic Seismicity

Ok, let's go back to the NEIC web page for the recent Lancaster earthquake.

Now click on the link down the page on Historic Seismicity.

click on above for larger image
from http://neic.usgs.gov/neis/bulletin/neic_bcah_h.html

This is a cool graphic. Previous earthquake epicenters are indicated with the circles. The radius of the circle indicates the earthquake magnitude. And the depth of the epicenter is shown by the color. So four dimensions of data are shown on a two-dimensional figure.

All of the historic quakes shown are small, and all are shallow.

Note the last line in the figure caption. Plate boundaries, that is, the type of boundary between different plates in the plate tectonics model, are indicated. In this area, there are no plate boundaries. Thus, these are examples of intraplate earhquakes, those that occur within a plate, as opposed to the interplate earthquakes that occur at boundaries between different plates.

It will be useful at a later time to compare this earthquake to one at a plate boundary, in an area of much higher seismicity.

My holiday earthquake theory

Two blogs back I wrote on earthquake (seismicity) patterns. Well, I have a pet theory that earthquakes tend to occur on holidays. Cases in point:

1. Lisbon earthquake, 1755 - All Saint's Day. According to Rob Zaretsky, professor of French history at the University of Houston, over 100,000 people died. The earthquake also pounded Europe's political and cultural landscapes. The brightest light of the Enlightenment, Voltaire, used the earthquake in his wonderful satire, Candide. From a ship in Lisbon harbor, Candide watched helplessly as the good drowned and the wicked survived.
2. Alaskan earthquake, 1964 - Good Friday. This is the second biggest earthquake ever recorded, surpassed only by the 1960 Chile quake. According to the Alaska Earthquake Information Center, the area of significant damage covered about 130,000 square kilometers. It was felt over 1,300,000 square kilometers (all of Alaska, parts of Canada, and south to Washington). The four minute duration of shaking triggered many landslides and avalanches. Major structural damage occurred in many of the cities in Alaska. The damage totaled $300-400 million dollars. You betcha.
   
3. Sumatra-Andaman earthquake, 2005 - day after Christmas (that's kind of a holiday, isn't it?). The IRIS special report states that approximately 1200 kilometers of the India-Burma plate boundary slipped, with an average displacement on the fault plane of about 15 meters. The resulting tsunami claimed 250,000 lives.
4. Lancaster, Pennsylvania, 1984 - Easter Sunday. This is actually the only earthquake I have ever experienced. It was studied by our own group's Charlie Scharnberger (see booklet on Earthquake Hazard in Pennsylvania) and John Armbruster. Actually, this is my favorite kind of earthquake - sensible, exciting, and useful for scientific research, yet it only caused a little bit of cracked plaster.
   

I like the web site at left, Today in Earthquake History. Check out other holidays. What do you think - does my theory amount to anything?

Hoping your solstice and upcoming holidays are disaster-free.