Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /usr/home/web/users/a0028728/html/blog/wp-includes/functions-formatting.php on line 83
Did you ever wish to know more about earthquakes? It used to be a cumbersome exercise, with the need to delve through books and strangely worded articles.
Not anymore! The reign of the Internet has started, the reign of the book is doomed!
Just click on:
http://earthquake.usgs.gov/eqcenter/recenteqsww/
and you will be presented with a world-map showing earthquakes of the last week, the last day, and the last hour. Click on any of the colored squares, and you’ll see smaller-scale maps, with the exact quake location, and the depth of quakes. Looking through it you’ll realize the very uneven global distribution of earthquakes.
In same places, the earth quakes every month. These are the major and minor plate boundaries. Most common are the extensional quakes (plates moving apart) occurring at a depth of some 10 km.
- In some zones, earth-quakes occur every week. These are so called active plate margins, were young tectonic processes are shaping the earth. The plate margins of the Pacific and of some Atlantic plates fall into this category, and also the compressive belt leading from the Alps to the Himalaya.
- In some zones, there is a quake on every day, or even every hour. These ‘hotspots’ are located in very specific zones, such as Kuril Islands offshore Alaska, Kamchatka, Sulawesi, the southern-most Atlantic, the Lesser Antilles, and a few more.
When you dig a little deeper, you’ll find that the distribution of earthquake depth is profoundly skewed.
- Most common quakes occur at a depth of 10 km or less. These quakes can stem from extension (= lateral pull), compression (= push), or (more rarely) shear along plate boundaries, and characterize areas of active volcanism.
- A large number of quakes occur at a depth of 10-100 km. These quakes are almost entirely related to plate subduction (=pushing one beneath the other) processes. Alaska and the Caribbean are good examples. These are commonly associated with volcanism, often parallel to the quakes at a distance of some 100 km or less. Areas located next to a subduction zones (Lima, Peru, for example) are earthquake and damage-prone, as the quake centers tend to be shallow, and the shaking is violent.
- Lateral movements (strike-slip) and the related quakes are common in a few specific areas around the Pacific margin: California, Oregon, Taiwan, Philippines, New Zealand. These zones can spark very violent quakes, too.
- Deep quakes (100-700 kms of depth) occur in a very few selected areas only. These are: Below the eastern cordilleras of South-America; in the Sulawesi Sea; the Western Pacific, such as near the Mariana Islands; in the Mediterranean, such as in the area of the Lipari Islands. Deep quakes relate to areas, where cold slabs of rigid crust have been submerged into the semi-liquid mantle, without haven smelted-up completely yet.
The damage originating from these quakes is normally small, compared to the others.
More practically, would you like to check-out the site of your domicile for dangers resulting from earthquakes? Very easy! Look for the button ‘historical earthquakes.’ Earthquakes do always come in groups. If an area has been completely quiet for 20 years, it highly suggests that such an area is relatively stable, and chances for major earth-quakes are extremely low. In many ways, earthquake-prone areas are smoking guns, and shine up in your earthquake statistic. To obtain that one, select your area of interest in latitude and longitude coordinates, and get your earthquake listing or plot from that area.
Earthquakes not only come in groups, they are mostly aligned on linear features such as fault lines. These are also often seen in the landscape (the many romantic stepping flanks and bents in places like San Diego or San Francisco, are fault lines). If several earthquakes line up, and your property is located on such alignment, better consult an expert!
Dear readers, I hope I have wetted your appetite. Thanks to the wonders of the Internet, we are now today truly empowered to do our own quake research. Good luck! I’ve attached a few USGS quake maps to farther illustrate the issue.
© 2007 by Franz L Kessler
2 Responses to “Earthquakes: An Ideal Field for Self-Study”
Leave a Reply
You must be logged in to post a comment.
Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /usr/home/web/users/a0028728/html/blog/wp-includes/functions-formatting.php on line 83
Thank you for the refresher course on earthquakes, Franz. As you know, my first time at university was as a geology major, so I loved reading this. And I loved the link.
The Internet makes it so much easier to learn about anything. Do you remember how when we were kids, we had to actually go to a brick and mortar library and pour through thousand page volumes and journals to do our own research? If we wanted a map such as what was shown on the USGS site, we’d have to make our own. I still have some of my old drawings from that time. LOL…life is so much easier now. I just don’t know if my brain is big enough to hold all this information?
~ Sara
Deprecated: preg_replace(): The /e modifier is deprecated, use preg_replace_callback instead in /usr/home/web/users/a0028728/html/blog/wp-includes/functions-formatting.php on line 83
Indeed! I remember these good old brick and mortar days too well. This said, I wrote my majors thesis on the precursor of a PC - not bad for 1981! It was run with a large floppy, and crashed all the time. We wrote also simple histogram programs ourselves - quite a change from then. Re technology, another twist has entered the scene - we have begun to use technology without a proper scientific background, and have become MEBBOM’s (=Moderately Educated Black Box Operating Monkeys) LOL.
It’s quits serious, though…I’m trying to direct my overloaden brain toward the simpe essence, and find some other monkey to run the black box for me.
Thanks and cheers!