Did you ever wish to know more about earthquakes? It used to be a tiring exercise, with the need to delve through books and cumbersome-styled scientific articles.
Not anymore! The reign of the internet has started, and the reign of the book is doomed!
Just click on:
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 extensional quakes 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, or 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. These are commonly associated with volcanism, often parallel to the quakes at a distance of some 100 kms or less.
- 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.
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 statistics. 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 stepping flanks 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 for your own private research. Thanks to the wonders of the internet, we are today truly empowered to do our own research. Good luck!
© 2007 by Franz L Kessler