Earthquakes have struck both Alaska and Southern California in the past 24 hours, less than two weeks after an extraordinary quake on the East Coast.

The Alaska quake on Friday registered at magnitude-7.1 and sparked a tsunami warning south-east of the remote Aleutian Islands.

On Thursday, a 4.2-magnitude quake rumbled through the Los Angeles region -- the biggest such tremor in the area in more than a year. No injuries or damage were reported.

Although earthquakes can be frighteningly calamitous (like the Japanese disaster in March), it should be remembered that they are rather routine geologic events.

For example, the U.S. Geologic Survey daily lists earthquake events around the world (including aftershocks) on its Web site.

Generally speaking, quakes below magnitude-2.5 are not even felt by the public.

According to the Los Angeles Times, the latest temblor was so quiet that most people in the city didn’t even realize that a quake had occurred. People in this quake-prone region are more than accustomed to the ground shaking.

One Los Angeles resident told the paper: “Just a rolly. It didn't even move my chair.

Another said: “There was no screaming out that I was aware of. It hardly got my notice. It's just Southern California, you know?

Quakes of magnitude of 4.5 or higher can cause damage. Also, it must also be kept in mind that the Richter scale is logarithmic, not linear. This means that a magnitude-5 earthquake would cause 10 times the amount of damages (level of shaking) as magnitude 4 -- and also release 32 times the amount of energy. (The Japanese earthquake from March 2011 was magnitude 9.0).

In any case, according to the U.S. Geological Survey site, on Friday Sept. 2 (the day of the Alaska quake), there had already been almost 50 seismic events (of minimum magnitude 1) in the U.S. this morning alone – the vast majority of which have received zero media coverage.

Tremors have been recorded in quake-prone states like Alaska and California, but also in places like Arkansas, Nevada, Washington State, and Puerto Rico.

Similarly, on Thursday, Sept. 1, geologist recorded almost 100 seismic events in the U.S. of magnitude 1.0 or greater. The vast majority of these quakes occurred in California and Alaska -- but some were also reported in Hawaii, Puerto Rico, Arkansas, Montana and Idaho.

This doesn't even include the hundreds, perhaps thousands, of seismic events that occur across the globe due to the endless shifting and moving around of tectonic plates.