March is Earthquake Month, and Other Shaky 'Facts'

By Michael Schirber, LiveScience Staff Writer

posted: 09 March 2005 06:52 am ET

: Alaska Earthquake March 27, 1964. One span of the Million Dollar truss bridge of the former Copper River and Northwestern Railroad was dropped into the Copper River by the earthquake, and the other truss spans were shifted on their piers. Credit: USGS.
: Alaska Earthquake March 27, 1964. Tsunami damage along the waterfront at Kodiak. Credit: USGS.

A glance at geologic statistics might lead one to believe March is earthquake month. After all, the two strongest recorded earthquakes in U.S. history occurred in this month.

A deeper look reveals the true randomness of the events, dispelling also myths about "earthquake weather" and early morning quake frequency. Location, however, is another story.

On March 28, 1964, Prince William Sound, Alaska, experienced a 9.2 magnitude event that killed 125 people and caused $311 million in property loss. On March 9, 1957, the Andreanof Islands, Alaska, felt a 9.1 temblor.

But the next three biggest U.S. earthquakes occurred in February, November, and December.

Top 10 U.S. Quakes

Rank	Locale	Size
1	Prince William Sound, AK	9.2
2	Andreanof Islands, AK	9.1
3	Rat Islands, AK	8.7
4	Shumagin Islands, AK	8.2
5	New Madrid, MO	8.1
6	Yakutat Bay, AK	8.0
7	Andreanof Islands, AK	8.0
8	New Madrid, MO	8.0
9	Cape Yakataga, AK	7.9
10	Fort Tejon, CA	7.9

LiveScience / SOURCE: USGS

The largest earthquake ever measured globally - a magnitude 9.5 in Chile - was on May 22, 1960. And the recent tsunami-causing earthquake off the coast of Sumatra happened the day after Christmas last year. It was first put at magnitude 9.0 but later raised to 9.3.

"Earthquakes occur randomly throughout the world, as well as the U.S.," said Waverly Person, a spokesman for the U.S. Geological Survey's National Earthquake Information Center.

Earthquake weather

There are claims that more earthquakes happen on hot, dry days - so-called "earthquake weather." But studies that have shown no tie between seismic activity and months or seasons.

Maps: Recent Quakes

U.S. / World

The forces that drive weather are not likely to have much of an effect on the movement of continental plates several miles below the surface, geologists say.

Even the tide-causing gravity of the Moon and Sun apparently play no role in the onset of an earthquake. Scientists have looked for a seismic relationship to the tides, but nothing has been seen except for a small correlation with aftershocks in some volcanic regions.

Morning madness

Another misconception is that most rumblings occur in the morning. Although the likelihood of an earthquake is unrelated to the time of day, an earthquake could be more deadly - and therefore more memorable - at certain hours.

"In the early morning, most people are in their beds sleeping. You might have higher casualties with a lot of people in one place," Person told LiveScience.

As opposed to times, there are, of course, places that are more earthquake-prone than others. Alaska is one of the most seismically active regions in the world - experiencing a major earthquake (magnitude 7.0 or greater) almost every year, whereas no earthquakes of more than moderate intensity have occurred within the borders of North Dakota during historical times.

Earthquake Frequency

Average number each year globally:

Type	Magnitude	Average
Great	8+	1 ¹
Major	7 - 7.9	17 ²
Strong	6 - 6.9	134 ²
Moderate	5 - 5.9	1319 ²
Light	4 - 4.9	13,000*
Minor	3 - 3.9	130,000*
Very Minor	2 - 2.9	1,300,000*
¹ Based on observations since 1900 ² Based on observations since 1990 * Estimated LiveScience / SOURCE: USGS