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San Francisco's catastrophic 1906 Earthquake a warning for today

San Francisco's catastrophic 1906 Earthquake a warning for today from

It was an unprecedented natural disaster that destroyed a coastal US city. A bungled government response made it worse. Racism plagued survivors. It wasn't Hurricane Katrina, which slammed New Orleans and the Gulf Coast last year. It was the 7.8-magnitude earthquake that rocked San Francisco one hundred years ago on April 18.

When the nominal moment of the 100-year anniversry of the Great San Fransisco Earthquate occurs--which will be 2006-04-18T05:12-0700--the duration since the event will actually have been 36524 days and 23 hours (876599 hours or 52595940 minutes,) and not 36525 days of 24-hours each. The reason is that back in 1906, Daylight Saving Time was not observed--not in San Francisco, not in the United States, and not anywhere in the world. In fact, in 1906, time zones with "Standard Time" had only been in use in the United States for 23 years.

The count of seconds since the event depends on which timescale one uses. Using UT0 or UT1, the count of seconds would be 3155756400. Using UTC, it is necessary to at least add the 23 leap seconds that have occurred since the adoption of the UTC timescale in its current form in 1972.

The UTC standard says nothing about whether leap seconds should proleptically be imputed to have occured before the adoption of leap seconds into UTC--although some date/time algorithms take just that approach. Whether that's "right" or not depends on the Use Cases that one is attempting to satisfy.

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