Comment: 12:49 - 14:18 (01:29)
Source: Annenberg/CPB Resources - Earth Revealed - 25. Living With Earth, Part I
Keywords: "Loma Prieta Earthquake", "San Francisco", Oakland, epicenter, "San Andreas Fault", earthquake, "fault segment", magnitude, "earthquake prediction", "North American Plate", "Pacific Plate"
Our transcription: The earthquake was also surprisingly brief, given its great power, with shaking felt for only about eight seconds.
The extent of the damage in parts of San Francisco and Oakland, a full 90 kilometers from the epicenter, also surprises most people.
And yet the event itself was hardly a surprise.
Earthquakes along the San Andreas Fault have no doubt occurred throughout its 30 million year history.
Whenever the plates on either side of the fault lock and strain against one another, a breaking point is eventually reached, and as the plates lurch past one another, an earthquake occurs.
But there's another reason why this particular quake was not unexpected.
Scientists have known for several years that the 1,200 kilometer long San Andreas Fault is actually composed of individual discrete segments.
Geophysicists have calculated the probability of major earthquakes in each of these regions, along with the maximum likely magnitude at each location.
The Loma Prieta Earthquake occurred along one of the six fault segments considered most like to sustain a magnitude 6.5 or larger event within the 30 year interval between 1988 and 2018.
Geology School Keywords