The earthquake that struck this morning was a frightening reminder that Southern California lies at the heart of earthquake country, but experts doubt that the 4.5 temblor was a precursor to a great quake.
The 9:57 shaker terrified many persons throughout the central city, but the quake was not nearly as bad as it seemed. It was just a modest quake that hit too close for comfort. It was proof once again that a small quake, if it's close enough, can rattle nerves even if it can't topple buildings.
The main shock was followed less than half an hour later by a 4.3 aftershock, a surprisingly large aftershock after such a short period of time.
"It's uncommon" for a 4.3 to follow a 4.5 that quickly, Caltech seismologist Kate Hutton said. But it's not all that rare, she added.
Hutton and U.S. Geological Survey seismologist Tom Heaton said today's temblor was not an aftershock to the Whittier Narrows quake of Oct. 1, 1987, which caused three deaths, but they said it occurred on the same fault system as the 1987 quake. The Elysian Park Thrust System, as it is called, runs from Whittier to Elysian Park east of downtown Los Angeles and is considered capable of a major earthquake.
However, no one could see any reason why the 4.5 quake was a precursor to a major shaker. Hutton said she expected more aftershocks but she said there is only about a 1% to 2% chance that a larger quake is yet to come.
However, that small measure of reassurance must be tempered with the fact that there is considerable uncertainty among the experts over the nature and size of faults underlying the Los Angeles Basin.
Some quakes do not even break the surface of the ground, thus denying valuable research data to seismologists.
Today's quake announced itself with a sharp, strong jolt over much of the central city, typical of a modest quake that is centered nearby. It shook tall buildings, despite its magnitude, because much of the downtown area is built on loose soils that allow an earthquake to make itself known over a wide area.