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Earthquakes: the danger continues in Southern California

Aftershocks continue from Chile's 8.2 quake
Aftershocks continue from Chile's 8.2 quake
Gary London

Strong aftershocks continue in Chile following Tuesday's 8.2 event.

Two major aftershocks, the strongest yet shook Chile late Wednesday measuring 6.5 and 7.6.

The recent upsurge in world-wide seismic activity has once again raised concerns about the likelihood of a major earthquake in Southern California.

Despite recent moderate activity in the Los Angeles area, accumulated strain on the nearby San Andreas faultline has not been diminished, in fact it may have been increased.

The San Andreas is the area's most significant and potentially dangerous fault, capable of generating a massive quake, as it has done in the past, and a repeat is long overdue.

The entire state of California is crisscrossed with fault systems both known and unknown. Strain and pressure have been building on the San Andreas north of Los Angeles since the last major quake in the region, back in 1857. Scientific research has confirmed the average interval between major quakes on that segment of the San Andreas is less than previously thought. What was once estimated to be an average of about 130 years between major quakes is now thought to be less, closer to about 100 years. This substantially increases the odds of an already long overdue major quake.

The 1857 quake, centered 75 miles northwest of Bakersfield was of an estimated 7.9 magnitude and ruptured the earth's surface for a distance of some 225 miles. Horizontal ground movement of as much as 30 feet occurred and only two people died as the area was sparsely populated at the time.

While an earthquake on one fault relieves accumulated strain there, adjacent fault lines with accumulated strain can be brought closer to breaking by a “triggering”effect caused by the energy released from the motion of nearby quake.

Of most extreme concern are the fault zones to the south and east of greater Los Angeles; these areas have not experienced a major fault break since the 1600's and pose an even greater risk that the San Andreas north of downtown L.A. Scientists have warned of this potential danger since the 1970s. From about Palm Springs south and eastward to the Mexican border are among the most potentially dangerous areas in the state for a major seismic upheaval. Many in the scientific community agree that Southern California has been very lucky so far, but the “borrowed time” concept might certainly apply here.

A critical consideration here might be that while emphasis on preparedness has been stressed over and over, a significant portion of Southern California's infrastructure (roads, bridges, buildings, schools etc.) might not be able to withstand a major shock. Budget shortfalls along with decreased manpower have slowed, hampered or diminished efforts to retrofit and reinforce some of these structures, which may or may not have been adequately updated despite earthquake building and safety codes put in place following the 1933 6.4 Long Beach earthquake. Recent strong earthquakes brought this fact to light, with structural damage in particular to freeway bridges and overpasses, and with the Olive View Hospital collapse during the 1971 6.6 Sylmar quake.

It should never be taken lightly that Southern California is overdue for and vulnerable to a major seismic upheaval, and preparedness is an absolute essential.

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