Dec 12 2013

 

 

 

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Whether a modern civic society could operate under such conditions is questionable. At the instant of the USGS model earthquake, debris would close roads, extinguish traffic lights, water supplies would be cut off, and emergency responders would have difficulty operating.

-BBC News

In a new report presented to American Geophysical Union meeting in San Francisco, Dr. Lucy Jones of the US Geological Survey painted a very bleak of the consequences of the next big California earthquake. She made clear it is not a question of 'if' the 'big one' hits but 'when' it hits. With almost 100% certainly, historical patterns indicate that a 7.0 or greater quake will hit in California.

Besides collapsed buildings and tens of thousands of building made inhabitable because of damage, the California infrastructure would be devastated. That includes the ability to obtain water, power, food and shelter.

If the earthquake should hit in the time of Santa Ana winds, massive uncontrolled fires should be expected with firefighters unable to reach many burning areas.

Few of us who experienced the Northridge Earthquake in 1994 will forever get the quake. The quake measured 6.7 and was one of the five top worse disasters in American history with close to $60 billion in damage and near 60 dead. (See photographs on this page)

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BBC News reports on Dr. Jones speech.

In addition, in the event of such a quake, some buildings that do not collapse will nonetheless remain uninhabitable, due to the risk of collapse in aftershocks. These are given a so-called "red tag".

Past experience shows that this is a significant multiplier. In the magnitude 6.7 earthquake that hit Northridge, 20 miles north-west of Los Angeles in 1994, around 230 buildings collapsed but around 2,300 red tags were issued.

Similarly, in a quake that hit the San Francisco Marina District in 1989, for every collapsed building, around 10 others receive a red tag.

Carrying these results over to the worst-case scenarios for Los Angeles, this suggest that almost all buildings could become uninhabitable and still satisfy the definition of success for the building code.

Seismologists at the US Geological Survey have simulated the effects of the next big Californian earthquake in a programme of study called ShakeOut. One of their computer models assumes that the next big event on the San Andreas fault will be magnitude 7.8, with a single event in which a rupture starts in Southern California near the Salton Sea and then shoots north along the fault to hit Los Angeles.

In their model, the thick sediments that downtown LA sits upon amplify the strong shaking of the quake, which would happen around 75 seconds after the first small signal of the earthquake.

Ground motions would be of "Intensity 9", corresponding to accelerations of one G, causing significant damage to buildings. The model suggests the collapse of possibly around 1% of the buildings in an area of 10 million people.

The end result would be that around half the buildings in the area would have to be abandoned. But the model's most disturbing results show that beyond the building damage there would be significant disruption of inter-dependent infrastructure.

Transportation, gas and electricity supplies, sewerage systems, water supplies and communications would all be affected.

Whether a modern civic society could operate under such conditions is questionable. At the instant of the USGS model earthquake, debris would close roads, extinguish traffic lights, water supplies would be cut off, and emergency responders would have difficulty operating.

Beyond that, the disruption of the supply chain also becomes an issue, pointed out Dr Jones. The move towards a "just in time" economy in grocery stores and elsewhere has introduced additional vulnerability.

There are few warehouses or stockpiles of food on the western side of the San Andreas fault.

The water system is vulnerable: 70% of the water pipes in Southern California are made of brittle concrete which would likely fail in a large quake, with LA served by water supplies that traverse the San Andreas fault.

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Even repairing the pipe network was stated as an issue, since current pipe manufacture in the US is insufficient to replace the damage in under six months. Replacement by polyurethane piping, which can withstand earthquake shaking, could overcome this problem.

The impact of Hurricane Katrina in New Orleans serves as a cautionary example of the impact on society of a major natural catastrophe.

If water, power, transport and other infrastructure was cut off to downtown LA for six months or more, it seems likely that many commercial businesses would fail.

In the case of earthquakes in particular, aftershocks could cause additional psychological distress that would likely result in the net movement of populations away from the stricken zone, again damaging local economies.