Archive for February, 2013

From California Rail News, California Rail Foundation, Train Riders Association of California, 1025 Ninth Street #223, Sacramento, CA 95814-3516, Volume 24 Number 3 Page 6

December, 2012

“Risk Muted on L’Aquila, Bridge & HSR”

by Wilhelm B. Reich

In October, U.S. press outlets accused Italian judges of attacking science by holding six experts responsible for not predicting the earthquake that killed 309 people in April 2009.

The AP reported, “Defying assertions that earthquakes cannot be predicted, an Italian court convicted seven scientists and experts of manslaughter Monday for failing to adequately warn residents before a temblor struck central Italy in 2009 and killed more than 300 people.”

The Christian Science Monitor stated: “An Italian court sentenced scientists to jail time for not having a functioning crystal ball ahead of the 2009 earthquake in L’Aquila. The arguments of science and reason fell on deaf ears.”

Provoked by this coverage, an array of scientific voices in the English-speaking world criticized the reported action of the Italian judiciary, although many lacked direct knowledge of the details, reported only later in scientific journals.

An article published October 12 in the journal Science explained the real point of the case against the scientists: “Prosecutors didn’t charge commission members with failing to predict the earthquake but with conducting a hasty, superficial risk assessment and presenting incomplete, falsely reassuring findings to the public. They have argued in court that the many tremors that L’Aquila experienced in the preceding months did provide at least some clues about a heightened risk.”

The British journal Nature said that the verdict was based on how the six scientists and one government official assessed and communicated risk before the earthquake hit on April 6, 2009.

Bernardo De Bernardinis, deputy head of Italy’s Department of Civil Protection, told the press a week before the quake: “The scientific community tells me there is no danger because there is an ongoing discharge of energy,” a statement many seismologists consider to be scientifically incorrect. Asked directly if the public should sit back and enjoy a glass of wine rather than worry about earthquakes, De Bernardinis was unreserved: “Absolutely, absolutely a Montepulciano DOC.”

Some independent seismic experts view the L’Aquila verdict differently. Lalliana Mualchin, the former chief seismologist for Caltrans, was called to testify as an expert witness for the prosecution. In 2010, when the indictment. was made, Mualchin and other experts criticized and refused to sign a letter supporting the indicted seismologists.

Mualchin’s expert opinion is that the hazards were not properly assessed in L’Aquila. “Italy is one of the countries with the best seismic knowledge in the world. And yet look at what a 6.3 earthquake has done to this city. That knowledge was not used, and scientists are responsible for that. They were conscious of the high risk in the area, and yet did not advise the people to take any precaution whatsoever,” he said.

Mualchin put the blame on the use of a probabilistic model. Italian authorities based their risk analysis on frequency of earthquakes in the area, not on their severity. This method is now considered state of the art in many countries, but in Mualchin’s view, systematically underestimates seismic hazard because it fails to consider extreme and rare events.

Mualchin says quake “frequency is not important, what really matters is the largest earthquake we can expect, the strongest one that has happened in the past. Risk prevention should be based on that.”

Deterministic seismic-hazard analysis (DSHA) used that philosophy. DSHA is now out of style on many campuses and younger seismologists do not even learn about it, according to Mualchin. “PSHA [Probabilistic Seismic Hazard Analysis] is a bad model California has exported elsewhere, and we see the results here in L’Aquila,” Mualchin told Nature in October.

Just under the surface, unmentioned by the press, is the motivation for PSHA. It was actually an industry reaction to the higher costs of fully recognizing the dangers exposed by the earthquakes of the 1980’s. Research on the Northridge, Loma Prieta, and Santa Clarita quakes didn’t expose the full extent of risks until nearly a decade later. Sticker shock at the needed fixes to structures resulted in pushback by construction firms, with the result that there was a lot of controversy. That made everyone in the field anxious.

Over the 1990’s, cozy arrangements intensified between the major design-build firms, state departments of transportation, and academics who more often than not work for both, leading to actions and decisions to downplay risk by adopting an actuarial approach instead of a safety approach. Less stringent seismic standards can save billions in civil costs while enriching engineering firms.

Until that time, most risk assessments used “deterministic” models in which structures were designed to withstand the worst-case scenario, Maximum Credible Earthquake, (MCE) for a given location. Since such large earthquakes are infrequent, clever engineers developed methods “borrowed” from the insurance industry in which risk is assessed by the probability of quakes of various intensities occurring within the service life of the structure.

This methodology yields loads smaller than those produced by MCE, therefore reducing construction costs. It appears that Californians should be even more concerned than Italians about the eventual consequences. The Bay Bridge East Span, expected to open by 2014, is exposed·to severe San Andreas and Hayward fault hazards, which were downplayed by use of a PSHA model.

The asymmetrical steel self-anchored suspension (SAS) bridge currently under construction as part of the East Span has never been tested at scale on a seismic simulator. No empirical data exists for the bridge, because one of its type and size has never been built. However, the EDAP panel, in charge of seismic review, picked a new probabilistic model, the “Seismic Evaluation Earthquake” (SEE) which assumed that the structure would only have to weather a temblor with lesser force than the MCE. Chair of the current Caltrans panel is Dr. Frieder Seible, a publishing partner with Prof. G.M. Calvi, one of the sentenced Italian experts.

In its 2000 Report on the bridge, the Army Corps of Engineers posed concerns about vulnerability of the SAS. “The bridge should be evaluated for a design that addresses the San Andreas MCE ground motions. These ground motions appears to be more forceful than the SEE ground motions in the period range significant to the bridge.” For example, the Loma Prieta quake had very low frequency, a rolling motion felt up to 100 miles away, but SEE uses a higher frequency temblor less likely to do damage.

In its assessment, the Corps clearly states the bridge is not seismically safe. The Corps says that the “performance of a replacement bridge during a Maximum Credible Earthquake (MCE) cannot be determined. The bridge has not been evaluated or designed for a MCE event, which is larger than the SEE event.”

Caltrans seismic experts never agreed with use of the SEE, but the Metropolitan Transportation Commission sidetracked them by demanding that the transportation agency cede design control to the “independent peer review” panel.

The Bay Bridge East Span is far from being the only vulnerable structure. Highspeed rail seismic analysis also relies entirely upon probabilistic modeling. High Speed Rail Authority officials have downplayed dangers of their proposed elevated viaducts in the Central Valley and on the Tehachapi grade, where the height of the structures would reach 330 feet between the White Wolf and Edison Faults.

Probabilistic models are a convenient way for HSRA to hide serious problems. Earthquakes in the Tehachapi area are very rare, but also very dangerous. The last major White Wolf earthquake was in 1952, but it was the most significant Southern California earthquake of the 20th century. It destroyed all major structures in Tehachapi, many in Bakersfield, and eradicated about 8 miles of rail line.

The PSHA model says we don’t need to worry because the big one probably won’t happen here in our lifetime, even if it did recently in Italy.


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