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February 2004                                                              Volume 6 - Number 1

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Earthquake...

The Twin Quakes of December

By Lori Fagan

Just four days apart and .1 magnitude difference, the December 2003 earthquakes in California and Iran resulted in impacts as much a world apart in difference as the regions are geographically. How could California escape with only two deaths, while in Iran, the country mourned more than 40,000 casualties?

On 22 December 2003, a magnitude 6.5 earthquake struck the central coast of California, centered approximately 25 miles west of Paso Robles, population 217,000, where the worst of the damage and the two casualties occurred. Forty-six buildings were damaged or destroyed, the most severe damages located in a five-block area of the historic downtown district of the city.

In 1988, Paso Robles passed a law requiring unreinforced masonry buildings to meet the state standards for withstanding earthquakes. The buildings that complied with this law prior to the December earthquake suffered little or no structural damage. One building that had not yet complied with these standards cost the lives of two shoppers that Monday morning. About forty others were treated for injuries, and an estimated 40,000 homes and businesses were left without electricity after resulting rockslides brought down power lines. Overall, California fared well, with credit attributed to enforced seismic resistant building codes.

In Iran, the 6.6 magnitude earthquake that struck in the early morning hours on 26 December 2003, was centered less than ten miles from Bam, a city of approximately 100,000. Most of the 40,000 plus victims were killed instantly as their homes, constructed mostly of sun-dried mud-brick and mud, collapsed on top of them as they slept. More than 30,000 other residents were injured and Bam was left with no electricity, running water or gas. Those with homes built of wood were, for the most part, more fortunate as these homes either survived or came down with less force than mud-brick homes, allowing the residents to escape death.

Tragically an estimated 60 percent of dwellings collapsed, causing the mass casualties. Iran’s Building and Housing Research Center (BHRC), prior to this recent earthquake, produced readily available guidelines, regulations and codes for seismic resistant construction of new buildings and reinforcement of existing buildings. The destruction experienced in Bam is attributed to inadequate attention to seismic resistant construction guidelines. The legal code regarding such construction will remain ineffective with disastrous results if the code is ignored. Iran, situated on a seismic belt, is likely to experience equally devastating earthquakes if changes are not made.

Both California and Iran historically have experienced severe earthquakes. As the December earthquakes demonstrated, taking mitigation seriously and enforcing seismic resistant building codes can make a world of difference.

References: CISN Report, “San Simeon Earthquake: Preliminary Earthquake Analysis,” 12/24/2003; Goel, Rakesh, M.EERI, California Polytechnic State University, “Preliminary Report on December 22, 2003 San Simeon Earthquake”; Eshghi and Zare, IIEES, “BAM (SE Iran) earthquake of 26 December 2003, Mw 6.5: A preliminary Reconnaissance Report,” 12/29/2003; Ministry of Housing and Urban Development, Building and Housing Research Center, Iran Strong Motion Network, “The Very urgent Preliminary report on Bam earthquake,” 12/28/2003.