Earthquakes Raise Questions of Future Shocks, Public Readiness

Just weeks after earthquakes rattled Nevada, the Midwest and the coast of Oregon, and on the heels of the 102nd anniversary of San Francisco’s 1906 earthquake, the public, government officials and insurance industry professionals are wondering whether towns across could face a “big one,” — and if so, are they prepared to handle it.

To help provide clarification, scientists at the U.S. Geological Survey (USGS) updated the USGS National Seismic Hazard Maps. USGS noted that earthquakes remain a serious threat in 46 of the United States. California has more than a 99 percent chance of having a magnitude 6.7 or larger earthquake within the next 30 years, scientists said.

Recent Rockings

Earthquakes are nearly synonymous with California. However, the location and type of temblors recently have puzzled some scientists.

Off the coast of Oregon, there have been more than 600 quakes underwater, which scientists said typically occurs before a volcanic eruption — although there are no volcanoes in the area. Researchers don’t know exactly what the swarm of earthquakes mean, but they could be the result of molten rock rumbling away from the recognized earthquake faults off Oregon, said Robert Dziak, a geophysicist for the National Oceanic and Atmospheric Administration and Oregon State University. The largest quake felt in the Oregon series had a magnitude of 5.4.

In Nevada, a continuing series of quakes that began on February 21 continue to rumble near Reno. While the state is the third most active in the nation for earthquakes, scientists said the recent activity is unusual because the quakes started out small and continue to build in strength. The normal pattern is for a main quake followed by smaller aftershocks. (See story on page 12 of this issue) The strongest hit the Reno area on April 25, with a magnitude of 4.7.

While not completely unexpected because it occurred along the New Madrid Fault, an earthquake that measured 5.2 on the Richter scale rocked the Midwest from Cairo, Ill., to Atlanta on April 18. The quake was the largest felt in the Midwest in years.

Scientists admit they know far too little about Midwestern seismic zones, but some of what they do know is unnerving. The New Madrid fault zone in the Midwest produced a series of quakes in 1811 and 1812 that reached an estimated magnitude 7.0, putting them among the strongest known quakes to have occurred east of the Rockies. The quakes changed the course of the Mississippi River and were felt in New England.

Mapping New Hazards

Russ Wheeler, a USGS geologist, said there is no way to predict an earthquake hitting at any specific time. “There are no hard and fast instruments or scientific ways of determining that kind of probability,” he said. Nevertheless, USGS has updated its seismic maps to incorporate new seismic, geologic and geodetic information on earthquake rates and the manner in which the energy released in earthquakes dies off with distance from the rupture.

“The hazard maps incorporate more than a century of seismic monitoring and decades of research,” said USGS Director Mark Myers. “These maps help policymakers and engineers make all of our structures from our homes to our hospitals to the utilities that run beneath our feet better able to withstand the earthquakes of tomorrow.”

For some areas such as western Oregon and Washington, USGS increased the estimates for how hard the ground will shake compared to earlier versions of the maps released in 1996 and 2002. But for most of the United States, the ground shaking estimates are lower.

The changes in earthquake ground shaking estimates are due principally to the incorporation of new models on the strength of earthquake shaking near faults, and the manner in which shaking decreases with distance, USGS said.

The increased hazard in western Washington and Oregon is due to new ground-motion models for the offshore Cascadia subduction zone. Because of new models, ground motion estimates in the Central and Eastern United States are about 10 percent to 25 percent lower. Ground motion estimates in most of California, Utah, Nevada, Arizona, Idaho and western Montana are as much as 30 percent lower for shaking that affects taller multi-story buildings, USGS added. For those same areas, ground motion estimates remain nearly the same for shaking that affects structures of one or a few stories.

However, USGS cautioned that because these maps are done at a national scale, they do not take into account local soil conditions and the depth of sedimentary basins, which can significantly amplify shaking relative to bedrock. As a result, site-specific factors are applied in the building codes to determine the seismic design needed for individual structures.

The map included the following regional changes:

• Several new faults were included or revised as a source of earthquake ground shaking in California, the Pacific Northwest and the Intermountain West.
• The Wasatch fault in Utah was modeled to include the possibility of a magnitude 7.4 earthquake, in addition to smaller earthquakes along the fault.
• The model for earthquakes along the New Madrid Seismic Zone in the Central United States includes a wider range of possible magnitudes and return periods between major earthquakes. The model was also adjusted to allow for sequences of earthquakes to occur in groups of three within a few years time, similar to what occurred in 1811-1812.
• Offshore faults were added as possible sources of earthquakes near Charleston, S.C.
• For the Cascadia Subduction Zone, more weight was given to a magnitude 9 earthquake that ruptures the length of the subduction zone, versus multiple smaller magnitude 8 earthquakes that fill the zone during the same 500-year time period.

California Concentration

Meanwhile, a USGS study of California determined the likelihood of a major quake of magnitude 7.5 or greater in the next 30 years is 46 percent, and such a quake is most likely to occur in the southern half of the state, USGS said. Using a new model that comprehensively combines information from seismology, earthquake geology, and geodesy (measuring precise locations on the earth’s surface) to determine the probability of big quakes, scientists predicted California has more than a 99 percent chance of having a magnitude 6.7 or larger earthquake within the next 30 years.

The official earthquake forecasts, known as the Uniform California Earthquake Rupture Forecast (UCERF), were developed by a multidisciplinary group of scientists and engineers, known as the Working Group on California Earthquake Probabilities. Building on previous studies, the Working Group updated and developed the first-ever statewide, comprehensive model of California. Previously the science used in determining CEA earthquake insurance rates differed depending on whether the insured property was located in Northern California or Southern California.

The consensus of the scientific community on forecasting California earthquakes allows for meaningful comparisons of earthquake probabilities in Los Angeles and the San Francisco Bay Area, as well as comparisons among several large faults, USGS said.

Highlights of the forecasts include:

• The probability of a magnitude 6.7 or larger earthquake over the next 30 years striking the greater Los Angeles area is 67 percent, and in the San Francisco Bay Area it is 63 percent, similar to previous Bay Area estimates.
• For the entire California region, the fault with the highest probability of generating at least one magnitude 6.7 quake or larger is the southern San Andreas (59 percent in the next 30 years).
• For northern California, the most likely source of such earthquakes is the Hayward-Rodgers Creek Fault (31 percent in the next 30 years). Such quakes can be deadly, as shown by the 1989 magnitude 6.9 Loma Prieta and the 1994 magnitude 6.7 Northridge earthquakes.

Earthquake probabilities for many parts of the state are similar to those in previous studies, but the new probabilities calculated for the Elsinore and San Jacinto Faults in southern California are about half those previously determined, USGS said. For the far northwestern part of the state, a major source of earthquakes is the offshore 750-mile-long Cascadia Subduction Zone, the southern part of which extends about 150 miles into California. For the next 30 years there is a 10 percent probability of a magnitude 8 to 9 quake somewhere along that zone. Such quakes occur about once every 500 years on average.

The new model does not estimate the likelihood of shaking (seismic hazard) that would be caused by quakes. Even areas in the state with a low probability of fault rupture could experience shaking and damage from distant, powerful quakes, USGS cautioned. (Read about more California earthquake predictions on page 72 of this issue.)

Construction Issues

The results of the UCERF study and new USGS maps serve as a reminder that nearly the entire United States, not just California, is in earthquake country and should be prepared. Although earthquakes cannot be prevented, the damage they do can be greatly reduced through prudent planning and preparedness, USGS advised.

For example, national-scale maps of earthquake shaking hazards describe ground shaking at many points across the country and are used by insurance companies to set insurance rates for properties in various areas of the country, by civil engineers to estimate the stability and landslide potential of hillsides, by the U.S. Environmental Protection Agency to set construction standards that ensure the safety of waste-disposal facilities, and by the Federal Emergency Management Agency to plan the allocation of assistance funds for earthquake education and preparedness, USGS said.

The timing of the National Seismic Hazard Map release is tied to the schedule for revising model building codes that are developed by international code committees and then considered by state and local governments for adoption. Cities and counties rely on seismic design provisions in creating and updating building codes to ensure that structures such as buildings, bridges, highways and utilities are earthquake resistant, USGS said.

The USGS also is incorporating the UCERF model into its official estimate of California’s seismic hazard, which in turn will be used to update building codes. Other subsequent studies will add information on the vulnerability of manmade structures to estimate expected losses, which is called “seismic risk.” In these ways, the UCERF will help to increase public safety and community resilience to earthquake hazards, USGS added.

Keith Lessner, vice president of loss control for the Property Casualty Insurers Association of America (PCI), said that the Illinois earthquake provides an excellent opportunity to create greater awareness of the need for appropriate building codes throughout the United States and in particular in the Midwest.

“In the last few years, most attention related to building codes has focused on wind damage in hurricane prone areas,” Lessner said. “But regardless of the peril, building codes can play an important role in saving lives and reducing property losses. Retrofitting homes and businesses to meet current codes can also provide an extra measure of safety and security from the potential of natural disaster.”

It is important for residents and businesses to take precautionary steps to secure their property from earthquake damage, Lessner said, calling the recent quakes “a wake up call that we hope will not be ignored.”

Justin Roth, senior director of public affairs for the National Association of Mutual Insurance Companies (NAMIC), agreed and said that NAMIC, PCI and other national groups have formed the “Building Code Coalition” with the goal of encouraging all states to adopt statewide building codes.

“A recent study told us that if Louisiana had building codes at the time Katrina hit up to 80 percent of insurance losses could have been avoided,” Roth said

Roth added that the Coalition is pushing for bigger federal incentives for extra dollars for states that adopt statewide building codes, bumping up the percentage of monies states would receive by 4 percent if they enact the codes.

Insurance Lacking

While building codes are improved, insurance industry professionals said earthquake insurance take-up rates need improvement as well. Despite the USGS’ predictions, “only a very small percentage of home and business owners outside of California purchase earthquake insurance,” said Michael Barry, vice president of media relations for the Insurance Information Institute.

Industry experts estimate that only roughly 12 percent of California homeowners have purchased earthquake insurance policies, down from 30 percent in 1996 — “a figure that may prove catastrophic in its own right,” said Candysse Miller, executive director of the Insurance Information Network of California.

Yet polling by IINC in 2007 found that 19 percent of California homeowners believed they had earthquake insurance, indicating possible confusion over coverage.

Earthquakes are not covered under standard homeowners or business insurance policies. Coverage is usually available through a supplemental policy. Cars and vehicles are covered for earthquake damage under the comprehensive part of an auto insurance policy.

The cost of policies and high deductibles often are attributed to the low purchase rate. Deductibles normally are in the form of a percentage than a dollar amount, ranging from 2 percent to 20 percent of the structure’s value. That means if it costs $100,000 to rebuild a home and there was 2 percent deductible, the policyholder would be responsible for paying the first $2,000, I.I.I. said.

The California Earthquake Authority, which is a publicly managed, largely privately funded organization that provides catastrophic residential earthquake insurance, offers two deductible options — 10 percent and 15 percent.

“With a catastrophic earthquake a near certainty in the next few decades, far too few homeowners have a financial recovery plan in place. The result could be billions of dollars in uninsured damage to homes and small businesses,” Miller said.

Given the USGS’ predictions, particularly in Washington and Oregon, where risks were increased, states are not nearly as prepared as they need to be, Barry said. “We want homeowners not just in California and the Pacific Northwest, but in other parts of the country, to make sure they have the right type of coverage should an earthquake hit,” he said.

Map and Model Info

The geologic and geophysical data-collection, research and modeling results that underpin the U.S. Geological Survey maps and models have been generated by USGS scientists as well as their colleagues in academia, state government, and the private sector funded by external grants from the USGS Earthquake Hazards Program and other sources. The new maps represent the best available science based on an extensive information gathering and review process involving state and university experts nationwide, USGS said.

The USGS National Seismic Hazard Maps are available at www.earthquake.usgs.gov. The full UCERF report is available at www.pubs.usgs.gov/of/2007/1437/. A fact sheet is available at pubs.usgs.gov/fs/2008/3027/. And supplemental information is available at www.scec.org/ucerf/.

The California Earthquake Authority (CEA) announced it will begin using a newly released, uniform scientific method in determining insurance rates and the most accurate prices for earthquake insurance for consumers.

Partially funded by the CEA, the new Uniform California Earthquake Rupture Forecast (UCERF) model allows for more uniform and accurate determination of seismic hazard throughout California, CEA said. UCERF is the first statewide, uniform scientific system to determine the probability of earthquakes.

Previously, the science used in determining CEA earthquake insurance rates differed depending on whether the insured property was located in Northern California or Southern California. That meant, for example, that risks in Los Angeles and San Francisco were analyzed using different techniques.

“Having uniform science available when determining earthquake rates represents real progress,” said CEA CEO Glenn Pomeroy. “It allows us to more accurately price our product for the consumer.”

“This new, comprehensive forecast advances our understanding of earthquakes and pulls together existing research with new techniques and data,” said USGS geophysicist and lead scientist Ned Field. “Planners, decision makers and California residents can use this information to improve public safety and mitigate damage before the next destructive earthquake occurs.”

The full effects of the UCERF model on insurance rates will not be determined until the CEA’s rate review in the summer of 2008.

“To be clear, the actual hazard hasn’t changed. What has changed is our understanding of earthquake risk, and this understanding will be reflected in future insurance rates,” Pomeroy said.

The California Earthquake Authority is one of the largest providers of residential earthquake insurance in the world. By law, CEA rates must be actuarially sound and supported by the best available science.