James Walfish was asleep when the shockwaves from yesterday's earthquake reached his Wilhelmina Rise home.

"I woke up, looked around and said, 'Uh-oh, this is it,' " Walfish said.

When the quake and subsequent aftershocks subsided, Walfish, owner of an engineering consulting firm and a practicing structural engineer for 35 years, went outside to assess the damage.

What he found, as did a surprising number of O'ahu residents, was no damage at all.

As an initial check, homeowners should take a close look for cracks in the interior drywall, stucco and masonry. Damage to siding can be difficult to spot. If serious damage is suspected, residents are advised to contact Civil Defense, which can dispatch an expert.

While serious structural damage was reported at Kona Hospital and Wal-Mart on the Big Island, Walfish said, the initial indications suggest that Hawai'i's homes and buildings were generally well-equipped to handle the force of the quake.

That, Walfish said, largely can be attributed to enhanced guidelines for home and building designs pushed by civil engineer Gary Chock and the Structural Engineering Association of Hawai'i, and others.

"There's no such thing as 'earthquake-proof,' but in the past 15 or 20 years, the structural engineering profession has upgraded the design by a considerable margin."

Key to this effort has been upgrading the ratings for key islands. As late as the 1980s, O'ahu held a Seismic Zone 1 designation, the lowest of four such designations. That has since been upgraded to a Zone 2-A designation, based on more critical assessments of seismic activity and other measures. Maui is considered a Zone 2-B; the Big Island, the most prone to serious seismic activity, is Zone 4.

It's significant because engineers are obligated to apply minimum design requirements (set by the International Building Code) that take these designations into account. (It wasn't until 1997 that soil properties were considered in zone designations.)

In terms of design, the zone designations define the relative "strength" of a building, as determined by a lateral-force resistance formula. For a Zone 4 area like Kona, buildings have to be designed to withstand a lateral force equal to 20 percent to 40 percent of the building's weight, depending on the surrounding area and soil.

Walfish said it was not surprising that his and many other homes avoided serious damage. Houses, regardless of the materials used in their construction, have significantly less dead weight. Walfish's concern, however, is for those homes in Kona that are raised on thin masonry piers, which can easily collapse.

Local engineers also have to consider requirements for hurricane safety, but Walfish explained that the two are complementary. "The clips and restraints we use for wind do double duty for earthquakes. The (protections) for 105-mile winds are more than enough for (yesterday's) earthquake."

Older buildings are exempt from current regulations. Walfish said buildings built before 1970 generally were not built with quake protection in mind.

Ian Robertson, a University of Hawai'i professor of civil and environmental engineering, said it is common for bridges to be retrofitted to conform to current standards, though rare for buildings and private homes.

Robertson said he hopes yesterday's quake will serve as an impetus for the state to provide tax credits as an incentive for home and building owners to retrofit their structures to current codes. He'd also like to see insurance companies offer reduced rates for people who upgrade their structures for safety.

Robertson said that while structures on O'ahu and Kona fared well during yesterday's event, it's important to keep in mind that nature had a hand in the relatively mild damage.

The quake originated approximately 25 miles underground, so deep that the energy released spread out over a wider-than-normal area. If the quake had started higher up, Kona would have absorbed much more of the impact.

Reach Michael Tsai at mtsai@honoluluadvertiser.com.