The 1992 earthquake in southern Utah did little damage in St. George because the force was directed away from that city, a geologist has concluded.
The magnitude 5.8 quake channeled its energy eastward and upward along the Hurricane Fault, said Susan Olig, a former Utah Geological Survey geologist who now works for a consulting firm in California.So the quake's force was directed away from St. George, which is six miles west of the epicenter, and toward Hurricane, about nine miles east of the epicenter.
Olig also concluded seismic waves from the quake were absorbed more efficiently as they moved west into relatively warm rock near the Basin and Range terrain. To the east, colder, harder rock near the Colorado Plateau absorbed less destructive energy, Olig said.
Three homes were destroyed when the quake triggered a landslide near Springdale, 28 miles northeast of the epicenter. Olig said the shaking there was less intense than in St. George. Other scientists determined the landslide "was ready to go" anyway, and did not need much shaking to collapse, she said.
Olig presented her findings Thursday during the Geological Society of America's regional meeting near Durango, Colo.
The study provided more evidence the quake snapped the Hurricane Fault, although the rupture failed to break the ground surface.
The St. George quake was that city's strongest in 90 years and Utah's largest since 1975, causing $1 million in damage.
Jim Pechmann, a University of Utah seismologist, called Olig's conclusions "perfectly reasonable . . . She did a very good study."
The lack of building collapses in St. George was "surprising because there are a lot of old, unreinforced masonry buildings - adobe, brick, even some stone," Olig said. "In general, that was what was damaged. But the damage was relatively minor."
Other than the Springdale slide, she found the worst damage near Hurricane, where a "couple of unreinforced masonry buildings showed partial collapse."