The first three-dimensional look inside Mount Rainier has scientists speculating that there is a potential earthquake hazard in the southeastern corner of the volcanic peak about 60 miles southeast of Seattle.

In 1974, a magnitude 4.8 earthquake, the largest ever recorded in the national park, was centered on the Ohanapecosh visitors’ center and campground.

“We are definitely observing a systematic change in the geology beneath the surface in the area of the 1974 earthquake,” University of Washington research scientist Seth Moran said Wednesday. He said it is possible this change represents a buried fault that could be long enough to generate a magnitude 6 earthquake.

Geologists have said for years that the active volcano, the largest in the Cascades, is a potential risk to the communities around it. There is strong geological evidence that massive landslides and mudslides have buried the surrounding area several times over the last 6,000 years.

UW researchers have been trying to determine a possible trigger for such a devastating event, and earthquakes may be the answer.

Locating buried active faults is vitally important because earthquakes close to the mountain “pose a much greater threat” to Mount Rainier than those that are more distant, said Moran, whose research was the basis for his recently completed doctoral dissertation.

Moran made 3-D images of the peak using a technology known as seismic tomography. The technique is similar to CT scan imaging of the body’s organs. But instead of sending X-rays through the body, researchers record waves of energy from earthquakes. Seismometers pick up a quake’s signature in the form of a P (primary) wave, something like a shock wave that radiates out from a temblor’s epicenter.

Moran assembled his portrait by adding 18 seismometers, mostly on the east side of Mount Rainier, to the 15 permanent stations around the volcano.

“This makes a big difference in our understanding of Mount Rainier,” he said.

Another geological puzzle has involved trying to determine whether earthquakes occurring within the volcano itself may be a result of the mountain actively disintegrating.

“We know that earthquakes occur directly beneath the summit. What we don’t know is why,” said Moran, in part because their precise depths have been difficult to determine.

The 3-D images indicate for the first time that the quakes are likely located deep below the mountain - perhaps a half to one mile below sea level.

This suggests that the earthquakes are probably not caused by the volcano falling apart from the inside. Instead, Moran thinks the earthquakes may be caused by hot fluids circulating in the ground beneath Mount Rainier.

Despite the quality of the 3-D images, “the depths of the earthquakes beneath the summit are still somewhat uncertain,” noted Moran, because there is no seismograph at the summit to provide the needed data.

“At this point, my guess is that there is no direct relationship between these particular earthquakes and hazards at Mount Rainier.”

The historical record shows only two examples of earthquakes triggering landslides on volcanoes: the 1980 eruption of Mount St. Helens, when a large landslide occurred at the same time as a magnitude 5.2 earthquake directly beneath the volcano; and a 1984 landslide on On-take in Japan, apparently triggered by a magnitude 6.8 earthquake about six miles southeast of that volcano.

The last great landslide on Mount Rainier occurred about 500 years ago. It generated a mudflow that enveloped what is now the community of Orting, northwest of the mountain. Although there is no evidence this landslide was caused by an earthquake, “earthquakes are potential triggers for landslides,” Moran said.