An archaeology museum in Philadelphia has moved thousands of ancient treasures offsite and is using vibration sensors to monitor delicate items still on display while an earth-shaking demolition project continues next door.

The Penn Museum -- which houses mummies, a Sphinx, pottery and other historical pieces excavated worldwide -- has also modified exhibits to prevent damage to fragile objects and ensure they can remain on view.

"We've tried to minimize our impact on the visitors, so that we're keeping things up as long as we can and as much as we can," said head conservator Lynn Grant.

The museum is part of the University of Pennsylvania, which has been dismantling a nearby 850-car parking garage and 23-story medical office tower to make room for a new hospital pavilion.

Demolition should be finished by August, said Patrick Dorris, an associate vice president for the university's health system. However, the museum's seismic challenges won't end then because the hospital construction will require digging into bedrock. No timeline has been set, Dorris said.

Vibrations from heavy machinery "can really mess with the integrity of the artifacts" and cause some to move within their exhibits, said museum special projects coordinator Robert Thurlow.

The museum cares for about 1 million items, but only a small percentage is displayed to its more than 160,000 annual guests. The rest are in storage, on loan or being studied in labs by students and researchers.

Officials with the museum and health system, which is paying the yet-to-be calculated moving and storage costs, have been coordinating closely for more than a year. The ongoing changes are large and small, both visible and invisible to the public.

Visitors won't notice that much of the Egyptian collection in onsite storage has been moved off the premises. They won't see the new, shock-absorbing layer of material under the case housing 1,400-year-old horse figurines from the Tang Dynasty. They probably won't realize that glass shelves in some displays have been replaced by sturdier wood or acrylic boards.

Guests will notice the walls of the ancient Egyptian tomb chapel of Kaipure have been disassembled, and the closure of the Islamic Near East gallery. In June, they'll see that workers have removed a pair of 500-year-old Buddhist murals made of mud plaster that have adorned the museum's signature Chinese rotunda for nearly a century. Officials hope to replace them temporarily with replica scrims.

"It's difficult to anticipate every single fixture or shelf and how they're going to respond" to vibrations, said Andrew Smyth, a Columbia University professor of civil engineering and engineering mechanics who serves as a consultant for the project. "You have so many objects and they're represented and displayed in so many ways, and they all have their own unique fragilities."

Vigilance has required museum staff to babysit galleries during night demolition work. Employees also get cellphone alerts from the vibration sensors when certain thresholds are reached, and Grant said they've learned to recognize the difference between truly unusual movements and large school groups tramping through the mummy room.

There have been a few emergency calls to the demolition site superintendent when the shaking became too intense, according to Thurlow, but nothing has been damaged.

Staff members have inventoried items while evaluating them for temporary removal or preservation work. That's led to the re-discovery of objects that have been in storage for decades -- some of which haven't been unpacked since their original excavation.

"We're finding a lot of neat things that people really haven't looked at, or haven't researched, since the '40s or '50s," Thurlow said.

Museum officials stress that there is still plenty to see. The newest exhibit, "The Golden Age of King Midas," opened Saturday and runs through Nov. 27.